Improved hybrid cereal parent line selection

Abstract

This invention relates to improved methods or uses for hybrid cereal, such as wheat, parent line selection or cultivation, and a new use of a solution comprising gibberellic acid so as to selectively increase plant height of male parent plants.

Description

[0001] IMPROVED HYBRID CEREAL PARENT LINE SELECTION

[0002] Introduction

[0003] This invention relates to improved methods or uses for hybrid cereal, such as wheat, parent line selection or growing, and a new use of plant growth regulators based on gibberellic acid so as to selectively increase plant height of male parent plants.

[0004] Background

[0005] Essentially self-fertilizing (autogamous) crops need male sterile lines for hybrid seed production, as cross-pollination between 2 hybrid parent lines (namely a male sterile female line and a fertile male line) is required. While in some autogamous crops male-sterile plants (genetically, chemically or mechanically made male-sterile) and commercial hybrid seed production methods were developed, in some other crops, like wheat, only very few commercial hybrids are on the market, and efforts are ongoing to improve hybrid seed production to make it economically viable and sustainable. Particularly grain cereals like wheat, barley, rye, or triticale that have bisexual or hermaphroditic flowers (male and female organs in the same flower), and are not pollinated by insects, and are challenging for hybrid seed production. While some published documents are discussed herein, this is not to be taken as any admission that any of these forms part of the common general knowledge of the person of ordinary skill in the art.

[0006] EP3116302 suggests a method of producing hybrid cereal seeds comprising crossing a stand of shorter female (male sterile) plants with a stand of taller male fertile plants and limiting the proportion of self-fertilized male seed in the produced seed stock, wherein limiting the self-fertilized male seed proportion comprises passing a tool extending above the height of the shorter female plants between anthesis and harvest, which tool contacts these male fertile plants standing above this height and causes preventing or reducing normal development thereof. Shorter plants have (one or several) height-reducing (semi-)dwarf genes, or based on selection of short plants in a plant breeding population, and the tool exemplified is a weed wiper or brush, and the exemplified herbicide is glyphosate.

[0007] Zhao et al. (2001 , Journal of Triticeae Crops 21 (1): 6-9) describes the use of the GA3-sensitive dwarfing gene Rht12 in (row-planted) male sterile plant maintenance trials, where rows of male- sterile plants containing Rht12 (with T. timopheevii CMS) are planted next to rows of the fertile maintainer plants containing Rht12 in a strip planting system, so as to produce seed that will grow into male-sterile plants. Selective application of 50, 80 and 100 mg / kg GA3 on the maintainer plant rows between the jointing and booting stage could increase maintainer plant height and male sterile seed production. Zhao et al. describe that within these periods and concentration ranges, the earlier the spraying period and the higher the concentration of GA3, the more the plant height of the dwarfing lines could be increased.

[0008] Arya et al. (2009, Annals of Agri-Bio Research 14(2): 99-102) reported no significant improvement in seed set on 2 wheat CMS lines after GA3 application at 50, 75 or 100 ppm at 5-10 % ear emergence on the nine pollen-providing wheat parents tested. They say this could be due to the presence of GA insensitive genes (like Rht1 , Rht2, and Rht3) in the study material, or that the dosages used were insufficient.

[0009] CN 108040869 apparently describes a method for breeding a gibberellin insensitive sterile line in rice with an endogenous herbicide resistance and a seed color gene, where gibberellin is sprayed during ear heading in the mixed sowing seed production process of the two-line sterile line, so that the male parent is high, the female parent is low, pollination is easier, the sterile seed production yield is increased, and the seed production efficiency is improved, and wherein after pollination, a herbicide is sprayed to ensure that the male parent dies and the female parent does not die.

[0010] Wang et al. (2019, Agronomy 9(12), 861) describe that poor panicle exertion of male sterile lines is a major problem in hybrid rice seed production. Hence, the foliar application of GA3 at the start of panicle emergence has been widely adopted as an essential technology for improving plant height and panicle exertion of male sterile rice lines. Gao and Chen (Plant and Cell Physiology, 61 :1902-1911 , world wide web at doi.org / 10.1093 / pcp / pcaa104 (2020)) describe that GA plays an indispensable role in hybrid rice seed production, since rice male sterile lines have a common defect in the elongation of the uppermost internode, leading to incomplete panicle exertion, which blocks pollination. Consequently, exogenous GA has to be used in hybrid rice to get normal pollination.

[0011] Pin et al. (2019, Science & Technology Asia, Vol.24, No.4, pp. 126-134) investigated the effects of GA3 application at different flowering stages on agronomic traits and seed yield of hybrid rice parental lines in micro-crossing plot trials, and reported that applying GA3 at 30% panicle heading stage resulted in the highest seed yield of a CMS male-sterile (A) rice line, while applying GA3 at 0% panicle heading stage produced lower seed yield of both the male-sterile A line and the maintainer B line.

[0012] US2024 / 0016153 (published 18 / 01 / 2024) describes a method of increasing wheat hybrid seed production in a field comprising the steps of (a) planting male (such as GA-sensitive male) and female (such as GA-insensitive female) parent wheat plants in a field; (b) treating the male parent plants with a topical treatment; and (c) quantifying hybrid seed production; wherein hybrid seed production is increased with respect to a control planting. In one aspect, the topical treatment is a spray. In a further aspect, the topical treatment is selected from the group of a gibberellin such as GA3, a plant growth regulator with trinexapac-ethyl as the active ingredient, a sodium chlorate desiccant, and a phenoxy herbicide with MCPA (2-methyl-4-chlorophenoxyacetic acid) as the active ingredient. Treating the male parent plants with a topical treatment is said to result in : the male parent plant height at least 3 inches greater than the female parent plant height; a delay in male flowering by at least 1 day; a delay in pollen shed by at least 1 day; a shortened male flowering window of at least 1 day; decreased tillering; or combinations thereof. It is said that GA3 application resulted in a 0.5 to 1.5-day delay in heading date and flowering date among the GA sensitive male genotypes (heading and flowering did not change in GA-insensitive genotypes). Yield of GA sensitive male genotypes decreased by 11 % as a result of the GA3 application, while yield of female GA insensitive genotypes still had to be evaluated. US2024 / 0016153 plans studies to validate the use of GA insensitive genotypes paired with GA sensitive genotypes for improving hybrid wheat seed production in mixed / blended planting. US2024 / 0016153 says that when male flowering is delayed so that it minimizes overlap with flowering in the female plant, the opportunity for the male plants to self-fertilize is reduced, thereby reducing the production of male inbred seed and contamination of hybrid seed production. It is also said that reducing seeding rate of the male plants in a seed production system can delay male flowering by as much as 2.5 days, which is enough to decrease contamination of (hybrid) seed from self-pollinated males.

[0013] There still is a need for improving hybrid seed production, particularly in cereals, such as wheat, so that seed production of the male-sterile lines and the hybrid seed is optimal and at acceptable costs. In this context mixed planting is especially desirable, since it offers higher productivities of hybrid seeds per area land as compared to row planting, since less area is dedicated to the male plants only and the pollen is shed in close vicinity to the female flowers. Mixed planting comes along with the difficulty that male and female plants cannot be treated differentially (as is the case in strip / row planting). This aspect is addressed in the current invention.

[0014] Figure legends

[0015] Figure 1 : Honeycomb mixed planting structure, with light dots representing male plants / seeds and the dark dots representing female plants / seeds.

[0016] Figure 2: Seedling elongation after GA treatment in seedling growth assay (in % versus untreated) for different wheat genotypes.

[0017] Figure 3: Seedling elongation data from seedling growth assay (in %) and plant height increase data from the field (in %) after application of GA for 6 wheat genotypes. Figure 4a: Actual data (in cm) for plant height at flowering start compared to untreated plots for the most GA-responsive wheat lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0018] Figure 4b: Actual data (in cm) for plant height at flowering start compared to untreated plots for the low or not GA-responsive wheat lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0019] Figure 5a: Actual data (in cm) for plant height at the end of flowering compared to untreated plots for the most GA-responsive lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0020] Figure 5b: Actual data (in cm) for plant height at the end of flowering compared to untreated plots for the low or not GA-responsive lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0021] Figure 6a: The contrast / difference (in cm) for plant height at flowering start compared to untreated plots for the most GA-responsive lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0022] Figure 6b: The contrast / difference (in cm) for plant height at flowering start compared to untreated plots for the low or not GA-responsive lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0023] Figure 7a: The contrast / difference (in cm) for plant height at the end of flowering compared to untreated plots for the most GA-responsive lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0024] Figure 7b: The contrast / difference (in cm) for plant height at the end of flowering compared to untreated plots for the low or not GA-responsive lines, from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0025] Figure 8: The contrast / difference (in %) for spike length for all genotypes, comparing treated versus untreated (for all treatments), from the Moregem field trial (see Example 2.1 ; GA: gibberellic acid treatment, GR: plant growth regulator treatment, GR+GA: plant growth regulator and gibberellic acid treatment).

[0026] Figure 9a: Table with the contrast / difference between the results for GA-treated and untreated wheat plants in absolute values, from the Gatersleben field trial (Example 2.2).

[0027] Figure 9b: Table with the contrast / difference between the results for GA-treated and untreated wheat plants in %, from the Gatersleben field trial (Example 2.2).

[0028] Figure 10: Actual plant height measured (in cm) for the tested lines (GA-treated vs. untreated plots), from the Gatersleben field trial (Example 2.2).

[0029] Figure 11 : Actual peduncle length (in cm) for untreated and GA-treated plots, per genotype tested, from the Gatersleben field trial (Example 2.2).

[0030] Figure 12: Actual width of the peduncle measured in the middle of the peduncle (in mm) for untreated and GA-treated plots, per genotype tested, from the Gatersleben field trial (Example 2.2). Figure 13: The contrast / difference in peduncle length (in %) for untreated and GA-treated plots, per genotype tested, from the Gatersleben field trial (Example 2.2).

[0031] Figure 14: The contrast / difference in peduncle width (in %) for untreated and GA-treated plots, per genotype tested, from the Gatersleben field trial (Example 2.2).

[0032] Figure 15: Plant height at Z65 of A- and R-lines in mixed planting untreated / GA-treated (actuals, in cm), from outdoor container tests (Example 2.3).

[0033] Figure 16: Plant height at Z65 of A- and R-lines in mixed planting of GA-treated vs. untreated (contrast, in cm), from outdoor container tests (Example 2.3).

[0034] Figure 17: Plant height at Z91 of A- and R-lines in mixed planting untreated / GA-treated (actuals, in cm), from outdoor container tests (Example 2.3).

[0035] Figure 18: Plant height at Z91 of A- and R-lines in mixed planting of GA-treated vs. untreated (contrast, in cm), from outdoor container tests (Example 2.3).

[0036] Figure 19: Difference in plant height (in cm) between R- and A-line in mixed planting with and without GA3-treatment at Z65 growth stage, from outdoor container tests (Example 2.3).

[0037] Figure 20: Difference in plant height (in cm) between R- and A-line in mixed planting with and without GA3-treatment at Z91 growth stage, from outdoor container tests (Example 2.3).

[0038] Figure 21 : Scheme indicating the proportion of R-line seeds above and below the upper canopy layer of A-line plants in mixed planting with / without GA treatment, from outdoor container tests (Example 2.3).

[0039] Figure 22: Actual data of the proportion of R-line seeds above and below the upper canopy layer of A-line plants in mixed planting with / without GA treatment (in % of total R-line seeds), from outdoor container tests (Example 2.3).

[0040] Figure 23: Field trial design scheme for Example 5 (H1 is hybrid 1 , H2 is hybrid 2, PGR is (plantheight decreasing) plant growth regulator, Ctrl is untreated control, GA is GA3, Rep1 and Rep2 are 2 repetitions, m is length / width in meter), not drawn to scale.

[0041] Figure 24: Field map ’23-’24 Strip and Strip + Mix trials in Example 6.1 (SD: seed density, not drawn to scale, abbreviations for treatments: see Example 6.1).

[0042] Figure 25: Field map mixed / blended plantings ’23-’24 trials in Example 6.1 (SD: seed density, not drawn to scale, abbreviations for treatments: see Example 6.1).

[0043] Figure 26: Yield for different treatments and planting schemes in Example 6.1 , in % of strip planting (strip planting set at 100 %), for each of the 3 seed densities tested (abbreviations for treatments: see Example 6.1).

[0044] Figure 27: % hybridity (% hybrid seed in total seed harvested) for different treatments and planting schemes (Example 6.1).

[0045] Figure 28: Heading dates (HD) for R1 and R9 male lines for treatments 1-4 vs. check (untreated control) (see Example 6.2, d = day).

[0046] Figure 29: Plant height (H, in cm) after flowering for R1 and R9 male lines for treatments 1-4 vs. check (see Example 6.2).

[0047] Figure 30: Field trial design scheme (Caen, not drawn to scale, see Example 8).

[0048] Figure 31 : Raw total seed yield (in tons / hectare) from Caen field trial, with % male in the mixed planting used indicated, showing the % increase in the average value by GA3 application (light grey is without GA3, dark grey is with GA3 application, median is shown as lighter bar (while the dotted line connects the median values for ease of reference, the % increase (and P-value) indicated (e.g., +21 %) is the % increase in the average value)) (see Example 8). Figure 32: Field trial design scheme (Catillon, not drawn to scale, see Example 8).

[0049] Figure 33: Raw total seed yield (in tons / hectare) from Catillon field trial, with % male in the mixed planting used indicated, showing the % increase in the average value by GA3 application (light grey is without GA3, dark grey is with GA3 application, median is shown as lighter bar (while the dotted line connects the median values for ease of reference, the % increase (and P-value) indicated (e.g., +21%) is the % increase in the average value)) (see Example 8).

[0050] Figure 34: Schematic representation of relative height differences in the treatments of Example 7.2 (illustrative / indicative, not drawn to scale, not based on actual data).

[0051] Description

[0052] The current invention is related to creating a sufficient height difference between pollen-producing (male, fertile) and pollen-receiving (female, male-sterile) cereal, such as wheat, plants, to improve hybrid parent plants and hybrid production. In the current invention the pollen-producing (male) cereal, such as wheat plants are made taller by application of plant height promoting factors or hormones such as gibberellic acid (GA) or compounds with the same plant height effect as gibberellic acid (including but not limited to GA1 , GA3, GA4, GA7 or mixtures thereof), because the pollen-producing (male) plants are highly GA-responsive, while the pollen-receiving (female) plants are low or not GA-responsive, so that application of GA over a field planted with such male and female plants will make the pollen-producing plants significantly taller than the pollenreceiving plants. This is particularly useful in mixed planting wherein a smaller quantity of pollenproducing (male) plants occurs randomly in between a majority of pollen-receiving (female) plants, or for GA application across an entire field planted with separate bays / rows of pollen-producing (male) plants separated in different rows from the pollen-receiving (female) plants. This method also has the benefit that the taller pollen-producing plants can be removed before harvest of the hybrid seeds (e.g., mechanically, by cutting above the height of the pollen-receiving (female) plants, or chemically, by applying herbicide to the heads of the pollen-producing (male) plants (e.g., herbicide wicking or wiping)) which will result in improved purity of hybrid seeds produced (improved hybridity). A benefit of this method is that pollen-producing hybrid parent (male) plants are made taller by application of GA and that no genetically taller male plants need to be used, so that the hybrid plants have appropriate height and there are less concerns with lodging of resulting tall hybrid plants. When using a genetic basis to get a height difference, such as using (semi- )dwarf female plants and tall male plants, the downside is that the hybrid plants become tall, and will have a higher risk to lodge than (semi-dwarf) cereal, such as wheat, plants. If the height difference between male and females is obtained by using more extreme dwarf females (e.g., double (semi-)dwarfs), seed production will even be compromised.

[0053] Similarly, one can envisage to use hybrid parent plants wherein the female plants are selectively made shorter by using male-sterile (female) plants that are very responsive to a plant growth inhibitor, while using male plants that are less or not responsive to that plant growth inhibitor, and application of that growth inhibitor over the male and female plants in a field. One way to obtain differential responsiveness is, for example, interplanting males and females with sufficient difference in early development, so that the application window of the one gender is met (so that the growth regulator is effective) whereas for the other gender is not. This also allows mixed planting, and the creation of a selective height difference between male pollen-producing and female (male-sterile) pollen-receiving plants. This can also be combined with the application of GA when the male plants are highly GA-responsive and the female plants are low or not GA- responsive.

[0054] Since in traditional cereal, such as wheat, cultivation, often plant growth regulators (“PGR”) are used (often Gibberellin / GA-inhibitors, so as to reduce plant height and improve yield) so as to prevent tall plants (that can lodge and cause severe harvest losses and / or losses in seed quality), the current invention also allows use of such plant growth regulators in addition to the use of growth stimulators such as GA. In the current invention, it has been found that while PGR application makes plants shorter than untreated control plants, GA application will increase the plant height, and the (delta) difference in plant height obtained between PGR treated plants and PGR treated plants on which GA was applied is similar to the (delta) difference in plant height obtained for the same plants between untreated and GA-treated control plants, when no PGR was applied. In one embodiment, the invention relates to the simultaneous (such as a tank mix) or sequential / consecutive application (like at the same day, but from different tanks) of a PGR solution and a GA solution (e.g., the PGR application is at the traditional timing for a standard PGR application, such as between Z30 and Z32, or at Z30, Z31 or at Z32), or before the plants begin to rapidly elongate), on a field planted with cereal, such as wheat, plants with highly GA- responsive pollen-producing (male, fertile) plants and low or not GA-responsive pollen-receiving (female, male-sterile) plants. In such simultaneous or sequential application, the PGR ensures (female) plants are kept short to prevent lodging, and GA ensures that the highly GA-responsive male plants get taller than the female plants, which allows for improved hybrid seed production and improved hybrid seed purity (hybridity). In one embodiment, in case needed, also a second (later) PGR application can be done, such as when the initial PGR application did not have the intended effect (e.g., too much rain or when it was too dry after the initial PGR application), and hence at least one PGR application and at least one GA application are done over the same field of male and female plants during a cereal, such as wheat, plant growing season, in one embodiment of the invention. In one embodiment, such PGR includes a (or at least one) surfactant or adjuvant.

[0055] Surprisingly, it has been found that GA application can also increase peduncle length (the stalk of the ear / spike) and decrease peduncle thickness in some highly GA-responsive cereal, such as wheat, plant genotypes. Hence, in one embodiment, such genotypes are used as male pollenproducing plants to be interplanted (ideally in mixed planting) with female (male-sterile) plants that are low or not GA-responsive, and GA application over the field of male and female plants will then increase peduncle length and / or reduce its width in the male plants, so that the male heads are more mobile, and therefore spread the pollen better and with several applications of GA, or with high dose application of GA, the heads may even bend down (lodge) during grain filling so that male seed development is disturbed / halted and smaller male seeds are produced, which can then be removed at harvest using seed sorting based on difference in grain size / weight with the hybrid grain produced. In one embodiment, such peduncle length increase / width decrease is after application of 100-500 ppm, such as 100-400 ppm, 200-400 ppm, or 100, 150, 200, 250, 300, 350, or 400 ppm (w / w) (at a volume of 100-500 l / ha, such as 200-400 l / ha) GA between Z40 and Z50, or between Z41 and Z50, or between Z42 and Z49, or between Z43 and Z49, or between Z44 and Z49, or between Z45 and Z49 or between Z43 and Z48, such as at Z41 , Z42, Z43, Z44, Z45, Z46, Z47 or Z48, which may be preceded by an earlier GA application as described herein. Female cereal, such as wheat, plants that are low or not GA-responsive will hardly or not elongate their peduncle, so that the GA application can cause a selective peduncle length increase and peduncle thickness decrease in the highly GA-responsive male plants when treated with GA, when such female plants are planted next to (preferably interplanted in a mixed planting setup with) such male plants. Also, multiple application of higher doses (> 100 ppm, such as 200 or 300 ppm (w / w) (at a volume of 100-500 l / ha, such as 200-400 l / ha)) of GA or multiple applications of GA between Z41 and Z50 (or at any other stage as described herein for peduncle length increase / width decrease) can then even cause bending / lodging of the male heads (only) which results in smaller male grains produced on the male plants (which can then be removed at or after harvest by their small seed size and / or weight using known seed sorting devices, which are mostly included in current harvesting combines). In an embodiment of the invention, peduncle thickness is best measured in the middle of the peduncle.

[0056] A combination of an elongated and thinner peduncle is considered very beneficial for cross pollination, since it results in stronger spike movement upon mechanical or wind agitation, resulting in better and wider pollen shedding. In lines with a strong GA responsiveness on peduncle length and thickness this may allow to achieve (peduncle / spike) lodging or stem bend down during grain filling, when the weight of the spike increases. High (at least 300 ppm) and / or repeated applications of GA in between Zadok stage Z41 and Z50 or between Z44 and Z50 (or at any other stage as described herein for peduncle length increase / width decrease) are considered a novel opportunity to achieve male lodging (of the peduncle / spike), allowing to increase the hybridity of seeds obtained from mixed planting, via removal of small or shriveled seeds resulting from lodged spikes / peduncles by means of seed sorting or weight fractionation.

[0057] Also, a significant spike length increase after GA application was noted in the majority of high GA- responsive and low or not GA-responsive plant lines tested, without a concomitant significant increase in the number of spikelets per spike, and can also be beneficial in hybrid seed production, as this results in a less compact spike structure, allowing the florets to open easier which on the males can help to extrude the anthers better (Arp, A.L., Master Thesis: Pollen Amount And Distribution In Relation To Seed Set Of Male Sterile Triticum Aestivum (1967)) and on the females results in a higher chance to receive pollen. Hence, in one embodiment of the invention, when selecting hybrid cereal, such as wheat, parent lines, female parent plants are selected that do not significantly respond to GA application by a peduncle length increase but significantly respond to GA application by a spike length increase without significantly increased spikelets per spike, and male parent plants are selected which significantly respond to GA application by a peduncle length increase and significantly respond to GA application by a spike length increase without significantly increased number of spikelets per spike. In one embodiment, such male plants show an improved spike length increase after (sequential / simultaneous / consecutive) application of a gibberellin-inhibiting plant growth regulator (such as an early season application, in a standard application of a PGR, such as between Z30 and Z32, or at Z30, Z31 or Z32, which can be followed by a later PGR application as needed) and a GA solution as described herein between Z30 and Z50, and any uses or methods to increase spike length of cereal, such as wheat, plants (based on analysis of the main spikes) as described herein, included a treatment with a gibberellininhibiting plant growth regulator as described herein (such as at the standard application time / dosage for that crop / field), and a treatment with a GA solution as described herein.

[0058] A less compact spike architecture creates more room for spikelet opening / gaping which can help to improve anther extrusion from male florets and pollen retrieval on the stigmas of female florets. As used herein, plants “without significantly increased spikelets per spike”, or ’’without significantly increasing spikelets per spike”, after GA application, refers to the main spike of said plants having an increase in number of spikelets per spike of less than 5 % (or less than 4 %, less than 3 % , or less than 2 %) after GA application, or having no increase in number of spikelets per spike after GA application, when that number of spikelets per spike is measured at Zadoks growth stage Z59, or at the start of flowering, or at the end of flowering, compared to said plants at said (same) stage when not treated with GA.

[0059] As used herein, “GA” or “gibberellic acid”, refers to GA3 and any gibberellin that gives a height increase in (GA-responsive) cereals, such as (GA-responsive) wheat plants, such as GA1 or GA4 or GA7 or mixtures of GA1 and / or GA3 and / or GA4 and / or GA7. This includes naturally existing plant hormones or synthetic growth factors derived from or based on a gibberellin. In one embodiment, GA as used herein refers to GA3 or to a mixture of GA4 and GA7.

[0060] As used herein, “highly GA-responsive plants”, when referring to plants in a field, refers to plants treated with GA in the field having at least a 12 % (or at least 13 %, at least 14 %, or at least 15 %, at least 20 %, or at least 25 %) increase in plant height at the start of flowering, or just before flowering, such as at Z59, compared to said plants at said (same) stage when not treated with GA. In one embodiment, highly GA-responsive male plants refers to the plants in the preceding sentence that are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller (after GA application from Z25 to Z50) at the start of flowering, or just before flowering, such as at Z59 (or at the end of flowering), than the matching female (male-sterile) plant used to produce hybrid seed with said male plant in hybrid seed production field. In one embodiment, the majority of the main spikes of the said highly GA-responsive plants stick out by at least 1 / 3rdor at least half of their length (or at least 2 / 3 of their length, or with their entire length) above the layer formed by the tip of the female main spikes within a plot or production area. In one embodiment, the majority of said highly GA-responsive male plants become at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller at the start of flowering, or just before flowering, such as at Z59, upon the application of gibberellic acid between Z25 and 250, than the majority of the low or not GA-responsive female plants. As used herein, low or not GA-responsive when referring to plants in a field, refers to plants treated with GA in the field having less than 12 % (or less than 10 %, less than 9 %, less than 8 %, less than 7 %, or less than 6 %) increase in plant height at the start of flowering, or just before flowering, such as at Z59, compared to said plants when not treated with GA. In one embodiment, low or not GA-responsive female (male-sterile) plants refers to the plants in the preceding sentence that are at least 5 cm, at least 10 cm, or at least 15 cm shorter (after GA application from Z25 to Z50) at the start of flowering, or just before flowering, such as at Z59 (or at the end of flowering), than the matching highly GA-responsive male plant used to produce hybrid seed with said female plant in hybrid seed production field.

[0061] As used herein, “GA-responsive seeds”, when referring to seeds in a seedling growth (lab) assay (such as the one exemplified herein), refers to seedlings of GA-treated seeds in such assay having at least a 20 % (or at least 25 %, or at least 30 %) increase (on average over at least 10-15 seeds) in seedling height 7 days after sowing compared to untreated control seeds of the same genotype. These GA-responsive seeds are candidate male plants to test for highly GA-responsive male plants in the field.

[0062] As used herein, “not GA-responsive seeds”, when referring to seeds in a seedling growth (lab) assay (such as the one exemplified herein), refers to seedlings of GA-treated seeds in such assay having less than 20 % (or less than 15 %, or less than 10 %) increase (on average over at least 10- 15 seeds) in seedling height 7 days after sowing compared to untreated control seeds of the same genotype. These GA-responsive seeds are candidate female plants to test for low or not GA- responsive female plants in the field.

[0063] As used herein, plants “with significantly longer peduncle” or “with significant increase in peduncle length”, after GA application, refers to the peduncle of the main tiller of said plants having an increased length of at least 15 % (or at least 20 %, at least 25 %, or at least 30 %) compared to the peduncle of the main tiller of said plants when not treated with GA.

[0064] As used herein, plants “with significantly thinner peduncle” or “with significant reduction in peduncle width”, after GA application, refers to the peduncle of the main tiller of said plants having a decreased width (such as measured in the middle of the peduncle length) of at least 5 % (or at least 6 %, at least 7 %, or at least 8 %) compared to the peduncle of the main tiller of said plants when not treated with GA.

[0065] As used herein, “a significant spike length increase” in plants, or plants “with significantly longer spike” after GA application, refers to the main spike of said plants having an increased length of at least 5 % (or at least 6 %, at least 7 %, or at least 8 %) compared to the main spike of said plants when not treated with GA.

[0066] The selective elongation of the high GA-responsive male plant line by means of foliar (spray) application of GA, allows better cross-pollination and facilitates the pre-harvest removal (or selective male spike treatment / application (e.g., to prevent / reduce seed growth or kill seeds)) of male spikes (e.g., by cutting, or by separately harvesting taller male heads), which allows to harvest hybrid seeds of higher purity (less male seed contamination) from the hybrid seed production field. In one embodiment, the selective elongation of male plants by GA is done in mixed planting of male and female plants, such as when a seed mix of male and female parent line seed is sown in the field.

[0067] In one embodiment, GA application causes a height increase of the male plants so that the heads of the male plants stand out above the height of the female heads by 4 or 5 cm, which can already be sufficient to improve cross-pollination. But if GA application causes a height increase of the male plants so that the heads of the male plants stand out above the female heads by 10 to 15 cm, cross-pollination will be further improved, as most or all of the male anthers will be above the female flowers. In one embodiment, GA application causes a height increase of the male plants so that the majority of main spikes of the male plants stand out above the majority of the main spikes of the female plants by at least 10 cm, or by 10 to 30 cm (such as by 15 to 30 cm, by 20 to 30 cm, by 10 to 20 cm, or by at least 15, by at least 20 cm; or by (at least) 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29 or 30 cm) so that the male heads can be (almost) entirely removed, destroyed, or harvested before harvest of the hybrid seeds formed on the female plants, or so that the peduncle of the male heads is tall and / or thin and male heads being more mobile (even with low wind) and spread pollen better, or so that the male heads bend down and lodge. Removal, destruction or harvest of the male heads can be done by a cutting equipment / device that cuts off the male heads standing above the female heads (and drops cut parts to the ground or collects them as plant waste (with or without shredding)), by a cutting device that also harvests the male grain, by wicking / wiping with a herbicide solution, or by electrocution of the male heads. This obviously in a manner that the female plant heads and the hybrid seeds they contain are not negatively affected.

[0068] In one embodiment the seeds are sown using a smart / precision planting equipment, wherein a mixed sowing pattern is obtained following a hexagonal honeycomb structure, wherein at each of the six edges of the honeycomb structure a female seed is sown, and in the center of the honeycomb structure a male seed is sown, or where 3 neighboring rows 1 , 2, and 3 are repetitively sown in the field, with row 1 and 2 having only female seeds and row 3 having a male seed every third seed and the other seeds in row 3 are female seeds, such as shown in the example in Figure 1 . The example in Figure 1 , will result in approximately 8 % males that are planted in between female plants, if in every third row 1 / 3 of male seeds are equally planted between female seeds, using a precision planter.

[0069] In one embodiment, a method is provided to produce bags or containers of highly GA-responsive male and low or not GA-responsive female cereal, such as wheat, hybrid parent seeds for hybrid seed production, comprising : a) selecting fertile male seeds that are highly GA-responsive, and filling a bag or container with said male seeds, b) selecting male-sterile female seeds that are low or not GA-responsive, and filling a bag or container with said female seeds. In one embodiment, said separate bags or containers are attached to a smart planter or emptied in separate channels of a smart planter so that each male and female seed can be sown at a pre-set location in the field by said planter.

[0070] In one embodiment, the (male-sterile) female or A line used herein is a dwarf or semi-dwarf line, and can also be a double or triple dwarf line.

[0071] In one embodiment, the male sterility is based on cytoplasmic male sterility, or genic male sterility. An embodiment of genic male sterility is one wherein the male sterility is a recessive gene, and the restorer gene is linked to a phenotypic marker gene, such as a color gene. In one embodiment, the male sterility is not transgenic, in another embodiment the male sterility system was produced using genome editing, such as gene knock out of a critical male fertility gene (typically in all functional versions of that gene in the plant genome).

[0072] Purity of hybrid seeds and the (cost) efficiency of both hybrid seed production and efficient A line maintenance are key factors for commercial success of cereal, such as wheat, hybrids. These aspects are expected to be significantly improved if the male plants can be selectively elongated in accordance with the current invention, especially in mixed planting.

[0073] Gibberellins which may be useful in the present invention include gibberellins GA1 , GA3 (= gibberellic acid), GA4 and GA7, in one embodiment this is gibberellic acid or GA3 (also known as Gibberellin A3 or GA3). Gibberellins are well known in the art (e.g., Yamaguchi, Ann. Rev. Plant Biology 59:225-251 (2008); Gao and Chu, Plant and Cell Physiology, 61 :1902-1911 , world wide web at doi.org / 10.1093 / pcp / pcaa104 (2020)).

[0074] In one embodiment, testing if a plant is highly GA-responsive, as used herein with respect to plant height increase, is easily done by foliar (spray) application of GA in the field and by later checking or measuring plant height (such as just before flowering (e.g., at Z59), or at the start of flowering to measure height difference between male and female plants before pollination, or at the end of flowering to measure height difference between male and female plants before harvest (e.g., it can then be decided to separately harvest male seeds before harvesting hybrid seeds)), and comparing to a control treatment without GA (such as water or the same solution as the GA treatment including any solvents, adjuvants or surfactants used, but without the GA), or to plants not treated with GA. Checking if a fertile male parent plant is taller than a female (male-sterile) parent plant after GA application is easily done, as it can immediately be seen if and how much the male plant heads stand above the height of the female heads - certainly in mixed planting with a minority of male (fertile) plants in between a majority of female (male-sterile) plants, that is easy to see / measure.

[0075] An initial test to determine GA-responsiveness of a plant line in accordance with the invention, and which can be used to pre-select candidate male and female plants to be used in the invention is checking if a significant height difference is measured in the length of the coleoptile and / or the first leaf of the seedling in a seedling growth assay, between seeds of that plant line treated with water (or the same solution as the GA treatment, but lacking the GA) and seeds of that plant line treated with a GA-containing solution, where the length measurement is several days after the GA application. E.g., seeds can be dipped in water (or control solution without GA) or GA solution for some minutes, air dried, and then sown at the same depth in soil, and grown as usual, and then the height from the soil to the tip of the seedling can be measured after several days (e.g., after a week or 10 days) - if a significantly taller seedling is measured after GA application compared to the control, the plant line is GA-responsive. In one embodiment, the method as described herein is used (essentially treating seeds with either GA or control solution, stratifying or pre-germinating the seeds, then planting them in soil, and measuring the height of the seedling that has grown from the seeds, and checking if there is a significant height difference between control and GA treatment), but in another embodiment published GA seedling growth tests such as those described by Pavlista et al. (2013, American Journal of Plant Sciences 4, pp. 2015-2022) or Chen et al. (PLoS ONE 9: e86431 (2014), world wide web at: doi:10.1371 / journal. pone.0086431) can be used. Seeds of plants that show a significant increase in seedling height when treated with GA in this seedling growth assay (compared to untreated seeds) are candidate male parent plants for use in the invention. In one embodiment this increase is expressed as % height increase compared to untreated control, since the absolute height can be different in different seedlings. Also, the plants that show the biggest increase in seedling height when treated with GA in this seedling growth assay are candidate male parent plants for use in this invention when separate harvest / removal of the male heads is intended before the hybrid seed harvest, or when a long and thin peduncle is wanted on male plants; and seeds of plants that show no or little increase in seedling height when treated with GA in this seedling growth assay (compared to untreated seeds) are candidate female parent plants for use in the invention.

[0076] In one embodiment, the desired difference in GA responsiveness between a particular male and a female parent combination depends on the height of the male and female plant without the application of GA. The primary goal of the GA application in the context of this invention is to create a situation in which the majority of the male main spikes at least stick out by half of their length (or 2 / 3 or entirely) above the layer formed by the majority of the tips of the female main spikes within a plot or production area. Therefore, in case where the male of two particular hybrid parents is intrinsically shorter than the female a higher difference in GA responsiveness between male and female is required (such as very highly GA-responsive male and a no GA-responsive female), as compared to a situation where the male is of approximately the same height as the female. Also, if male and female plants are of approximately the same height in absence of GA application, and the female parent plants have no height response after GA application in the field, then the male parent plants need not be very highly responsive to GA, and a moderate or weak response of the male plants to GA in the field may suffice, as long as at least half of the majority of the main spikes of the male plants stick out above the majority of the main spikes of the female plants. While ideally the male parent increases in plant height so that it is taller than the female plant, and best so that a majority of the male plant (primary) ears stand out (partially or entirely) above the female plants it is paired with, in one embodiment, when in absence of GA application, the male parent plant is shorter than the female parent plant, then an increase in plant height of the male plant by GA application (as described herein) so that the male parent plant becomes at least as tall as the female plant just before or at flowering (e.g., Z59 or Z60) can be sufficient to improve hybrid seed production, as shown herein, and in one embodiment (said male plant is selected so that) heading of such male plant is not delayed upon GA application or the flowering period of such male is not shortened by GA application (compared to said male when not treated with GA). Hence, GA application can expand the pool of male plants that can be used with a certain female plant, since males that are normally too short compared to the female plant can be made selectively taller if they are GA-responsive (and the female plant is less GA-responsive), and if heading is not delayed or the flowering period is not shortened by GA application, said male can better pollinate the female plant.

[0077] In one embodiment, in absence of any GA application, the majority of said highly GA-responsive male plants as described herein are of the same height or are shorter than the majority of the low or not GA-responsive female plants described herein (when grown in the same field with the same standard agronomic treatments), or in absence of any GA application the majority of said male plants are less than 4 cm, less than 5 cm, less than 6 cm, less than 7 cm or less than 8 cm taller than the majority of said female plants. The height can be measured just before flowering (such as at Z59), at the start of flowering, or at the end of flowering.

[0078] In one embodiment of the invention, in a pair of parent plants for hybrid seed production, the male parent plant is shorter than the female parent plant, or is of approximately the same height as the female (e.g., the majority of the male main spikes do not stick out above the layer formed by the majority of the tips of the female main spikes within a plot or production area, or stick out by less than half of their spike length) in absence of GA application in the field, wherein the height is measured in the field or just before flowering, such as at Z59, at the start of flowering or at the end of flowering. In another embodiment, in a pair of parent plants for hybrid seed production, the male parent plant can be shorter or taller or can be of approximately the same height as the female parent plant in absence of GA application, and the male responds to GA application in the field by a significantly increased peduncle length and / or decreased peduncle width, and the female does not respond to GA application in the field by a significantly increased peduncle length and / or decreased peduncle width, wherein the peduncle length / width is measured in the field just before flowering, such as at Z59, or at the start of flowering or at the end of flowering. In another embodiment, in a pair of parent plants for hybrid seed production, the male parent plant can be shorter or taller or can be of approximately the same height as the female parent plant in absence of GA application, and the male and / or female plants respond to GA application in the field by a significantly increased spike length increase, wherein the spike length is measured in the field just before flowering, such as at Z59, at the start of flowering or at the end of flowering.

[0079] The presence of GA-sensitive Rht (reduced height) alleles allows a height response if GA is applied, whereas plants carrying GA-insensitive Rht alleles do not respond to GA. In this regard, this application refers to the term as used in the literature that refers to Rht alleles / genes as either being “GA-insensitive” or “GA-sensitive”, when referring to Rht alleles / genes. If none of the (semi- )dwarf Rht genes is present in a plant, so that no reduced height is obtained, the plant is GA- responsive. Wheat plants that have both a GA-sensitive and a GA-insensitive Rht allele (so-called sesqui dwarfs) are GA-insensitive. Known Rht genes said to be GA-sensitive in wheat include Rht4, Rht5, Rht7, Rht8, Rht9, Rht12, Rht13, Rht14, Rht15, Rht16, Rht18, Rht20, Rht24 and Rht25. Known Rht genes said to be GA-insensitive in wheat include Rht-B1 , Rht-D1 , Rht-B1c, Rht-B1c semi-dwarf mutants like Rht-B1c.21 , Rht-B1c.23 or Rht-B1c.26 described in WO2014 / 028980, Rht10, and Rht11. In the wheat genotypes exemplified herein the highly GA- responsive plants mostly contain Rht24 (and no GA-insensitive gene), and the low or not GA- responsive plants contain Rht-B1d and / or Rht-D1 b.

[0080] Also some other genes are known to reduce plant height in wheat, and are independent of the GA pathway, and hence should be GA-sensitive, such as ZnF deletion / inactivation resulting in semidwarf wheat plants (see, e.g., Song et al. Nature 617, 118-124 (2023), world wide web at: doi.org / 10.1038 / s41586-023-06023-6). Hence, GA-responsive semi-dwarf wheat plants with ZnF deletion or inactivation (and without any GA-insensitive Rht genes) can also be used in male plants of the invention.

[0081] In one embodiment of the invention, the male parent plants contain no known Rht gene causing reduced height (such as wild-type tall Rht gene like Rht-B1a or Rht-D1a), or contain Rht8, Rht13, Rht18, Rht25, or contain Rht24 as height reduction gene. In one embodiment the cereal plants of the invention are wheat plants (including common / bread wheat (Triticum aestivum), durum wheat (Triticum durum), einkorn (Triticum monococcum), Khorasan wheat (T. turgidum ssp. turanicum), spelt (Triticum spelta), or emmer (T. turgidum subsp. dicoccum )), such as hexapioid spring or winter wheat, or are the closely related barley (Hordeum vulgare), rye (Secale cereale) or Triticale plants (Triticale is a cross between wheat (Triticum durum or Triticum aestivum) and rye). In one embodiment, in a hybrid parent pair for hybrid seed production, the male plants are taller than the female plants in the field (at the start or at the end of flowering) and this height difference is caused by GA application in the field over said plants, and does not exist in absence of any GA application in the field.

[0082] If the intention is to later cut the male plants after pollination so as to decrease the amount of male selfed seeds in harvested hybrid seed produced, which can be particularly useful in mixed planting so as to allow a larger proportion of males in seed production but still meet hybridity levels required by regulators, it may be advantageous to select a male plant that has a strong height response to an application of GA, and a female plant that has no or a very low height response to an application of GA.

[0083] In one embodiment of the invention, besides application of GA, (additional) measures are taken to broaden / enlarge the pollination window of the fertile male plants of the invention, optionally without changing the pollination window of the male-sterile female plants of the invention, and / or (additional) measures are taken to increase tillering of said male plants, optionally without changing the tillering of said male-sterile female plants.

[0084] In one embodiment, the GA solution contains one or more auxiliaries or surfactants. Suitable auxiliaries include solvents, liquid carriers, solid carriers or fillers, surfactants, dispersants, emulsifiers, wetters, adjuvants, solubilizers, penetration enhancers, protective colloids, adhesion agents, thickeners, humectants, repellents, attractants, feeding stimulants, compatibilizers, bactericides, anti-freezing agents, anti-foaming agents, colorants, tackifiers and binders.

[0085] Suitable surfactants include surface-active compounds, such as anionic, cationic, non-ionic and amphoteric surfactants, block polymers, polyelectrolytes, and mixtures thereof. Such surfactants can be used as emusifier, dispersant, solubilizer, wetter, penetration enhancer, protective colloid, or adjuvant. Examples of surfactants are listed in McCutcheon’s, Vol.1 : Emulsifiers & Detergents, McCutcheon’s Directories, Glen Rock, USA, 2008 (International Ed. or North American Ed.).

[0086] Suitable anionic surfactants or (ammonium) salts of sulfonates, sulfates, phosphates, carboxylates, and mixtures thereof. Examples of sulfonates are alkylarylsulfonates, diphenylsulfonates, alpha-olefin sulfonates, lignine sulfonates, sulfonates of fatty acids and oils, sulfonates of ethoxylated alkylphenols, sulfonates of alkoxylated arylphenols, sulfonates of condensed naphthalenes, sulfonates of dodecyl- and tridecylbenzenes, sulfonates of naphthalenes and alkylnaphthalenes, sulfosuccinates or sulfosuccinamates. Examples of sulfates are sulfates of fatty acids and oils, of ethoxylated alkylphenols, of alcohols, of ethoxylated alcohols, or of fatty acid esters. Examples of phosphates are phosphate esters. Examples of carboxylates are alkyl carboxylates, and carboxylated alcohol or alkylphenol ethoxylates.

[0087] Suitable nonionic surfactants include alkoxylates, N-subsituted fatty acid amides, amine oxides, esters, sugar-based surfactants, polymeric surfactants, and mixtures thereof. Examples of alkoxylates are compounds such as alcohols, alkylphenols, amines, amides, arylphenols, fatty acids or fatty acid esters which have been alkoxylated with 1 to 50 equivalents. Ethylene oxide and / or propylene oxide may be employed for the alkoxylation, preferably ethylene oxide. Examples of N-subsititued fatty acid amides are fatty acid glucamides or fatty acid alkanolamides. Examples of esters are fatty acid esters, glycerol esters or monoglycerides. Examples of sugar- based surfactants are sorbitans, ethoxylated sorbitans, sucrose and glucose esters or alkylpolyglucosides. Examples of polymeric surfactants are home- or copolymers of vinylpyrrolidone, vinylalcohols, or vinylacetate.

[0088] Suitable cationic surfactants include quaternary surfactants, for example quaternary ammonium compounds with one or two hydrophobic groups, or salts of long-chain primary amines. Suitable amphoteric surfactants include alkylbetains and imidazolines. Suitable block polymers include block polymers of the A-B or A-B-A type comprising blocks of polyethylene oxide and polypropylene oxide, or of the A-B-C type comprising alkanol, polyethylene oxide and polypropylene oxide. Suitable polyelectrolytes include polyacids or polybases. Examples of polybases are polyvinylamines or polyethyleneamines. Examples of adjuvants or surfactants that can be used in a GA solution are Mero® (an emulsifiable concentrate containing rapeseed fatty acids esters and ethoxy (7) tridecanol, see world wide web at: assets.ctfassets.net / l2hapltrg3cz / 3owDAXTrHeGTHmnE81 P2C1 / 4de0957699e32094a7a50740 e6a296b8 / mero_gb_ra6a.pdf) or Actirob® (an emulsifiable concentrate containing rapeseed oil methyl ester, see world wide web at: www.edppiveteau.fr / files / notices / actirob-b-securite- 52ecbb172af4a.pdf), or any emulsifiable concentrate containing plant fatty acid esters, such as oilseed rape oil fatty acid esters. In one embodiment, the GA solution is neutral or weakly acidic.

[0089] In one embodiment, the GA solution, as used herein, can be an existing GA solution such as the water-soluble granules containing GA3 in Berelex® 40 SG (Valent BioSciences LLC), or the water- soluble granules containing GA3 in Proliant® (Valent BioSciences LLC), particularly such existing GA solution with an added surfactant (such as Actirob® or Mero®, or any surfactant containing an emulsifiable concentrate containing rapeseed fatty acids esters and ethoxy (7) tridecanol, or containing an emulsifiable concentrate containing rapeseed oil methyl ester, or any non-ionic surfactant). In one embodiment, Berelex® 40 SG can be combined with Actirob® or Mero®, or with any surfactant containing an emulsifiable concentrate containing rapeseed fatty acids esters and ethoxy (7) tridecanol, or containing an emulsifiable concentrate containing rapeseed oil methyl ester, or with any non-ionic surfactant, to obtain a GA solution according to the current invention. In another embodiment, Proliant® can be combined with Actirob® or Mero®, or with any surfactant containing an emulsifiable concentrate containing rapeseed fatty acids esters and ethoxy (7) tridecanol, or containing an emulsifiable concentrate containing rapeseed oil methyl ester, or with any non-ionic surfactant, to obtain a GA solution according to the current invention. In one embodiment, the GA solution is a solution containing GA3, optionally containing a surfactant, that has been registered for use on wheat or cereals, particularly wheat, barley, rye, or triticale. In one embodiment, the adjuvant or surfactant is Heliosol® (Terpineol (CAS n°8000-41-7) emulsifiable concentrate, from Action Pin (world wide web at: agriculture.action-pin.com / en / produit / adjuvants / heliosol)), or Gondor® (lecithin emulsifiable concentrate, from De Sangosse (world wide web at: www.desangosse.fr / produit / gondor / ), or Exsentia® (methyl esters + ammonium sulphate, from De Sangosse (world wide web at: www.desangosse.fr / produit / adjuvant-exsentia-in-tech / )), or any other adjuvant authorized / registered for use with a PGR.

[0090] In one embodiment, the GA solution of the invention includes a surfactant to increase uptake of the GA by the plant.

[0091] In one embodiment, a seed treatment is applied on the male and female seeds as used herein. In one embodiment, seed treatments with different color are used so that the male seeds have a different color from the female seeds after application of said seed treatment, and can be readily distinguished in a seed bag containing a mix of male and female seeds.

[0092] In one embodiment, the first GA application to the cereal, such as wheat, plants of the invention is done after sowing or after seed germination, particularly after / at growth stage Z25 on the Zadoks growth scale and before heading, particularly before growth stage Z51 on the Zadoks growth scale.

[0093] In one embodiment, in jurisdictions where such processes are excluded from patent protection, any of the methods or uses described herein is not an essentially biological process for the production of plants. In one embodiment, in jurisdictions where such processes are excluded from patent protection, any of the methods or uses described herein does not contain a step of sexual crossing or selfing of plants (in one embodiment, such method or use is before the first spike starts flowering, or after the last spike ends flowering, such as when all plants are fully mature and ready for harvest). In another embodiment, in jurisdictions where such processes are not excluded from patent protection, included herein are methods or uses including the pollination of (male-sterile) female plants by (fertile) male plants to produce hybrid seed, and the selfing of male plants.

[0094] In one embodiment, the GA treatment of the invention is an application of GA between stages Z25 to Z50, which can be followed by a second later application of GA (as needed) between stages Z30 to Z50. In one embodiment, the GA treatment of the invention is an application of GA between stages Z30 to Z36, which can be followed by a second application of GA (as needed) between stages Z37 to Z50, Z38 to Z50, Z39 to Z50, or Z38 to Z50, so as to sufficiently increase male plant height in hybrid seed production, particularly in mixed planting. In one embodiment, the GA treatment of the invention is an application of GA at stage Z30, at stage Z31 , at stage Z32, at stage Z33, at stage Z34, at stage Z35, or at stage Z36, which can be followed by a second application of GA (as needed) at stage Z37, at stage Z38, at stage Z39, at stage Z40, at stage Z41 , at stage Z42, at stage Z43, at stage Z44, at stage Z45, at stage Z46, at stage Z47, at stage Z48, at stage Z49, or at stage Z50, so as to sufficiently increase male plant height in hybrid seed production, particularly in mixed planting of female male-sterile plants and fertile male plants. In one embodiment, a third GA application can be envisaged if insufficient male height increase was obtained with the above two GA applications in a certain field (e.g., due to unfavorable environment), or so as to significantly elongate the peduncle and / or decrease peduncle thickness in male plants to improve male head mobility or get male head lodging, and that third GA application is between stages Z40 and Z56, or between Z40 and Z50. In one embodiment, that third GA application is between Z40 and Z60. In one embodiment, the third GA treatment of the invention is an application of GA at stage Z40, at stage Z41 , at stage Z42, at stage Z43, at stage Z44, at stage Z45, at stage Z46, at stage Z47, at stage Z48, at stage Z49, or at stage Z50, or between Z41 and Z50, or any of the other stages described herein with respect to peduncle length increase / width decrease. A later GA application such as a second and / or third GA application is an option, and depends on the height difference caused by the earlier GA application, and the intended height difference at anthesis, or if male head lodging is intended. When the intention is to selectively cut away / remove the male heads standing out of a mixed planting field after flowering, or to selectively harvest the male heads standing out of a mixed planting field before harvesting the hybrid seed from the female plants, a second and / or third GA application may be useful to get a sufficient height difference with the female heads. In one embodiment of the invention, the GA application over the male and female plants as described herein is after sowing and before heading, or is after sowing and before the start of anthesis.

[0095] In one embodiment, the GA treatment is an early application at (around) Z30, leaving the option later in the season (e.g. at around Z48), to apply GA a second time in case the first GA application fails due to environmental effects (such as drought and or too much rain) or due to insufficient difference in responsiveness between male and female to obtain the desired height difference or peduncle length increase / width decrease (and similarly a 3rdGA application may be done when there is insufficient effect from a 1stand / or 2ndGA application).

[0096] Z stages as used herein refer to the Zadoks cereal growth staging scales (“Zadoks growth scales” herein, see Zadoks et al., Weed Research 14:415-421 (1974), world wide web at: / / en. wikipedia.org / wiki / Cereal_growth_staging_scales). A comparison to other cereal / wheat growth stage scales (such as Feekes and BBCH scales) and figures and terms for plant parts at several growth stages can be found in Celestina et al. (Eur. J. Agronomy 147(2023)126824:1-22, world wide web at doi.org / 10.1016 / j.eja.2023.126824), or can be found at the world wide web at: en.wikipedia.org / wiki / Cereal_growth_staging_scales, or can be found at the world wide web at: www2.ca.uky.edu / agcomm / pubs / agr / agr224 / agr224.pdf.

[0097] In one embodiment, the GA application on said cereal, such as wheat, plants can be combined with a herbicide or fungicide active ingredient (as tank-mix or application from separate tanks on the same tractor), for example an early GA application (around Z30) with a herbicide and a later GA application (e.g. Z37 to Z50) with a foliar fungicide.

[0098] In one embodiment, the highly GA-responsive male plant of the invention has no known GA- insensitive allele resulting in (semi-)dwarf growth in wheat, or has no known GA-insensitive allele and has a GA-sensitive (semi-)dwarf Rht gene which can be a native gene or a mutated gene, including but not limited to an Rht gene such as Rht8, Rht13, Rht18, Rht25, or Rht24, or has no known GA-insensitive allele and has a non-Rht GA-sensitive gene causing (semi-)dwarf growth, such as a deleted / inactivate ZnF gene (Song et al. Nature 617, 118-124 (2023), world wide web at: doi . org / 10.1038 / s41586-023-06023-6) .

[0099] CN1029721A apparently describes a method to cultivate improved wheat seeds by chemical sterilization, wherein at the early heading stage, a mixture containing a male sterilization agent (2- chloroethylphosphonic acid (also known as Ethrel)), triacontanol and gibberellin are applied, and the latter 2 growth regulators are apparently used to alleviate toxicity / poisoning caused by the male sterilization agent used. Hence, in one embodiment, the GA solution of the invention does not cause male sterility, or the GA solution of the invention does not contain a chemical hybridization agent, or the GA solution of the invention does not contain 2-chloroethylphosphonic acid (also known as Ethrel) in a concentration that causes male sterility.

[0100] In one embodiment of the invention, the male-sterile female cereal plant, such as wheat, is obtained using cytoplasmic male sterility (CMS, such as CMS from Triticum timopheevii), or is obtained using a chemically-induced male sterility (using a chemical hybridization agent (CHA)), or is obtained using a genic male sterility, such a 2-line hybrid system. A 2-line male sterility system may be used with a maintainer plant producing sterile seeds with normal seed color, and fertile cereal seeds with a different seed color (like blue or purple) upon selfing - the maintainer plant contains one or more mutations in an endogenous gene that causes male sterility, and a chromosome or chromosome part comprising a fertility restoration gene that restores male fertility, which is linked to a locus conferring a sortable seed phenotype (such as a different seed color). Any regular cereal, such as wheat, plant can act as male parent to restore fertility. The sortable seed phenotype (such as seed color) locus and the fertility restoration gene may be located on a monosomic addition chromosome (42+1 Chr plants) or on a homoeologous chromosome pair (42 Chr plants). The color locus and the restorer gene may be either on the same or different arms of the same chromosome. For possible embodiments of such a 2-line male sterility systems, reference may be made to e.g. Whitford et al., 2013, J. Exp. Botany 64 (18): 5411-5428, and Zhou et al., 2006, CropScience 46:250-255, CN 100420368, WO 2019 / 043082 A1 , WO 2020 / 056259 A1 and WO 2023 / 005883 A1. In one embodiment, the color locus and the restorer gene may preferably be located on the same chromosome arm of a monosomic addition chromosome, or on the same arm of one of the 2 chromosomes in a homoeologous chromosome pair. Thus, these genes may be closely linked, or alternatively the color locus and the restorer gene may be each located on another chromosome arm of the same addition or homoeologous chromosome. As an example, the restorer gene may be a MS1 , MS5, MS9, MS22, MS26, or MS45, specifically depending on what causes the male sterility. For example if a mutation or inactivation or deletion of an MS1 gene causes male sterility, then MS1 may be the restorer gene to use, and if mutation or inactivation or deletion of all MS45 genes (on each wheat sub-genome (A, B and D)) causes male sterility, then MS45 may be the restorer gene to use. In one embodiment, the color locus can be the blue aleurone locus as described in US 11 ,390,877 B2, WO 2019 / 043082 A1 or WO 2020 / 056259 A1. The blue aleurone locus may be obtainable or obtained, e.g., from Agropyron elongatum, Agropyron trichophorum, Triticum boeoticum, Triticum monococcum, Triticum thaoudar, Triticum aestivum, or Thinopyrum ponticum or from wheat lines having an introgressed BLA locus or may be from known seed accessions Sebesta Blue, Blue Sando, Blue Baart, Blue Onas, Blue 1 , PBB, or Blue Norco.

[0101] In one embodiment of the invention, the male-sterile female plants of the invention comprise triple homozygous mutations of the MS45 male-fertility polynucleotide in wheat, which mutations cause a male sterility phenotype. In one embodiment, such male-sterile plants can be obtained from a 2-line hybrid system in wheat that comprises triple homozygous mutations of a MS45 male-fertility polynucleotide, and a plant restoration donor chromosomal component comprising a 4E chromosomal component from Thinopyrum or Agropyron, the 4E chromosomal component comprising: a) a plant polynucleotide that confers a plant seed phenotype (such as seed color, e.g. blue aleurone, P gene, anthocyanin, or Kala 4); and (b) a MS45 male-fertility restoration locus restoring male-fertility in a ms45 male-sterile wheat plant by the 4E chromosomal component, wherein expression of the 4E donor chromosomal component functionally complements the malesterility phenotype from the triple homozygous MS45 mutations so that the wheat plant is male- fertile. In one embodiment, the plant polynucleotide that confers the plant phenotype (such as seed color) is located on the same chromosomal arm of the 4E chromosomal component as the MS45 male-fertility restoration locus (not separated by a centromere). In one embodiment, said MS45 hybrid system and the male-sterile female wheat plant are as described in W02020056259.

[0102] In another embodiment, the male-sterile female cereal, such as wheat, plants of the invention are obtained from a 2-line hybrid system in wheat that comprises a homozygous mutation in the MS1 gene (such as the known mutations ms1a, ms1 b, ms1c, ms1d, ms1e, or ms 1f), and a plant restoration chromosomal component comprising: a) a plant polynucleotide that confers a sortable plant seed phenotype (such as seed color, e.g. blue aleurone, P gene, anthocyanin, or Kala 4), and (b) an MS1 plant polynucleotide restoring male-fertility in an ms1 male-sterile wheat plant, wherein expression of the chromosomal component functionally complements the male-sterility phenotype from the homozygous MS1 mutation so that the wheat plant is male-fertile. In one embodiment, the plant polynucleotide that confers the sortable plant seed phenotype (such as seed color) is located on the same chromosomal arm of the chromosomal component as the MS1 male-fertility restoration locus (not separated by a centromere). In one embodiment, said MS1 hybrid system and the male-sterile female wheat plant are as described in published patent applications CN100420368, W02019043082 or W02023005883.

[0103] In one embodiment of the invention, any use or method of the invention includes the step of crossing or cross-pollination of the male and female plants of the invention, which is done by man based on plants selected by man as being highly GA-responsive and low or not GA-responsive.

[0104] In one embodiment of the invention, based on the surprising finding that low or not GA-responsive plants have a lower height decrease when treated with a (gibberelline pathway inhibitor) plant growth regulator than highly GA-responsive plants, the male and female plants of the invention are highly GA-responsive and are planted in separate rows or strips and said GA solution is applied only on the male plants and said plant growth regulator is applied only on the female plants.

[0105] In one embodiment of the invention, the GA-responsive male plants of the invention have (or were selected to have) no (significant) delay in heading or flowering date, or have a (significantly) earlier heading or flowering date, when treated with a GA solution as described herein (which is in contrast to what was reported for the GA-responsive male plants in US2024 / 0016153).

[0106] In one embodiment of the invention, the female plants of the invention have (or were selected to have) no decrease in hybrid seed yield, or have an increased hybrid seed yield, when treated with a GA solution as described herein (which is in contrast to what was reported for the GA-responsive male plants in US2024 / 0016153).

[0107] In one embodiment of the invention, the taller male plants of the invention, as obtained after application of a GA solution, allow to improve the hybrid purity of the hybrid seed harvested from a mixed planting field (wherein no row planted contains only male or only female plants), by removing or separately harvesting all or part of the male plant ears standing out above the female plants, before harvesting the hybrid seed - this surprisingly allows higher % of males such as at least 7.5 %, at least 10 %, at least 12 %, at least 15 %, or even at least 20, 25 or 30 % male plants / seeds, to be used in a mixed planting field, while still obtaining a hybrid seed purity above 85 or 90 %. In one embodiment, the male plant seed of the invention has a white seed color, and the hybrid seed of the invention that is produced on the female plants has a red seed color, so that hybrid seed purity can be further improved by removing most or all of the male plant seed from the hybrid seed using a seed color sorter, as is known in the art.

[0108] In one embodiment of the invention, application of the GA solution is at least once between Z25 and Z60, such as between Z40 and Z60, or after Z45 (or after the end of the vegetative stage), and in one embodiment at least 2 applications with a GA solution as described herein are done, one earlier treatment so that the male plants, particularly when the male plant is shorter or grows less vigorous than the female plants, can grow out to capture light and establish themselves in the mixed planting field amongst the majority of female plants (such as between Z25 and Z41 , or between Z29 and Z41), and one later treatment so that the male plants are significantly taller at the start of flowering, or at full maturity, just before harvest (such as a treatment between Z40 and Z60, or between Z40 and Z50 or between Z45 and Z60 or between Z45 and Z50).

[0109] In one embodiment, the low or not GA-responsive female plant of the invention is responsive to GA or is not GA-insensitive, even when containing GA-insensitive Rht dwarf alleles such as Rht1 and / or Rht2, so that it increases plant height after treatment with a GA solution in the field, but the plant height response is significantly less than that of the highly GA-responsive male plant of the invention. In one embodiment, the plant growth regulator of the invention comprises trinexapac-ethyl as active ingredient, or comprises a surfactant to improve uptake by the plants.

[0110] Also described herein are the following numbered embodiments:

[0111] 1 . A method to improve growing or cultivation of hybrid cereal, such as wheat, parents, comprising the steps of: a) sowing seeds growing into highly GA-responsive male plants and seeds growing into low or not GA-responsive female plants in the same field, so that said male plants are randomly interspersed amongst said female plants in a mixed planting setup, or said male plants are planted in (a special or random configuration in) rows containing male and female plant(seed)s, and b) applying a solution comprising gibberellic acid over the top of that field of male and female plants between stage Z25 and Z50 on the Zadoks growth scale, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 15 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than 10 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, iii) optionally, the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid (such as 100, 150, 200, 250, 300, 350, 400, 450 or 500 ppm, or 200-400 ppm) and is applied in a volume between 100 and 500 liter per hectare (such as 100-400 or 200-400 l / ha) between Zadoks growth scale stages Z25 and Z50 (such as between Z30 and Z50, between Z35 and Z50, or between Z40 and Z50).

[0112] 2. Embodiment 1 , including the step of mixing 3-30 %, such as 3-25 % or 3-20 % of seeds growing into said highly GA-responsive male plants with 97-80 % of seeds growing into said low or not GA- responsive female plants in a bag or container, or including the step or planting / sowing in a field a combination of male and female seeds / plants in a specific planting / sowing scheme or structure (such as in a honeycomb structure as in Fig. 1) or randomly, such as wherein said mixed seed or said field contains 3 to 4%, 4 to 5%, 5 to 6%, 6 to 7%, 7 to 8%, 8 to 9%, 9 to 10%, 10 to 11 %,11 to 12%, 12 to 13%, 13 to 14%, 14 to 15%, 15 to 16%, 16 to 17%, 17 to 18%, 18 to 19%, or 19 to 20%, or contains 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of male seeds, or contains 7.5-25 %, 7.5-20 %, 7.5-15 %, or 10-15 % of male seeds.

[0113] 3. Embodiment 2, including the step of applying a gibberellic acid solution between and including growth stage Z30 and Z50 on the Zadoks growth scale, such as between Z30 to Z48, Z30 to Z39, or Z30 to Z36, or any of the stage(s) described herein, so as to increase the height difference between the male and the female plants; optionally including the step of harvesting hybrid seed; optionally the GA treatment is an application of GA between stages Z25 or Z36 or Z30 to Z36, which can be followed by a second application of GA between stages Z37 to Z50, Z38 to Z50, Z39 to Z50, or Z38 to Z50.

[0114] 4. Any one of the prior embodiments, wherein the total number of said mixed male and female seeds contains from 3 to 30 %, such as 3 to 25 % or 3 to 20 % fertile male seeds, such as 3 to 4%, 4 to 5%, 5 to 6%, 6 to 7%, 7 to 8%, 8 to 9%, 9 to 10%, 10 to 11 %,11 to 12%, 12 to 13%, 13 to 14%, 14 to 15%, 15 to 16%, 16 to 17%, 17 to 18%, 18 to 19%, or 19 to 20% , or 20 to 21 %, or 21 to 22 %, or 22 to 23 %, or 23 to 24 %, or 24 to 25 % or 25 to 30 %, or 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21 %, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30 % fertile male seeds.

[0115] 5. A method to improve hybrid cereal, such as wheat, seed purity from a mixed planting field containing highly GA-responsive male cereal, such as wheat, plants and low or not GA-responsive female cereal, such as wheat, plants at full maturity, ready to be harvested (e.g., Z91 or Z92), wherein said plants were previously treated with a solution containing gibberellic acid between Zadoks growth scale stages Z25 and Z50, said method comprising the steps of: a) cutting off, destroying or separately harvesting the male plant spikes standing above the height of the female plant spikes after the end of flowering (of all plants in said field) using a cutting or destruction or harvesting device above the height of the female plant spikes, and b) harvesting the hybrid seeds from said female plants in that field, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 15 % increase in plant height just before the start of flowering at Z59, compared to said plants at that stage when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % increase in plant height just before the start of flowering at Z59, compared to said plants at that stage when not treated with a gibberellic acid solution, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and was applied in a volume between 100 and 500 liter per hectare, such as such a method that includes the step of GA application between Z25 and Z50, or any one or all of the steps of: selecting GA-responsive seeds or plants as described herein, mixing seeds as described herein, sowing seeds in the field, applying GA and any of the stages or doses / volumes as described herein, or applying standard agronomic treatments which may include a (or at least one) plant growth regulator (PGR) application (such as between Z30 and Z32).

[0116] 6. A method to produce bags or containers of cereal, such as wheat, seed for sowing, comprising: a) selecting (fertile) male cereal, such as wheat, seeds and (male-sterile) female cereal, such as wheat, seeds, wherein plants grown from said male seeds are highly GA-responsive male plants and plants grown from said female seeds are low or not GA-responsive female plants, b) filling bags or containers with 3-20 % or 3-30 % of said male seeds and 97-80 % or 97- 70 % of said female seeds, so that said bags or containers each contain a predetermined mixture of male and female seeds, and optionally c) closing said bags or containers, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 15 % increase in plant height at growth stage Z59 (before the start of flowering), compared to said plants when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % increase in plant height at growth stage Z59 (before the start of flowering), compared to said plants when not treated with a gibberellic acid solution, iii) optionally, the majority of said highly GA-responsive male plants become at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants upon application of a gibberellic acid solution, and iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50.

[0117] 7. A kit containing a stable gibberellic acid product for making a gibberellic acid solution, and the bag or container of embodiment s, optionally with gibberellic acid spraying instructions.

[0118] 8. Any of the prior embodiments, wherein said gibberellic acid solution comprises 100 to 300 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare. 9. A method to improve hybrid cereal, such as wheat, parent plant selection, comprising the steps of: a) providing a population of cereal, such as wheat, plant seeds that are fertile male parent plant seeds and providing a population of cereal, such as wheat, plant seeds that are male-sterile female parent plant seeds for hybrid cereal, such as wheat, seed production, b) selecting highly GA-responsive seeds from said population of male plant seeds, and c) selecting low or not GA-responsive seeds from said population of female plant seeds, and optionally d) mixing 3-20 % or 3-30 % of said highly GA-responsive male plant seeds with 97-80 % or 97-70 % of said low or not GA-responsive female plant seeds in a bag or container, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 15 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, iii) optionally, the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, and iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50, such as such a method that includes the step of sowing the seeds in a field, and GA application over the top of the plants in said field between Z25 and Z50 or at any stage described herein, or any one or all of the steps of: (pre-)selecting GA-responsive seeds or plants as described herein (such as by testing GA- responsiveness in a seedling growth assay as described herein), or applying standard agronomic treatments which may include a(t least one) plant growth regulator (PGR, gibberellin pathway inhibitor) application (such as between Z30 and Z32, or at Z30, Z31 or Z32) before the GA application or at the same day / time as the GA application (in a separate tank or as a tank mix), and optionally includes the step of harvesting the hybrid seeds produced (with removal / destruction / prior harvest of the male seeds that stick out above the female spikes, or removal of smaller male seeds as described herein by size / density sorting), or such as a method as described in this embodiment, wherein said male plants are selected for increased peduncle length and / or decreased peduncle width, as described herein, after application of said GA solution between Z41 and Z50.

[0119] 10. Embodiment 9 including the step of sowing said seeds in a field so that male plants will emerge randomly, or in a specific pattern (such as a honeycomb pattern), in between female seeds in a mixed planting setup.

[0120] 11 . Any one of the above or below numbered embodiments, wherein the male seeds have a different color, fluorescence, shape, size, or other sortable marker profile so that they can be sorted from the hybrid seeds using a seed-sorting device.

[0121] 12. Any of the above or below numbered embodiments, wherein said male plant is a male plant selected to have a significant peduncle length increase and / or peduncle width decrease (as described herein) after application of gibberellic acid between Z41 and Z50 compared to untreated plants, or compared to the female plants also treated with gibberellic acid.

[0122] 13. Embodiment 12, wherein said selected male plant has an increase in peduncle length at Z59 of at least 10 %, or at least 15 % (or at least 20 %, at least 25 %, or at least 30 %) in the peduncle of the main tiller of said male plants after GA application, compared to said male plants at said stage when not treated with GA, and / or the peduncle of the main tiller of said plants has a decreased width at Z59 (such as measured in the middle of the peduncle length) of at least 5 % (or at least 6 %, at least 7 %, or at least 8 %) after GA application, compared to the peduncle width of the main tiller of said plants at said stage when not treated with a gibberellic acid solution. 14. A method to improve selection of parent plants to produce hybrid cereal, such as wheat, seed, comprising determining the GA-responsiveness to pre-select candidate fertile male and candidate male-sterile female cereal, such as wheat, seeds, by selecting male seeds that are GA-responsive and female seeds that are not GA-responsive in a seedling growth assay, wherein said male seeds are GA-responsive in said assay when seedlings of said male seeds when treated with a gibberellic acid solution have at least a 20 % (or at least 25 %, or at least 30 %) increase in seedling height 7 days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay, and wherein said female seeds are not GA-responsive in said assay, when seedlings of said female seeds when treated with a gibberellic acid solution have less than 20 % (or less than 15 %, or less than 10 %) increase in seedling height 7 days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay, such as such a method comprising sowing seeds for GA- responsive male plants and seeds for not GA-responsive female plants in a field, such as in mixed planting as described herein, and / or comprising applying GA over the top of said plants between Z25 and Z50, and / or comprising harvesting hybrid seed with improved purity / hybridity from said field, as described herein.

[0123] 15. Use of the method of embodiment 14 to pre-select the highly GA-responsive male plants and the low or not GA-responsive female plants of any one of these numbered embodiments.

[0124] 16. Use of the highly GA-responsive male cereal, such as wheat, plant seeds or plants and the low or not GA-responsive female cereal, such as wheat, plant seeds or plants of any one of the prior embodiments, for mixed planting in a field, wherein a gibberellic acid solution is applied to said plants before heading so that the male plants become taller than the females plants at Z59, wherein said male plants are shorter than said female plants at Z59 in absence of treatment with gibberellic acid, or use of the highly GA-responsive male cereal, such as wheat, plant seeds or plants and the low or not GA-responsive female cereal, such as wheat, plant seeds or plants of any one of the prior embodiments, for mixed planting in a field, wherein a gibberellic acid solution is applied to said plants before heading so that the height difference at Z59 between male and female plants becomes significantly larger upon the application of a gibberellic acid solution, compared to the height difference at Z59 between male and female plants in absence of application of a gibberellic acid solution, such as wherein said GA application is between Z25 and Z50, or at any one of the stages described herein.

[0125] 17. The use of a gibberellic acid solution over a field of highly GA-responsive male cereal, such as wheat, plants and low or not GA-responsive female cereal, such as wheat, plants interplanted in mixed planting, wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 10 %, at least a 15 % or at least a 20 % increase in plant height just before the start of flowering at Z59, compared to said plants at said stage when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % or less than a 12 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, iii) optionally, the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, and iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50, or at any of the stages as described herein, such as application between Z41 and Z50 to increase peduncle length and / or peduncle width in said male plants, or application between Z30 and Z50, or between Z40 and Z50 to increase spike length of said male and / or female plants, preferably without increase of spikelets per spike.

[0126] 18. Any one of the prior or later numbered method or use embodiments, or use of a gibberellic acid solution as described herein, to increase the peduncle length in said male cereal, such as wheat, plants, wherein said male plants were selected so as to have an increase in peduncle length after application of a gibberellic acid solution of at least 15 % (or at least 20 %, at least 25 %, or at least 30 %) in the peduncle of the main tiller of said male plants at Z59, compared to said male plants at said stage when not treated with gibberellic acid, wherein gibberellic acid is applied over the top of said male and female plants between Zadoks growth scale stages Z41 and Z50.

[0127] 19. Any one of the prior or later numbered method or use embodiments, to decrease the width of the peduncle of said male cereal, such as wheat, plants at flowering, wherein said male plants were selected so as to have a decreased peduncle width after application of a gibberellic acid solution (such as measured in the middle of the peduncle length), of at least 5 % (or at least 6 %, at least 7 %, or at least 8 %) in the peduncle of the main tiller of said male plants at Z59, compared to the peduncle width of the main tiller of said plants when not treated with gibberellic acid, wherein gibberellic acid is applied between Z41 and Z50, including such use or method wherein the male spikes lodge / bend down, so that male seed development is reduced or prevented, and wherein smaller male seeds are removed from harvested hybrid seed based on size / density, such as by the harvesting combine (and need not be separately harvested or removed prior to hybrid seed harvest to achieve sufficient hybrid seed purity).

[0128] 20. Any one of the prior or later numbered method or use embodiments wherein without gibberellic acid treatment, the majority of the main spikes of said male plants do not stick out above the majority of the main spikes of the female plants, or stick out above the majority of the main spikes of the female plants by at most 1 / 3rd or by less than half of their spike length within a plot or production area, just before the start of flowering at Z59, or wherein said male plants are at least as tall as said female plants, or are taller than said female plants at Z59 in absence of GA application, but a selective increase in male plant height is desired, or an increase in the difference in height between male and female plants, such as between male and female main spikes, is wanted, so as to improve hybrid seed set and / or hybrid seed purity.

[0129] 21 . Any one of the prior or later numbered method or use embodiments, wherein the majority of said highly GA-responsive male plants becomes at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller at Z59 than the majority of the low or not GA-responsive female plants, upon treatment with a gibberellic acid solution over the top of these plants in the field, or wherein the majority of the main spikes of said highly GA-responsive male plants sticks out (such as by at least half a (male) spike, 2 / 3rdof a (male) spike, or by an entire (male) spike, or by more (such as by at least 1 , 2, 3, 4 or 5 cm more) than the length of an entire (male) spike) above the majority of the tips of the low or not GA- responsive female plants, upon treatment with a gibberellic acid solution (as described herein) over the top of these plants in the field.

[0130] 22. Any one of the prior or later numbered method or use embodiments, wherein a standard application of a gibberellic acid-inhibitor plant growth regulator is applied to said cereal, such as wheat, field before said gibberellic acid application, or at the same day (or at the same time, from the same or different spray tanks) of said gibberellic acid application.

[0131] 23. Any one of the prior or later numbered method or use embodiments, comprising determining the GA-responsiveness of candidate fertile male and candidate male-sterile female cereal, such as wheat, seeds to gibberellic acid in a seedling growth assay, and selecting candidate male plant seeds that are highly GA-responsive and candidate female plant seeds that are low or not GA-responsive in said seedling growth assay, wherein said male seeds are GA-responsive in said assay when seedlings of said male seeds when treated with a gibberellic acid solution have at least a 20 % (or at least 25 %, or at least 30 %) increase in seedling height 7 (or 7 to 10) days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay, and wherein said female seeds are not GA-responsive in said assay, when seedlings of said female seeds when treated with a gibberellic acid solution have less than 20 % (or less than 15 %, or less than 10 %) increase (including no increase in height or a decrease in height) in seedling height 7 (or 7-10) days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay, such as wherein said treated and untreated seeds / seedlings are tested under the same conditions, preferably at the same time in the same assay.

[0132] 24. Any one of the prior or later numbered use or method embodiments, wherein said highly GA- responsive male seed or plant contains at least any one of the (semi-)dwarf alleles Rht8, Rht13, Rht18, Rht24 or Rht25, or a non-functional or deleted ZnF allele, or a wild-type tall Rht gene, and no GA- insensitive Rht allele.

[0133] 25. Any one of the prior or later numbered use or method embodiments, wherein a gibberellic acid solution is applied, wherein said method or use includes a second (or a second and a (later) third) application of a gibberellic acid solution between stage Z30 and Z50 or between Z37 and Z50 on the Zadoks growth scale (or any one of the stages as described herein) over said male and female plants, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare.

[0134] 26. Any one of the prior or later numbered use or method embodiments, wherein the gibberellic acid solution comprises a surfactant or adjuvant.

[0135] 27. Use of a gibberellic acid solution over a field of fully fertile male hybrid cereal, such as wheat, parent plants and male-sterile female hybrid cereal, such as wheat, parent plants to increase spike length in the main spike of said male and / or female cereal (such as male and female), such as wheat, plants by application of a gibberellic acid solution, compared to said main spike when said plants where not treated with a gibberellic acid solution, wherein the spike length increases at least 5 % (or at least 6, at least 7 or at least 8 %) after application of a gibberellic acid solution compared to said main spike when said plants where not treated with a gibberellic acid solution, preferably without increasing the number of spikelets per spike in said main spike (compared to said main spike when said plants where not treated with a gibberellic acid solution), or with increasing the number of spikelets per spike in said main spike less than 5 % (or less than 4, less than 3, or less than 2 %) after application of a gibberellic acid solution, compared to said main spike when said plants where not treated with a gibberellic acid solution, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50, such as said use wherein also a (or at least one) gibberellin-inhibiting plant growth regulator (PGR) as described herein is applied over said plants (such as between Z30 and Z32, or at Z30, Z31 , or Z32), and the application of said PGR and GA solution cause a significant (further) increase in spike length (such as on said male plants), compared to only application of a GA solution.

[0136] 28. A method to increase spike length in the main spikes of fully fertile male hybrid cereal, such as wheat, parent plants and male-sterile female hybrid cereal, such as wheat, parent plants in a field, by application of a composition comprising gibberellic acid over said field, wherein the spike length of said main spikes increases at least 5 % (or at least 6, at least 7 or at least 8 %) after application of a gibberellic acid solution compared to said main spike when said plants where not treated with a gibberellic acid solution, preferably without increasing the number of spikelets per spike in said main spike (compared to said main spike when said plants where not treated with a gibberellic acid solution), or with increasing the number of spikelets per spike in said main spike less than 5 % (or less than 4, less than 3, or less than 2 %) after application of a gibberellic acid solution, compared to said main spike when said plants where not treated with a gibberellic acid solution, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50.

[0137] 29. Any one of the prior or later numbered method or use embodiments, comprising the a) cutting off, destroying or separately harvesting of the male plant spikes standing above the height of the female plant spikes after the end of flowering (such as at full maturity or at Z91 or Z92 when harvesting male spikes) using a cutting or destruction or harvesting device above the height of the female plant spikes, and b) harvesting the hybrid seeds from said female plants in that field, such as wherein said cutting or destruction or harvesting device is a cutting device that cuts off (part of) the male spikes standing above the female spikes (and drops cut parts to the ground or collects them as plant waste (with or without shredding)), is a height-adjustable harvesting combine with a cutting device / plate that harvests the male grain, is a weed wicking / wiping device containing a herbicide solution that negatively affects male seed growth (wherein said herbicide wicking / wiping is done some time before full maturity / harvest, such as after pollination), or is a device for electrocution of the male spikes, preferable wherein said female plant spikes and the hybrid seeds they contain are not cut / destroyed / harvested in step a), or are not negatively affected when cutting off, destroying or separately harvesting the male plant spikes.

[0138] 30. Any one of the prior or later numbered method or use embodiments, wherein the hybrid seeds are harvested from the female plants, such as after the removal of the male spikes standing above the female spikes.

[0139] 31 . Any one of the prior or later numbered method or use embodiments, wherein instead of measuring at Z59, the measurement (of plant height, spike or peduncle length or peduncle width as described herein) is done at the start of flowering, at the end of flowering, or at full maturity, just before harvest (e.g., Z91 or Z92).

[0140] 32. Any one of the prior or later numbered method or use embodiments, wherein said male plant is male and female fertile, and said female plant is male-sterile (such as with (T. timopheevii or other) cytoplasmic male sterility (CMS), or (non-GM) genic male sterility, or chemically-induced male sterility (using a chemical hybridization agent or CHA)), and said male and female plants are suitable or matching parents for hybrid cereal, such as wheat, seed production.

[0141] 33. Use of a gibberellic acid solution over a field of fully fertile male hybrid wheat parent plants and male-sterile female hybrid wheat parent plants to increase spike length in the main spike of said male and / or female wheat plants by application of a gibberellic acid solution, wherein the spike length at Z59 increases at least 5 % (or at least 6, at least 7 or at least 8 %) after application of a gibberellic acid solution, compared to said main spike at said stage when said plants where not treated with a gibberellic acid solution, preferably without increasing the number of spikelets per spike in said main spike at Z59, or with increasing the number of spikelets per spike in said main spike at Z59 less than 5 % (or less than 4, less than 3, or less than 2 %) after application of a gibberellic acid solution, compared to said main spike at said stage when said plants where not treated with a gibberellic acid solution, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50, such as when said gibberellic acid solution comprises a surfactant or adjuvant.

[0142] 34. A method to increase spike length in the main spikes of fully fertile male hybrid wheat parent plants and male-sterile female hybrid wheat parent plants in a field, by application of a composition comprising gibberellic acid over said field, wherein the spike length of said main spikes at Z59 increases at least 5 % (or at least 6, at least 7 or at least 8 %) after application of a gibberellic acid solution compared to said main spike at said stage when said plants where not treated with a gibberellic acid solution, preferably without increasing the number of spikelets per spike in said main spike at Z59, or with increasing the number of spikelets per spike in said main spike at Z59 less than 5 % (or less than 4, less than 3, or less than 2 %) after application of a gibberellic acid solution, compared to said main spike at said stage when said plants where not treated with a gibberellic acid solution, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z50.

[0143] 35. A method or use of applying a gibberellic acid solution in a hybrid wheat production field, wherein said field contains highly GA-responsive male plants as described herein, planted in one or more rows or strips and highly GA-responsive or low or not GA-responsive female plants planted in one or more other rows or strip, wherein said male rows or strips only contain fertile male plants, and said female rows or strips contain only or mostly female plants with no or at most 5 %, 10 %, or 15 % of said highly GA-responsive male plants, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare between Zadoks growth scale stages Z25 and Z60, and said gibberellic acid solution is applied only over the male rows or strips if the female plants are highly GA-responsive, or said gibberellic acid solution is applied over the entire field if the female plants are not or low GA-responsive, optionally wherein a plant growth regulator decreasing plant height is applied over said entire field or only over said female rows or strips when said female plants are highly GA-responsive.

[0144] 36. Use of the highly GA-responsive male wheat plant seeds or plants and either GA-responsive female wheat plants seeds or plants or the low or not GA-responsive female wheat plant seeds or plants of any one of the prior numbered embodiments or as described herein, for row / strip planting in a field, wherein rows or strips planted with only or mostly male-sterile females plants are alternated with rows or strips planted with male plants, and wherein a gibberellic acid solution is applied over said male plants or over said male and said female plants so that the male plants get to the same plant height or become taller than the females plants at Z59 or Z80 when said male plants are shorter than said female plants at Z59 orZ80 in absence of treatment with gibberellic acid, or wherein a gibberellic acid solution is applied to said plants so that the male plants become taller and the height difference at Z59 or Z80 between male and female plants becomes significantly larger upon the application of a gibberellic acid solution, compared to the height difference at Z59 orZ80 between male and female plants in absence of application of a gibberellic acid solution, when said male plants are taller than or of the same plant height as said female plants at Z59 or Z80 in absence of treatment with gibberellic acid, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare between Zadoks growth scale stages Z25 and Z60, optionally before heading or before flowering.

[0145] 37. The use or method of any one of the prior or later numbered embodiments or as otherwise described herein as being part of the current invention, wherein the male plants (were selected to) have no (significantly) delayed heading or flowering start, or have no (significantly) shortened pollination window (e.g., the male plants can have no change in heading / flowering or have an earlier heading or flowering, or can have no change in pollination window or can have a wider pollination window) after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution in one or more control plot(s), optionally wherein the female heading or flowering start, or flowering time / window is not (significantly) changed after treatment with said gibberellic acid solution compared to said female when not treated with said gibberellic acid solution in one or more control plot(s), where in each instance the control is planted in the same area in an identical or similar field setup and treatment, except for the gibberellic acid treatment.

[0146] 38. Any method or use involving the application of gibberellic acid in a hybrid cereal, such as wheat, seed production in mixed or strip planting in a field, as described in any numbered embodiment or as otherwise described herein as being part of the current invention, wherein a selective height increase is created in the male plants by the gibberellic acid application, and wherein the hybrid seed set and / or hybrid purity (the hybridity or the % of hybrid seed in the total seed harvest) from said field is improved / increased, which method or use can involve the removal or reduction of at least a part of the male heads from said field before harvesting the hybrid seed (mechanically and / or chemically and / or physically eliminating or destroying (part of) male heads, such as cutting), and which method can involve application of a plant growth regulator over said field or said female plants, and wherein the male plants are fertile and highly GA-responsive as described herein, and the female plants are male- sterile and can be highly GA-responsive or low or not GA-responsive, as described herein, and wherein if said female plants are highly GA-responsive, said gibberellic acid is only applied on the male plants with optionally at least one application of a plant growth regulator that decreases plant height only on said female plants, and wherein said gibberellic acid can include a surfactant, and wherein said gibberellic acid is applied at least once over said male plants or over said field of male and female plants, and said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare between Zadoks growth scale stages Z25 and Z60, such as in one embodiment an early application between Z25 and Z40 and / or one later application between Z40 and Z60, preferably at least with a dose of 300 ppm of gibberellic acid.

[0147] 39. The method or use of embodiment 38, wherein highly GA-responsive male plants are planted next to low or not GA-responsive male-sterile female plants, and wherein the gibberellic acid application on said male plants significantly decreases the selfed male seed yield compared to untreated male plants, and the gibberellic acid application on said low or not GA-responsive female plants does not significantly decrease or significantly increases the hybrid seed yield on the female plants compared to untreated female plants, or wherein the gibberellic acid application on said male plants does not delay the heading or flowering, or results in earlier heading or flowering or in a broadening of the pollination window of said male plants, compared to untreated male plants.

[0148] 40. The method or use of embodiment 38 or 39, wherein said gibberellic acid solution when applied over the entire field of male and female plants in mixed / blended planting results in a decreased seed set on the male plants, without decreasing hybrid seed set on the male-sterile female plants, and / or does not result in a delay in heading or flowering date of the male plants, and / or broadens the pollination window and / or results in an earlier heading or flowering of said male plants, compared to control male and female plants not treated with said gibberellic acid solution, where the control is planted in an identical or similar field setup and treatment, except for the gibberellic acid treatment.

[0149] 41 . The method or use of any one of embodiments 38 to 40, wherein the highly GA-responsive male plants do not contain Rht12, or do contain Rht24 as reduced plant height (semi-dwarf) gene (and no GA-insensitive Rht allele).

[0150] 42. A method to make male cereal plants taller than female cereal plants in a row / strip planting field containing rows or strips of fertile male plants and rows or strips of male-sterile female plants, wherein only said male plants are responsive to a gibberellic acid solution as described herein, or wherein said male and female plants are both responsive to a gibberellic acid solution as described herein so that plant height increases when treated with said gibberellic acid solution, and wherein said male plant rows or strips are (selectively) treated with a gibberellic acid solution solution between stages Z25 and Z60, and said female plant rows or strips are (selectively) treated with a plant-height decreasing plant growth regulator between stages Z25 and Z45, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than said female plants at stage Z60 or Z92.

[0151] 43. A method to make fertile male cereal plants taller in a mixed planting field containing fertile male cereal plants and male-sterile female cereal plants, such as wheat plants, wherein said male plants are more GA-responsive than said female plants so that plant height of said male plants increases more than the plant height of said female plants when said mixed planting field is treated with a gibberellic acid solution as described herein, and wherein said field is treated with at least one gibberellic acid solution between stages Z25 and Z60, and said field is treated with at least one plantheight decreasing plant growth regulator between stages Z25 and Z40, wherein said gibberellic acid solution is applied significantly later than said plant growth regulator application, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than the female plants at stage Z60 or Z92, and such as wherein said gibberellic acid solution is applied at least 2-12, 2-10, 2-8, 2-6 or 2-4 weeks later than said plant growth regulator application.

[0152] 44. Any one of the above or below numbered method or use embodiments, wherein a plant growth regulator and a gibberellic acid solution are applied over said (mixed planting), wherein said gibberellic acid solution is applied over said field between stages Z25 and Z41 , and said gibberellic acid solution is applied over said field a second time between stages Z40 and Z60, and said gibberellic acid solution is applied at least 2, 3, 4, or 5 weeks later than said plant growth regulator application.

[0153] 45. A method to improve purity and / or yield of harvested hybrid wheat seeds from a mixed planting field containing highly GA-responsive male wheat plants and low or not GA-responsive female wheat plants at full maturity (ready to be harvested), wherein said plants were previously treated with a solution containing gibberellic acid between Zadoks growth scale stages Z25 and Z60, said method comprising the steps of: a) cutting off, destroying or separately harvesting the male plant ears standing above the height of the female plant ears after the end of flowering using a cutting or destruction or harvesting device above the height of the female plant spikes, and b) harvesting the remaining seeds, including the hybrid seeds from said female plants, from said field, and wherein: i) said highly GA-responsive male plants are fertile plants that are shorter than, of the same height as, or less than 5 cm or less than 10 cm taller than, said low or not GA-responsive male-sterile female plants just before the start of flowering at Z59, when said field is not treated with a solution containing gibberellic acid, ii) said highly GA-responsive male plants show an increase in plant height when treated with solution containing gibberellic acid between Z25 and Z60, which increase is larger than the increase in plant height for said low or not GA-responsive male-sterile female plants, iii) the majority of said highly GA-responsive male plants are at least as tall, or at least 5 cm, at least 10 cm, or at least 15 cm taller than the majority of the low or not GA-responsive female plants just before the start of flowering at Z59 or at full maturity, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and was applied in a volume between 100 and 500 liter per hectare, such as said method wherein said harvested remaining seed contains at least 85 %, or at least 87 %, or at least 90 %, hybrid seed when said mixed planting field was sown with a seed mix containing at least 7.5 %, at least 10 %, at least 12 %, or at least 15 % seeds that grow into a highly GA-responsive male wheat plant.

[0154] 46. Any of the above or below numbered use or method embodiments for a field sown or planted with a mix or blend of 5-30 %, 7.5- 30 % or 10-30 % fertile male seeds or plants and 95-70 %, 92.5-70 % or 90 -70 % male-sterile female seeds or plants, respectively (such as from a seed mix or blend), wherein a first application with a gibberellic acid solution as described herein is done between stages Z25 and 40 so that the male plants can establish themselves between (or are not overgrown by) the female plants, and wherein a second application of a gibberellic acid solution as described herein is done between Z40 and Z60, such as between Z46 and Z60, so as to increase male plant height compared to said female plants at Z59 for optimal pollination, or so as to increase male plant height compared to said female plants after flowering so that the male ears standing out above the female plant ears can be cut off, optionally with a third application of a gibberellic acid solution after said 1stand 2ndapplications.

[0155] 47. The use or method of any one of the prior or later numbered embodiments or as otherwise described herein as part of the present invention, wherein the application of a gibberellic acid solution over a field with low or not GA-responsive male-sterile female plants and GA-responsive fertile male plants as described herein : a) does not delay heading or flowering (start date) of the GA-responsive male plants of the invention, b) does not shorten the flowering window of the GA-responsive fertile male plants of the invention, c) does not decrease hybrid seed yield on the low or not GA-responsive female plants of the invention, d) increases hybrid seed yield on the low or not GA-responsive female plants of the invention, e) is with a gibberellic acid solution containing a surfactant or adjuvant as described herein, or f) is accompanied by the application of a plant growth regulator over said field as described herein, to prevent lodging, or any combination of two or more of a) to f), such as a combination of a) to f).

[0156] 48. The use or method of any one of the prior or later numbered embodiments, such as in embodiment 37, or as otherwise described herein as being part of the current invention, wherein the male plants (were selected to) have a significant decrease in seed yield after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution in one or more control(s), and the hybrid seed set on said male-sterile female plants is not (significantly) changed or is significantly increased after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution in one or more controls, where in each instance the control is planted in the same area in an identical or similar field setup and treatment, except for the gibberellic acid treatment.

[0157] 49. Use of a gibberellic acid solution as described herein, to make male cereal plants taller than female cereal plants in a row / strip planting field containing rows or strips of fertile male plants and rows or strips of male-sterile female plants, wherein only said male plants are responsive to said gibberellic acid solution so that plant height increases when treated with said gibberellic acid solution, or wherein said male and female plants are both responsive to said gibberellic acid solution so that plant height increases in male and female plants when treated with said gibberellic acid solution, comprising (selectively) treating said male plant rows or strips with a gibberellic acid solution as described herein between stages Z25 and Z60, and treating said female plant rows or strips (selectively) with a plantheight decreasing plant growth regulator solution between stages Z25 and Z45, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than said female plants at stage Z60 or Z92.

[0158] 50. The use or method of any of the above or below numbered embodiments or as otherwise described herein as being part of the invention, such as the use of a solution containing gibberellic acid as described herein, wherein the male plants became taller after application of a solution containing gibberellic acid, but said male plants did not become taller than the female plants in said field (on average), wherein the hybrid seed yield is significantly increased, compared to a control not treated with a solution containing gibberellic acid, such as in mixed planting of GA-responsive male plants and not or low GA-responsive female plants.

[0159] 51 . The use or method of any of the above or below numbered embodiments or as otherwise described herein as being part of the invention, to increase hybrid seed yield from a mixed planting field of male and female plants, wherein the male plants are GA-responsive and become taller after application of a solution containing gibberellic acid (compared to said plants when not treated with a gibberellic acid solution), but wherein said male plants did not become taller than the female plants (on average) at stage Z59 or Z60.

[0160] 52. A method to produce hybrid seed, comprising planting male and female parent plants in separate rows or strips, wherein the male parent is highly GA-responsive as defined herein and the matching female parent is either low or not GA-responsive or is highly GA-responsive as defined herein, and wherein only the male rows / strips are treated with a gibberellic acid solution so that the male plants will get taller, and can better pollinate the female plant rows; or wherein the entire field is sprayed with a gibberellic acid solution if the female parent is low or not GA-responsive as defined herein, and then only the male plants will show a significant height increase, and the taller males can then be separately harvested or the male spikes / seeds can be mechanically / chemically / physically eliminated or destroyed (or their seed growth can be prevented / reduced). 53. Any one of the uses or methods of the above or below numbered embodiments or as otherwise described herein, involving application of a plant growth inhibitor or plant growth regulator, wherein the female plants are selectively made shorter by using male-sterile plants that are very responsive to a plant growth inhibitor, while using male plants that are less or not responsive to that plant growth inhibitor, and application of that growth inhibitor over the male and female plants in a field (which can be obtained by interplanting males and females with sufficient difference in early development, so that the application window of the one gender is met (so that the growth regulator is effective) whereas for the other gender it is not).

[0161] 54. The use or method of any one of the prior or later numbered embodiments or as otherwise described herein as being part of the current invention, wherein the male plants have no delayed heading or flowering, or have no shorter pollination window after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution in one or more control plots, where said control plots are planted in the same area with an identical or similar field setup and treatment, except for the gibberellic acid treatment.

[0162] 55. The use or method of any one of the prior or later numbered embodiments or as otherwise described herein as being part of the current invention, wherein said male and female plants are treated with at least one plant growth regulator inhibiting gibberellin biosynthesis (such as at any of the growth stages from Z30 to Z40, or between growth stages Z29 and Z41), and with at least one gibberellic acid solution (such as between growth stages Z29 and Z60), preferably wherein the last gibberellic acid solution is applied after stage Z40 (as of stage Z41)and the last plant growth regulator is applied before stage Z41 (up to stage 40), such as wherein the last gibberellic acid solution is applied after stage Z44 (as of stage Z45) and the last plant growth regulator is applied before stage Z37.

[0163] 56. Use of a gibberellic acid (“GA”) solution to improve hybrid seed purity in a mixed cereal planting field, comprising at least one application of a GA solution of 100-300 ppm (at 100-550 l / ha) between stage Z25 and Z60, such as after stage Z39, over a field comprising 8-20 % fertile male plants and 92- 80 % male-sterile female plants, wherein said male plants are highly GA-responsive as described herein, and said female plants are low or not GA-responsive as described herein, and wherein a hybrid seed purity (after seed cleaning to remove dirt etc.) of at least 85 or 90 % is obtained, and wherein said hybrid seed purity is obtained by reducing the amount of male plant seeds by a) cutting all or part of the male ears standing above the female plants before harvesting hybrid seed, and / or b) sorting hybrid seed from male seed if there is a sortable difference in seed phenotype between male and hybrid seed (such as seed color, preferably the male seed being white / non-colored seed and the female seed being red-colored seed), such as wherein said field was sown with a seed mix of 8-20 % male plant seeds and 92-80 % female seeds, preferably wherein said GA solution contained a surfactant and said GA solution does not (significantly) delay heading and / or does not shorten the pollination window of said male plants, compared to control male plants not treated with a GA solution.

[0164] 57. A method to improve hybrid seed purity from a mixed cereal planting field, comprising cutting all or part of the ears of the male plants standing above the height of the female plants after pollination, wherein said male plants are highly GA-responsive as described herein, and said female plants are not or low GA-responsive as described herein, and wherein a hybrid seed purity (after seed cleaning to remove dirt etc.) of at least 85 %, such as at least 90 %, is obtained from a field comprising 8-20 % fertile male plants and 92-80 % male-sterile female plants, wherein said field had at least one application of a GA solution of 100-300 ppm (at 100-550 l / ha) after stage Z39, preferably wherein said GA solution contained a surfactant, such as wherein said male plants do not have a (significant) delay in heading and / or do not have a (significantly) shorter pollination window when treated with said GA solution, compared to control male plants not treated with a GA solution.

[0165] 58. Use of a gibberellic acid (“GA”) solution to selectively make male plants taller and / or improve hybrid seed purity in a mixed cereal planting field, comprising at least one application of a GA solution of 100- 500 (such as 200-400, or 250 to 350) ppm (at 100-600 l / ha) after stage Z39 over a field comprising 8- 20 % fertile male plants and 92-80 % male-sterile female plants, wherein said male plants are highly GA-responsive as described herein, and said female plants are not or low GA-responsive as described herein, preferably wherein at least 2 applications of a GA solution of 100-500(such as 200-400, or 250 to 350) ppm (at 100-600 l / ha) are done over said field, particularly wherein said GA solution contained a surfactant, or said GA solution does not (significantly) delay heading, or does not shorten the pollination window of said male plants, compared to control male plants not treated with a GA solution). 59. The use of a gibberellic acid (“GA”) solution as described in any of the above or below numbered embodiments or as otherwise described herein, to improve hybrid seed purity and / or hybrid seed yield in a mixed cereal planting field wherein between 8 and 20 % fertile male plants are growing next to male-sterile female plants without said male plants being in a row of only male plants, comprising at least one application of said GA solution of 100-500 (such as 200-400, or 250 to 350) ppm (at 100-600 l / ha) over said mixed planting field, and wherein said hybrid seed yield from said mixed planting field per area is significantly higher compared to row / strip planting of rows of said fertile male plants next to rows of said male-sterile female plants, and wherein harvested hybrid seed from said mixed planting field has a hybrid seed purity of above 85 % or above 90 % hybrid seed.

[0166] 60. The use or method of any one of the prior numbered embodiments or as otherwise described herein as being part of the current invention, comprising determining the GA-responsiveness of candidate fertile male and candidate male-sterile female wheat seeds to gibberellic acid in a seedling growth assay, and selecting male plant seeds that are highly GA-responsive and female plant seeds that are low or not GA-responsive in said seedling growth assay, wherein said male seeds are GA- responsive when seedlings of said male seeds when treated with a gibberellic acid solution have at least a 20 % (or at least 25 %, or at least 30 %) increase in seedling height 7 days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay, and wherein said female seeds are not GA-responsive, when seedlings of said female seeds when treated with a gibberellic acid solution have less than 20 % (or less than 15 %, or less than 10 %) increase in seedling height 7 days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay.

[0167] 61 . Use of the highly GA-responsive male wheat plant seeds or plants and either GA-responsive female wheat plants seeds or plants or the low or not GA-responsive female wheat plant seeds or plants of any one of the numbered embodiments or as otherwise described herein, for row / strip planting in a field, wherein rows or strips planted with only or mostly male-sterile females plants are alternated with rows or strips planted with male plants, and wherein a gibberellic acid solution is applied over said male plants or over said male and said female plants so that the male plants become taller than the females plants at Z59 or Z80 when said male plants are shorter than said female plants at Z59 or Z80 in absence of treatment with gibberellic acid, or wherein a gibberellic acid solution is applied to said plants so that the male plants become taller and the height difference at Z59 or Z80 between male and female plants becomes significantly larger after the application of a gibberellic acid solution, compared to the height difference at Z59 or Z80 between male and female plants in absence of application of a gibberellic acid solution, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare between Zadoks growth scale stages Z25 and Z60, optionally before heading or before flowering.

[0168] 62. Any method or use involving the application of gibberellic acid in hybrid cereal, such as wheat, seed production in mixed or strip planting in a field, as described herein, such as wherein an increased height increase is created between male and female parent plants by the gibberellic acid application, or so that hybrid seed set and / or hybrid purity (the hybridity or the % of hybrid seed in the total seed harvest) from said field is improved, which method or use can involve the removal of at least a part of the male heads standing out above the female plants from said field before harvesting the hybrid seed, and which method can involve application of a plant growth regulator over said field or said female plants, and wherein the male plants are fertile and highly GA-responsive as described herein, and the female plants are male-sterile and can be highly GA-responsive or low or not GA-responsive, as described herein, and wherein if said female plants are highly GA-responsive, said gibberellic acid is only applied on the male plants with optionally at least one application of a plant growth regulator that decreases plant height only on said female plants, and wherein said gibberellic acid can include a surfactant, and wherein said gibberellic acid is applied at least once over said male plants or over said field of male and female plants, and said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z60, such as in one embodiment an early application between Z25 and Z40 and / or one later application between Z40 and Z60, preferably at least with a dose of 300 ppm of gibberellic acid.

[0169] 63. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, to improve hybrid seed purity and / or hybrid seed yield of harvested hybrid cereal, such as wheat, seeds from a mixed planting field containing highly GA- responsive fertile male wheat plants and low or not GA-responsive male-sterile female wheat plants, said method comprising the steps of: a) treating said plants at least once with a solution containing gibberellic acid between Zadoks growth scale stages Z25 and Z60, b) cutting off, destroying or separately harvesting the male plant ears standing above the height of the female plant ears after the end of flowering or at full maturity using a cutting or destruction or harvesting device above the height of the female plant spikes, and c) harvesting the remaining seeds, including the hybrid seeds from said female plants, from said field, and wherein: i) said highly GA-responsive male plants are fertile plants that are shorter than, of the same height as, or less than 5 cm or less than 10 cm taller than, said low or not GA-responsive male-sterile female plants just before the start of flowering at Z59, when said plants are not treated with a GA3 solution, ii) said highly GA-responsive male plants show an increase in plant height when treated with a solution containing gibberellic acid between Z25 and Z60, which increase is significantly larger than the increase in plant height for said low or not GA-responsive male- sterile female plants, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller than the majority of the low or not GA-responsive female plants just before the start of flowering at Z59 or at full maturity, when said plants were treated at least once with a solution containing gibberellic acid between Z25 and Z60, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and was applied in a volume between 100 and 600 liter per hectare, wherein said harvested remaining seed contains at least 85 %, or at least 87 %, or at least 90 %, hybrid seed when said mixed planting field was sown with a seed mix containing at least 7.5 %, at least 10 %, at least 12 %, or at least 15 % seeds that grow into a highly GA-responsive male wheat plant, such as said use or method wherein said hybrid seed yield is higher than the hybrid seed yield obtained on said same male and female plant genotypes when grown in the same or similar conditions, but without treatment with a solution containing gibberellic acid.

[0170] 64. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said male seed has a white seed color and said hybrid seed has a red seed color, so that hybrid seed purity can be further improved, if required, by removing the male seed by color sorting.

[0171] 65. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said gibberellic acid solution comprises 300-500 ppm (w / w) of gibberellic acid and is applied in a volume of 300 to 600 l / ha for each gibberellic acid solution application, such as wherein said application is at least between Z40 and Z50, or is between Z45 and Z60 or between Z47 and Z60.

[0172] 66. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said cereal plant is wheat, barley (Hordeum vulgare), rye (Secale cereale) or Triticale, including common / bread wheat (Triticum aestivum), durum wheat (Triticum durum), einkorn (Triticum monococcum), Khorasan wheat (T. turgidum ssp. turanicum), spelt (Triticum spelta), or emmer (T. turgidum subsp. dicoccum), such as hexapioid Spring or Winter wheat.

[0173] 67. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, including the step of mixing 3-30 %, such as 3-25 % or 3- 20 % of seeds growing into said highly GA-responsive male plants with seeds growing into said low or not GA-responsive female plants in a bag or container, or including the step or planting / sowing in a field a combination of male and female seeds / plants in a specific planting / sowing scheme or structure (such as in a honeycomb structure as in Fig. 1) or randomly, such as wherein said mixed seed or said field contains 3 to 4%, 4 to 5%, 5 to 6%, 6 to 7%, 7 to 8%, 8 to 9%, 9 to 10%, 10 to 11 %, 11 to 12%, 12 to 13%, 13 to 14%, 14 to 15%, 15 to 16%, 16 to 17%, 17 to 18%, 18 to 19%, or 19 to 20%, or contains 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of male seeds, or contains 7.5-25 %, 7.5-20 %, 7.5-15 %, or 10-15 % of male seeds. 68. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein: a) said highly GA-responsive male plant (was selected to have or) has no delay in heading date or flowering date after application of said gibberellic acid (“GA”) solution, compared to said plant when not treated with said GA solution, such as said male plant that has an unchanged or an earlier heading date or flowering date after application of said GA solution, compared to said plant when not treated with said GA solution, b) said highly GA-responsive male plant (was selected to have or) has no shortened flowering window after application of said GA solution, compared to said plant when not treated with said GA solution, such as said male plant that has an unchanged or a wider flowering window after application of said GA solution, compared to said plant when not treated with said GA solution.

[0174] 69. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein the female plants have or were selected to have no significantly decreased hybrid seed yield after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution, when said female plants are planted with the same male plant as pollinator in the same or a similar setup, such as wherein said female plants have or were selected to have no significant difference in or have a significant increase in hybrid seed yield after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution, when said female plants are planted with the same male plant as pollinator in the same or a similar setup, such as said use or method wherein the male plants have or were selected to have a significantly decreased seed yield after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution.

[0175] 70. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein a gibberellic acid solution is applied on a hybrid wheat production field, wherein said field contains said highly GA-responsive male plants, planted in one or more rows or strips and highly GA-responsive or low or not GA- responsive female plants planted in one or more other rows or strips, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare between Zadoks growth scale stages Z25 and Z60, and wherein said gibberellic acid solution is applied only over the male rows or strips if the female plants are highly GA-responsive, or said gibberellic acid solution is applied over the entire field if the female plants are not or low GA-responsive, and wherein a plant growth regulator decreasing plant height is applied over said entire field or only over said female rows or strips when said female plants are highly GA-responsive, such as wherein said male rows or strips only contain fertile male plants, and said female rows or strips contain only or mostly female plants with 0 to 5 % of said highly GA-responsive male plants, (randomly) mixed in said female plant rows or strips.

[0176] 71. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, to make male cereal plants taller than female cereal plants in a row / strip planting field containing rows or strips of fertile male plants and rows or strips of male-sterile female plants, wherein said male and female plants are highly GA- responsive so that their plant height significantly increases when treated with a gibberellic acid solution, and wherein said male plant rows or strips and not said female rows or strips are treated with a gibberellic acid solution between stages Z25 and Z60, and said female plant rows or strips and not said male rows or strips are treated with a plant-height decreasing plant growth regulator between stages Z25 and Z45, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than said female plants at stage Z60 or Z92, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare.

[0177] 72. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein fertile male cereal plants are made taller than male-sterile female cereal plants in a field with 5-20 % fertile male plants and 95-80 % male-sterile female plants, wherein said field contains male and female plants in the same row(s), and wherein said male plants are more GA-responsive than said female plants so that plant height of said male plants increases significantly more than the plant height of said female plants when treated with a gibberellic acid solution, and wherein said field is treated with at least one gibberellic acid solution between stages Z25 and Z60, and said field is treated with at least one plant-height decreasing plant growth regulator between stages Z25 and Z40, wherein said gibberellic acid solution is applied significantly later than said plant growth regulator application, or at least one gibberellic acid solution is applied between stages Z25 to Z41 , and at least one gibberellic acid solution is applied between stages Z40 and Z60 or between stages Z45 and Z60, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than the female plants at stage Z60 or Z92, such as wherein said gibberellic acid solution is applied at least 1 or 2 weeks later than said plant growth regulator application, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare.

[0178] 73. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, to improve hybrid seed purity and / or hybrid seed yield of harvested hybrid cereal, such as wheat, seeds from a mixed planting field containing highly GA-responsive fertile male wheat plants and low or not GA-responsive male-sterile female wheat plants, wherein said plants were previously treated at least once with a solution containing gibberellic acid between Zadoks growth scale stages Z25 and Z60, said method comprising the steps of: a) cutting off, destroying or separately harvesting the male plant ears standing above the height of the female plant ears after the end of flowering or at full maturity using a cutting or destruction or harvesting device above the height of the female plant spikes, and b) harvesting the remaining seeds, including the hybrid seeds from said female plants, from said field, and wherein: i) said highly GA-responsive male plants are fertile plants that are shorter than, of the same height as, or less than 5 cm or less than 10 cm taller than, said low or not GA-responsive male-sterile female plants just before the start of flowering at Z59, when said plants are not treated with a GA3 solution, ii) said highly GA-responsive male plants show an increase in plant height when treated with a solution containing gibberellic acid between Z25 and Z60, which increase is significantly larger than the increase in plant height for said low or not GA-responsive male-sterile female plants, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller than the majority of the low or not GA-responsive female plants just before the start of flowering at Z59 or at full maturity, when said plants were treated at least once with a solution containing gibberellic acid between Z25 and Z60, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and was applied in a volume between 100 and 600 liter per hectare, wherein said harvested remaining seed contains at least 85 %, or at least 87 %, or at least 90 %, hybrid seed when said mixed planting field was sown with a seed mix containing at least 7.5 %, at least 10 %, at least 12 %, or at least 15 % seeds that grow into a highly GA-responsive male wheat plant.

[0179] 74. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein a first application with a solution comprising gibberellic acid is done between stages Z25 and 40 so that the male plants can establish themselves between (or are not overgrown by) the female plants, and wherein a second application with a solution comprising gibberellic acid is done between Z40 and Z60, or between Z45 and Z60 so as to increase male plant height compared to said female plants at Z59 for optimal pollination, or to increase male plant height compared to said female plants at Z92 for cutting the male ears standing out above the female plant ears, optionally with a third application with a solution comprising gibberellic acid after said first and second applications, and wherein said application is done on a field planted with a mix or blend of 5-20 % fertile highly GA-responsive male and 95-20 % low or not GA-responsive male-sterile female plants (such as from a seed mix or blend), or wherein an application or a first and second application with a solution comprising gibberellic acid is done between stages Z45 and Z60.

[0180] 75. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein the purity of the harvested hybrid seed or the yield of harvested hybrid seed is increased compared to said use or method not involving application of a solution comprising gibberellic acid, wherein said hybrid seed is harvested from a mixed planting field comprising at least 7.5 %, at least 10 %, at least 12 %, or at least 15 % or highly GA-responsive male wheat plant planted between a majority of low or not GA-responsive female plants, such as wherein at least part of the male heads standing out above the female plants are cut off before harvesting the hybrid seed.

[0181] 76. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said low or not GA-responsive male-sterile female plant, even if it contains gibberellin-insensitive Rht dwarf alleles such as Rht1 and / or Rht2, shows a (significant) plant height increase in the field after application of a gibberellic acid solution between Z25 and Z60, compared to said female plant when not treated with a gibberellic acid solution, wherein said female plant height increase is significantly less than the plant height increase of the highly GA-responsive male plant after application of a gibberellic acid solution between Z25 and Z60, or wherein said low or not GA-responsive male-sterile female plant is not a plant that is not responsive to treatment with a gibberellic acid solution, or is a plant that is responsive to treatment with a gibberellic acid solution.

[0182] 77. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said gibberellic acid solution comprises 300 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 300 and 600 liter per hectare.

[0183] 78. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said male plants have or were selected to have no delay in heading or flowering date, or to have no shortened pollination window, after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution, optionally wherein the female heading or flowering date or pollination window is not changed by application with said gibberellic acid solution, such as said male plants that have or were selected to have the same or an earlier heading or flowering date, or have the same or a wider pollination window, after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution.

[0184] 79. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein the female plants have or were selected to have no significantly decreased hybrid seed yield after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution, when said female plants are planted with the same male plant as pollinator in the same or a similar setup, such as wherein said female plants have or were selected to have no significant difference in or have a significant increase in hybrid seed yield after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution, when said female plants are planted with the same male plant as pollinator in the same or a similar setup.

[0185] 80. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein at least one application with said gibberellic acid solution is after Zadoks growth stage Z45.

[0186] 81. The use or method of any one of the numbered embodiments herein, or as otherwise described herein as being part of the current invention, wherein said gibberellic acid solution comprises a surfactant that improves efficiency of the gibberellic acid solution or that improves uptake of the gibberellic acid by the plants. As used herein, the term “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps or components, or groups thereof. As used herein, “between”, when referring to a range from one value to another in the current invention, is inclusive, and includes the begin and end value recited.

[0187] All patents, patent applications, and publications or public disclosures (including publications on internet) referred to or cited herein are incorporated by reference in their entirety.

[0188] The invention will be further described with reference to the examples described herein. However, it is to be understood that the invention is not limited to such examples.

[0189] EXAMPLES

[0190] 1. GA-responsiveness seedling growth test

[0191] As initial test to pre-select for GA-responsiveness of a wheat plant line, a seedling elongation test was used, wherein the length of a seedling after GA treatment as compared to a control solution was measured. A 500 ppm gibberellic acid (GA3) solution in water was made (using ethanol as dissolvent for the GA3).

[0192] Then 15 seeds of that plant line were dipped / soaked in the GA3 solution for 5-7 minutes (e.g., in a 3 ml solution) and in the same experiment, also 15 seeds of that plant line were dipped / soaked in a control solution (e.g., in a 3 ml solution) for some (e.g., 5-7 minutes) - that control solution contains water and the same amount of solvent used in the GA3 solution, but lacking the GA3. Then the seeds were air dried for 3 days, and then stratified to prepare the seeds for germination (e.g., in a growth chamber in zip lock bags with germination paper and 12 ml water) for 7 days at 4° C. After stratification, the seeds were sown in soil and placed in the greenhouse (e.g., in 51- well trays). At 7 days after sowing (“DAS”), the plant length was measured from the soil to the leaf tip of the seedling, to compare seedling length of treated vs untreated seedlings. The length difference was expressed in % to the control for better comparability. The average length of all 15 seeds was used. Figure 2 shows the % seedling elongation versus control obtained across 11 different wheat genotypes. The ones showing a strong response are useful candidates for highly GA-responsive wheat lines that can be used as potential male parents, the ones showing no or low response are useful candidates for low or not GA-responsive wheat lines that can be used as potential female parent plants (with the appropriate male parent plant). Table 1 (below) also shows the results obtained in the seedling growth assay and the height as measured in the field (at full maturity (just before harvest)) after GA application for some of these lines, when compared to untreated control (in %).

[0193] Table 1 :

[0194] Table 1 shows for some lines the % plant height increase as measured in the field (by measuring from the soil to the tip of the plant) when applying GA (300 ppm at Z50, 400l / ha with 0,05% Mero®) in the field when compared to the untreated plants in the same field. It can be seen that only plant lines with a strong GA-response in the GA seedling growth assay show a really significant height increase in the field after GA application. Figure 3 shows the data for those lines tested in the GA seed assay (% seedling elongation data) and in the field (after GA treatment, % plant height increase (at full maturity (just before harvest)). While the most GA-responsive lines in the seedling elongation assay were also the most GA- responsive lines in the field, it is not always the best responder in the seed elongation assay that is the best responder in the field, but the seedling elongation is a more qualitative rather than a quantitative indication of GA responsiveness.

[0195] Hence, the GA seed elongation test is a useful test to (pre-)select different parent lines to combine in field trials, as one can combine a low or not GA-responding female parent plant (made male sterile by chemical (CHA) or genetic (e.g., cytoplasmic or genic male sterility) means) with a highly responsive male parent plant to obtain a desired height difference between male (taller) and female plants in the field.

[0196] 2. GA application in wheat field trials

[0197] 2.1. Field trial with GA and / or GR application

[0198] This winter wheat field trial in Moregem (Belgium) was sown in autumn ’22 using standard equipment. Standard fertilizer and crop protection treatments were applied under good agriculture practice to ensure good plant health.

[0199] Agronomics and field trial set-up:

[0200] Plots were sown with 4 rows per entry with a length of 3 meter (bruto), which was later trimmed to 2,5 meter to have better uniformity of plots. Sowing density was 300 seeds / m2. Entries were sown in different blocks for the four different treatments:

[0201] 1) control (untreated)

[0202] 2) Application of Plant growth regulator (“GR”)

[0203] 3) Application of Gibberelic acid (“GA”)

[0204] 4) Application of Plant growth regulator and Gibberelic acid (“GR + GA”)

[0205] Per entry three plots were sown for each of the treatments (3 reps). The trial was split in two “sub-trials” with a first trial (N23TA81C) containing untreated and GR treated plots, and a second trial (N23TA81 D) containing untreated, GA-treated and GR+GA treated plots. These two trials were located next to each other.

[0206] Treatments:

[0207] 1) control (untreated) - an identical amount of solution used for the other treatments was applied on control plots (at the same time), but not including GR or GA.

[0208] 2) Plant Growth regulator (“GR”) - Prodax ® (BASF, a water dispersible granulate containing Prohexadion-calcium and Trinexapac-ethyl, see world wide web at: www.google.de / url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahllKEwi3_fq66Pq CAxllfUqQEHVoMBc4QFnoECBAQAQ&url=https%3A%2F%2Fdownload.basf.com%2F p1 %2F000000000030655412_SDS_CPA_IE%2Fen_IE%2FProdax_0000000000306554 12_SDS_CPA_I E_en_6- 0.pdf&usg=AOvVaw0ty3tllxgPHs4CjSAxDVNqy&opi=89978449) was used with a dosage of 0,65 kg / ha applied at growth stage Z31 (400 l / ha).

[0209] 3) Gibberellic acid (“GA”) - GA3 was applied in dosage of 300 ppm dissolved in water with 0,05 % Mero® (Bayer, an emulsifiable concentrate containing rapeseed fatty acids esters and ethoxy(7)tridecanol, see world wide web at: assets.ctfassets.net / l2hapltrg3cz / 3owDAXTrHeGTHmnE81 P2C1 / 4de0957699e32094a7 a50740e6a296b8 / mero_gb_ra6a.pdf) at growth stage Z50. The volume applied was 400 l / ha. 4) Application of Plant growth regulator and Gibberellic acid (“GR + GA”) was a combination of treatment 2) above with GR at Z31 and later treatment 3) above with GA at Z50.

[0210] Observations:

[0211] Plant height was measured at start and at the end of flowering. Height was determined as average height of the plot surface at two different points of the plots using a ruler. Height represents the distance from the soil surface to the upper tip of the plant / plant layer.

[0212] For the spike parameters, ten spikes were harvested randomly per plot. Spike length was determined with a ruler from the tip of the spike to the junction between spike and peduncle. Number of spikelets were counted per spike.

[0213] Figures 4 to 8 and Tables 2-4 (below) show the results for the different treatments (GA, GR, or GR+GA, compared to untreated) for the number of days to flowering (in days), the plant height at the start and at the end of flowering (in cm, from the soil to the tip of the plant), spike length (in cm), and the number of spikelets per spike (10 spikes per plot were harvested before harvest of the whole plot at full maturity). For the absolute data shown in Figs. 4-5 (Fig. 4a, 4b, 5a, and 5b), the data for the untreated control shown is the average of the untreated controls from the two different trials (the contrasts shown as actuals or as percentage difference in the Tables / Figs. are calculated with respect to the control in the corresponding sub-trial). It can be seen that some plants have a low or no height increase response after GA application (at most an about 9 % increase in height at the start of flowering, and at most an about 5 % increase in height compared to untreated check at the end of flowering), and some plants have a high height increase response after GA application (about 24 % to about 30 % height increase at the start of the flowering, and about 18 % to about 21 % height increase at the end of the flowering, compared to the untreated check). Also, while a GR application will mostly reduce height of the wheat plants compared to untreated checks (from about -1 % to about -10 % to at start of flowering and from about 0 % to about -7 % to at the end of flowering), a later application of GA (after the GR application) on the same plants increases height. Remarkably, the delta / difference seen between GR-treated and GR+GA treated plants is in most cases about the same or just slightly below the delta / difference seen between untreated checks and GA treated plants. It can be concluded that application of GA to increase height does not interfere with the standard agronomical practices in wheat so as to ensure yield performance and / or reduce lodging such as application of growth regulators (PGRs). While a spike length increase of about 4-9 % is seen across all plants tested after GA application (with limited change in the number of spikelets per spike (about -2 to +2 %) after GA application), most remarkable is the spike length increase seen for the GR + GA application in the most GA-responsive plants (an about 13 % and an about 15 % increase in spike length, compared to an 8 % or 9 % increase in spike length after application of GA (without PGR)).

[0214] Table 2 (below) shows the actual results for all treatments in each of the 2 sub-trials (with untreated control of each sub-trial). Table 3 (below) shows the absolute contrast / difference of treated versus untreated control for the results of Table 2, in the same units as Table 2. Table 4 (below) shows the contrast / difference in percentage (%) of treated versus untreated control for the results of Table 2, in the same units as Table 2.

[0215] Table 2. Actual data for all treatments:

[0216] Table 3. Absolute contrast / difference of treated versus untreated control:

[0217] Table 4. Percentage contrast / difference of treated versus untreated control: Figs. 4a and 4b show the actual data (in cm) for plant height at flowering start compared to untreated plots for the most GA-responsive lines (Fig. 4a) and for the low or not GA-responsive lines (Fig. 4b). The data for the untreated control shown is the average of the untreated controls from the two different sub-trials. Figs. 5a and 5b show the actual data (in cm) for plant height at the end of flowering compared to untreated plots for the most GA-responsive lines (Fig. 5a) and for the low or not GA-responsive lines (Fig. 5b). The data for the untreated control shown is the average of the untreated controls from the two different sub-trials.

[0218] Figs. 6a and 6b show the contrast / difference (in cm) for plant height at flowering start compared to untreated plots for the most GA-responsive lines (Fig. 6a) and for the low or not GA-responsive lines (Fig. 6b).

[0219] Figs. 7a and 7b show the contrast / difference (in cm) for plant height at the end of flowering compared to untreated plots for the most GA-responsive lines (Fig. 7a) and for the low or not GA- responsive lines (Fig. 7b).

[0220] Fig. 8 shows the contrast / difference (in %) for spike length for all genotypes, comparing treated versus untreated (for all treatments).

[0221] 2.2. GA application in wheat field trial

[0222] Winter wheat field trials in Gatersleben (Germany) were sown in autumn using standard equipment. Standard fertilizer and crop protection treatments were applied under good agriculture practice to ensure good plant health.

[0223] Agronomics and field trial set-up:

[0224] Plots were sown with 6 rows per entry with a length of 2 meter resulting in a plots size of 3 m2. Sowing density was 330 seeds / m2for most of the lines and 200 seeds / m2for some other lines. Entries were sown in different blocks for the two different treatments:

[0225] 1) control (untreated),

[0226] 2) Application of Gibberellic acid (GA)

[0227] Per entry one plot was sown for each treatment.

[0228] Treatments:

[0229] 1) control (untreated) - an identical amount of solution used for the other treatment was applied on control plots at the same time, but not including GA.

[0230] 2) Gibberellic acid (GA) - GA3 was applied in dosage of 370 ppm (first dissolved in ethanol and then diluted in water) at Z45. Applied volume was 200 l / ha.

[0231] Observations:

[0232] Plant height was measured close to maturity. Height was determined as average height of the plot surface at two different points of the plots using a ruler. Height represents the distance from the soil surface to the upper tip of the plant / plant layer.

[0233] For each plot ten spikes together with the complete peduncle (from the junction with the spike until the next node) were harvested randomly from ten plants per plot. Spike length was determined with a ruler from the tip of the spike to the junction between spike and peduncle. Number of spikelets were counted per spike. Peduncle length was measured with a ruler from the junction with the spike to the next node. Peduncle width was measured with a caliper at the middle of the peduncle, and at 1 cm distance from the junction with the spike.

[0234] Results are shown in Figures 9 to 14 and in Tables 5 and 6 below. Table 5 (below) shows the averages of the actual data obtained for treated and untreated plants across several genotypes tested, for plant height at maturity (in cm), spike length (in cm), number of spikelets per spike, peduncle length (in cm), peduncle width measured in the middle of the peduncle (in mm), and peduncle length measured at 1 cm distance from the junction with the spike (in mm). Table 6 (below) shows the difference / delta in plant height measured for the different genotypes tested, for GA-treated vs. untreated plots, as actual (in cm) and in %. Figures 9a and 9b shows the contrast / difference between the results (as in Table 5) for treated and untreated plants in absolute values (Fig. 9a) and in % (Fig. 9b). Figure 10 shows the actual plant height measured (in cm) for the tested lines for GA-treated vs. untreated. Figure 11 shows the actual peduncle length (in cm) for untreated and GA-treated plots, per genotype tested. Figure 12 shows the actual width of the peduncle measured in the middle of the peduncle (in mm) for untreated and GA-treated plots, per genotype tested. Figure 13 shows the contrast / difference in peduncle length (in %) for untreated and GA-treated plots, per genotype tested. Figure 14 shows the contrast / difference in peduncle width (in %, measured in the middle of the peduncle length) for untreated and GA-treated plots, per genotype tested (showing in most lines tested a decrease in peduncle width of about 5 to 18 %).

[0235] Table 5:

[0236] Table 6:

[0237] Several of the tested plants show a height increase (close to maturity) of 21-25 % after GA application (corresponding to 15-20 cm here) compared to untreated check, while 2 tested plants only showed an about 7 % height increase (corresponding to 5 cm here) after GA application compared to untreated check. For one of the most height responsive lines a clear increase in spike length could be observed without any real impact on spikelet number. In two of the most height-responsive lines a strong increase of the peduncle length was seen, with also a decrease in peduncle width.

[0238] 2.3. Outdoor container tests:

[0239] Containers with the following dimensions were used (120 cm length x 100 cm width x 65 cm height). These containers were filled with soil from a regular farmers field (approx. 780 liters). Per container 9 rows of each 22 winter wheat plants (20 A-line plants, 2 B-line plants) were grown.

[0240] Seeds for two different A-lines (male-sterile female plants containing T. timopheevii CMS) and one R-line (fully fertile male plants containing restorer genes for T. timopheevii CMS) were stratified for one week at 4°C - the R (male) line plants were GA-responsive as they had a significant plant height increase compared to the R line plants when not treated with GA3, while the A (female) line plants were low or not GA-responsive as they had no or only a very low plant height increase compared to the A line plants when not treated with GA3. After that seeds were sown in 51 -well trays and cultivated in the greenhouse until plants reached the 1-2 leaf stage. Trays were transferred to a growth chamber with 16 hours light at 4°C to vernalize the plants for 9 weeks.

[0241] Early April plants were transplanted to the outside container in 9 rows of 22 plants. Each row contained 20 A-line plants and 2 R-line plants, where the position of the R-line plants per row was randomized (simulation of a mixed planting setup). R-line plants were labelled with a ring at the base of the plant. For each of the two AxR-line combinations 8 containers were transplanted.

[0242] An irrigation system was installed after transplanting and the containers were supplied with fertilizer and any required application to maintain good plant health. If needed, weeds were removed manually.

[0243] 40 ml / m2GA3 (300 ppm + 0,05% Mero®) was applied from the top with a hand sprayer at booting stage (Z45) to 4 of the 8 containers per AxR-line combination (the other 4 containers served as untreated controls). The untreated containers were also sprayed with water plus Mero® but without GA.

[0244] Plant height was measured for representative A- and R-line plants per container at flowering start (Z65) and shortly before harvest (Z91). Measurement was done with a ruler from the surface of the soil to the tip of the spike.

[0245] At harvest, all R-line plants were harvested individually. R-line plants were placed on a table and the plants were cut at a height which was the same height as the height from soil level to the upper surface of the canopy (the tips of the main spikes) formed by the A-line plants. The height was determined for each container separately. R-line spikes and seeds above and below the cutting line were collected separately, cleaned, and counted. A-line plants were harvested as bulk, but due to very low seed set (poor nicking in these experimental lines), data have not been further considered.

[0246] The results (averages across all containers per AxR-line combination) are shown in Tables 7 to 10 below, and in Figures 15 to 22. The A-line indicated as “A1” in the Tables 7-10 and Figures 12- 22 in this Example was of genotype 21 NGTA002590, the A-line indicated as “ A2” in the Tables 7- 10 and Figures 15-22 was of genotype 23NGTA000112, and the R-line used was of genotype 21 NGTA002932 (1 R-line was used, but in the experiments where it was interplanted with female line A1 this was named R_A1 , and in the experiments where it was interplanted with female line A2 this was named R_A2). Figures 15 and 16 show the plant height at Z65 of A- and R-lines in mixed planting untreated / GA-treated (actuals in cm in Fig. 15, and contrast in cm in Fig. 16). Figures 17 and 18 show the plant height at Z91 of A- and R-lines in mixed planting untreated / GA-treated (actuals in cm in Fig. 17, and contrast in cm in Fig. 18), from outdoor container tests. Figures 19 and 20 show the difference in plant height (in cm) between R- and A-line in mixed planting with and without GA3- treatment at respectively the Z65 (Fig. 19) and Z91 (Fig. 20) growth stage. Figures 21 and 22 show the proportion of R-line seeds above and below the upper canopy layer of A-line plants in mixed planting with / without GA treatment (in % of total R-line seeds).

[0247] For one AxR-line combination, it was found that the majority of the R line seeds (about 80 %) were positioned below the tip of the A line spikes without application of gibberellic acid. This positioning was completely reversed as a consequence of gibberellic acid application. After gibberellic acid application the majority of the R line seeds (about 70 %) were positioned above the tip of the A line spikes (see Figs. 21 and 22 and Table 10 below). This means that far more male seeds can be removed (before harvest of the hybrid seeds) by cutting above the layer formed by the tip of the main spikes of the female plants (containing the hybrid seeds), when the male plants respond strongly in height to the GA application (with little or no height increase seen in female plants). Hence, improved hybridity in hybrid seed production of wheat can be obtained by mixed-planting highly GA-responsive male and low or not GA-responsive male-sterile (female) wheat parents that have a sufficient height difference at end of flowering or at harvest, applying GA over the top of the plants, and after anthesis (or after then end of flowering), cutting the male plant heads so that purer hybrid seed can be harvested.

[0248] Table 1. Actual plant height for all lines with / without GA treatment:

[0249] Table 8. Contrast / difference between GA-treated and untreated lines in absolute plant height and in %:

[0250] Table 9. Contrast / Difference between R- and A-lines, GA-treated and untreated:

[0251] Table 10. Proportion of R-line seeds above and below the upper canopy layer of A1-line plants in mixed planting with / without GA treatment:

[0252] 3. Hybrid wheat seed production by row / strip planting

[0253] Hybrid seed production can also be done by planting male and female plants in separate rows or strips, and if the male parent is highly GA-responsive (the matching female parent is preferably low or not GA-responsive, but can also be highly GA-responsive) then only the male rows / strips can be treated with GA so that male plants will get taller, and can better pollinate the female plant rows. Since only male rows were sprayed with GA, the females will have no or very limited height response (due to possible drift). If the female parent is low or not GA-responsive, then the entire field can be sprayed with GA, and then only the male plants will show a significant height increase, and the taller males can then be separately harvested or the male spikes / seeds can be mechanically / chemically / physically eliminated or destroyed (or seed growth can be prevented / reduced). When a male is selected that has a clear increase in peduncle length after GA application so that most male heads will bend down and lodge (or the peduncle will break) as seeds mature, the male can also be harvested together with the hybrid seed produced on the female, and most of the male seed which will be smaller in size, and can then be removed from the hybrid seed based on size / density in standard harvesting equipment (equipped to remove debris and small or weed seeds from the hybrid seed).

[0254] 4. Hybrid wheat seed production

[0255] Hybrid seed production is done by planting male and female plants in mixed planting, where the male plants are randomly occurring between the female plants in a hybrid seed production field (or are planted in a specific configuration wherein the male plants are in a more ideal configuration with respect to the female plants, such as the honeycomb configuration in Fig.1 ). This is achieved by planting a seed lot containing from 3 to 30 %, such as 3 to 20 %, male plant seeds mixed with a majority of female plant seeds. The male parent plant is selected as being highly GA-responsive and the matching female parent is selected as being low or not GA-responsive, as described herein. Then GA3 is applied between growth stages Z30 and Z50 (1-500 ppm, 100- 500l / ha) over the entire field (adapted to the specific parent lines used and the intended height difference between male and female at Z59, or at the start or end of flowering (and a second later GA application is done if the first GA application did not have the intended effect)). Only the male plants show a significant height increase response to the GA, so that their heads / spikes stick out above the tips of the female plants and the taller male spikes can be separately harvested before harvesting the hybrid seed, or the male spikes can be mechanically and / or chemically and / or physically eliminated or destroyed (or seed growth can be prevented / reduced) before harvesting the hybrid seed from the female parent plants. When a male was selected that has a clear increase in peduncle length after GA application so that most male heads will bend down and lodge as seeds mature, the male seeds can also be harvested together with the hybrid seed produced on the female, as most of the male seed (which will be smaller in size) can then be removed from the hybrid seed based on size / density separation in standard harvesting equipment (equipped to remove debris and small or weed seeds from the hybrid seed). Compared to using male plants that are genetically taller than female plants in absence of any GA application, this production method has the benefit that the hybrid plants (grown from the harvested hybrid seed) will not become too tall (to avoid plant lodging, making harvest of the grain formed on the hybrid plants difficult or impossible).

[0256] 5. Yield determination after GA application in strip trials

[0257] In seed production field trials in 2024, GA3 is applied to GA-responsive male plants and to not or low GA-responsive male-sterile female plants. In some plots, also a plant growth regulator (PGR) was applied.

[0258] In all plots receiving GA3 treatment, gibberellic acid (GA3) is applied at BBCH stage 30-31 and at BBCH stage 40-45. The dose used is 300 ppm (200l / ha) with 0,05% of surfactant (ACTIROB B (an emulsifiable concentrate containing rapeseed oil methyl ester, see world wide web at: www.edppiveteau.fr / files / notices / actirob-b-securite-52ecbb172af4a.pdf)). Application is preferably in the morning.

[0259] For plots receiving plant growth regulator (PGR) and GA3 treatment at the same day, PGR is sprayed when GA3 is dried.

[0260] The PGR (no surfactant added) in Gatersleben, Germany, is one treatment with CCC (1 l / ha) at BBCH30, the PGR in Kemmes is a first spray with Prodax (0,6 l / ha, at BBCH 30-32), and a second spray of Medax Top (0,5 l / ha, at BBCH 37-39), and the PGR in Poland is Moddus 250 EC 0,3 l / ha (at 200 l / ha), a first time at BBCH 31 , and a later application at BBCH 40.

[0261] These treatments are tested on 1 male winter wheat line (R1 , genotype PMWH131094139) and 2 female (CMS male-sterile) winter wheat lines (A8, CMS male-sterile line PMWH140233691) and A1 (different to the A1 line in Ex. 2 above, genotype PMWH140333311), that are planted in strips so as to allow the female plants to be pollinated by the male plants and produce hybrid seed, and to allow separate observation of response of male and female plants to the treatments.

[0262] The trial is a split plot design with 2 repetitions at 3 locations (2 in Germany (Kemmes and Gatersleben) and 1 in Poland (Kazmierz)), so that there are 12 experimental units for each treatment (48 experimental units in total). The field trial design scheme is shown in Fig. 23 (dark bars are male rows, light grey and dotted bars are female rows, H1 and H2 are the 2 hybrids tested, Ctlr is untreated control, GA refers GA3 application (without PGR), GA+PGR refers to GA3 and PGR application as described, PGR refers to plant growth regulator application without GA3). In these trials, 3 blocks of 2 male rows (6m long and 0.5 m wide in total) are planted next to 2 blocks of 5 female plant rows (6 m long and 1 .5 m wide in total) as shown in Fig. 23 for each treatment (or as control / check with no GA3 and / or PGR treatment).

[0263] Plant height is measured after the end of flowering, and at most an average increase in height of 3 % is seen for the female plants after GA3 application, while the height of the R1 male increases by at least 15 % after GA3 application in the different locations (vs. untreated control). The female plant height (at the end of flowering) after GA3 application does not differ significantly from the height of untreated female plants, while the male plant height increases significantly after GA3 application when compared to the untreated male plant. Also, when PGR is applied close to the GA application on the same day, plant height is not significantly different between the GA only and GA + PGR treatments.

[0264] Also, yield of the male plants decreases significantly after GA application compared to untreated male plants, while yield on both females when treated with GA does not differ significantly from the yield of the untreated control female plants. The number of ears per m2of male plants does not differ significantly between GA treated and untreated males, showing that the yield decrease in male plants is not due to less ears being made.

[0265] 6. Comparing different hybrid seed production methods

[0266] 6.1 ■ ’23-’24 season winter wheat field trials

[0267] A hybrid field trial test was done in France with European winter wheat lines (3 different male-sterile female lines (A1 (genotype PMWH140333311), A3 (genotype PMWH174427856), and A7 (genotype PMWH 166930426)) and 1 male CMS restorer line, R1 (genotype PMWH131094139), to compare several different hybrid production methods using standard agronomy for wheat in the area:

[0268] -in mixed planting (abbreviated as Mix or M, with either 4%, 7.5%, 15% or 30 % male seed mixed with the female seed and then planted),

[0269] -in traditional row / strip planting (abbreviated as Strip or S, alternating blocks of male and female rows), and

[0270] -in row / strip planting with alternative blocks of male and female rows, where 4% male seed was mixed with the female seed and then sown (abbreviated as Strip + Mix 4% or S+M4%, the female rows contain 4 % of male seed).

[0271] A solution with GA3 (300 mg / l (5101 / ha)) containing Actirob (2,55 l / ha) was applied at BBCH stage 43-45 (flag leaf sheath swollen (see Lancashire et al. (1991) Ann. Applied Biol., 119: 561-601 , for BBCH scale)) to the mixed planting plots that contained 15 or 30 % males. Also, after pollination, the ears of the male plants sticking out above the female plants were removed by cutting them off with a hedge trimmer in those mixed planting plots that contained 15 % or 30 % males. Plots having 4 % or 7.5 % of male in mixed planting, as well as the Strip and Strip + Mix plots, were not treated with GA3, and also no cutting / removal of male heads was done there.

[0272] The female plants (or the mixture thereof with 4 % male seeds) in the Strip and Strip + Mix plots were planted at different seed densities (125, 250 or 400 seeds / m2). In the Strip and Strip+Mix trials, the male-only rows that were planted in strips were sown at a density of 200 seeds / m2. The seed mix containing male and female seed, as used in the 4%, 7.5%, 15%, and 30% mixed planting trials, was also planted at 3 different seed densities (125, 250 or 400 seeds / m2).

[0273] The field design scheme is shown in Figures 24 and 25, for, respectively the Strip and Strip+Mix row plantings where the male rows are in a separate block from the female rows (Fig. 24), and for the mixed planting trials where the rows contain a mixture of male and female plants (Fig. 25). The weather in 2024 was far from optimal with a lot of rain at the key time of flowering, so conditions for cross-pollination were sub-optimal, resulting in rather low hybrid seed production.

[0274] At full maturity, the plots were harvested and cleaned from debris to get the net seed weight. Seed was harvested separately from the male and female rows in the Strip and Strip+Mix plots, and total seed was harvested from the mixed planting plots. Since the R1 male used in these trials had white seed (with light seed color, recessive), and the A1 , A3 and A7 females all had red seed (with darker red seed color, dominant), the hybrid seed had a red seed coIor and could be easily sorted from the (selfed) male (white) seed using a standard color seed sorter. This allowed to calculate rather accurately the % of male and hybrid seed in the total harvested seed from the mixed planting trials.

[0275] The results for the 125 and 400 seeds / m2 seed density plots is shown in the Tables below and in Figures 26 and 27 for all seed densities tested. Since the weather conditions this season were sub- optimal for cross-pollination, the plots with a lower seed density (resulting in more tillers per plant, extending the pollination window) showed better than expected hybrid seed set on the male-sterile female lines. It turned out that also higher % of male seeds in mixed planting (even a 30 % male seed in the seed mix sown) allows to produce hybrid seed at a hybridity above 80 % in one female genotype (the same genotype when using a 4 % or 7.5 % male seed mix, without use of GA and with no removal of taller male heads, resulted in a hybridity of only 60-63 %) and a hybridity of about 90 % in the 2 other female genotypes. Such high hybridity is achievable when using GA-responsive males and low or not GA-responsive male-sterile females as parent lines in a mixed planting approach, and removing the heads of the male plants (by cutting them) sticking out above the female plants. In the table below the Qx / ha refers to the 10Okg / hectare yield of hybrid seed, and TSW refers to thousand seed weight (the weight of 1 .000 seeds, also named TKW).

[0276] Results from ’23-’24 trials (sown at 125 seeds / m2density)

[0277] The data given in the above column “female seed hybridity %” shows the % of hybrid seed in the harvested seed, based on the number of hybrid (red) seed in the total number of seeds harvested. The enclosed Figure 27 shows these results in graphical form. Also, Figure 26 shows the yield per treatment calculated on the same plot area (using the entire Qx / ha value (the value in the above Table is an abbreviation)), taking the strip value as 100 %, to better compare strip and mixed plantings on the same per area basis (strip plots occupied almost double the area of the mixed planting plots, as seen in the above Table).

[0278] Also, it was clear in this trial that the height of the GA-responsive male (R1) increased after GA3 application (see the table below, showing the plant height (measured when all plants (male and female) ended flowering in the field (BBCH stage 71-75)) for the plots with 125 and 400 seeds / m2(similar results were seen for the other seed density tested). At 125 seeds / m2average male plant control height (no GA3 applied) was about 91 ,8 cm for the male across all plots, while average male plant height after GA3 application was about 105,4 cm. Also, the average height difference between the R1 male and each of the females at this seed density increased with 14,2, 14,5 and 14,2 cm, by GA3 treatment (compared to untreated) for the A1 , A7 and A3 females, respectively. GA3 treatment caused an average height increase in the male compared to the female plants of 18,3 cm for the A7 female, 16 cm for the A1 female, and 18 cm for the A3 female.

[0279] Height measurements (in cm, shown for 125 seeds / m2plots) Height measurements (in cm, shown for 400 seeds / m2plots) No A3 400 ip+mix4% 86 L I

[0280] Also, the heading dates were taken for the different treatments (the heading date is expressed in number of days after January 1). Results are shown in the below tables.

[0281] Average heading dates (HD, for plots with 125 seeds / m2):

[0282] Average heading dates (HD, for plots with 400 seeds / m2):

[0283] Clearly, the R1 male had a heading date that was about 2 days earlier after GA3 application (compared to untreated). 6.2. ’22-’23 season winter wheat field trials

[0284] The above more detailed results confirm the initial field trial results of 2023 in France with this R1 male (genotype PMWH131094139) and another GA-responsive winter wheat male (R9, genotype PMWH 139907986), where also an average heading of - (minus) 2 days (for R1) and - (minus) 1 day (for R9), was seen after GA3 application (vs. untreated, so the males were heading 2 and 1 day earlier, respectively, after GA3 application).

[0285] This field trial included 4 low or not GA-responsive winter wheat (R (CMS restorer) or B (maintainer)) lines: maintainer line B1 (PMWH20525459, containing Rht1), restorer line R8 (PMWH24628328, containing Rht1), R line PMWH90984662 (containing Rht2), and R line PMWH20743432 (containing Rht2), besides 2 highly GA-responsive winter wheat lines: R1 (genotype PMWH 131094139), and R9 (genotype PMWH139907986), both not containing Rht1 or Rht2. 5 treatments were tested for each of the 6 different genotypes (GA3 was applied at 510 l / ha):

[0286] 1-GA3 application in a dose of 300 mg / l at Zadoks growth stage Z37-Z39,

[0287] 2-GA3 application in a dose of 500 mg / l at Zadoks growth stage Z37-Z39,

[0288] 3-GA3 application in a dose of 300 mg / l at Zadoks growth stage Z40-Z45,

[0289] 4-GA3 application in a dose of 500 mg / l at Zadoks growth stage Z40-Z45,

[0290] 5-untreated control

[0291] The results (see Fig. 28 and the table below) show that after any of the above GA3 applications, the highly GA-responsive lines (R1 , R9) have an earlier heading date (HD) compared to the untreated check, and that GA3 increases the flowering period, wherein GA3-treated plots with highly GA- responsive lines would typically start flowering one or two days earlier than the untreated check, and end flowering at the same time as the untreated check (hence expanding the flowering period).

[0292] A clear effect on height increase was seen in the highly GA-responsive lines, which was more pronounced for the earlier applications (1 and 2 above). Average height increased by 11 cm versus untreated check for R1 , and 15 cm for R9, after application of GA3 at the Z37-Z39 growth stage. See Fig. 29. The low or not GA-responsive lines (having either Rht1 or Rth2), did not show a difference in heading date after GA3 application, and no real difference was seen in plant height after GA3 application.

[0293] 7 ■ Research field trials in Belgium

[0294] 7.1. Plant height tests when GA3 was applied in different doses and at different times

[0295] In a field trial in Astene, Belgium, 9 treatments were tested: dosages of 0, 100, or 300 ppm GA3 (200 l / ha, with surfactant: Mero® - 0,05%, applied with a backpack sprayer), were applied at developmental stage(s): 1) Z30 / 31 and / or 2) Z48 / 49. 4 winter wheat lines were used: 2 A-lines (male-sterile females, with CMS) and 2 R-lines (fertile males, with restorer(s)): female A8 (genotype PMWH 140233691) was paired with male R2 (genotype PMWH139907993), and female A1 (genotype PMWH 140333311) was paired with male R1 (genotype PMWH 131094139). The females were not or low GA-responsive, the males were GA-responsive. 54 plots / blocks were tested in total, plots were 6.75 m2in size, 3 replicates were included per line and treatment, the field design was using a randomized block design, with mixed / blended planting of 8% male (R-line) mixed in 92 % female seed before sowing. The effect of GA application on plant height was monitored at different developmental stages. Since stage Z60 (flowering) and Z80 (maturity) are the more relevant timepoints in view of hybrid seed production, the plant height at Z60 and Z80 are shown below.

[0296] The following table shows the treatments applied with the early (Z30 / 31) and / or late (Z48 / 49) application, at the 0, 100 or 300 ppm GA dosages :

[0297] GA3 treatments:

[0298] The following plant heights were measured at anthesis (HEI_Z60) for the different treatments (SE: Standard Error, F: female, M: Male):

[0299] A so, the following plant heights were measured at maturity (HEI_Z80) for the different treatments (SE: Standard Error, F: female, M: Male):

[0300]

[0301] The contrast / delta in plant height between male and female plants at Z60 orZ80 is shown in the below tables:

[0302]

[0303] The results show a clear response of the male lines on the GA3 treatments, while the response of the female lines is weak. At key stage Z60 for hybrid seed production (flowering start), the strongest effect comes from the second treatment (Z48 late booting) with the highest GA3 dose (300ppm). Combined with 300ppm at Z30 (early stem extension), this results in the maximum difference in height between the male and the female for both combinations:

[0304] 1 . A1xR1 : from -4 cm (untreated, male shorter (at stage Z60)) to +24 cm (male taller than female, stage Z60) by GA3 treatment (300+300 ppm), a significant increase of 28 cm.

[0305] 2. A8xR2: from +10 cm (untreated, male taller than female at stage Z60) to +34 cm (male taller than female, stage Z60) by GA3 treatment (300+300 ppm), a significant increase of 24 cm.

[0306] Also, measurement of the days to heading in this trial showed a significantly earlier heading date (p- value < 0,05) for the R2 and R1 male (1-3 days earlier) for some (3-4 of the 8) treatments with GA, while other GA treatments showed no significant difference in heading date, when compared to untreated plants - hence, no consistent difference with heading date of untreated plants was seen, but if any effect was seen at one of the 8 treatments it was an earlier heading date, never a later heading date. Indeed, none of the 2 tested males showed a delay in heading after application of a GA3 solution, and certainly not any significant delay in heading. Of the females tested, one (A1) never showed a significant difference in heading to the control plants in any of the 8 GA treatments, and the other (A8) showed a significant earlier heading in 3 of the 8 GA treatments.

[0307] Measurement of the days to flowering start also showed no consistent difference to untreated plants for the R1 and R2 males, but if any significant effect (p-value < 0,05) was seen for some of the GA treatments (in 1 or 3 of the 8 treatments), it was an earlier flowering (1 -1 .5 days). Measurement of the start of flowering of the 2 male lines and flowering period for one male did not show a significant difference to the untreated control for any of the 8 treatments, while for one males (R2) 2 of the 8 GA treatments showed a significantly longer flowering window (1.5-2 days). Hence, no consistent difference was seen for the males in the flowering window, and if any significant effect was seen on flowering period after a GA treatment in the 2 males tested, it was a longer flowering window. No shortening of the flowering window was observed in this trial by any of the 8 GA applications, for the males tested.

[0308] 7.2. Application of GA3 and PGR

[0309] In a field trial in Astene, Belgium, 5 treatments were tested: (1) control / untreated, 2) GA3 at Z40, 3) PGR at Z30, 4) PGR+GA3 - applied same day (at Z30), and 5) PGR+GA3 - applied with two weeks difference (PGR at Z30, GA3 at Z48). GA3 was applied by backpack sprayer in a dose of 300 ppm (at 300-400 l / ha). GA3 contained Mero® as surfactant (0,05 %). The PGR (plant growth regulator) used here was Percival® (BASF, 0,75 kg / ha).

[0310] In this trial, 4 winter wheat lines were tested: CMS maintainer (B) line 1012 (genotype PMWH20743769), male CMS restorer line 1200 (genotype PMWH84562645), and 2 lines containing Rht1 or Rht2 (B line 1256 (genotype PMWH93616596) and B line 1341 (genotype PMWH22885922)). The field trial design consists of 60 plots in total with a plot / block size (area) of 4 rows - 1 ,8 m2, 3 replicates per line and treatment, in a randomized block design.

[0311] The single PGR treatment at Z30 caused the GA responsive lines to grow significantly less tall, on average 15 cm across both lines and across the growth stages. The response on the PGR treatment of the less GA responsive lines is clearly weaker. Similar sensitivities can be observed for the separate GA3 treatment at Z40, with an opposite effect on plant height. For the more GA responsive lines the single GA3 application results in a significant height increase of + / - 15 cm at flowering stage Z60.

[0312] For line 1012 the PGR treatment reduces the effect of GA3, e.g. at Z60 and effect sizes (compared to PGR only) : +31 cm (single GA3), +18 cm (PGR (Z30) combined with GA3 at Z48), +12 cm (PGR combined with GA3 at Z30). For line 1200 the PGR treatment has less impact on the effect of GA3 (compared to PGR only): +30 cm (single GA3), +34 cm (PGR (Z30) combined with GA3 at Z48), +20 cm (PGR combined with GA3 at Z30).

[0313] This trial demonstrated the shortening effect of PGR and the lengthening effect of GA3 on plant height of GA responsive lines. The fact that PGR may inhibit the GA3 effect more or less in a combined treatment seems to depend on the genotype and time of (GA) application. The effect seen on plant height by the PGR / GA3 applications (compared to untreated) is schematically shown in Fig. 34.

[0314] Plant height measured at Z60 (flowering):

[0315] Height measured at Z80, close to harvest:

[0316] Below the height contrast in % for this trial, of treatment 1 (TRT1) when compared to untreated or PGR treatment (TRT2) (e.g., line 1012 was 16,4 % taller at Z60 when treated with GA3 at Z40 compared to untreated, and was 19,6 % shorter at Z60 when treated with PGR at Z30 compared to untreated):

[0317] This clearly shows that more GA-responsive plants respond stronger to PGR treatment with a height reduction, compared to less GA-responsive plants: see the 20 and 16 % reduction in height versus the control (untreated) for the more GA-responsive plants treated with the PGR at Z30 when measuring the plant height at Z60, versus the less GA-responsive plants at Z60 (only 7 or 2 % height reduction vs. untreated when PGR-treated). See also Fig. 34, schematically representing the height differences on GA-responsive male plants for the different treatments (illustrative / indicative, not drawn to scale, not based on actual data).

[0318] Also, at Z80 the height difference in % for the less GA-responsive plants was clearly lower than that for the more GA-responsive plants when treated with PGR vs. untreated (1or 3 % vs. 12 or 10 %).

[0319] Hence, as to getting the maximum height difference between male and female plants, it could be beneficial to apply the PGR only on GA-responsive male-sterile female plant rows in row / strip planting, and to apply the GA3 only on GA-responsive male plant rows. Alternatively, for a mixed planting setup, a low or not GA-responsive male-sterile female can be selected that responds more to the PGR with a plant height reduction compared to other female parent lines, and this female can then be mixed / combined with a GA-responsive male (such as the 1200 male above) that responds well to GA3 and less to the PGR compared to other male lines, and PGR and GA are applied over the mixed planting field on both male and female plants (preferably the PGR at its recommended application around stage Z30-Z31 , and the GA3 later, such as between Z40 and Z60).

[0320] Measurement of days to heading, days to flowering and flowering time / period in this trial showed no significant difference after any of the 3 treatments including GA3 compared to untreated plants, in the GA-responsive males (1012, 1200) and in the low to not GA-responsive female plants tested (1341 , 1256). Only the PGR application at Z30 without GA application resulted in a significantly later heading date (2.5-5 days) in all male and female plants tested (p-value < 0,05). Hence, in the combined application of PGR atZ30 and GA3 at either Z30 orZ48, the GA3 application caused an earlier heading compared to the PGR-only treatment. For the PGR only application, no significant effect on days to flowering or on flowering time was found for any of the tested male and female plants.

[0321] 8. Mixed planting yield trials in France A mixed planting trial was done in 2 locations in France (Caen and Catillon), with seed mix planted at 300 seeds / m2, containing either 10 % or 15 % male plant seeds in the seed mix sown, for the winter wheat hybrid parent plant combinations A1 x R1 and A1 x R2 (A1 (genotype PMWH140333311) is a male-sterile CMS female, R1 (genotype PMWH131094139) and R2 (genotype PMWH139907993) are 2 different (fertile) male plants restoring fertility). A GA3 solution (300 ppm, 220 l / ha, 0,05 % surfactant added (Mero® (an emulsifiable concentrate containing rapeseed fatty acids esters and ethoxy (7) tridecanol)) was applied over some plots, first at BBCH stage 30-31 and later at BBCH stage 40-45, while other plots were not treated with GA3. The field design used in Caen is shown in Fig. 30 (not drawn to scale), and the very similar field design used in Catillon is shown in Fig. 32 (not drawn to scale).

[0322] The setup and results from the field trial in Caen are shown in the below Table and in Fig. 30 (plot weight (in kg) and raw yield (t / ha, 14 % moisture) are for the total harvested seeds):

[0323] In the field trial in Caen, these were the average and median values obtained for the harvested (total) raw seed yield (t / ha, at 14 % seed moisture) for the GA3 treatment compared to untreated (“Check” below), for the mixed planting of male-sterile female plants and male plants, with either 15 % or 10 % of male plant seeds in the seed mix sown, for the respective parent combination tested (as shown in Fig. 31 , also indicating the % increase in average total raw yield between control and GA3-treated, and the corresponding P-value):

[0324] This clearly shows that the total seed yield increased when more male was planted, but also shows that median and average yield values for the GA3 application are always higher than the untreated control.

[0325] Interestingly, the untreated R1 male was shorter than the untreated A1 female, which resulted in a situation that the female heads were above the male heads at flowering, if no GA was applied. As a result of the GA application the height of the R1 male plants increased, so that the heads of the male and female plants were at the same height when treated with GA. Also, the TKW (thousand kernel weight, in gram) values from the Caen field trial (see above T able and below summary, no TKW values were taken in Catillon) show that the majority of the difference in yield results from an increase in grain number, as a consequence of improved cross-pollination. The R2 male plants were observed to be a bit taller than the female plants, and after application of GA more male spikes could be seen to rise above the female spikes.

[0326] In Catillon, a similar planting scheme as shown in Fig. 30 was used (see Fig. 32, with (“+ GA3”) or without GA3), and the results are shown in the below Table and in Figure 33 ((plot weight (in kg) and raw yield (t / ha, 14 % moisture) are for the total harvested seeds)):

[0327] In the field trial in Catillon, these were the average and median values obtained for the harvested (total) raw seed yield (t / ha, at 14 % seed moisture) for the GA3 treatment compared to untreated (“Check” below), for the mixed planting of male-sterile female plants and male plants, with either 15 % or 10 % of male plant seeds in the seed mix sown, for the respective parent combination tested (as shown in Fig. 33, also indicating the % increase in average total raw yield between control and GA3-treated, and the corresponding P-value):

[0328] These results show that GA3 consistently increased seed yields, often statistically significant. Overall, these field trials show that the hybrid seed set on the male-sterile female plants is always increased, and that increase is either not significant or is a significant increase, after treatment with a gibberellic acid solution, when compared to said female plants when not treated with said gibberellic acid solution. No significant decrease in hybrid seed yield is observed on the female plants.

Claims

CLAIMS1 . A method to improve cultivation of hybrid wheat parents, comprising the steps of: a) sowing seeds growing into highly GA-responsive male plants and seeds growing into low or not GA-responsive female plants in the same field, so that said male plants are randomly interspersed amongst said female plants in a mixed planting setup, and b) applying a solution comprising gibberellic acid over the top of that field of male and female plants between stage Z25 and Z60, on the Zadoks growth scale, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 12 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than 10 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z60.

2. The method of claim 1 , including the step of mixing 3-20 % of seeds growing into said highly GA-responsive male plants with 97-80 % of seeds growing into said low or not GA-responsive female plants in a bag or container.

3. A method to improve purity of harvested hybrid wheat seeds from a mixed planting field containing highly GA-responsive male wheat plants and low or not GA-responsive female wheat plants at full maturity, ready to be harvested, wherein said plants were previously treated with a solution containing gibberellic acid between Zadoks growth scale stages Z25 and Z60, said method comprising the steps of: a) cutting off, destroying or separately harvesting the male plant spikes standing above the height of the female plant spikes after the end of flowering using a cutting or destruction or harvesting device above the height of the female plant spikes, and b) harvesting the hybrid seeds from said female plants in that field, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 12 % increase in plant height just before the start of flowering at Z59, compared to said plants at that stage when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % increase in plant height just before the start of flowering at Z59, compared to said plants at that stage when not treated with a gibberellic acid solution, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and was applied in a volume between 100 and 500 liter per hectare.

4. A method to improve hybrid wheat parent plant selection, comprising the steps of: a) providing a population of wheat plant seeds that are fertile male parent plant seeds and providing a population of wheat plant seeds that are male-sterile female parent plant seeds for hybrid wheat seed production, b) selecting highly GA-responsive seeds from said population of male plant seeds, and c) selecting low or not GA-responsive seeds from said population of female plant seeds, and optionally d) mixing 3-20 % of said highly GA-responsive male plant seeds with 97-80 % of said low or not GA-responsive female plant seeds in a bag or container, and wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 12 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, and iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z60 and optionally, said method includes the step of sowing said seeds in a field so that male plants will emerge randomly in between female seeds in a mixed planting setup.

5. Any of the above methods, wherein said male plant is a male plant selected to have a significant peduncle length increase and / or peduncle width decrease after application of gibberellic acid between Z41 and Z50 compared to untreated plants, or compared to the female plants also treated with gibberellic acid, such as wherein said selected male plant has an increase in peduncle length of at least 15 % (or at least 20 %, at least 25 %, or at least 30 %) in the peduncle of the main tiller of said male plants, compared to said male plants when not treated with GA, and / or the peduncle of the main tiller of said plants has a decreased width (such as measured in the middle of the peduncle length) of at least 5 % (or at least 6 %, at least 7 %, or at least 8 %) compared to the peduncle width of the main tiller of said plants when not treated with a gibberellic acid solution.

6. A method to improve selection of parent plants to produce hybrid wheat seed, comprising determining the GA-responsiveness to pre-select candidate fertile male and candidate male- sterile female wheat seeds, by selecting male seeds that are GA-responsive and female seeds that are not GA-responsive in a seedling growth assay, wherein said male seeds are GA-responsive in said assay when seedlings of said male seeds when treated with a gibberellic acid solution have at least a 20 % (or at least 25 %, or at least 30 %) increase in seedling height 7 days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay, and wherein said female seeds are not GA-responsive in said assay, when seedlings of said female seeds when treated with a gibberellic acid solution have less than 20 % (or less than 15 %, or less than 10 %) increase in seedling height 7 days after sowing compared to untreated control seeds of the same genotype in a seedling growth assay.

7. Use of the method of claim 6 to pre-select the highly GA-responsive male plants and the low or not GA-responsive female plants of any one of claims 1-5.

8. Use of the highly GA-responsive male wheat plant seeds or plants and the low or not GA- responsive female wheat plant seeds or plants of any one of the prior claims, for mixed planting in a field, wherein a gibberellic acid solution is applied to said plants before heading so that the male plants become taller than the females plants at Z59 when said male plants are shorter than said female plants at Z59 in absence of treatment with gibberellic acid, or wherein a gibberellic acid solution is applied to said plants before heading so that the height difference at Z59 between male and female plants becomes significantly larger upon the application of a gibberellic acid solution, compared to the height difference at Z59 between male and female plants in absence of application of a gibberellic acid solution.

9. The use of a gibberellic acid solution over a field of highly GA-responsive male wheat plants and low or not GA-responsive female wheat plants interplanted in mixed planting, wherein: i) said highly GA-responsive male plants are fully fertile plants that when treated with a gibberellic acid solution in the field have at least a 10 %, at least a 15 %, or at least a 20 % increase in plant height just before the start of flowering at Z59, compared to said plants at said stage when not treated with a gibberellic acid solution, ii) said low or not GA-responsive female plants are male-sterile plants that when treated with a gibberellic acid solution in the field have no or a less than a 10 % or less than a 12 % increase in plant height just before the start of flowering at Z59, compared to said plants when not treated with a gibberellic acid solution, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller just before the start of flowering at Z59 than the majority of the low or not GA-responsive female plants, and iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z60, such as when said gibberellic acid solution comprises a surfactant or adjuvant.

10. Any one of the prior method or use claims, to: a) increase the peduncle length in said male wheat plants, wherein said male plants were selected so as to have an increase in peduncle length after application of a gibberellic acid solution of at least 15 % (or at least 20 %, at least 25 %, or at least 30 %) in the peduncle of the main tiller of said male plants at Z59, compared to said male plants at said stage when not treated with gibberellic acid, wherein gibberellic acid is applied between Z41 and Z60, or b) decrease the width of the peduncle of said male wheat plants at flowering, wherein said male plants were selected so as to have a decreased peduncle width after application of a gibberellic acid solution (such as measured in the middle of the peduncle length), of at least 5 % (or at least 6 %, at least 7 %, or at least 8 %) in the peduncle of the main tiller of said male plants at Z59, compared to the peduncle width of the main tiller of said plants when not treated with gibberellic acid, wherein gibberellic acid is applied between Z41 and Z60.11 . Any one of the prior methods or uses wherein without gibberellic acid treatment, the majority of the main spikes of said male plants do not stick out above the majority of the main spikes of the female plants, or stick out above the majority of the main spikes of the female plants by at most 1 / 3 or by less than half of their spike length within the plot or field, just before the start of flowering at Z59.

12. Any of the above methods or uses, wherein a standard application of a gibberellic acid(pathway)-inhibitor plant growth regulator is done to said wheat field before said gibberellic acid application, or at the same day of said gibberellic acid application.

13. Any one of the above uses or methods wherein said highly GA-responsive male seed or plant contains at least any one of the (semi-)dwarf alleles Rht8, Rht13, Rht18, Rht24 or Rht25, or a non-functional or deleted ZnF allele, or a wild-type tall Rht gene, and no GA-insensitive Rht allele, such as said male seed or plant containing Rht24.

14. A method or use of applying a gibberellic acid solution in a hybrid wheat production field, wherein said field contains highly GA-responsive male plants as described in claim 1 , planted in one or more rows or strips and highly GA-responsive or low or not GA-responsive female plants planted in one or more other rows or strips, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 500 liter per hectare between Zadoks growth scale stages Z25 and Z60, and wherein said gibberellic acid solution is applied only over the male rows or strips if the female plants are highly GA-responsive, or said gibberellic acid solution is applied over the entire field if the female plants are not or low GA-responsive, and wherein a plant growth regulator decreasing plant height is applied over said entire field or only over said female rows or strips when said female plants are highly GA-responsive, such as wherein said male rows or strips only contain fertile male plants, and said female rows or strips contain only or mostly female plants with 0 to 5 % of said highly GA-responsive male plants, (randomly) mixed in said female plant rows or strips.

15. A method to make male cereal plants taller than female cereal plants in a row / strip planting field containing rows or strips of fertile male plants and rows or strips of male-sterile female plants, wherein said male and female plants are GA-responsive so that plant height increases when treated with a gibberellic acid solution, and wherein said male plant rows or strips and not said female rows or strips are treated with a gibberellic acid solution between stages Z25 and Z60, and said female plant rows or strips and not said male rows or strips are treated with a plant-height decreasing plant growth regulator between stages Z25 and Z45, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than said female plants at stage Z60 or Z92, and wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare.

16. A method to make fertile male cereal plants taller than male-sterile female cereal plants in a field with 5-20 % fertile male plants and 95-80 % male-sterile female plants, wherein said field contains rows with male and female plants, and wherein said male plants are more GA- responsive than said female plants so that plant height of said male plants increases significantly more than the plant height of said female plants when treated with a gibberellic acid solution, and wherein said field is treated with at least one gibberellic acid solution between stages Z25 and Z60, and said field is treated with at least one plant-height decreasing plant growth regulator between stages Z25 and Z40, wherein said gibberellic acid solution is applied significantly later than said plant growth regulator application, or at least one gibberellic acid solution is applied between stages Z25 to Z41 , and at least one gibberellic acid solution is applied between stages Z40 and Z60 or between stages Z45 and Z60, such as wherein said male plants are on average at least 5 cm, at least 10 cm, at least 15 cm, or at least 20 cm taller than the female plants at stage Z60 or Z92, and such as wherein said gibberellic acid solution is applied at least 1 or 2 weeks later than said plant growth regulator application, wherein said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 100 and 600 liter per hectare.

17. A method to improve hybrid seed purity and / or hybrid seed yield of harvested hybrid cereal, such as wheat, seeds from a mixed planting field containing highly GA-responsive fertile male wheat plants and low or not GA-responsive male-sterile female wheat plants, wherein saidplants were previously treated at least once with a solution containing gibberellic acid between Zadoks growth scale stages Z25 and Z60, said method comprising the steps of: a) cutting off, destroying or separately harvesting the male plant ears standing above the height of the female plant ears after the end of flowering or at full maturity using a cutting or destruction or harvesting device above the height of the female plant spikes, and b) harvesting the remaining seeds, including the hybrid seeds from said female plants, from said field, and wherein: i) said highly GA-responsive male plants are fertile plants that are shorter than, of the same height as, or less than 5 cm or less than 10 cm taller than, said low or not GA-responsive male-sterile female plants just before the start of flowering at Z59, when said plants are not treated with a GA3 solution, ii) said highly GA-responsive male plants show an increase in plant height when treated with a solution containing gibberellic acid between Z25 and Z60, which increase is significantly larger than the increase in plant height for said low or not GA-responsive male- sterile female plants, iii) the majority of said highly GA-responsive male plants are at least 4 cm, at least 5 cm, at least 10 cm, or at least 15 cm taller than the majority of the low or not GA-responsive female plants just before the start of flowering at Z59 or at full maturity, when said plants were treated at least once with a solution containing gibberellic acid between Z25 and Z60, iv) said gibberellic acid solution comprises 100 to 500 ppm (w / w) of gibberellic acid and was applied in a volume between 100 and 600 liter per hectare, wherein said harvested remaining seed contains at least 85 %, or at least 87 %, or at least 90 %, hybrid seed when said mixed planting field was sown with a seed mix containing at least 7.5 %, at least 10 %, at least 12 %, or at least 15 % seeds that grow into a highly GA- responsive male wheat plant.

18. Any one of the above uses or methods, wherein a first application with a solution comprising gibberellic acid is done between stages Z25 and 40 so that the male plants can establish themselves (are not overgrown by) between the female plants, and wherein a second application with a solution comprising gibberellic acid is done between Z40 and Z60, or between Z45 and Z60 so as to increase male plant height compared to said female plants at Z59 for optimal pollination, or to increase male plant height compared to said female plants at Z92 for cutting the male ears standing out above the female plant ears, optionally with a third application with a solution comprising gibberellic acid after said first and second applications, and wherein said application is done on a field planted with a mix or blend of 5-20 % fertile highly GA-responsive male and 95-20 % low or not GA-responsive male-sterile female plants (such as from a seed mix or blend), or wherein a first application with a solution comprising gibberellic acid is done between stages Z45 and Z60.

19. Any one of the above uses or methods, wherein the purity of harvested hybrid seed or the yield of harvested hybrid seed is increased compared to said use or method not involving application of a solution comprising gibberellic acid, wherein said hybrid seed is harvested from a mixed planting field comprising at least 7.5 %, at least 10 %, at least 12 %, or at least 15 % or highly GA-responsive male wheat plant planted between a majority of low or not GA-responsive female plants.

20. Any one of the above used or methods, wherein said low or not GA-responsive male-sterile female plant, even if it contains gibberellin-insensitive Rht dwarf alleles such as Rht1 and / or Rht2, shows a (significant) plant height increase in the field after application of a gibberellic acid solution between Z25 and Z60, compared to said female plant when not treated with a gibberellic acid solution, wherein said female plant height increase is significantly less than the plant height increase of the highly GA-responsive male plant after application of a gibberellic acid solution between Z25 and Z60, or wherein said low or not GA-responsive male-sterile female plant is not a plant that is not responsive to treatment with a gibberellic acid solution, or is a plant that is responsive to treatment with a gibberellic acid solution.21 . Any one of the above uses or methods, wherein said gibberellic acid solution comprises 300 to 500 ppm (w / w) of gibberellic acid and is applied in a volume between 300 and 600 liter per hectare.

22. Any one of the above uses or methods, wherein said male plants have or were selected to have no delay in heading or flowering date, or to have no shortened pollination window, after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution, optionally wherein the female heading or flowering date or pollination window is not changed by application with said gibberellic acid solution, such as said male plants that have or were selected to have the same or an earlier heading or flowering date, or have the same or a wider pollination window, after treatment with said gibberellic acid solution compared to said male plants when not treated with said gibberellic acid solution.

23. Any one of the above uses or methods, wherein the female plants have or were selected to have no significantly decreased hybrid seed yield after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution, when said female plants are planted with the same male plant as pollinator in the same or a similar setup, such as wherein said female plants have or were selected to have no significant difference in or have a significant increase in hybrid seed yield after treatment with said gibberellic acid solution compared to said female plants when not treated with said gibberellic acid solution, when said female plants are planted with the same male plant as pollinator in the same or a similar setup.

24. Any one of the above uses or methods, wherein at least one application with said gibberellic acid solution is after Zadoks growth stage Z45.

25. Any one of the above uses or methods, wherein said gibberellic acid solution comprises a surfactant that improves efficiency of the gibberellic acid solution or that improves uptake of the gibberellic acid by the plants.

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