Method for promoting flower bud formation, cultivation method, and breeding method for onion plants

Abstract

To provide a technique for efficiently promoting flower bud formation in onion plants.SOLUTION: A method for promoting flower bud formation in onion plants comprises: a low-temperature treatment step of growing seedlings of onion plants under a condition set at a first temperature lower than 10°C; and a moderate-temperature treatment step of growing the seedlings, after the low-temperature treatment step, under a condition set at a second temperature higher than the first temperature and lower than 20°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for promoting flower bud formation in onion species plants, a method for cultivating them, and a method for breeding them. [Background technology]

[0002] In onion breeding, lines and varieties with desirable characteristics are developed through repeated crossbreeding and selection. Traditionally, onions were actually cultivated in fields and promising individuals were selected based on trait evaluation, but in recent years, with the development of molecular markers, it is becoming possible to select promising individuals from their genotypes at the seedling stage. The individuals selected in this way are used as breeding parents, and further crossbreeding and selection are required, but onions have a two-year generation period from sowing to flowering and fruiting. Since the length of this generation period is a major constraint in increasing breeding efficiency, there is a demand to shorten this period.

[0003] As a technique for shortening the period of flower bud formation within the onion generation period, Non-Patent Documents 1 and 2 describe a technique in which onion seedlings are grown in a low temperature environment to induce untimely bolting and induce flower bud formation. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Shishido, Y., & Saito, T., Journal of the Japanese Society for Horticultural Science, 44, 122-130 (1975) [Non-Patent Document 2] Shishido, Y., & Saito, T., Journal of the Japanese Society for Horticultural Science, 45, 160-167 (1976) Summary of the Invention [Problem to be solved by the invention]

[0005] The techniques described in Non-Patent Documents 1 and 2 have a low bolting rate, which indicates the ratio of onion seedlings that bolt untimely, and thus do not induce flower bud formation sufficiently. Therefore, there is a demand for a technique that can more efficiently promote flower bud formation in onion seed plants.

[0006] An object of one aspect of the present invention is to provide a technique capable of efficiently promoting flower bud formation in onion species plants. [Means for solving the problem]

[0007] In order to achieve the above object, a method for promoting flower bud formation in an onion seed plant according to one embodiment of the present invention includes a low temperature treatment step of growing a seedling of an onion seed plant in an environment set at a first temperature lower than 10° C., and an intermediate temperature treatment step of growing the seedling of the onion seed plant after the low temperature treatment step in an environment set at a second temperature higher than the first temperature and lower than 20° C.

[0008] A method for cultivating an onion species plant according to one aspect of the present invention includes a step of cultivating an onion species plant grown using the method for promoting flower bud formation in an onion species plant according to one aspect of the present invention.

[0009] The method for breeding an onion species plant according to one aspect of the present invention includes a selection step of selecting an onion species plant individual having desired traits from an onion species plant grown using the method for promoting flower bud formation in an onion species plant according to one aspect of the present invention. Effect of the Invention

[0010] According to one aspect of the present invention, a technique can be realized that can efficiently promote flower bud formation in onion-species plants. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Method for promoting flower bud formation in onion seed plants] A method for promoting flower bud formation in an onion seed plant according to one embodiment of the present invention comprises a low temperature treatment step of growing seedlings of an onion seed plant in an environment set at a first temperature lower than 10° C., and an intermediate temperature treatment step of growing the seedlings of the onion seed plant after the low temperature treatment step in an environment set at a second temperature higher than the first temperature and lower than 20° C. This method for promoting flower bud formation can be carried out in a facility in which cultivation environmental conditions such as temperature can be controlled.

[0012] In the present method for promoting flower bud formation, the onion-species plant includes onion (Allium cepa) and shallot, which is an onion variety. Examples of varieties of onion-species plants include "Okhotsk", "Momiji 3gou", and "Kitamomiji 2000". The number of seedlings of the onion-species plant grown in the present method for promoting flower bud formation is not particularly limited, but may be 50 or more, 100 or more, 200 or more, 300 or more, 500 or more, and may be 1000 or less, 800 or less, 700 or less, 600 or less, and the like.

[0013] One onion generation generally lasts for two years, consisting of sowing, the seedling stage, the bulb thickening stage, the dormancy stage, the budding stage, the bolting and flowering stage, and the unexpected bolting stage. In the first year, the bulb thickening (bulb thickening) and the dormant bulbs are harvested and stored at low temperatures in the dark or replanted in a field and exposed to low temperatures in winter to induce flower bud formation, which leads to flowering in the spring and summer of the second year. Therefore, it takes at least two years to obtain onion individuals to be used for breeding, and the long generation period causes the problem of reduced breeding efficiency.

[0014] According to this method for promoting flower bud formation, the low temperature treatment step and the medium temperature treatment step are used to promote flower bud formation, thereby shortening the period until flower bud formation and shortening the onion generation period. As a result, the period required to obtain onion species plant individuals to be used for breeding is shortened, and breeding efficiency can be improved. Furthermore, according to this method for promoting flower bud formation, the formation rate of flower buds formed in a short period of time is high, and flower bud formation can be promoted efficiently. Therefore, onion species plant individuals to be used for breeding can be efficiently obtained, and breeding efficiency can be improved. Furthermore, according to this method for promoting flower bud formation, it is also possible to increase the leaf sheath diameter of the onion species plant during the low temperature treatment step.

[0015] (Low temperature treatment process) In the low temperature treatment step, seedlings of onion seed plants are grown in an environment set at a first temperature lower than 10° C. The first temperature in the low temperature treatment step may be lower than 10° C., and may be, for example, 9° C. or lower, 8° C. or lower, 7° C. or lower, 6° C. or lower, 5° C. or lower, or 4° C. or lower. For example, the first temperature is preferably 2° C. or higher, or 3° C. or higher. The period during which the low temperature treatment step is carried out may be a period during which the seedlings of the onion seed plants are in an untimely bolting state, and is not particularly limited, and may be 10 days or more, 20 days or more, 40 days or more, 60 days or more, etc.

[0016] The period for which the low temperature treatment step is carried out may be determined depending on the leaf sheath diameter of the seedling of the onion seed plant, and for example, the low temperature treatment step may be carried out until the leaf sheath diameter increases to 10 mm or more. Therefore, in the low temperature treatment step, the leaf sheath diameter of the seedling of the onion seed plant is measured to judge whether it exceeds a predetermined standard, and if it exceeds the predetermined standard, the process may proceed to the next intermediate temperature treatment step.

[0017] In the low temperature treatment step, seedlings of onion seed plants before bulb formation are grown. The seedlings of onion seed plants before bulb formation may be seedlings from germination to the seedling stage after sowing, and may be seedlings in which bulbs have not swelled and have a leaf sheath diameter of less than 10 mm. Such seedlings can be obtained by cultivating onion seed plants by a conventionally known method, and seedlings of onion seed plants without bulbs that have been cultivated by a conventionally known method may be obtained. Whether or not the seedlings of onion seed plants have formed bulbs can be determined based on the leaf sheath diameter of the seedlings.

[0018] The present method for promoting flower bud formation may further include a seedling raising step of growing seedlings of onion seed plants before the formation of bulbs, prior to the low temperature treatment step. In the low temperature treatment step, the seedlings grown in the seedling raising step may be grown in a low temperature environment. In the seedling raising step, as one example, the onion seed plants after sowing are grown in an environment set at a temperature higher than a second temperature described below, and under artificial light with an illuminance lower than a second illuminance described below. This allows the seedlings of the onion seed plants to grow without forming bulbs.

[0019] In the low temperature treatment step, the onion seed plant seedlings are grown under artificial light with a first illuminance having a light intensity of 250 photosynthetic photon flux density (PPFD) or more. When the first illuminance is expressed as photosynthetic photon flux density (PPFD), it may be 250 PPFD or more. The artificial light may be, for example, LED light. The intensity of the artificial light may be 250 PPFD or more, for example, 300 PPFD or more, 350 PPFD or more, 400 PPFD or more, etc.

[0020] The day length in the low temperature treatment step is 8 hours or more and 16 hours or less. In addition, in the low temperature treatment step, the light period may be controlled to 8 hours or more and 16 hours or less, and the dark period may be controlled to 8 hours or more and 16 hours or less. Other cultivation conditions in the low temperature treatment step, such as water collection and fertilization, may be conventionally known conditions.

[0021] (Medium temperature treatment process) In the middle temperature treatment step, the seedlings of the onion seed plant after the low temperature treatment step are grown in an environment set at a second temperature higher than the first temperature and lower than 20° C. The second temperature in the middle temperature treatment step may be higher than the first temperature and lower than 20° C., and may be, for example, 10° C. or higher and 19° C. or lower, 13° C. or higher and 18° C. or lower, 15° C. or higher and 17° C. or lower. The period during which the middle temperature treatment step is carried out may be the period until flower buds are formed in the seedlings of the onion seed plant, and is not particularly limited, and may be 40 days or more, 60 days or more, 80 days or more, 100 days or more, etc.

[0022] The period for which the middle temperature treatment step is carried out may be determined depending on the leaf sheath diameter of the seedlings of onion seeds, and for example, the middle temperature treatment step may be carried out until the leaf sheath diameter increases to 15 mm or more. Therefore, in the middle temperature treatment step, the leaf sheath diameter of the seedlings of onion seeds is measured to judge whether it exceeds a predetermined standard, and if it exceeds the predetermined standard, the process may proceed to the high temperature treatment step described later.

[0023] In the middle temperature treatment step, seedlings of onion seed plants are grown under artificial light having a second illuminance lower than the first illuminance. In the middle temperature treatment step, seedlings of onion seed plants are grown under artificial light having a second illuminance lower than the first illuminance, whereby the leaf sheath diameter is significantly increased and flower bud formation can be further promoted. The artificial light may be LED light, for example. The second illuminance may be lower than the first illuminance, and may be, for example, 250 PPFD or less, 220 PPFD or less, 200 PPFD or less, etc.

[0024] The day length in the mid-temperature treatment step is 8 hours or more and 16 hours or less. In addition, in the mid-temperature treatment step, the light period may be controlled to 8 hours or more and 16 hours or less, and the dark period may be controlled to 8 hours or more and 16 hours or less. Other cultivation conditions in the mid-temperature treatment step, such as water collection and fertilization, may be conventionally known conditions.

[0025] (High temperature treatment process) The method for promoting flower bud formation may further include a high temperature treatment step of growing the seedlings of the onion species plant after the medium temperature treatment step in an environment set at a third temperature higher than the second temperature. By including the high temperature treatment step, the period until flower bud elongation and flowering can be shortened. The third temperature in the high temperature treatment step may be higher than the second temperature, and is, for example, 20° C. or higher, 22° C. or higher, or 25° C. or higher. For example, the third temperature is preferably 28° C. or lower, 30° C. or lower, or 33° C. or lower. The period during which the high temperature treatment step is performed may be the period until flower buds of the seedlings of the onion species plant elongate and flower, and may be, but is not limited to, 40 days or more, 60 days or more, 80 days or more, 100 days or more, etc.

[0026] In the high temperature treatment step, the onion seed plant seedlings may be grown under artificial light having a third illuminance higher than the second illuminance. The artificial light may be, for example, LED light. The third illuminance may be higher than the second illuminance, and may be, for example, 250 PPFD or more, 300 PPFD or more, 350 PPFD or more, 400 PPFD or more, etc.

[0027] The day length in the high temperature treatment step is 8 hours or more and 16 hours or less. In addition, in the high temperature treatment step, the light period may be controlled to 8 hours or more and 16 hours or less, and the dark period may be controlled to 8 hours or more and 16 hours or less. Other cultivation conditions in the high temperature treatment step, such as water collection and fertilization, may be conventionally known conditions.

[0028] [Method of cultivating onion seed plants] A method for cultivating an onion species plant according to one embodiment of the present invention comprises a step of cultivating an onion species plant grown using the method for promoting flower bud formation in an onion species plant according to one embodiment of the present invention. The onion species plants used in this cultivation method are grown using the method for promoting flower bud formation in an onion species plant according to one embodiment of the present invention described above. Therefore, according to this cultivation method, the generation period of onions is shortened, so that onion species plants can be cultivated efficiently. Furthermore, according to this cultivation method, the formation rate of flower buds formed in a short period of time is high, so that onion species plants can be cultivated efficiently.

[0029] [Method of breeding onion species plants] A method for breeding onion species plants according to one embodiment of the present invention includes a selection step of selecting onion species plant individuals having desired traits from onion species plants grown using the method for promoting flower bud formation in onion species plants according to one embodiment of the present invention. The onion species plants used in this breeding method are grown by the method for promoting flower bud formation in onion species plants according to one embodiment of the present invention described above. Therefore, according to this breeding method, onion species plant individuals to be used for breeding can be efficiently obtained, and breeding efficiency can be improved. Furthermore, according to this cultivation method, the formation rate of flower buds formed in a short period of time is high, so that onion species plants can be efficiently bred.

[0030] According to the above-mentioned configuration, the time required for breeding onion species plants is shortened, which contributes to the advancement of breeding techniques for onion species plants and leads to the maintenance and development of agriculture. Such an effect also contributes to the achievement of Goal 2 "Zero Hunger" and Goal 15 "Life on Land" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0031] [Additional Note 1] The present invention can also be expressed as follows.

[0032] The method for promoting flower bud formation in an onion seed plant according to embodiment 1 of the present invention includes a low temperature treatment step of growing a seedling of an onion seed plant in an environment set at a first temperature lower than 10° C., and an intermediate temperature treatment step of growing the seedling of the onion seed plant after the low temperature treatment step in an environment set at a second temperature higher than the first temperature and lower than 20° C.

[0033] A method for promoting flower bud formation in an onion seed plant according to a second aspect of the present invention may be configured in such a manner that, in the low temperature treatment step, seedlings of the onion seed plant are grown under artificial light having a first illuminance having a light intensity of 250 PPFD or more, and, in the medium temperature treatment step, seedlings of the onion seed plant are grown under artificial light having a second illuminance lower than the first illuminance.

[0034] A method for promoting flower bud formation in an onion species plant according to a third aspect of the present invention may be characterized in that the day length in the low temperature treatment step and the medium temperature treatment step is not less than 8 hours and not more than 16 hours.

[0035] The method for promoting flower bud formation in an onion seed plant according to a fourth aspect of the present invention may further include a high temperature treatment step of growing a seedling of the onion seed plant after the middle temperature treatment step in an environment set to a third temperature higher than the second temperature in any one of the first to third aspects.

[0036] A fifth aspect of the present invention relates to a method for promoting flower bud formation in an onion seed plant, in any one of the first to fourth aspects, wherein the low temperature treatment step may involve growing seedlings of an onion seed plant before bulb formation.

[0037] A method for cultivating an onion species plant according to a sixth aspect of the present invention comprises a step of cultivating an onion species plant grown using the method for promoting flower bud formation in an onion species plant according to any one of the first to fifth aspects.

[0038] The method for breeding an onion species plant according to a seventh aspect of the present invention includes a selection step of selecting an onion species plant individual having desired traits from an onion species plant grown using the method for promoting flower bud formation in an onion species plant according to any one of the first to fifth aspects.

[0039] [Additional Note 2] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. EXAMPLES

[0040] The effects of this flower bud formation promotion method on promoting flower bud formation and increasing the leaf sheath diameter in onion seed plants were investigated. Three commercially available onion varieties, "Momiji No. 3," "Okhotsk 222," and "Kita Momiji 2000" (all developed by Shippo Co., Ltd.), 16 individuals each, were used in the cultivation test. The cultivation test was conducted under the following conditions 1 to 5.

[0041] (Condition 1) During the seedling period, the light / dark period was 8 hours / 16 hours, the temperature was room temperature, and the illuminance of the fluorescent light was 200 PPFD or less. During the low temperature treatment period, the light / dark period was 12 hours / 12 hours, the temperature was 9°C, and the illuminance of the LED light was 250 PPFD or more. The low temperature treatment period was 40 days. During the medium temperature treatment period, the light / dark period was 16 hours / 8 hours, the temperature was 10°C or more, and the illuminance of the LED light was 200 PPFD or more. The number of individuals that had formed flower buds by approximately the 100th day was counted for each variety, and the flower bud formation rate was calculated by dividing the number by the total number of individuals for each variety.

[0042] (Condition 2) The seedling period was divided into two conditions. In the first condition, the light / dark period was 16 hours / 8 hours, and the temperature was higher than room temperature. The cultivation period was 30 days. In the second condition, the seedling period was the same as in Condition 1. The low temperature treatment period and the medium temperature treatment period were the same as those in Condition 1.

[0043] After 40 days of the medium temperature treatment period, a high temperature treatment period was set up with a light / dark period of 16 hours / 8 hours, the temperature at room temperature, and the illuminance of the LED light higher than that of the LED light during the low temperature treatment period under condition 1. After 40 days of the high temperature treatment period, the number of plants that had formed flower buds was counted, and the flower bud formation rate was calculated in the same manner as for condition 1.

[0044] (Condition 3) The conditions for the seedling period were the same as those for Condition 2. The conditions for the low temperature treatment period were the same as those for Condition 1, and the treatment period was 20 days. The conditions for the medium temperature treatment period were the same as those for Condition 1, and after treatment for 60 days, the number of individuals that had formed flower buds was counted and the flower bud formation rate was calculated in the same manner as for Condition 1.

[0045] (Condition 4) As a comparative example, in condition 4, no medium temperature treatment period was set. The conditions for the seedling period were the same as those for condition 2. The conditions for the low temperature treatment period were the same as those for condition 1, and the treatment period was 60 days. A high temperature treatment period was set after the low temperature treatment period, and the conditions were the same as those for condition 2. The flower bud formation rate was calculated in the same manner as for conditions 1 to 3.

[0046] (Condition 5) As a comparative example, no low temperature treatment period was set in condition 5. The seedling raising period, medium temperature treatment period, and high temperature treatment period were the same as those in condition 2. The medium temperature treatment period was 60 days, and the high temperature treatment period was 40 days. The flower bud formation rate was calculated in the same manner as in conditions 1 to 3.

[0047] (result) Under condition 1, the flower bud formation rates of the three varieties were as high as 75% to 100%. A repeat test was conducted under condition 1, and the flower bud formation rates were similarly 87.5% to 100%. Under condition 2, the flower bud formation rates were 75% for "Okhotsk 222" and 100% for "Kita Momiji 2000". Under condition 3, the flower bud formation rates were approximately 60% for "Okhotsk 222" and approximately 80% for "Kita Momiji 2000". On the other hand, under condition 4, no flower buds were formed in any of the three varieties, and the flower bud formation rates were 0%. Under condition 5, the flower bud formation rates of the three varieties were as low as 0% to 18.75%. This indicates that the flower bud formation rate is significantly improved by the present invention.

[0048] In addition, for conditions 1 to 3, the leaf sheath diameter was measured before the cold treatment period, on the 20th day, and on the 40th day of the cold treatment period. In all three varieties under conditions 1 to 3, the leaf sheath diameter after the cold treatment period was more than twice as large as that before the cold treatment period, and the leaf sheath diameter further increased as the cold treatment period became longer. This indicates that the leaf sheath diameter increases during the cold treatment period. [Industrial Applicability]

[0049] The present invention can be used in the agricultural field, such as plant cultivation and breeding.

Claims

1. A low temperature treatment step of growing a seedling of an onion seed plant in an environment set at a first temperature lower than 10°C; a middle temperature treatment step of growing the seedlings of the onion seed plant after the low temperature treatment step in an environment set to a second temperature higher than the first temperature and lower than 20° C.; The method for promoting flower bud formation in an onion species plant comprises the steps of:

2. In the low temperature treatment step, a seedling of the onion seed plant is grown under artificial light having a first illuminance of 250 PPFD or more; In the middle temperature treatment step, the seedling of the onion species plant is grown under artificial light having a second illuminance lower than the first illuminance. The method for promoting flower bud formation in an onion species plant according to claim 1.

3. 3. The method for promoting flower bud formation in an onion species plant according to claim 1, wherein the day length in the low temperature treatment step and the medium temperature treatment step is 8 hours or more and 16 hours or less.

4. 3. The method for promoting flower bud formation in an onion seed plant according to claim 1 or 2, further comprising a high temperature treatment step of growing a seedling of the onion seed plant after the medium temperature treatment step in an environment set at a third temperature higher than the second temperature.

5. 3. The method for promoting flower bud formation in onion seed plants according to claim 1 or 2, wherein seedlings of the onion seed plants before bulb formation are grown in the low temperature treatment step.

6. 3. A method for cultivating an onion species plant, comprising a step of cultivating an onion species plant grown using the method for promoting flower bud formation in an onion species plant according to claim 1 or 2.

7. 3. A method for breeding onion species plants, comprising a selection step of selecting onion species plant individuals having desired traits from onion species plants grown using the method for promoting flower bud formation in onion species plants according to claim 1 or 2.