Method for promoting flowering, method for producing seeds, and plant body

Abstract

To provide a new technology that enables reduction of the time required for perennial plants to reach flowering.SOLUTION: The method for promoting flowering comprises a step of grafting in which a portion including a growth point of a juvenile plant body of a perennial plant that has not formed a flower bud is used as a scion 1, and a plant that has formed a flower bud is used as a rootstock 2, wherein the juvenile plant body used as the scion 1 and the plant used as the rootstock 2 are plants belonging to the same family.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for promoting flowering, a method for producing seeds, and a plant. [Background technology]

[0002] Plants include annual plants, which flower and die within one year of germination, and perennial plants, which live for multiple years. In this specification, the term "perennial plants" will be used to refer to biennial plants as well. Perennial plants generally flower from the second year onwards after germination.

[0003] For example, in Japan, the perennial legume Glycyrrhiza (Glycyrrhiza spp.) will flower in the second year after germination or after the stolons are trained as seedlings, and especially in cold regions, from the third year onwards. From then on, seeds can be collected every year after flowering.

[0004] Licorice plants are known as important raw materials, particularly in traditional Chinese medicine, and have long been used as analgesics, antispasmodics, antitussives, expectorants, etc. The 18th revised Japanese Pharmacopoeia defines the crude drug licorice as the roots and stolons (stolon) of G. uralensis and G. glabra, which contain 2.0% or more glycyrrhizinic acid on a dry basis.

[0005] In the case of Glycyrrhiza plants, the content of glycyrrhizinic acid is important as described above, and therefore, it is common practice to train stolons collected from parent plants containing a large amount of glycyrrhizinic acid as seedlings and cultivate them in a field, as described in Patent Document 1. According to this method, the seedlings become clones with the same genetic information as the parent plants, and therefore the content of glycyrrhizinic acid is stable. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-139593 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the collection of stolons and the process of preparing them as seedlings require a great deal of labor, and the amount of stolons collected is not as large as that of seeds, making them unsuitable for large-scale cultivation.

[0008] Furthermore, because it takes at least two or three years after germination to flower perennial Glycyrrhiza plants and obtain seeds, there has been little progress in breeding strains with phenotypes containing a lot of glycyrrhizinic acid. For this reason, even individuals cultivated from seeds obtained from parent plants containing a lot of glycyrrhizinic acid are genetically unstable and often do not meet the required glycyrrhizinic acid content.

[0009] Similarly, perennial plants other than those of the genus Glycyrrhiza also have the problem that it is difficult to breed strains with desirable phenotypes because of the long cultivation period required before flowering.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a novel technique that can shorten the period until flowering of perennial plants. [Means for solving the problem]

[0011] In order to solve the above problems, one aspect of the present invention includes the following aspects.

[0012] [1] A method for promoting flowering, comprising the step of grafting a part of a young plant of a perennial plant that has never formed flower buds, including a growing point, as a scion, onto a plant that has formed flower buds as a rootstock, wherein the young plant used as the scion and the plant used as the rootstock are plants of the same family.

[0013] [2] The method for promoting flowering according to [1], wherein the young plant is a plant of the genus Glycyrrhiza, and the plant used as a rootstock is a legume.

[0014] [3] The method for promoting flowering described in [2], wherein the plant used as the rootstock is a plant of the genus Licorice.

[0015] [4] The method for promoting flowering according to any one of [1] to [3], wherein the plant used as the rootstock has flower buds or is in flower at the time of grafting.

[0016] [5] The method for promoting flowering according to any one of [1] to [4], further comprising the steps of cultivating the plant grafted in the grafting step and causing the flowers derived from the young plant to bloom.

[0017] [6] A method for producing seeds, comprising pollinating the pistil of the flower that has been caused to bloom by the flowering promotion method described in [5] with pollen from a plant of the same species as the young plant.

[0018] [7] A method for producing seeds, comprising pollinating the pistil of a plant of the same species as the seedling with pollen from the stamens of the flower that has been caused to bloom by the flowering promotion method described in [5].

[0019] [8] A plant formed by grafting a scion, which is a part of a young plant of a perennial plant that has never formed flower buds, including a growing point, onto a rootstock, which is a plant that has formed flower buds, and the scion and rootstock are plants of the same family.

[0020] [9] The plant body described in [8], wherein the scion is a plant of the genus Glycyrrhiza and the rootstock is a plant of the family Fabaceae.

[0021]

[10] The plant body described in [8] or [9], wherein the rootstock is a plant of the genus Glycyrrhiza.

[0022]

[11] A plant whose flowering has been promoted by the method for promoting flowering described in any one of [1] to [5] above. [Effects of the Invention]

[0023] According to the present invention, by using a part of a seedling of a perennial plant that has never formed flower buds, including a growing point, as a scion and grafting it onto a rootstock of a plant that has formed flower buds, florigen can be supplied to and accumulated in the seedling (scion) at an early stage, causing it to flower. Thus, a novel technique can be provided that can shorten the time until flowering of perennial plants. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a flow chart of a method for promoting flowering according to a preferred embodiment of the present invention. [Figure 2] 1 is an image showing a plant obtained by grafting. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail, with reference to the drawings as needed. [Flowering promotion method] FIG. 1 is a flow chart of a method for promoting flowering according to a preferred embodiment of the present invention. As shown in FIG. 1 , the flowering promotion method according to this embodiment includes a step S1 of grafting a part including a growing point of a young plant of a perennial plant that has never formed flower buds onto a rootstock of a plant that has formed flower buds (hereinafter referred to as the "grafting step"). Furthermore, in this embodiment, the flowering promotion method further includes a step S2 of cultivating the plant grafted in the grafting step S1 and causing flowers derived from the young plant to bloom (hereinafter referred to as the "cultivation and flowering step"). It is not necessary for the flowering promotion method of the present invention to include the cultivation and flowering step S2; as long as it includes the grafting step S1, flowering can be promoted (in other words, florigen can be supplied to the part).

[0026] <Grafting process> (Scion) The scion used in the grafting process is a part including the growing point of a young plant of a perennial plant that has never formed flower buds. Note that the plant species of the scion may be a perennial plant that is biennial or longer, and the rootstock described in detail below and the grafted plant (the plant obtained by grafting) may be either annual or perennial.

[0027] "Seedlings of perennial plants that have never formed flower buds" refers to either individual plants (plants) of perennial plants that have never formed flower buds since germination, or individual plants of perennial plants that have never formed flower buds since being trained as seedlings from stolons, etc. (stolons, runners).

[0028] These young plant bodies may preferably be individuals that are not expected to form flower buds at least within the year (until the end of December of the year of grafting) judging from their age (age) and / or growth rate after germination or after being trained as seedlings from stolons, etc.

[0029] There is no particular limitation on the method for determining whether or not a young plant of a perennial plant used as a scion has formed flower buds, but a person skilled in the art can make a determination, for example, from the type and age (age of the plant), as well as from the height of the plant and the thickness of the stem, etc.

[0030] Examples of individuals that are not expected to form flower buds within the year include those that are within one year of germination or of being trained as seedlings from stolons, etc. However, for plant species that flower from the third year onwards after germination, or for plants that grow slowly relative to their age, individuals that are in the second year or more after germination may also fall under the category of individuals that are not expected to form flower buds within the year.

[0031] The part of the young plant used as a scion may be any part including the meristem (the upper part of the plant), and although its length is not particularly limited, it is preferably at least 3 cm long from the shoot apex (towards the root), and more preferably at least 5 cm long from the shoot apex. In this specification, the meristem refers to the apical meristem of the shoot apex.

[0032] The plant species of the young plant to be used as the scion is not particularly limited as long as it is a perennial plant, but may be, for example, a legume. The legume used as the scion may be, for example, a plant of the genus Glycyrrhiza, Glycyrrhiza uralensis, or Glycyrrhiza spanishii.

[0033] When the seedling to be used as a scion is a Licorice plant, the seedling may be a seedling obtained by harvesting stolons from a Licorice plant (a high glycyrrhizinic acid content strain) having roots containing 2.0% or more (preferably 2.5% or more) of glycyrrhizinic acid based on the dry matter of the roots, and training the stolons as seedlings, or may be a seedling germinated from seeds obtained from the high glycyrrhizinic acid content strain.

[0034] (Rootstock) The plant used as the rootstock is a "plant that has produced flower buds," and there are no particular restrictions on the type, as long as it is a plant of the same family as the young plant used as the scion, and it may be an annual plant, a biennial plant, or a perennial plant that lives for three years or more. It is well known that grafting is more likely to be successful if the scion and rootstock are plants of the same family. However, the scion and rootstock may also be plants of the same genus.

[0035] The above-mentioned "plants that have formed flower buds" refers more specifically to plants that have formed flower buds, are in flower (have flowers), or have formed flower buds in the past at the time of grafting. All of these plants are capable of supplying florigen to the scion immediately or early (within 3 months, 6 months, etc.). However, annual plants that have previously flowered but have all withered flowers are excluded, as they are unsuitable as a source of florigen.

[0036] For example, when a legume such as a Glycyrrhiza plant is used as the scion, the plant used as the rootstock is a legume. As the legume, for example, an annual (monennial) legume (soybean, chickpea, etc.), a perennial legume (such as a Glycyrrhiza plant) that has been confirmed to have flowered in the previous year or the current year (the year of grafting), or a perennial legume (such as a Robinia pseudoacacia) can be preferably used as the rootstock.

[0037] When an annual plant is used as a rootstock, florigen is almost certainly expressed in the year that the annual plant germinates and is supplied to the scion.

[0038] In perennial plants, once flower buds are formed, they usually form flower buds and flower almost every year thereafter. Therefore, if flower buds or flowering have been confirmed in the past (for example, the previous year or the current year), it is almost certain that the scion will be supplied with florigen in the current or following year.

[0039] As described above, by using a plant that can immediately or early express and supply florigen as a rootstock, it is possible to promote the accumulation of florigen in the scion, which is a perennial plant, and shorten the time until flowering.

[0040] For example, in the case of Glycyrrhiza plants, breeding a line with a high glycyrrhizic acid content requires crossbreeding high glycyrrhizic acid-containing strains over several generations to achieve genetic stability. However, as mentioned above, it takes more than two or three years for Glycyrrhiza plants to flower, and so the reality is that little progress has been made in breeding strains with high glycyrrhizinic acid content. However, this technology can shorten the time until flowering, which is expected to accelerate the crossbreeding of strains with high glycyrrhizinic acid content and lead to more efficient breeding of strains with high glycyrrhizinic acid content.

[0041] While it is common to graft melons, cucumbers, and other plants onto pumpkins to promote fruit growth, prevent disease, and prevent damage from continuous cropping, there has been no example of grafting perennial plants as scions to hasten flowering. In particular, there are no examples of promoting flowering by grafting Glycyrrhiza plants, which are commonly cultivated as clones using stolons.

[0042] The type of plant used as the rootstock is preferably one whose flowering period at least partially overlaps with that of the type of young plant used as the scion.

[0043] The rootstock preferably has roots and at least some stems and leaves (i.e., above-ground parts), which allows the florigen synthesized in the leaves to be sufficiently supplied to the scion through the phloem.

[0044] (grafting) The method of grafting the scion and rootstock is not particularly limited, and any known method can be used, for example. Examples of grafting methods include simply cutting the scion and rootstock at an angle and aligning the cut surfaces, or making slits in the stems of the rootstock and scion and engaging the slits (so-called "yobi-tsugi" grafting).

[0045] When grafting, it is preferable that the rootstock is rooted in soil or other medium (i.e., in-situ grafting), but it may also be pulled out of the medium. If the rootstock is pulled out of the medium, it is then transplanted into the medium.

[0046] (Time to graft) The timing of grafting the scion onto the rootstock is not particularly limited, but it is preferable that the plant used as the rootstock has flower buds or is in flower (flowers) at the time of grafting, which allows florigen to be supplied to the scion more reliably and immediately, thereby promoting flowering.

[0047] For example, if the scion and rootstock are legumes such as Glycyrrhiza, the time to graft the scion and rootstock is preferably from the month in which the vernal equinox falls to the month following the month in which the autumnal equinox falls (March to October in Japan), more preferably from the month following the month in which the vernal equinox falls to the month following the month in which the summer solstice falls (April to July in Japan), or may be from the month before the month in which the summer solstice falls to the month in which the summer solstice falls (May to June in Japan).

[0048] In addition, the flowering promotion method of the present invention may further include, prior to the grafting step S1, a step of preparing a scion to be used for grafting (scion preparation step) and a step of preparing a rootstock to be used for grafting (rootstock preparation step). However, it is also possible to graft a scion that has already undergone the scion preparation step onto a rootstock that has already undergone the scion preparation step, without previously carrying out the scion preparation step and the rootstock preparation step.

[0049] In the scion preparation step, a portion including the growing point of a young plant of a perennial plant whose flowering is to be promoted is cut off. At this time, the shape of the cut surface may be processed to facilitate grafting. In the rootstock preparation process, the upper part of the stem (eg, the apex) of the plant to be used as the rootstock is cut or a notch is made. The scion preparation step and the rootstock preparation step may be carried out in either order. For example, the rootstock preparation step may be carried out first, the scion preparation step may be carried out first, or the scion preparation step and the rootstock preparation step may be carried out simultaneously.

[0050] <Cultivation and flowering process> In the cultivation and flowering step S2, the plant grafted in the above-mentioned grafting step S1 is cultivated, and flowers derived from the young plant used as the scion are allowed to flower. In other words, the "flowers derived from the young plant" are flowers differentiated from cells of the young plant used as the scion, and in other words, flowers having the same genome as the young plant.

[0051] For example, each flower of a Licorice plant contains both stamens and pistils. When a young plant of a Licorice plant is used as a scion, the pollen containing the stamen sex cells and the ovule containing the pistil egg cell in the flower differentiated from the young plant each have the same genome as the young plant (germ cells are haploid).

[0052] The cultivation method in the cultivation and flowering step S2 is not particularly limited, and may be, for example, a cultivation method suited to the plant species of the rootstock. A person skilled in the art can cultivate the plant obtained by grafting until flowering using an appropriate method suited to the plant species.

[0053] [Seed manufacturing method] A seed production method according to a preferred embodiment of the present invention includes pollinating the pistil of a flower derived from a young plant body that has been caused to flower through the grafting step and cultivation and flowering step of the flowering promotion method described above with pollen from a plant of the same species as the young plant body (scion) (first pollination step). The first pollination step produces seeds having a genome derived from the seedling. The seed production method of this embodiment can also be used as a seed formation method or a seed formation promotion method.

[0054] When the seedling is of a plant species capable of self-pollination, the pollen that pollinates the flowers derived from the seedling may be pollen from the stamens of the seedling, or may be pollen from another strain of the same species as the seedling.

[0055] In contrast, if the seedling is of a plant species that is self-incompatible, pollen from another strain of the same species as the seedling will pollinate the pistil of a flower derived from the seedling.

[0056] For example, if the young plant used as a scion is a plant of the genus Licorice, the genus Licorice is self-incompatible, so the pollen that pollinates the pistil of a flower derived from the young plant is pollen from another strain of the same species of Licorice plant as the young plant. If the scion and rootstock are the same species of Licorice, it is also possible to pollinate the pistil of a flower that has the genome of the scion (pistil of the flower of the scion) with pollen that has the genome of the rootstock. Note that Licorice plants are bisexual flowers.

[0057] Regardless of whether it is self-pollination or cross-pollination, the pollination method is not particularly limited, and may be artificial pollination, for example, by collecting stamens and bringing them into contact with the pistils of flowers derived from young plants, or natural pollination by insects or wind.

[0058] According to the seed production method of this embodiment, the process from harvesting (preparing) the young plant body to be used as a scion to grafting and seed production can be completed in a short period of time, which accelerates the crossbreeding of perennial plants such as Glycyrrhiza plants with useful phenotypes, thereby facilitating the production of genetically stable seeds.

[0059] [Other seed manufacturing methods] Another preferred embodiment of the seed production method of the present invention includes pollinating the pistil of a plant of the same species as the young plant with pollen from the stamens of a flower derived from a young plant that has been allowed to flower through the grafting step and cultivation and flowering step of the flowering promotion method described above (second pollination step). The second pollination step allows the pollinated plant to produce seeds having a genome derived from the seedling. The seed production method of this embodiment can also be used as a seed formation method or a seed formation promotion method.

[0060] When the seedling is of a plant species capable of self-pollination, the pistil that is pollinated with pollen from a flower derived from the seedling may be the pistil of the seedling itself, or may be the pistil of another plant of the same species as the seedling.

[0061] In contrast, when the seedling is of a plant species having self-incompatibility, the pistil that is pollinated by the pollen of a flower derived from the seedling is the pistil of another plant of the same species as the seedling.

[0062] For example, if the young plant used as a scion is a plant of the genus Licorice, the pistil that is pollinated with pollen from a flower derived from the young plant is the pistil of another plant of the same species of Licorice as the young plant, because the genus Licorice is self-incompatible. If the scion and rootstock are of the same species of Licorice, it is also possible to pollinate the pistil of a flower that has the genome of the rootstock (the pistil of a flower of the rootstock) with pollen that has the genome of the scion.

[0063] The pollination method is not particularly limited, and may be artificial pollination, for example, by collecting the stamens of flowers that have differentiated from cells derived from the young plant body and contacting them with the pistils of flowers of other plants or rootstocks, or natural pollination by insects or wind.

[0064] According to the seed production method of this embodiment, the process from harvesting (preparing) the young plant body to be used as a scion to grafting and seed production can be completed in a short period of time, which accelerates the crossbreeding of perennial plants such as Glycyrrhiza plants with useful phenotypes, thereby facilitating the production of genetically stable seeds.

[0065] [Plant body] The plant of this embodiment is formed by grafting a scion, which is a portion including a growing point of a young plant of a perennial plant that has never formed flower buds, onto a rootstock that is a plant that has formed flower buds. In other words, the plant of this embodiment comprises a portion including a growing point of a young plant of a perennial plant that has never formed flower buds, and (a portion of) a rootstock that is a plant that has formed flower buds, and the portion including the growing point and the rootstock are connected in a manner that allows the transfer of florigen. More specifically, florigen is transferred from the rootstock to the portion including the growing point through the phloem. The scion and rootstock are plants of the same family.

[0066] The plant of this embodiment is a plant obtained by the grafting step of the above-mentioned flowering promotion method. Therefore, the scion and rootstock of the plant of this embodiment are the same as the scion and rootstock in the above-mentioned flowering promotion method, respectively. The young plant to be used as the scion is preferably a plant of the genus Licorice, and in that case, the plant used as the rootstock may be any plant in the family Fabaceae, such as a plant of the genus Licorice, an annual herbaceous plant in the family Fabaceae, or a perennial woody plant in the family Fabaceae.

[0067] A perennial plant used as a scion that has never formed flower buds is in a state without flower buds or flowers. A plant that has formed flower buds and is used as a rootstock may be in a state with flower buds or flowers. Those skilled in the art can determine whether a plant has never formed flower buds based on the age and species of the scion part of the grafted plant, as well as its thickness, etc.

[0068] According to the plant of this embodiment, it is possible to make the flowers derived from the scion, that is, the young plant, flower early, and therefore it is possible to obtain seeds having a genome derived from the young plant in a short period of time.

[0069] [Another aspect of the plant] According to another preferred embodiment of the present invention, the plant is one whose flowering has been promoted by the above-described flowering promotion method, and is obtained by grafting the scion and rootstock described in detail in the embodiment of the above-described flowering promotion method. Therefore, the part of the plant according to this embodiment that is derived from the scion and the part that is derived from the rootstock are as described above.

[0070] In the plant of this embodiment, the portion derived from the scion (the portion having the genome of the scion) is supplied with florigen from the portion derived from the rootstock (the portion having the genome of the rootstock), thereby promoting flowering of the portion derived from the scion. In the plant of this embodiment, the portion derived from the scion may not yet have flower buds, may have flower buds, or may have flowers.

[0071] According to the plant of this embodiment, seeds having a genome derived from the scion, that is, the young plant, can be obtained in a short period of time.

[0072] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these modifications are also included within the scope of the present invention. [Example]

[0073] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0074] In this example, the rootstock used was a Ural licorice in its fifth year of cultivation, which had been confirmed to have flowered in the past (before last year), and the scion used was a Ural licorice in its first year of cultivation, which normally does not flower in the current year. FIG. 2 is an image showing a plant obtained by grafting.

[0075] (Scion preparation process) The above-ground parts of a high glycyrrhizinic acid-containing strain of Glycyrrhiza uralensis grown outdoors were harvested so that the growing point 1a remained, and the cut surface was stored in water to prevent it from drying out, and this was used as scion 1 for the grafting process.

[0076] (Rootstock preparation process) The apex of the stem of a Glycyrrhiza uralensis plant that had been confirmed to be flowering and was used as rootstock 2 was cut off, and an incision was made in the remaining stem.

[0077] (Grafting process) The scion 1 prepared in the scion preparation step was inserted into the incision and fixed with parafilm 3. As shown in Figure 2, at the time of grafting, buds 2a were present on the rootstock 2 and were in a state where florigen could be supplied. [Explanation of symbols]

[0078] 1...Scion, 1a...Growth point, 2...Rootstock, 2a...Bud, 3...Parafilm

Claims

1. The method includes a step of grafting a part including a growing point of a young plant of a perennial plant that has never formed flower buds as a scion onto a plant that has formed flower buds as a rootstock, The method for promoting flowering, wherein the young plant used as a scion and the plant used as a rootstock are plants of the same family.

2. 2. The method for promoting flowering according to claim 1, wherein the young plant is a plant of the genus Glycyrrhiza, and the plant used as a rootstock is a legume.

3. 3. The method for promoting flowering according to claim 2, wherein the plant used as a rootstock is a plant of the genus Licorice.

4. 4. The method for promoting flowering according to claim 1, wherein the plant used as a rootstock has flower buds or is in flower at the time of grafting.

5. The method for promoting flowering according to any one of claims 1 to 3, further comprising the steps of cultivating the plant grafted in the grafting step and causing flowers derived from the young plant to bloom.

6. A method for producing seeds, comprising pollinating the pistil of the flower that has been caused to bloom by the flowering promotion method according to claim 5 with pollen from a plant of the same species as the young plant.

7. A method for producing seeds, comprising pollinating a pistil of a plant of the same species as the young plant with pollen from the stamens of the flower that has been made to bloom by the flowering promotion method according to claim 5.

8. It is formed by grafting a scion, which is a part including the growing point of a young plant of a perennial plant that has never formed flower buds, onto a rootstock, which is a plant that has formed flower buds; A plant body in which the scion and the rootstock are plants of the same family.

9. The plant body according to claim 8, wherein the scion is a plant of the genus Licorice and the rootstock is a plant of the family Fabaceae.

10. The plant body according to claim 9, wherein the rootstock is a plant of the genus Licorice.

11. A plant whose flowering has been promoted by the method for promoting flowering according to any one of claims 1 to 3.

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