Mycorrhizal fungal symbiosis promoter, microbial material containing the same, and method of cultivating plants using the same.

Abstract

This invention provides a mycorrhizal fungal symbiosis promoter that, when applied to arbuscular mycorrhizal fungi, can improve their symbiotic ability with plants, and furthermore, can maintain its effect even after multiple harvests of the crop plant. [Solution] A mycorrhizal fungal symbiosis promoter containing (A) one or more selected from the group consisting of cis-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, (B) one or more selected from the group consisting of trans-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, and (C) one or more selected from the group consisting of saturated fatty acids having 12 to 18 carbon atoms and their salts, wherein the content ratios of components (A), (B), and (C) are 10 to 78 parts by mass, 0.01 to 2 parts by mass, and 20 to 89.99 parts by mass, respectively.

Description

Technical Field

[0001] The present invention relates to a mycorrhizal symbiosis promoter that acts on mycorrhizal fungi, particularly arbuscular mycorrhizal fungi, improves the symbiotic ability of arbuscular mycorrhizal fungi with plants, and can exert the effect of promoting plant growth by arbuscular mycorrhizal fungi even after multiple harvests, a microbial material containing the same, and a method for cultivating plants using these.

Background Art

[0002] Arbuscular mycorrhizal fungi (AM fungi) are a group of fungi called Glomus that symbiotically associate with the roots of plants and are known to be present in approximately 80% of vascular plants. When arbuscular mycorrhizal fungi symbiotically associate with the roots of plants, they exhibit effects such as promoting the absorption of nutrients such as phosphorus, improving disease resistance, and promoting water absorption, and as a result, show the effect of promoting the growth of the symbiotic plants. For this reason, arbuscular mycorrhizal fungi are expected to be used as microbial materials in the agricultural field, but at present, their spread has not advanced much because they are not always satisfactory in terms of quality stability and usability. In order to promote the use of mycorrhizal fungi as microbial materials, it is necessary to enhance the symbiotic ability and persistence of mycorrhizal fungi with plant roots.

[0003] As a technique for enhancing the symbiotic ability and persistence of mycorrhizal fungi with plant roots, a symbiosis promoter for arbuscular mycorrhizal fungi containing oxidized glutathione and / or cystathionine as an active ingredient has been proposed, and a method for promoting the symbiosis of arbuscular mycorrhizal fungi in plant roots by bringing oxidized glutathione and / or cystathionine into contact with arbuscular mycorrhizal fungi has been disclosed (Patent Document 1). Furthermore, since arbuscular mycorrhizal fungi are obligate symbiotic fungi that require the roots of a host plant, they cannot be cultured in general culture media, and a plant host is necessary for pure culture. Patent document 2 proposes a simple method for pure cultureing only arbuscular mycorrhizal fungi by adding saturated fatty acids with 13 to 18 carbon atoms, such as myristic acid and palmitic acid, to the culture medium. As mentioned above, Patent Document 1 discloses the application of oxidized glutathione and / or cystathionine to arbuscular mycorrhizal fungi, but it does not mention the persistence of the symbiotic effect on arbuscular mycorrhizal fungi. Furthermore, while Patent Document 2 discloses the application of fatty acids to arbuscular mycorrhizal fungi, it does not relate to a technique for improving the symbiotic ability of arbuscular mycorrhizal fungi. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-159019 [Patent Document 2] Japanese Patent Publication No. 2018-170973 [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, in view of the circumstances described above, the present invention aims to provide a mycorrhizal fungus symbiosis promoter that can improve the symbiotic ability of arbuscular mycorrhizal fungi to plants by acting on them, and that can maintain its effect even after multiple harvests of crop plants, and further to provide microbial materials containing this and methods for cultivating plants using these. [Means for solving the problem]

[0006] The present inventors, after diligent research to solve the above problems, have found that by applying a mycorrhizal fungus symbiosis promoter containing (A) one or more cis-type unsaturated fatty acids and their salts having 16 to 18 carbon atoms, (B) one or more trans-type unsaturated fatty acids and their salts having 16 to 18 carbon atoms, and (C) one or more saturated fatty acids and their salts having 12 to 18 carbon atoms, in a specific content ratio, to arbuscular mycorrhizal fungi, the symbiotic ability of arbuscular mycorrhizal fungi to plants can be improved. Furthermore, they have found that the effect of improving symbiotic ability can be sustained even after the plants are harvested multiple times as crops. After further research, they have completed the present invention. In other words, the present invention relates to the following. [1] A mycorrhizal fungal symbiosis promoter comprising (A) one or more selected from the group consisting of cis-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, (B) one or more selected from the group consisting of trans-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, and (C) one or more selected from the group consisting of saturated fatty acids having 12 to 18 carbon atoms and their salts, wherein the content ratios of components (A), (B), and (C) are 10 to 78 parts by mass, 0.01 to 2 parts by mass, and 20 to 89.99 parts by mass, respectively. A mycorrhizal fungal symbiosis promoting solution containing the mycorrhizal fungal symbiosis promoting agent described in [2][1], wherein the content of the mycorrhizal fungal symbiosis promoting agent described in [1] is 0.05 ppm by mass to 650 ppm by mass. A microbial material containing the mycorrhizal fungal symbiosis promoter described in [3] [1] or the mycorrhizal fungal symbiosis promoter liquid described in [2] and arbuscular mycorrhizal fungi. A method for cultivating plants, comprising supplying the mycorrhizal fungus symbiosis promoter described in [4] [1] or the mycorrhizal fungus symbiosis promoter solution described in [2] to the soil of a site where the plant to be cultivated is to be grown, and allowing the mycorrhizal fungus symbiosis promoter described in [1] or the mycorrhizal fungus symbiosis promoter solution described in [2] to act on arbuscular mycorrhizal fungi present in the soil or arbuscular mycorrhizal fungi symbiotic to the roots of the plant to be cultivated, or supplying arbuscular mycorrhizal fungi that have been previously treated with the mycorrhizal fungus symbiosis promoter described in [1] or the mycorrhizal fungus symbiosis promoter solution described in [2] to the soil of a site where the plant to be cultivated is to be grown. A method for cultivating plants, comprising supplying the microbial material described in [5][3] to the soil of a site where the plant to be cultivated is to be grown. [Effects of the Invention]

[0007] The present invention provides a mycorrhizal fungal symbiosis promoter that acts on mycorrhizal fungi, particularly arbuscular mycorrhizal fungi, and can improve the symbiotic ability of mycorrhizal fungi to plants. Furthermore, the present invention provides a mycorrhizal fungal symbiosis promoter that can sustain the symbiotic effect of arbuscular mycorrhizal fungi even after the plants have been harvested multiple times as crops, without the need to add arbuscular mycorrhizal fungi. Therefore, the present invention makes it possible to induce arbuscular mycorrhizal fungi to coexist with plants more efficiently and simply. Furthermore, the plant cultivation method of the present invention allows the use of arbuscular mycorrhizal fungi with improved symbiotic ability, enabling the full expression of the plant growth-promoting effect of the arbuscular mycorrhizal fungi and resulting in plants with accelerated growth. Moreover, the plant cultivation method of the present invention allows the use of arbuscular mycorrhizal fungi with improved sustainability of symbiotic effect, ensuring that the plant growth-promoting effect of the arbuscular mycorrhizal fungi is exerted even after multiple harvests, allowing for the sustained production of plants with accelerated growth. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below. In this invention, a numerical range defined using the symbol "~" includes the values ​​at both ends (upper and lower limits) of "~". For example, "10~30" represents a range of 10 or more and 30 or less.

[0009] [Mycorrhizal fungal symbiosis promoter] The present invention provides a mycorrhizal fungal symbiosis promoting agent (hereinafter also referred to as "the symbiosis promoting agent of the present invention" in this specification). The symbiosis-promoting agent of the present invention contains (A) one or more selected from the group consisting of cis-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, (B) one or more selected from the group consisting of trans-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, and (C) one or more selected from the group consisting of saturated fatty acids having 12 to 18 carbon atoms and their salts, with the content ratios of components (A), (B), and (C) being 10 to 78 parts by mass, 0.01 to 2 parts by mass, and 20 to 89.99 parts by mass, respectively.

[0010] (A) One or more selected from the group consisting of cis-type unsaturated fatty acids with 16 to 18 carbon atoms and their salts. The cis-type unsaturated fatty acid having 16 to 18 carbon atoms contained as component (A) in the symbiosis promoter of the present invention can be any fatty acid having 16 to 18 carbon atoms and possessing one or more unsaturated carbon bonds, without any particular limitations. The unsaturated carbon bonds are usually carbon double bonds, and if there are two or more double bonds, it is preferable that all of them are cis-type double bonds.

[0011] Fatty acids with 16-18 carbon atoms and one cis-type double bond include (Z)-5-hexadecenoic acid, (Z)-6-hexadecenoic acid (sapienic acid), (Z)-7-hexadecenoic acid, (Z)-9-hexadecenoic acid (palmitoleic acid), (Z)-10-hexadecenoic acid, (Z)-11-hexadecenoic acid, (Z)-7-heptadecenoic acid, (Z) Examples include (Z)-8-heptadecenoic acid, (Z)-9-heptadecenoic acid, (Z)-10-heptadecenoic acid, (Z)-9-octadecenoic acid (oleic acid), (Z)-11-octadecenoic acid (cis-vaccenoic acid), (Z)-12-octadecenoic acid, (Z)-13-octadecenoic acid, (Z)-14-octadecenoic acid, and (Z)-15-octadecenoic acid. Fatty acids with 16-18 carbon atoms and two cis-type double bonds include (5Z,9Z)-5,9-hexadecadienoic acid, (6Z,9Z)-6,9-hexadecadienoic acid, (7Z,10Z)-7,10-hexadecadienoic acid, (9Z,12Z)-9,12-hexadecadienoic acid (palmitrinolic acid), (11Z,13Z)-11,13-hexadecadienoic acid, (6Z,9Z)-6,9-heptadecadienoic acid, and (8Z,11Z)-8 Examples include 11-heptadecadienoic acid, (4Z,15Z)-4,15-octadecadienoic acid, (6Z,9Z)-6,9-octadecadienoic acid (isolinoleic acid), (8Z,15Z)-8,15-octadecadienoic acid, (9Z,11Z)-9,11-octadecadienoic acid (9,11-conjugated linoleic acid), (9Z,12Z)-9,12-octadecadienoic acid (linoleic acid), and (12Z,14Z)-12,14-octadecadienoic acid. Fatty acids with 16-18 carbon atoms and three or more cis double bonds include (4Z,7Z,10Z)-4,7,10-hexadecatrienoic acid, (6Z,9Z,12Z)-6,9,12-hexadecatrienoic acid, (7Z,10Z,13Z)-7,10,13-hexadecatrienoic acid, (5Z,9Z,12Z)-5,9,12-heptadecatrienoic acid, (8Z,11Z,14Z)-8,11,14-heptadecatrienoic acid, (5Z,9Z,12Z)-5,9,12-octadecatrienoic acid (pinolenic acid), (6Z,9Z,1 Examples include (2Z)-6,9,12-octadecatrienoic acid (γ-linolenic acid), (6Z,9Z,15Z)-6,9,15-octadecatrienoic acid, (8Z,11Z,14Z)-8,11,14-octadecatrienoic acid, (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid (α-linolenic acid), (5Z,9Z,12Z,15Z)-5,9,12,15-octadecatetraenoic acid (coniferonic acid), and (6Z,9Z,12Z,15Z)-6,9,12,15-octadecatetraenoic acid (stearidonic acid). From the viewpoint of promoting the symbiotic effect of arbuscular mycorrhizal fungi on plants, component (A) is preferably a fatty acid having a cis-type double bond at the 9-position, with (Z)-9-hexadecenoic acid (palmitoleic acid), (Z)-9-octadecenoic acid (oleic acid), (9Z,12Z)-9,12-octadecadienoic acid (linoleic acid), (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid (α-linolenic acid), (6Z,9Z,12Z)-6,9,12-octadecatrienoic acid (γ-linolenic acid), etc. being more preferably used, and (Z)-9-hexadecenoic acid (palmitoleic acid) and (Z)-9-octadecenoic acid (oleic acid) being even more preferably used.

[0012] As long as the salts of cis-type unsaturated fatty acids having 16 to 18 carbon atoms do not adversely affect plant growth, there are no particular restrictions, but examples include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; transition metal salts such as iron salts and manganese salts; and aluminum salts. Among these, alkali metal salts and alkaline earth metal salts are preferred, and from the viewpoint of solubility in water, alkali metal salts are more preferred, with sodium salts and potassium salts being particularly preferred.

[0013] The symbiosis-promoting agent of the present invention may be used as component (A) by selecting one from the group consisting of cis-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, or by selecting two or more and using them in combination. Furthermore, from the viewpoint of promoting the symbiotic effect of arbuscular mycorrhizal fungi on plants, it is preferable to use a salt of a cis-type unsaturated fatty acid having 16 to 18 carbon atoms as component (A), and it is more preferable to use an alkali metal salt of a cis-type unsaturated fatty acid having 16 to 18 carbon atoms. As cis-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, they may be synthesized as appropriate by known manufacturing methods, but commercially available products from various companies can also be used.

[0014] When using a salt of a cis-type unsaturated fatty acid having 16 to 18 carbon atoms as component (A), it is possible to use it in the form of the salt or to form the salt beforehand. Alternatively, the fatty acid and a salt that acts as a counterion for the fatty acid, such as potassium hydroxide, may be added separately to the mixing tank and neutralized to form a fatty acid salt.

[0015] Furthermore, from the viewpoint of the plant growth promoting effect of arbuscular mycorrhizal fungi and the persistence of the said plant growth promoting effect, it is preferable to use a combination of one or more selected from the group consisting of cis-type unsaturated fatty acids having 16 carbon atoms and their salts, and one or more selected from the group consisting of cis-type unsaturated fatty acids having 18 carbon atoms and their salts, as component (A). When used in combination with one or more selected from the group consisting of cis-unsaturated fatty acids having 16 carbon atoms and their salts and one or more selected from the group consisting of cis-unsaturated fatty acids having 18 carbon atoms and their salts, the content ratio [(one or more selected from the group consisting of cis-unsaturated fatty acids having 16 carbon atoms and their salts) / (one or more selected from the group consisting of cis-unsaturated fatty acids having 18 carbon atoms and their salts)] is preferably 10 / 90 to 90 / 10 and more preferably 20 / 80 to 80 / 20 in terms of mass ratio when the total of these contents is 100 parts by mass.

[0016] The content of component (A) in the symbiosis promoter of the present invention is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass of the symbiosis promoter of the present invention in order to exhibit a sufficient effect as a mycorrhizal symbiosis promoter. Also, from the viewpoint of the storage stability of the symbiosis promoter of the present invention, it is preferably 78 parts by mass or less, more preferably 58 parts by mass or less, and still more preferably 38 parts by mass or less.

[0017] (B) One or more selected from the group consisting of trans-unsaturated fatty acids having 16 to 18 carbon atoms and their salts As the trans-unsaturated fatty acids having 16 to 18 carbon atoms contained as component (B) in the symbiosis promoter of the present invention, fatty acids having 16 to 18 carbon atoms and having one or more carbon unsaturated bonds can be used without particular limitation as long as they are trans-unsaturated fatty acids. Also, the unsaturated carbon bond is usually a carbon double bond, and when having two or more double bonds, it is preferably all trans double bonds.

[0018] As fatty acids having 16 to 18 carbon atoms and one trans double bond, there may be mentioned (E)-2-hexadecenoic acid, (E)-5-hexadecenoic acid, (E)-8-hexadecenoic acid, (E)-9-hexadecenoic acid (palmitelaidic acid), (E)-9-heptadecenoic acid, (E)-10-heptadecenoic acid, (E)-6-octadecenoic acid, (E)-7-octadecenoic acid, (E)-9-octadecenoic acid (elaidic acid), (E)-10-octadecenoic acid, (E)-12-octadecenoic acid, (E)-13-octadecenoic acid, (E)-15-octadecenoic acid, etc. As fatty acids having 16 to 18 carbon atoms and two trans double bonds, there may be mentioned (2E,4E)-2,4-octadecadienoic acid, (6E,8E)-6,8-octadecadienoic acid, (6E,12E)-6,12-octadecadienoic acid, (9E,12E)-9,12-octadecadienoic acid, (12E,14E)-12,14-octadecadienoic acid, etc. As fatty acids having 16 to 18 carbon atoms and three or more trans double bonds, there may be mentioned (4E,6E,8E)-4,6,8-octadecatrienoic acid, (6E,8E,10E)-6,8,10-octadecatrienoic acid, (7E,9E,11E)-7,9,11-octadecatrienoic acid, (10E,12E,14E)-10,12,14-octadecatrienoic acid, (11E,13E,15E)-11,13,15-octadecatrienoic acid, (9E,11E,13E,15E)-9,11,13,15-octadecatetraenoic acid (β-parinaric acid), etc. From the viewpoint of the symbiosis promoting effect of arbuscular mycorrhizal fungi on plants, as component (B), unsaturated fatty acids having a trans double bond at the 9-position are preferably used, and (E)-9-hexadecenoic acid (palmitelaidic acid), (E)-9-octadecenoic acid (elaidic acid), etc. are more preferably used.

[0019] The salts of trans-type unsaturated fatty acids having 16 to 18 carbon atoms are not particularly limited as long as they do not adversely affect plant growth. However, similar to the salts of cis-type unsaturated fatty acids having 16 to 18 carbon atoms contained as component (A), examples include alkali metal salts, alkaline earth metal salts, transition metal salts, and aluminum salts. Among these, alkali metal salts and alkaline earth metal salts are preferred, and sodium salts and potassium salts are particularly preferred.

[0020] The symbiosis-promoting agent of the present invention may be used as component (B) by selecting one from the group consisting of trans-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, or by selecting two or more and using them in combination. Furthermore, from the viewpoint of promoting the symbiotic effect of arbuscular mycorrhizal fungi on plants, it is preferable to use a salt of a trans-type unsaturated fatty acid having 16 to 18 carbon atoms as component (B), and it is more preferable to use an alkali metal salt of a trans-type unsaturated fatty acid having 16 to 18 carbon atoms. Trans-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts may be synthesized as appropriate by known manufacturing methods, but commercially available products from various companies can also be used.

[0021] When using a salt of a trans-type unsaturated fatty acid having 16 to 18 carbon atoms as component (B), it is possible to use it in the form of the salt or to form the salt beforehand. Alternatively, the fatty acid and a salt that acts as a counterion for the fatty acid, such as potassium hydroxide, may be added separately to the mixing tank and neutralized to form a fatty acid salt.

[0022] Furthermore, from the viewpoint of the plant growth promoting effect of arbuscular mycorrhizal fungi and the persistence of the said plant growth promoting effect, it is preferable to use a combination of one or more trans-type unsaturated fatty acids with 16 carbon atoms and their salts as component (B), and one or more trans-type unsaturated fatty acids with 18 carbon atoms and their salts. When using a combination of one or more trans unsaturated fatty acids having 16 carbon atoms and their salts, and one or more trans unsaturated fatty acids having 18 carbon atoms and their salts, the content ratio [(one or more trans unsaturated fatty acids having 16 carbon atoms and their salts) / (one or more trans unsaturated fatty acids having 18 carbon atoms and their salts)] is preferably 10 / 90 to 90 / 10 by mass ratio, and more preferably 20 / 80 to 80 / 20, when the total content of these is 100 parts by mass.

[0023] From the viewpoint of storage stability of the mycorrhizal fungal symbiosis promoter, the content of component (B) in the symbiosis promoter of the present invention is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the symbiosis promoter of the present invention. Furthermore, in order for the symbiosis promoter of the present invention to exert a sufficient effect, it is preferably 2 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less.

[0024] (C) One or more saturated fatty acids and their salts selected from the group consisting of 12 to 18 carbon atoms. The saturated fatty acid having 12 to 18 carbon atoms contained as component (C) in the symbiosis promoter of the present invention is not particularly limited, and either straight-chain fatty acids or branched-chain fatty acids can be used. Examples include dodecanoic acid (lauric acid), tridecanoic acid (tridecyl acid), tetradecanoic acid (myristic acid), pentadecanoic acid (pentadecyl acid), hexadecanoic acid (palmitic acid), 14-methylpentadecanoic acid (isopalmitic acid), heptadecanoic acid (margaric acid), octadecanoic acid (stearic acid), and 16-methylheptadecanoic acid (isostearic acid). From the viewpoint of promoting mycorrhizal fungal symbiosis in plants, straight-chain saturated fatty acids are preferred, and straight-chain saturated fatty acids having 14 to 16 carbon atoms are more preferred.

[0025] As long as the saturated fatty acid salts having 12 to 18 carbon atoms do not adversely affect plant growth, there are no particular restrictions, and examples include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; transition metal salts such as iron salts and manganese salts; and aluminum salts. Among these, alkali metal salts and alkaline earth metal salts are preferred, and sodium salts and potassium salts are particularly preferred.

[0026] The symbiosis-promoting agent of the present invention may be used as component (C) by selecting one from the group consisting of saturated fatty acids having 12 to 18 carbon atoms and their salts, or by selecting two or more and using them in combination. Furthermore, from the viewpoint of promoting the symbiotic effect of arbuscular mycorrhizal fungi on plants, it is preferable to use a salt of a saturated fatty acid having 12 to 18 carbon atoms as component (C), and it is more preferable to use an alkali metal salt of a saturated fatty acid having 12 to 18 carbon atoms. As saturated fatty acids having 12 to 18 carbon atoms and their salts, they may be synthesized as appropriate by known manufacturing methods, or commercially available products from various companies may be used. When using a salt of a saturated fatty acid having 12 to 18 carbon atoms as component (C), it is possible to use it in the form of the salt or to form the salt beforehand. Alternatively, the fatty acid and a salt that acts as a counterion for the fatty acid, such as potassium hydroxide, may be added separately to the mixing tank and neutralized to form a fatty acid salt.

[0027] Furthermore, from the viewpoint of the plant growth promoting effect of arbuscular mycorrhizal fungi and the persistence of the said plant growth promoting effect, it is preferable to use a combination of one or more saturated fatty acids selected from the group consisting of saturated fatty acids having 12 to 14 carbon atoms and their salts as component (C), and it is more preferable to use a combination of one or more saturated fatty acids selected from the group consisting of saturated fatty acids having 16 to 18 carbon atoms and their salts. When using one or more saturated fatty acids selected from the group consisting of saturated fatty acids having 12 to 14 carbon atoms and their salts, and one or more saturated fatty acids selected from the group consisting of saturated fatty acids having 16 to 18 carbon atoms and their salts, the content ratio [(one or more selected from the group consisting of saturated fatty acids having 12 to 14 carbon atoms and their salts) / (one or more selected from the group consisting of saturated fatty acids having 16 to 18 carbon atoms and their salts)] is preferably 10 / 90 to 90 / 10 by mass ratio, and more preferably 20 / 80 to 80 / 20, when the total content of these is 100 parts by mass.

[0028] The content of component (C) in the symbiosis promoter of the present invention is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the symbiosis promoter of the present invention, in order to exert a sufficient effect as a mycorrhizal fungus symbiosis promoter. Furthermore, from the viewpoint of storage stability of the symbiosis promoter of the present invention, it is preferably 89.99 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less.

[0029] The symbiosis-promoting agent of the present invention may contain general additives such as emulsifiers like polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters; dispersants described later; and auxiliary agents described later, to the extent that they do not impair the characteristics of the present invention. The symbiotic promoter of the present invention can be prepared in liquid, emulsion, suspension, powder, granular, or other forms by mixing components (A) to (C) and adding general additives as described above as necessary.

[0030] The symbiosis-promoting agent of the present invention can promote symbiosis between mycorrhizal fungi, particularly arbuscular mycorrhizal fungi, and plants. Mycorrhizal fungi, whose symbiosis with plants is promoted by the symbiosis-promoting agent of the present invention, are fungi that form mycorrhizae, i.e., filamentous fungi in the soil, which attach to the surface or inside of plant roots and live in symbiosis with plants. Mycorrhizae are classified into arbuscular mycorrhizae, ectomycorrhizae, endoexomycorrhizae, ericoid mycorrhizae, arbutoid mycorrhizae, monotropoid mycorrhizae, and orchid mycorrhizae based on their host, species, and morphology. The symbiosis-promoting agent of the present invention particularly promotes symbiosis of arbuscular mycorrhizal fungi, which are symbiotic hosts of arbuscular mycorrhizae. The arbuscular mycorrhizal fungi whose symbiosis with plants is promoted by the symbiosis-promoting agent of the present invention are not particularly limited, and all mycorrhizal fungi belonging to the phylum Glomeromycota may be targeted. In particular, examples of arbuscular mycorrhizal fungi whose symbiosis is promoted by the symbiosis-promoting agent of the present invention include fungi of the genus Rhizophagus belonging to the family Glomeraceae in the order Glommales (e.g., Rhizophagus arabicus, Rhizophagus clarus, Rhizophagus custos, Rhizophagus diaphanum, Rhizophagus fasciculatus, Rhizophagus intraradices, Rhizophagus iranicus, Rhizophagus irregularis, Rhizophagus manihotis, Rhizophagus proliferus), fungi of the genus Glomus (e.g., Glomus aggregatum, Glomus intraradices), and fungi of the genus Gigaspora belonging to the family Gigasporaraceae in the order Gigasporales (e.g., Gigaspora margarita).

[0031] [Mycorrhizal fungus symbiosis promoting solution] The present invention provides an aqueous solution or aqueous dispersion containing the symbiosis promoting agent of the present invention as a mycorrhizal fungus symbiosis promoting agent solution (hereinafter also referred to as "the symbiosis promoting agent solution of the present invention" in this specification). From the viewpoint of ensuring sufficient symbiosis-promoting effect of mycorrhizal fungi on plants, the content of the symbiosis-promoting agent in the symbiosis-promoting agent solution of the present invention is preferably 0.05 ppm by mass or more, more preferably 0.1 ppm by mass or more, more preferably 1 ppm by mass or more, and even more preferably 10 ppm by mass or more. Furthermore, from the viewpoint of storage stability of the symbiosis-promoting agent solution of the present invention, the content is preferably 650 ppm by mass or less, more preferably 500 ppm by mass or less, more preferably 300 ppm by mass or less, and even more preferably 200 ppm by mass or less.

[0032] In addition to the symbiosis promoter of the present invention, the symbiosis promoter solution of the present invention may contain, to the extent that it does not impair the characteristics of the present invention, general additives such as surfactants described later; dispersants such as dodecylbenzenesulfonate, α-olefin sulfonate, and dioctyl sulfosuccinate; and antifoaming agents such as dimethylpolysiloxane. The amount of general additives added to the symbiosis promoter solution of the present invention is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the mycorrhizal fungus symbiosis promoter, so as not to impair the effect or storage stability of the symbiosis promoter of the present invention.

[0033] [Microbial materials] The present invention can also provide a microbial material (hereinafter referred to as "the microbial material of the present invention") that can be supplied to the soil to promote plant growth. The microbial material of the present invention contains the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention and arbuscular mycorrhizal fungi. The microbial material of the present invention may contain, in addition to the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention and arbuscular mycorrhizal fungi, various carriers and additives such as emulsifiers, dispersants, defoamers, and auxiliary agents, to the extent that the characteristics of the present invention are not impaired. Furthermore, the microbial material of the present invention may contain fertilizer components.

[0034] Examples of carriers that can be contained in the microbial material of the present invention include liquid carriers and solid carriers. Examples of liquid carriers include phosphate buffer, carbonate buffer, and physiological saline. Furthermore, as solid carriers, silicate minerals such as kaolin, clay, talc, bentonite, vermiculite, silica sand, mica, zeolite, quartz, attapulgite, and montmorillonite; silicate rocks such as diatomaceous earth; silicates such as silicic acid and white carbon (sedimented silica); pyroclastic materials such as pumice; inorganic materials such as carbon (charcoal, etc.), metallic magnesium, aluminum oxide (alumina), gypsum (calcium sulfate), calcium carbonate, dolomite, slaked lime (calcium hydroxide), superphosphate, and ammonium sulfate; chalk; compos Examples include compost; plant deposits such as peat; plant flours such as rice husks, rice bran, soybean flour, tobacco flour, walnut flour, wheat flour, and wood flour; plant polysaccharides such as starch (corn starch, etc.), crystalline cellulose, and alginic acid; gelatin; synthetic resins such as coumarone resin, petroleum resin, alkyd resin, polyvinyl chloride, and ketone resin; natural resins such as ester gum (rosin ester), copal gum, and dammar gum; waxes such as carnauba wax and beeswax; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; and urea. In the microbial material of the present invention, the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention and arbuscular mycorrhizal fungi may be supported on a single carrier, or the material may contain a carrier supporting the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention and a carrier supporting arbuscular mycorrhizal fungi.

[0035] The dispersants, emulsifiers, and defoaming agents that may be contained in the microbial material of the present invention are as described above for the symbiosis promoter or the symbiosis promoter liquid of the present invention. Examples of auxiliary agents that may be contained in the microbial material of the present invention include anionic surfactants such as alkyl sulfate esters, alkyl sulfonates, alkylaryl sulfonates, and dialkyl sulfosuccinates; cationic surfactants such as higher fatty acid amidoamine salts; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyhydric alcohol fatty acid esters; thickeners such as gelatin and gum arabic; stabilizers such as casein; bulking agents such as talc, clay, bentonite, and precipitated silica; and binders such as pregelatinized starch, carboxymethylcellulose, and calcium ligninsulfonate.

[0036] The microbial material of the present invention can be provided in the form of a liquid, powder, granules, emulsion, oil, suspension, wettable powder, aqueous solvent, paste, capsule, fumigant (aerosol), etc., by mixing the symbiosis promoter of the present invention or the symbiosis promoter liquid of the present invention with arbuscular mycorrhizal fungi, and, if necessary, supporting it on the carrier described above or adding the additive described above.

[0037] By supplying the microbial material of the present invention to the soil at the site where the target plant is cultivated and cultivating the plant, it is possible to promote symbiosis of arbuscular mycorrhizal fungi with the plant and thereby promote the growth of the plant.

[0038] [How to Grow Plants] Furthermore, the present invention provides a method for cultivating plants (hereinafter also referred to as "the cultivation method of the present invention" in this specification). The cultivation method of the present invention includes supplying the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention to the soil of the area where the plant to be cultivated is to be grown, and allowing the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention to act on arbuscular mycorrhizal fungi present in the soil or arbuscular mycorrhizal fungi that live in symbiosis with the roots of the plant to be cultivated, supplying arbuscular mycorrhizal fungi that have been previously treated with the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention to the soil of the area where the plant to be cultivated is to be grown, or supplying the microbial material of the present invention to the soil of the area where the plant to be cultivated is to be grown. The symbiosis promoter, the symbiosis promoter liquid, the arbuscular mycorrhizal fungus, and the microbial material of the present invention are as described above.

[0039] In the cultivation method of the present invention, the plants to be cultivated are not limited in any way as long as they are plants in which arbuscular mycorrhizal fungi can live symbiotically in their roots. Such plants may be gymnosperms or angiosperms (monocotyledonous and dicotyledonous plants), and may be not only edible plants but also non-edible plants if they can be used industrially. In the cultivation method of the present invention, specific examples of plants that can be cultivated include monocotyledonous plants such as onions, leeks, garlic, chives, wild onions (a variety of wild onion), shallots, and leeks (Amaryllidaceae plants); and grasses such as rice, wheat, barley, corn, and sorghum. Furthermore, dicotyledonous plants include legumes such as soybeans, kidney beans, adzuki beans, peas, broad beans, peanuts, clover, cowpeas, and lotus; roses such as apricots, strawberries, plums, quince, cherries, Japanese apricots, pears, loquats, peaches, and apples; carrots such as angelica tree, celery, carrots, parsley, and Japanese parsley; cucurbits such as melons, cucumbers, pumpkins, watermelons, zucchini, winter melons, and cantaloupes; nightshade plants such as eggplants, tomatoes, bell peppers, potatoes, chili peppers, shishito peppers, and paprika; mallows such as okra, molokhia, and cotton; and morning glory plants such as water spinach and sweet potatoes. Among these, plants belonging to the genus Allium in the Amaryllidaceae family, the Fabaceae family, the Poaceae family, and the Rosaceae family are preferred, with onions, leeks, strawberries, rice, wheat, barley, Lotus corniculatus, peas, soybeans, and corn being more preferred.

[0040] In the cultivation method of the present invention, the method of supplying the symbiosis promoter of the present invention, the symbiosis promoter liquid of the present invention, or the microbial material of the present invention to the soil is not particularly limited, but can be carried out by methods such as spraying, mixing, burying, injecting the symbiosis promoter of the present invention in liquid form, the symbiosis promoter liquid of the present invention, or the microbial material of the present invention in liquid form, or by irrigation. When supplying by directly spraying onto the soil, it is preferable to directly spray onto the soil the symbiosis promoter of the present invention in liquid form, the symbiosis promoter liquid of the present invention, or the microbial material of the present invention in liquid form. When supplying to the soil, it may be applied to a portion of the soil where plants are cultivated, or to the entire area. Specific examples of locations where the symbiosis promoter, the symbiosis promoter liquid, or the microbial material of the present invention may be supplied include, for example, planting holes or their vicinity, furrows or their vicinity, between plants, the entire growing medium, the entire soil surface, seedling boxes, seedling trays, seedling pots, seedling beds, etc. In the cultivation method of the present invention, it is preferable to supply arbuscular mycorrhizal fungi to the soil together with the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention, or to supply the microbial material of the present invention to the soil. By supplying arbuscular mycorrhizal fungi to the soil together with the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention, or by supplying the microbial material of the present invention to the soil, the plant growth promoting effect of arbuscular mycorrhizal fungi can be exerted more effectively and efficiently.

[0041] The timing for supplying the symbiosis promoter of the present invention, the symbiosis promoter liquid of the present invention, or the microbial material of the present invention can be appropriately set according to the type of plant to be cultivated, its growth stage, the cultivation environment, etc. For example, it may be supplied to the soil in advance before sowing the seeds of the plant to be cultivated or before planting the plant, or it may be supplied to the soil after sowing the seeds or planting the plant. Specific examples of timing for supplying to the soil include before sowing the seeds, at the time of sowing, from after sowing until before emergence, during the emergence period, during the seedling stage, at the time of transplanting seedlings, at the time of cuttings or grafting, during the growth period after planting (before flowering, during flowering, after flowering, just before heading or during heading, etc.), and at the start of fruit coloring. In this case, it may be supplied to the soil only once or multiple times. From the viewpoint of obtaining sufficient plant growth-promoting effects while keeping the supply amount as low as possible, it is preferable to supply the plant during the early growth stage (specifically, the period from germination to before flowering or heading) or earlier, and it is more preferable to supply it during the seedling stage or earlier.

[0042] Furthermore, when supplying arbuscular mycorrhizal fungi that have been pre-treated with the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention to the soil, the arbuscular mycorrhizal fungi are first cultured in the presence of the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention. The culture of arbuscular mycorrhizal fungi can be carried out using a dual culture method with symbiotic plants, or by culturing only the arbuscular mycorrhizal fungi. Methods for culturing only arbuscular mycorrhizal fungi include, for example, culturing them using MMN (Modified Melin-Norkrans) medium. Alternatively, methods using a medium to which tryptophan dimer or leucylproline has been added to the MMN medium (for example, Japanese Patent Publication No. 2009-095332), or methods using porous carriers such as vermiculite or perlite (for example, Japanese Patent Publication No. 2005-027546) can also be employed. To culture arbuscular mycorrhizal fungi in the presence of the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention, the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention should be added to the culture medium and then cultured. Furthermore, by culturing arbuscular mycorrhizal fungi in the above-mentioned culture medium, forming a cell suspension, and then adding the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention to the cell suspension and incubating it, the arbuscular mycorrhizal fungi can be subjected to the action of the symbiosis promoter of the present invention or the symbiosis promoter solution of the present invention. Any of the above methods can improve the symbiotic ability of arbuscular mycorrhizal fungi to plants after cultivation.

[0043] The cultivation method of the present invention can improve the symbiotic ability of arbuscular mycorrhizal fungi, thereby increasing the symbiotic rate of arbuscular mycorrhizal fungi with plants and promoting plant growth. When applying a substance that can promote the growth of a plant to be cultivated, there are problems such as the need to transplant the plant grown with the substance into soil, or the possibility that even if the substance is supplied to the soil, it may not reach the roots of the target plant sufficiently and therefore not be able to adequately affect the plant. In contrast, in the cultivation method of the present invention, in an embodiment in which the symbiosis promoter of the present invention or the symbiosis promoter liquid of the present invention is applied to arbuscular mycorrhizal fungi, there is no need to transplant the plant to be cultivated, and the symbiotic ability of arbuscular mycorrhizal fungi can be improved very easily. [Examples]

[0044] The present invention will be described in more detail below with reference to examples and comparative examples. Unless otherwise specified, "%" means mass percent, and "ppm" means mass ppm.

[0045] The fatty acids used as components (A), (B), and (C) in the symbiosis promoters of the examples and comparative examples were those shown in Table 1. Furthermore, the fatty acid salts contained as components (A), (B), and (C) were synthesized using the fatty acids shown in Table 1, as described in Synthesis Examples 1 to 8 below.

[0046] [Synthesis Example 1] Synthesis of potassium palmitoleate 20.0 g of palmitoleic acid was weighed into a 50 mL stainless steel flask and heated to 80°C while blowing nitrogen into it. Next, 9.2 g of 48% potassium hydroxide aqueous solution was added dropwise, and the mixture was stirred at 80°C for one hour. After that, potassium palmitoleate was obtained by distilling off the water using a vacuum dryer (50 Torr, 60°C, 12 hours).

[0047] [Synthesis Example 2] Synthesis of potassium oleate Potassium oleate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of oleic acid was used instead of palmitoleic acid.

[0048] [Synthesis Example 3] Synthesis of potassium palmitoelaidinate Potassium palmitoelaidate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of palmitoelaidic acid was used instead of palmitoleic acid.

[0049] [Synthesis Example 4] Synthesis of potassium elaidate Potassium elaidate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of elaidic acid was used instead of palmitoleic acid.

[0050] [Synthesis Example 5] Synthesis of potassium laurate Potassium laurate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of lauric acid was used instead of palmitoleic acid.

[0051] [Synthesis Example 6] Synthesis of potassium myristate Potassium myristate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of myristic acid was used instead of palmitoleic acid.

[0052] [Synthesis Example 7] Synthesis of potassium palmitate Potassium palmitate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of palmitic acid was used instead of palmitoleic acid.

[0053] [Synthesis Example 8] Synthesis of potassium stearate Potassium stearate was obtained in the same manner as in Synthesis Example 1, except that the same molar amount of stearic acid was used instead of palmitoleic acid.

[0054] [Table 1]

[0055] [Examples 1-12, Comparative Examples 1-3] Mycorrhizal fungal symbiosis promoters Components (A), (B), and (C) were mixed according to the compositions shown in Table 2 to prepare mycorrhizal fungal symbiosis promoters for Examples 1-12 and Comparative Examples 1-3.

[0056] [Table 2]

[0057] [Examples 13-27 and Comparative Examples 4-9] Mycorrhizal fungus symbiosis promoting solution and microbial material The mycorrhizal fungal symbiosis promoters of Examples 1-12 and Comparative Examples 1-3 were diluted with sterile water to the concentrations shown in Table 3 to prepare mycorrhizal fungal symbiosis promoter solutions. Next, 1000 mL of each mycorrhizal fungal symbiosis promoter solution was mixed with 50 g of a microbial soil conditioner containing arbuscular mycorrhizal fungi ("Dr. Kincon," Idemitsu Kosan Co., Ltd.) in a 1 L plastic cup to prepare the microbial materials of Examples 13-27 and Comparative Examples 4-9.

[0058] [Test Example 1] Evaluation of the effect of mycorrhizal fungi in promoting symbiosis The microbial materials of Examples 13-27 and Comparative Examples 4-9 were evaluated for their mycorrhizal fungal symbiosis-promoting effects as follows. Sterilized soil ("Best Mix No. 3", Nippon Rockwool Co., Ltd.) was mixed with 25% by weight of each microbial material from Examples 13-27 and Comparative Examples 4-9, and 2.5% by weight of fertilizer ("Peters 20-20-20", Hyponex Japan Co., Ltd.). After mixing thoroughly, the mixture was placed in a planter (50 cm wide, 12 cm deep, 8 cm high) to a height of 6 cm, and pea (Pisum sativum) seeds were planted at 3 cm intervals. This was placed in a sunny location and watered daily. After 10 days, roots were collected from the base, and the arbuscular mycorrhizal fungi inside the roots were stained using ink staining. The symbiotic rate of mycorrhizal fungi was measured by observing them under a microscope using the following procedure. Specifically, stained root cross-sections were spread uniformly on a petri dish with a 5 mm grid, and the points where the lines on the petri dish intersected with the roots were observed to check for the presence or absence of fungal hyphae invading the inside of the roots. The symbiosis rate was then calculated using the following formula (I). Symbiosis rate (%) = (Number of intersections where mycelium was observed / Total number of intersections) × 100 (I) The symbiotic effect of mycorrhizal fungi was evaluated according to the following evaluation criteria, and the evaluation results are shown in Table 3. <Evaluation Criteria> ◎: The symbiosis rate is 20% or higher. ○: The symbiosis rate is between 15% and 20%. △: The symbiosis rate is between 10% and 15%. ×: The symbiosis rate is less than 10%.

[0059] [Test Example 2] Evaluation of the effect of promoting plant growth The plant growth promoting effects of the microbial materials in Examples 13-27 and Comparative Examples 4-9 were evaluated as follows. (i) Measurement of the growth rate of control plants Sterilized soil ("Best Mix No. 3," Nippon Rockwool Co., Ltd.) was mixed with 25% by weight of sterilized water and 2.5% by weight of fertilizer ("Peters 20-20-20," Hyponex Japan Co., Ltd.) and thoroughly mixed. This mixture was then placed in a planter (50cm wide, 12cm deep, 8cm high) to a height of 6cm, and pea (Pisum sativum) seeds were planted at 3cm intervals. This was placed in a sunny location and watered daily. After 10 days, 10 plants were randomly selected, and the entire plant was harvested from the base of each plant. The length from the base was measured. The average length of the 10 plants was calculated and used as the control pea length. (ii) Evaluation of the plant growth promoting effect of each microbial material in the examples and comparative examples. In (i) above, instead of sterile water, the microbial materials from Examples 13-27 and Comparative Examples 4-9 were added, and peas were cultivated from seeds in the same manner. After 10 days, 10 plants were randomly selected and the whole plants were harvested from the base, the length from the base was measured, and the average length of the 10 pea plants was calculated. For each case in the examples and comparative examples where the microbial material was added, the growth rate was calculated using the following formula (II). Growth rate (%) = (Average length of pea plants with added microbial material / Average length of control pea plants) × 100 (II) The effect of promoting plant growth was evaluated according to the evaluation criteria below, and the evaluation results are shown in Table 3. <Evaluation Criteria> ◎: Growth rate is 125% or higher ○: Growth rate is between 115% and 125% △: Growth rate is between 105% and 115% ×: Growth rate is less than 105%

[0060] [Test Example 3] Evaluation of the persistence of the plant growth promoting effect Similar to the above example 2, each microbial material from Examples 13-27 and Comparative Examples 4-9 was added to sterilized soil, and peas were grown from seeds. After 10 days, the entire plant was harvested from the base, and the growth rate relative to the control was determined. Next, peas were grown again in the soil where the peas had been harvested, planted at 3 cm intervals, and cultivated in a sunny location with daily watering. After 10 days, the entire plant was harvested from the base. This procedure was repeated twice, and the length of the peas harvested on the third attempt was measured. The growth rate of the peas harvested on the third attempt was calculated using the following formula (III). Growth rate of peas harvested for the third time (%) = (Average length of peas at the third harvest / Average length of control peas) × 100 (III) The sustainability of the plant growth-promoting effect was evaluated according to the following evaluation criteria, and the evaluation results are shown in Table 3. <Evaluation Criteria> ◎: The growth rate of the peas harvested for the third time is 120% or more. ○: The growth rate of the peas harvested for the third time is between 110% and 120%. △: The growth rate of the peas harvested for the third time is between 105% and 110%. ×: The growth rate of the peas harvested for the third time was less than 105%.

[0061] [Table 3]

[0062] As shown in Table 3, the microbial materials of Examples 13 to 27, which contained mycorrhizal fungal symbiosis promoting solutions prepared by diluting the mycorrhizal fungal symbiosis promoting agents of Examples 1 to 12, were evaluated as having very good or good effects in promoting mycorrhizal fungal symbiosis in plants, promoting plant growth, and the persistence of these effects. In particular, the microbial materials of Examples 13 and 15, which used a mycorrhizal fungus symbiosis promoter solution containing 100 ppm or 180 ppm of the mycorrhizal fungus symbiosis promoter of Example 1, which contains potassium palmitoleate and potassium oleate as component (A), potassium palmitoelaidate and potassium elaidate as component (B), and potassium myristate and potassium palmitate as component (C), in more preferable amounts, and the microbial material of Example 23, which used a mycorrhizal fungus symbiosis promoter solution containing 100 ppm of the mycorrhizal fungus symbiosis agent of Example 8, were evaluated as having very good mycorrhizal fungal symbiosis promoting effect on plants, plant growth promoting effect, and persistence of effect.

[0063] On the other hand, for the microbial material that did not contain any mycorrhizal fungal symbiosis promoter (Comparative Example 4), no effect on promoting mycorrhizal fungal symbiosis or plant growth was observed. A microbial material (Comparative Example 5) using a mycorrhizal fungus symbiosis promoter solution containing a mycorrhizal fungus symbiosis promoter of Comparative Example 1 at a concentration of 100 ppm, in which the content of component (A) was less than 10 parts by mass per 100 parts by mass of the mycorrhizal fungus symbiosis promoter and the content of component (C) exceeded 89.99 parts by mass per 100 parts by mass of the mycorrhizal fungus symbiosis promoter, was evaluated as having inferior mycorrhizal fungus symbiosis promoting effect and insufficient plant growth promoting effect and its persistence. A microbial material (Comparative Example 6) using a mycorrhizal fungus symbiosis promoter solution containing a mycorrhizal fungus symbiosis promoter of Comparative Example 2, which contained more than 78 parts by mass of component (A) and less than 20 parts by mass of component (C), at a concentration of 100 ppm, was evaluated as having insufficient mycorrhizal fungus symbiosis promoting effect and plant growth promoting effect, and as having poor sustainability of the plant growth promoting effect. A microbial material (Comparative Example 7) using a mycorrhizal fungus symbiosis promoter solution containing 100 ppm of the mycorrhizal fungus symbiosis promoter of Comparative Example 3, which does not contain component (B), was evaluated as having insufficient plant growth promoting effect and poor sustainability. A microbial material (Comparative Example 8) using a mycorrhizal fungus symbiosis promoting solution containing the mycorrhizal fungus symbiosis promoting agent of Example 1 at a concentration of 0.01 ppm was evaluated as having insufficient effects in promoting mycorrhizal fungal symbiosis in plants, promoting plant growth, and the persistence of these effects. A microbial material (Comparative Example 9) using a mycorrhizal fungus symbiosis promoter solution containing the mycorrhizal fungus symbiosis promoter of Example 1 at a concentration of 750 ppm was evaluated as having insufficient sustained effect in promoting plant growth.

[0064] The results from Test Examples 1-3 suggest that by supplying a microbial material containing the symbiosis-promoting agent of the present invention to the soil and cultivating plants, the symbiosis of mycorrhizal fungi with the plants is promoted, plant growth is accelerated, and the effect of promoting plant growth persists even after multiple cycles of cultivation and harvesting. [Industrial applicability]

[0065] As detailed above, the present invention provides a mycorrhizal fungal symbiosis promoter that acts on mycorrhizal fungi, particularly arbuscular mycorrhizal fungi, and can improve the symbiotic ability of mycorrhizal fungi to plants. Furthermore, the present invention makes it possible to sustain the symbiotic effect of arbuscular mycorrhizal fungi even after the plants have been harvested multiple times as crops, without the need to add arbuscular mycorrhizal fungi. Therefore, the present invention makes it possible to establish arbuscular mycorrhizal fungi in symbiosis with plants more efficiently and simply. Furthermore, the present invention makes it possible to use arbuscular mycorrhizal fungi with improved symbiotic ability, allowing the plant growth-promoting effect of arbuscular mycorrhizal fungi to be fully exerted, and providing a plant cultivation method in which plant growth is sustainably promoted.

Claims

1. A mycorrhizal fungal symbiosis promoter comprising (A) one or more selected from the group consisting of cis-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, (B) one or more selected from the group consisting of trans-type unsaturated fatty acids having 16 to 18 carbon atoms and their salts, and (C) one or more selected from the group consisting of saturated fatty acids having 12 to 18 carbon atoms and their salts, wherein the content ratios of components (A), (B), and (C) are 10 to 78 parts by mass, 0.01 to 2 parts by mass, and 20 to 89.99 parts by mass, respectively.

2. An aqueous solution or aqueous dispersion containing the mycorrhizal fungal symbiosis promoting agent described in claim 1, wherein the content of the mycorrhizal fungal symbiosis promoting agent described in claim 1 is 0.05 ppm by mass to 650 ppm by mass, a mycorrhizal fungal symbiosis promoting agent solution.

3. A microbial material containing the mycorrhizal fungus symbiosis promoting agent described in claim 1 or the mycorrhizal fungus symbiosis promoting agent liquid described in claim 2, and arbuscular mycorrhizal fungi.

4. A method for cultivating plants, comprising supplying the mycorrhizal fungus symbiosis promoter described in claim 1 or the mycorrhizal fungus symbiosis promoter solution described in claim 2 to the soil of a site where the plant to be cultivated is to be grown, and allowing the mycorrhizal fungus symbiosis promoter described in claim 1 or the mycorrhizal fungus symbiosis promoter solution described in claim 2 to act on arbuscular mycorrhizal fungi present in the soil or arbuscular mycorrhizal fungi symbiotic with the roots of the plant to be cultivated, or supplying arbuscular mycorrhizal fungi that have been previously treated with the mycorrhizal fungus symbiosis promoter described in claim 1 or the mycorrhizal fungus symbiosis promoter solution described in claim 2 to the soil of a site where the plant to be cultivated is to be grown.

5. A method for cultivating plants, comprising supplying the microbial material described in claim 3 to the soil of a site where the plant to be cultivated is to be grown.

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