JP7813124B2 - Acetic acid slow-release plant stimulant - Google Patents

Description

This disclosure relates to biostimulants. Specifically, this disclosure relates to plant stimulants that have sustained release of acetic acid.

Biostimulants (also known as biological stimulants) are a new agricultural material that has been attracting attention in recent years. They refer to various substances and microorganisms that bring about better physiological conditions in plants and soil. Biostimulants utilize the natural power inherent in plants and their surrounding environment to have a positive effect on plant health, stress resistance, etc. In particular, biostimulants increase plant resistance to abiotic stresses such as high temperature damage and drought, resulting in increased yields, improved quality, improved post-harvest condition, and improved storage properties.

For example, it is known that the action of acetic acid activates genes that promote tolerance to environmental stress in plants. One form of biostimulant that utilizes this mechanism is a composition primarily composed of acetic acid. For example, Patent Document 1 (U.S. Patent No. 9,258,954) discloses a method for enhancing drought stress tolerance in plants, which includes the steps of pouring 10 mM or more acetic acid onto the plant and growing the plant under drought stress conditions. According to Patent Document 1, this method controls the expression of histone modifying enzymes in the plant, resulting in a plant with enhanced environmental stress tolerance.

Patent Document 2 (WO 2019/070027) discloses an agent for reducing the amount of irrigation water required for plants, which contains acetic acid, a salt thereof, or a solvate thereof as an active ingredient. Patent Document 3 (WO 2020/130145) proposes an agent for improving the heat tolerance or salt tolerance of plants, which contains acetic acid, a salt thereof, or a solvate thereof.

U.S. Patent No. 9,258,954 International Publication No. 2019/070027 International Publication No. 2020/130145

In Patent Documents 1-3, liquid compositions such as aqueous acetic acid solutions are used. When aqueous acetic acid solutions are sprayed on plants and the soil in which the plants grow, there is a problem in that the water-soluble acetic acid is washed away by rain or other factors. To achieve the desired effect using the liquid compositions disclosed in Patent Documents 1-3, multiple sprays were required.

The object of the present disclosure is to provide an acetic acid sustained-release plant stimulant that can stably release acetic acid over a long period of time, even when sprayed on soil, etc. Another object of the present disclosure is to provide a method for improving plant resistance to abiotic stress.

The acetic acid sustained-release plant stimulant disclosed herein contains an acetyl group-containing polymer as its main component.

The acetyl group-containing polymer contained in the acetic acid sustained-release plant stimulant of the present disclosure may be one or more selected from the group consisting of cellulose derivatives in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups, vinyl acetate polymers, and processed starches in which some of the hydroxyl groups of glucose have been substituted with acetyl groups. Preferably, the acetyl group-containing polymer includes a cellulose derivative in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups.

The cellulose derivative in which some of the hydroxyl groups of cellulose are substituted with acetyl groups may be cellulose acetate. The degree of acetyl substitution of the cellulose acetate may be 1.3 or more and 2.9 or less.

The content of the acetyl group-containing polymer may be 80% by weight or more based on the total weight of the acetic acid sustained-release plant stimulant of the present disclosure.

The acetic acid sustained-release plant stimulant of the present disclosure may further contain acetic acid. The combined amount of the acetyl group-containing polymer and acetic acid may be 90% by weight or more based on the total weight of the acetic acid sustained-release plant stimulant.

The acetic acid sustained-release plant stimulant of the present disclosure may further contain an alkali metal or alkaline earth metal. The total content of the alkali metal and alkaline earth metal may be 0.001% by weight or more and 0.300% by weight or less, based on the total weight of the acetic acid sustained-release plant stimulant.

The disclosed method for improving a plant's resistance to abiotic stress includes applying any of the aforementioned acetic acid sustained-release plant stimulants to the plant's growing environment.

The main component of the acetic acid sustained-release plant stimulant according to the present disclosure is a polymer containing acetyl groups ester-bonded to the polymer chain. This plant stimulant is inhibited from being washed away by rainfall, etc. Furthermore, in this plant stimulant, the ester bond dissociates and acetic acid is produced as the acetyl group-containing polymer undergoes a hydrolysis or biodegradation reaction. Even after the produced acetic acid is washed away by rainfall, etc., new acetic acid is produced by further hydrolysis or biodegradation in this plant stimulant. The plant stimulant according to the present disclosure can release acetic acid stably over an extended period of time, without the need for multiple sprays. Applying this plant stimulant to the plant's growing environment can improve the plant's stress tolerance.

The present disclosure will be described in detail below based on preferred embodiments. The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of configurations are possible as appropriate without departing from the spirit of the present disclosure. The present disclosure is not limited by the embodiments, but only by the scope of the claims. Furthermore, each aspect disclosed in this specification can be combined with any other feature disclosed in this specification.

In this specification, the range "X to Y" means "X or more and Y or less," "ppm" means "ppm by weight," and unless otherwise noted, all tests were conducted at room temperature (20°C ± 5°C).

[Acetic acid sustained-release plant stimulant]
The acetic acid sustained-release plant stimulant according to the present disclosure contains an acetyl group-containing polymer as a main component. In this specification, an "acetyl group-containing polymer" is defined as a polymer containing an acetyl group ester-linked to the main chain or side chain of the polymer. Here, "polymer" refers to a polymer compound formed by bonding one or more types of repeating units.

When the plant stimulant of the present disclosure is applied to soil, etc., the acetyl group-containing polymer undergoes hydrolysis upon contact with water, etc., or biodegradation by microorganisms. This hydrolysis or biodegradation reaction dissociates the ester bonds in the acetyl group-containing polymer, producing acetic acid.

According to the plant stimulant disclosed herein, acetic acid is gradually released as the acetyl group-containing polymer is hydrolyzed or biodegraded. The amount and duration of acetic acid release can be adjusted depending on the physical properties (e.g., molecular weight) of the acetyl group-containing polymer.

Although it depends on the physical properties of the acetyl group-containing polymer, the plant stimulant of the present disclosure is typically applied as a solid. Compared to an aqueous acetic acid solution, the plant stimulant of the present disclosure is less likely to be run off due to rainfall after application. Even if the acetic acid produced by the hydrolysis or biodegradation of the acetyl group-containing polymer is lost due to rainfall or the like, new acetic acid is subsequently produced and released by the hydrolysis or biodegradation of the remaining acetyl group-containing polymer.

The acetic acid sustained-release plant stimulant disclosed herein can release acetic acid stably over a long period of time, without the need for multiple sprays. Applying this plant stimulant to a plant's growing environment improves the plant's resistance to abiotic stresses such as drought and heat. This makes it possible to produce high-quality plants in high yields, even in dry or hot environments.

[plant]
The acetic acid sustained-release plant stimulant according to the present disclosure can be effectively used for plants that have a mechanism for activating stress tolerance genes with acetic acid. The type of plant is not particularly limited, and it can be used for vegetables, flowers, fruits, fruit trees, trees, etc.

Specific examples of plants to which the plant stimulant of the present disclosure can be applied include Solanaceae plants such as tomato and eggplant, Brassicaceae plants such as cabbage, lettuce, and sugar beet, Legumes such as soybean and alfalfa, Rosaceae plants such as apple and pear, Gramineae plants such as rice, wheat, and corn, Rutaceae plants, Vitaceae plants, Araceae plants, Orchidaceae plants, Rosaceae plants, Amaryllidaceae plants, Araliaceae plants, Brackenaceae plants, Palmaceae plants, Moraceae plants, Theaceae plants, Ericaceae plants, Mapleaceae plants, Birchaceae plants, Lauraceae plants, Cycadaceae plants, Bambusaceae plants, Cupressaceae plants, Pinaceae plants, Cornaceae plants, Oleaceae plants, Fagaceae plants, etc. From the perspective of high cost-effectiveness, plants used as agricultural or horticultural crops are preferred.

The plant cultivation method to which the plant stimulant of the present disclosure is applied is not particularly limited. The plant stimulant of the present disclosure can be suitably used in cultivation methods suitable for plants, such as soil, water, hydroponic cultivation solution, agar, and silica gel.

[shape]
As long as the effects of the present disclosure can be obtained, the shape of the acetic acid sustained-release plant stimulant is not particularly limited and can be selected appropriately depending on the application and purpose. For example, shapes with a large surface area, such as powder, flakes, and films, are preferred because hydrolysis or biodegradation occurs quickly, allowing acetic acid to be released in a short period of time after application to soil, etc. Furthermore, pellets, sheets, and the like are less likely to be washed away by rain, etc. Furthermore, pellets have a smaller surface area than powders, etc., and therefore have a slower decomposition rate, which allows the release of acetic acid to be delayed. Plant stimulants of different shapes may also be used in combination. This allows acetic acid to be released at the desired time after application to soil, etc.

[Acetyl group-containing polymer]
The acetyl group-containing polymer (hereinafter sometimes simply referred to as "polymer") is the main component of the acetic acid sustained-release plant stimulant of the present disclosure. Here, "main component" means that the acetyl group-containing polymer accounts for 80 to 100% by weight of the entire plant stimulant. From the viewpoint of controlling the amount of acetic acid released, the acetyl group-containing polymer may be 90% by weight or more, 95% by weight or more, 98% by weight or more, or 99% by weight or more, based on the total weight of the plant stimulant, with the upper limit being 100% by weight. The acetyl group-containing polymer may further have other substituents, as long as the effects of the present disclosure are not impaired.

The type and physical properties of the acetyl group-containing polymer are not particularly limited. A polymer that generates acetic acid upon hydrolysis or biodegradation in soil, etc., is appropriately selected and used. From the perspective of suppressing runoff due to rainfall, etc., an acetyl group-containing polymer that is insoluble or poorly soluble in water is preferred. Specifically, the amount of water (20±5°C) required to dissolve 1 g of the polymer is preferably 100 mL or more, more preferably 1,000 mL or more, and even more preferably 10,000 mL or more.

The acetyl group content of an acetyl group-containing polymer affects the amount of acetic acid released during use. In this specification, the acetyl group content is defined as the weight percentage of acetyl groups attached to the polymer chain, calculated as acetic acid. A low acetyl group content makes the polymer water-soluble and dissolves and washes away with rain, preventing its effectiveness from being maintained for a long period of time. To prevent washout during rain, the acetyl group content of the acetyl group-containing polymer is preferably 25.0 wt% or more, but may also be 39.0 wt% or more, 40.0 wt% or more, 42.0 wt% or more, 43.0 wt% or more, or 44.7 wt% or more. Polymers with a high acetyl group content tend to have a slower initial decomposition rate. The acetyl group content can be appropriately set depending on the desired decomposition rate. If a high decomposition rate is required initially, the acetyl group content of the acetyl group-containing polymer is preferably 40.0 wt% or less, and more preferably 38.0 wt% or less. The acetyl group content is measured by appropriately modifying the method for measuring the acetylation degree of cellulose acetate, described below, depending on the type of acetyl group-containing polymer.

The molecular weight and molecular weight distribution of the acetyl group-containing polymer affect the rate and duration of acetic acid release during use. From the perspective of being able to release acetic acid over a long period of time, the weight-average molecular weight Mw of the acetyl group-containing polymer is preferably 10,000 or more, and more preferably 20,000 or more. From the perspective of ease of hydrolysis or biodegradation, the weight-average molecular weight Mw of the acetyl group-containing polymer is preferably 1,000,000 or less, and more preferably 500,000 or less.

From the viewpoint of ease of hydrolysis or biodegradation, the molecular weight distribution Mw/Mn of the acetyl group-containing polymer is preferably 1.0 or greater, more preferably 2.0 or greater. From the viewpoint of being able to release acetic acid over a long period of time, the molecular weight distribution Mw/Mn of the acetyl group-containing polymer is preferably 6.0 or less, more preferably 4.0 or less. The molecular weight distribution Mw/Mn is expressed as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn. The molecular weight and molecular weight distribution of the acetyl group-containing polymer are measured by appropriately modifying the method for measuring the molecular weight and molecular weight distribution of cellulose derivatives described below depending on the type of acetyl group-containing polymer.

The BET specific surface area of the acetyl group-containing polymer contained in the acetic acid sustained-release plant stimulant of the present disclosure affects the acetic acid release rate during use. From the viewpoint of ease of hydrolysis or biodegradation, the BET specific surface area of the acetyl group-containing polymer is preferably 1.0 m ² /g or more, and is preferably 1.5 m ² /g or more, 2.0 m ² /g or more, 3.2 m ² /g or more, 4.8 m ² /g or more, and 5.0 m ² /g or more in that order. From the viewpoint of high storage stability, the BET specific surface area is preferably 6.0 m ² /g or less, more preferably 5.8 m ² /g or less, and even more preferably 5.7 m ² /g or less. The BET specific surface area of the acetyl group-containing polymer may be 1.0 to 6.0 ^{m 2} /g, may be 1.0 to 5.8 ^{m 2} /g, may be 1.0 to 5.7 m ² /g, may be 1.5 to 6.0 ^{m 2} /g, may be 1.5 to 5.8 ^{m 2} /g, may be 1.5 to 5.7 ^{m 2} /g, may be 2.0 to 6.0 m ² /g, may be 2.0 to 5.8 m ² /g, may be 2.0 to 5.7 m ² /g, may be 3.2 to 6.0 ^{m 2} /g, may be 3.2 to 5.8 m ² /g, may be 3.2 to 5.7 m ² /g, may be 4.8 to 6.0 m ² /g, may be 4.8 to 5.8 m ² /g, may be 4.8 to 5.7 m ² /g, 5.0 to 6.0 m ² /g, 5.0 to 5.8 m ² /g, or 5.0 to 5.7 m ² /g. The method for measuring the BET specific surface area will be described later in the examples.

Examples of acetyl group-containing polymers having a structure capable of releasing acetic acid upon hydrolysis or biodegradation during use include cellulose derivatives in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups, vinyl acetate polymers, and modified starches in which some of the hydroxyl groups of glucose have been substituted with acetyl groups. The acetyl group-containing polymer may be one or more selected from the group consisting of cellulose derivatives in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups, vinyl acetate polymers, and modified starches in which some of the hydroxyl groups of glucose have been substituted with acetyl groups, or may be two or more types including a cellulose derivative in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups. The acetic acid sustained-release plant stimulant of the present disclosure may contain, as a main component, a cellulose derivative in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups. The acetic acid sustained-release plant stimulant of the present disclosure may further contain another acetyl group-containing polymer, as long as the effects of the present disclosure are not impaired.

Examples of vinyl acetate polymers include polyvinyl acetate and partially saponified products thereof. The degree of saponification of the vinyl acetate polymer may be 0 mol%, but from the viewpoint of the amount of acetic acid released during use, it is preferably 5 mol% or more, and more preferably 10 mol% or more. Furthermore, from the viewpoint of suppressing runoff during rainfall, the degree of saponification of the vinyl acetate polymer is preferably 60 mol% or less, and more preferably 50 mol% or less. The degree of saponification of the vinyl acetate polymer may be 0 to 60 mol%, 0 to 50 mol%, 5 to 60 mol%, 5 to 50 mol%, 10 to 60 mol%, or 10 to 50 mol%.

The weight-average degree of polymerization of the vinyl acetate polymer is preferably 100 or higher. If the weight-average degree of polymerization is less than 100, the vinyl acetate polymer will be water-soluble, making it difficult to prevent runoff during rainfall. The weight-average degree of polymerization of the vinyl acetate polymer is preferably 2000 or lower, and more preferably 300 or lower. If the weight-average degree of polymerization exceeds 2000, the decomposition rate will decrease, resulting in a reduced amount of acetic acid released. The weight-average degree of polymerization of the vinyl acetate polymer may be 100 to 2000, or 100 to 300.

As long as the effects of the present disclosure are achieved, the processed starch may be starch acetate in which all of the hydroxyl groups of glucose have been substituted with acetyl groups, or a starch derivative in which some or all of the hydroxyl groups of glucose have been substituted with acetyl groups and acyl groups other than acetyl groups. Examples of acyl groups other than acetyl groups include propionyl groups, butyryl groups, carboxyl groups, carboxymethyl groups, 2-hydroxyethyl groups, 2-hydroxypropyl groups, and methyl groups.

[Cellulose derivatives]
As long as the effects of the present disclosure can be obtained, the cellulose derivative may be cellulose acetate in which all of the hydroxyl groups of cellulose are substituted with acetyl groups, or may be a cellulose mixed fatty acid ester in which some or all of the hydroxyl groups of cellulose are substituted with acetyl groups and acyl groups other than acetyl groups. Examples of acyl groups other than acetyl groups include propionyl groups, butyryl groups, carboxyl groups, carboxymethyl groups, 2-hydroxyethyl groups, 2-hydroxypropyl groups, and methyl groups.

From the viewpoint of excellent acetic acid sustained-release properties, the degree of acetyl substitution of the cellulose derivative is preferably 1.3 or more, more preferably 2.0 or more. From the viewpoint of excellent biodegradability, the degree of acetyl substitution is preferably 2.9 or less, more preferably 2.7 or less, and even more preferably 2.5 or less. The degree of acetyl substitution of the cellulose derivative may be 1.3 to 2.9, 1.3 to 2.7, 1.3 to 2.5, 2.0 to 2.9, 2.0 to 2.7, or 2.0 to 2.5.

From the viewpoint of suppressing washout during rainfall, the total degree of substitution of the cellulose derivative is preferably 1.3 or more, more preferably 2.0 or more. From the viewpoint of excellent biodegradability, the total degree of substitution is preferably 2.9 or less, more preferably 2.7 or less, and even more preferably 2.5 or less. The total degree of substitution of the cellulose derivative may be 1.3 to 2.9, 1.3 to 2.7, 1.3 to 2.5, 2.0 to 2.9, 2.0 to 2.7, or 2.0 to 2.5. The total degree of substitution of the cellulose derivative is the sum of the aforementioned acetyl substitution groups and the degree of substitution by acyl groups other than acetyl groups.

The degree of acetyl substitution and total degree of substitution of a cellulose derivative can be measured by NMR, for example, according to the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). Specifically, the free hydroxyl groups of the cellulose derivative are acylated with a carboxylic acid anhydride in pyridine. The type of carboxylic acid anhydride used here should be selected depending on the purpose of the analysis; for example, butyric anhydride can be used when analyzing the degree of acetyl substitution of cellulose acetate. The resulting sample is dissolved in deuterated chloroform, and the ^13C -NMR spectrum is measured. When the substituent is an acetyl group, the carbon signals of the acetyl group appear in the region from 169 ppm to 171 ppm, in the order of 2-, 3-, and 6-positions, from the highest magnetic field. The total degree of substitution of a cellulose derivative treated with carboxylic acid anhydride by Tezuka's method or a method similar thereto is 3.0, so if the sum of the areas of the carbonyl carbon signals of the acetyl groups originally present in the cellulose derivative and the carbonyl signals of the acyl groups introduced by carboxylic acid anhydride treatment is normalized to 3.0 and the abundance ratios of acetyl groups at the corresponding positions (in other words, the area ratios of each signal) are calculated, this can be taken as the degrees of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring in the cellulose derivative. Furthermore, the degrees of acetyl substitution and the total degree of substitution can also be analyzed by ^1H -NMR in addition to ^13C -NMR.

The acetyl group content (acetyl group %) of cellulose acetate can be calculated from the degree of acetyl substitution according to the following formula: The acetyl group content of cellulose acetate is the mass of acetyl groups relative to the total mass of cellulose acetate.
Acetyl group %=((43.04494*degree of substitution)/(162.14+(60.052-18.015)*degree of substitution))*100

From the viewpoint of excellent storage stability, the weight-average molecular weight Mw of the cellulose derivative is preferably 10,000 or more, more preferably 12,000 or more, even more preferably 15,000 or more, and particularly preferably 18,000 or more. From the viewpoint of ease of hydrolysis or biodegradation, the weight-average molecular weight of the cellulose derivative is preferably 300,000 or less, more preferably 280,000 or less, and even more preferably 250,000 or less. The weight average molecular weight Mw of the cellulose derivative may be 10,000 to 300,000, 10,000 to 280,000, 10,000 to 250,000, 12,000 to 300,000, 12,000 to 280,000, 12,000 to 250,000, 15,000 to 300,000, 15,000 to 280,000, 150,000 to 250,000, 18,000 to 300,000, 18,000 to 280,000, or 18,000 to 250,000. A cellulose derivative with a high weight average molecular weight can be obtained, for example, by using cellulose with a high degree of polymerization, such as linter cotton, as a raw material for the cellulose derivative. Additionally, cellulose derivatives with low weight-average molecular weights can be obtained by increasing the hydrolysis temperature during the cellulose derivative manufacturing process.

From the viewpoint of ease of hydrolysis or biodegradation, the molecular weight distribution Mw/Mn of the cellulose derivative is preferably 1.5 or more, more preferably 2.0 or more, and even more preferably 3.0 or more. From the viewpoint of being able to release acetic acid over a long period of time, the molecular weight distribution Mw/Mn of the cellulose derivative is preferably 5.0 or less, more preferably 4.0 or less. The molecular weight distribution Mw/Mn of the cellulose derivative may be 1.5 to 5.0, 1.5 to 4.0, 2.0 to 5.0, 2.0 to 4.0, 3.0 to 5.0, or 3.0 to 4.0. Cellulose derivatives with a wide molecular weight distribution can exert their effects even after repeated rainfall, with high molecular weight components remaining. Cellulose derivatives with a narrow molecular weight distribution can limit the period during which the acetic acid sustained-release effect is exerted.

The weight-average molecular weight Mw and molecular weight distribution Mw/Mn of a cellulose derivative can be measured by gel permeation chromatography (GPC) using the following apparatus and conditions (GPC-light scattering method) after esterifying all remaining hydroxyl groups in order to solubilize the cellulose derivative (sample) in a solvent.
Apparatus: Shodex GPC "SYSTEM-21H"
Solvent: acetone Column: 2 GMHxl (Tosoh), guard column (TSKgel guard column HXL-H manufactured by Tosoh)
Flow rate: 0.8ml/min
Temperature: 29℃
Sample concentration: 0.25% (wt/vol)
Injection volume: 100μl
Detection: MALLS (multi-angle light scattering detector) (manufactured by Wyatt, "DAWN-EOS")
MALLS correction standard material: PMMA (molecular weight 27600)

From the viewpoint of ease of hydrolysis or biodegradation, the BET specific surface area of the cellulose derivative is preferably 1.0 m ² /g or more, and is more preferably 1.5 m ² /g or more, 2.0 m ² /g or more, 3.2 m ² /g or more, 4.8 m ² /g or more, and 5.0 m ² /g or more in that order. From the viewpoint of high storage stability, the BET specific surface area of the cellulose derivative is preferably 6.0 m ² /g or less, more preferably 5.8 m ² /g or less, and even more preferably 5.7 m ² /g or less. The BET specific surface area of the cellulose derivative may be 1.0 to 6.0 ^{m 2} /g, may be 1.0 to 5.8 m ² /g, may be 1.0 to 5.7 m ² /g, may be 1.5 to 6.0 ^{m 2} /g, may be 1.5 to 5.8 ^{m 2} /g, may be 1.5 to 5.7 m ² /g, may be 2.0 to 6.0 m ² /g, may be 2.0 to 5.8 m ² /g, may be 2.0 to 5.7 m ² /g, may be 3.2 to 6.0 ^{m 2} /g, may be 3.2 to 5.8 ^{m 2} /g, may be 3.2 to 5.7 m ² /g, may be 4.8 to 6.0 m ² /g, may be 4.8 to 5.8 m ² /g, may be 4.8 to 5.7 m ² The BET specific surface area of the cellulose derivative may be 5.0 to 6.0 ^{m 2} /g, 5.0 to 5.8 m ² /g, or 5.0 to 5.7 m ² /g. The method for measuring the BET specific surface area of the cellulose derivative will be described later in the Examples.

Cellulose derivatives with a large BET specific surface area can be obtained by flake-pulverizing cellulose derivatives. Cellulose derivatives with a small BET specific surface area can be obtained by heating the cellulose derivative and forming it into granules. The BET specific surface area can also be adjusted by mixing flake-pulverized cellulose derivatives with unpulverized flakes.

[Optional ingredients]
The acetic acid sustained-release plant stimulant may further contain water as long as the effects of the present disclosure are achieved. The addition of water promotes hydrolysis of the acetyl group-containing polymer. From the viewpoint of enabling acetic acid release at the initial stage of use, the water concentration in the plant stimulant is preferably 1% by weight or more, more preferably 2% by weight or more. From the viewpoint of ease of handling, the water concentration in the plant stimulant is preferably 10% by weight or less, more preferably 7% by weight or less, and even more preferably 5% by weight or less. The water concentration in the plant stimulant may be 1 to 10% by weight, 1 to 7% by weight, 1 to 5% by weight, 2 to 10% by weight, 2 to 7% by weight, or 2 to 5% by weight. The acetic acid sustained-release plant stimulant of the present disclosure can exert its function through rainfall. Therefore, although water is not an essential component of the acetic acid sustained-release plant stimulant of the present disclosure, when used in situations where rainfall is unlikely, a higher water concentration facilitates the exertion of the acetic acid sustained-release effect.

The acetic acid sustained-release plant stimulant may further contain acetic acid, as long as the effects of the present disclosure are achieved. The addition of acetic acid promotes hydrolysis of the acetyl group-containing polymer. From the viewpoint of enabling acetic acid release at the initial stage of use, the acetic acid concentration in the plant stimulant is preferably 0.01 wt% or more, more preferably 0.03 wt% or more, and even more preferably 0.04 wt% or more. From the viewpoint of improving storage stability, the acetic acid concentration in the plant stimulant is preferably 0.10 wt% or less, more preferably 0.08 wt% or less, and even more preferably 0.07 wt% or less. The concentration of acetic acid in the plant stimulant may be 0.01 to 0.10% by weight, 0.01 to 0.08% by weight, 0.01 to 0.07% by weight, 0.03 to 0.10% by weight, 0.03 to 0.08% by weight, 0.03 to 0.07% by weight, 0.04 to 0.10% by weight, 0.04 to 0.08% by weight, or 0.04 to 0.07% by weight. Furthermore, when acetic acid is added as an aqueous acetic acid solution, from the standpoint of improving storage stability and ease of handling, the amount added as an aqueous acetic acid solution is preferably 10% by weight or less of the total plant stimulant.

To the extent that the effects of the present disclosure can be obtained, the acetic acid sustained-release plant stimulant may further contain an alkali metal or alkaline earth metal. The alkali metal and alkaline earth metal may, for example, be derived from the manufacturing process of the acetyl group-containing polymer (particularly a cellulose derivative). The alkali metal or alkaline earth metal in the plant stimulant inhibits hydrolysis of the acetyl group-containing polymer. From the viewpoint of improving storage stability, the total content of alkali metal and alkaline earth metal in the plant stimulant is preferably 0.1 wt% or more, more preferably 0.3 wt% or more, and even more preferably 1.0 wt% or more, based on the total weight. From the viewpoint of improving the acetic acid release rate, the total content of alkali metal and alkaline earth metal is preferably 7.0 wt% or less, more preferably 5.0 wt% or less. The total content of alkali metals and alkaline earth metals in the plant stimulant may be 0.1 to 7.0% by weight, 0.1 to 5.0% by weight, 0.3 to 7.0% by weight, 0.3 to 5.0% by weight, 1.0 to 7.0% by weight, or 1.0 to 5.0% by weight.

[Method for producing acetic acid sustained-release plant stimulant]
The method for producing the acetic acid sustained-release plant stimulant of the present disclosure is not particularly limited. The acetyl group-containing polymer, which is the main component, may be used as the plant stimulant of the present disclosure as is, or the optional components described above may be blended therein. Known additives may also be blended within a range that does not impair the effects of the present disclosure. Examples of such additives include excipients, fluidizers, binders, disintegrants, lubricants, dispersants, surfactants, thickeners, pH adjusters, colorants, solubilizers, fragrances, coating agents, etc. To accurately retain a small amount of water and maintain the effect, a highly water-absorbent polymer may be added. Examples include cross-linked acrylates and cross-linked carboxymethylcellulose salts. From the viewpoint of biodegradability, cross-linked carboxymethylcellulose salts are preferred, and from the viewpoint of preventing salt damage, cross-linked carboxymethylcellulose potassium salt and acid-type cross-linked carboxymethylcellulose are even more preferred. For example, the product name "Gelfine" manufactured by Daicel Miraize Corporation is exemplified.

When the acetic acid sustained-release plant stimulant of the present disclosure contains optional ingredients or additives, the optional ingredients or additives can be incorporated by the following method.

The plant stimulant of the present disclosure can be obtained by mixing the acetyl group-containing polymer, optional components, or additives with a solvent such as acetone and then removing the solvent. Alternatively, the plant stimulant of the present disclosure may be obtained by melting the acetyl group-containing polymer and kneading it with the additives.

As long as the effects of the present disclosure can be obtained, the method for producing the acetyl group-containing polymer is not particularly limited, and a polymer having the desired molecular weight and acetyl group content can be produced by a conventionally known method. Commercially available acetyl group-containing polymers with various molecular weights and acetyl group contents may also be appropriately selected and used.

Below, we will explain the production method using cellulose acetate, a typical acetyl group-containing polymer, as an example. One method for producing cellulose acetate is the so-called acetic acid process, which uses acetic anhydride as the acetylating agent, acetic acid as the diluent, and sulfuric acid as the catalyst. The basic production process of the acetic acid process includes: (1) a pretreatment step in which a pulp raw material (dissolving pulp) with a relatively high α-cellulose content is disintegrated and crushed, and then acetic acid is sprayed and mixed; (2) an acetylation step in which the pretreated pulp from (1) is reacted with a mixed acid consisting of acetic anhydride, acetic acid, and an acetylation catalyst (e.g., sulfuric acid); (3) an aging step in which the cellulose acetate is hydrolyzed to the desired acetylation level; and (4) a post-treatment step in which the cellulose acetate after the hydrolysis reaction is precipitated and separated from the reaction solution, purified, stabilized, and dried.

Cellulose acetate with the desired degree of acetyl substitution can be obtained by adjusting the time, temperature, etc., of the aging process. After the aging process, the reaction system is cooled to room temperature, and a precipitating solvent is added to precipitate cellulose acetate. The resulting precipitate (solid) is washed and neutralized with an organic solvent containing a basic substance to remove impurities such as the catalyst (e.g., sulfuric acid) used in the aging process. This organic solvent is a poor solvent for cellulose acetate, and examples of such organic solvents include alcohols such as methanol and ketones such as acetone. Examples of basic substances include alkali metal compounds (alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium bicarbonate; alkali metal carboxylates such as sodium acetate and potassium acetate; sodium alkoxides such as sodium methoxide and sodium ethoxide), and alkaline earth metal compounds (alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; alkaline earth metal carbonates such as magnesium carbonate and calcium carbonate; alkaline earth metal carboxylates such as magnesium acetate and calcium acetate; alkaline earth metal alkoxides such as magnesium ethoxide).

After washing and neutralization, cellulose acetate is usually in flake form, but if necessary, it can be ground, sieved, or granulated after or before drying to adjust the BET specific surface area or particle size to the desired value.

For grinding, conventional grinders such as a sample mill, hammer mill, turbo mill, atomizer, cutter mill, bead mill, ball mill, roll mill, jet mill, pin mill, etc. can be used. Freeze grinding, dry grinding at room temperature, or wet grinding may also be used. Due to their superior grinding processing capacity, a hammer mill or turbo mill is preferred.

For example, when milling using a screen, from the viewpoint of improving the decomposition rate of the resulting powder, the screen diameter is preferably 2.0 mm or less, more preferably 1.0 mm or less, and even more preferably 0.5 mm or less. From the viewpoint of ease of handling and improved storage stability, for example, prevention of dust explosions, the screen diameter is preferably 0.06 mm or more.

[Application]
The acetic acid sustained-release plant stimulant according to the present disclosure can stably release acetic acid over a long period of time, regardless of weather conditions such as rainfall. The acetic acid released from this plant stimulant improves plant resistance to abiotic stresses such as drought and heat. The plant stimulant according to the present disclosure may be used as an agricultural material for agricultural or horticultural crops.

The disclosed method for improving plant resistance to abiotic stress includes applying the aforementioned acetic acid sustained-release plant stimulant to the plant or the plant's growing environment. According to this method, a single dose of the plant stimulant results in a stable release of acetic acid over an extended period of time, eliminating the need for continuous administration of the plant stimulant. This results in labor savings and cost reductions.

Furthermore, the method disclosed herein allows for the adjustment of the form (specific surface area, particle size, etc.), acetyl group content, and molecular weight of the plant stimulant (particularly the acetyl group-containing polymer that is the main component) to achieve the desired acetic acid release rate depending on the type of plant being cultivated and the growing environment. Furthermore, when a cellulose derivative is used as the main component, the inherent biodegradability of cellulose derivatives also results in a lower environmental impact compared to other synthetic polymers.

The effects of the present disclosure will be demonstrated through the following examples, but the present disclosure should not be interpreted in a limited manner based on the description of these examples.

[Physical property measurement method]
(a) BET Specific Surface Area The BET specific surface area was measured by the continuous flow BET single-point method using an "AMS8000 Type Fully Automatic Powder Specific Surface Area Measurement Device" manufactured by Ohkura Riken. Nitrogen was used as the adsorption gas, and helium was used as the carrier gas. Specifically, the sample was heated and degassed in nitrogen gas at 150°C, and then cooled to liquid nitrogen temperature to adsorb nitrogen gas onto the sample. The sample was then warmed to room temperature, causing the nitrogen gas adsorbed onto the sample to desorb and be detected with a thermal conductivity detector. The specific surface area of the sample was calculated using the amount of desorbed nitrogen detected.

(b) Moisture Content: 1.0 g of a sample was weighed out and vacuum dried at 80°C for 3 hours to determine the loss on drying. The ratio of the loss to the sample weight before drying was calculated as the moisture content (unit: wt%).

(Test 1)
In Test 1, the amount of acetic acid produced by the acetic acid sustained-release plant stimulant of the present disclosure was measured using artificial soil.

[Experimental Example A-1]
First, cellulose acetate flakes (acetyl substitution degree: 2.5, weight average molecular weight: 2,2000) were pulverized using a Makino pulverizer (manufactured by Makino Sangyo Co., Ltd., model number: DD-2-3.7). The BET specific surface area of the cellulose acetate powder after pulverization was 5.2 m ² /g. The plant stimulant of Experimental Example A-1 was then obtained by storing the cellulose acetate powder for 2 days in an environment at a temperature of 23°C and a humidity of 60% RH. The water content of the obtained plant stimulant was 4.7% by weight.

Next, approximately 100 g of glass beads (Kenis Co., Ltd., product name "G15", 14.5-15.5 mm diameter) and 300 ml of ion-exchanged water were placed in a 500 ml Erlenmeyer flask, and the mixture was shaken at room temperature for 24 hours using a rotary shaker (Taitec Co., Ltd., product name "NR2") at a shaking speed of 40 r/min and an amplitude of 25 mm. After shaking twice under the same conditions, the mixture was dried in a vacuum dryer at 80°C for 24 hours to obtain artificial soil.

The plant stimulant was added to an Erlenmeyer flask containing 100 g of the resulting artificial soil in an amount equivalent to 12 g of cellulose acetate in solids, and the flask was then sealed to obtain a sample. A total of eight samples were prepared in the same manner, and an accelerated test was performed by leaving them at 70°C. After leaving them for 0, 1 , 4 , 6 , 8 , 11 , 14 , and 18 days , each sample was removed and the amount of free acetic acid generated over time was measured. The measurement results are shown in Table 2 below. The values in Table 2 are the cumulative amount of free acetic acid (unit: ppm).

The amount of free acetic acid was measured by high performance liquid chromatography (HPLC). Specifically, 300 ml of pure water was added to the sample after a predetermined time had elapsed, and the sample was shaken for 4 hours at room temperature with a shaking speed of 40 r/min and an amplitude of 25 mm using the rotary shaker described above. The supernatant was then collected and analyzed by HPLC under the following analytical conditions:
Column: Shimadzu GLC "ULTRON PS80H" and guard column (length 50 mm)
Column temperature: 60°C
Eluent: Perchloric acid aqueous solution (pH 1.8)
Flow rate: 1.5ml/min
Detector: UV detector (wavelength 210 nm)
Injection volume: 50 μl

[Experimental Examples A-2 to A-4]
The moisture content and the amount of free acetic acid in the artificial soil of the plant stimulants obtained in Experimental Examples A-2 to A-4 were measured in the same manner as in Experimental Example A-1, except that the storage conditions were as shown in Table 1 below. The results obtained are shown in Tables 1 and 2 below, respectively.

In Table 1, storage conditions A-1 are models of mild weather conditions, storage conditions A-2 are models of hot and humid weather conditions, and storage conditions A-3 and A-4 are models of weather conditions that simulate rainfall. As shown in Table 2, it was confirmed that the plant stimulant of the present disclosure stably released acetic acid for 18 days in an accelerated test at 70°C under all weather conditions. Note that 18 days in an accelerated test at 70°C is equivalent to 144 days at 40°C.

(Test 2) Drought Tolerance Test In Test 2, the effect of the acetic acid sustained-release plant stimulant of the present disclosure on plant growth under dry conditions was evaluated. Note that the cellulose acetate used in Examples 1 and 2 was prepared by pulverizing flakes having an acetyl substitution degree of 2.5 and a weight-average molecular weight of 20,000 so as to pass through a screen with a diameter of 0.5 mm.

[Example 1]
First, 10 premium cherry tomato seedlings (CF Petit Puyo) were grown in 9 cm diameter plastic pots (0.3 L capacity) in a greenhouse for 2 weeks. The greenhouse was ventilated to maintain a maximum temperature of 25-30°C and a minimum temperature of 12-15°C. During the cultivation period, watering was performed only after the soil in the pots had dried, and watering continued until water began to flow from the bottom of the plastic pot into the bottom watering tray.

Next, each plastic pot was transferred to a dry water tray, and excess water was removed by gravity from the bottom. After that, 10 g of cellulose acetate was sprayed around the base of each plant in the plastic pot as a plant stimulant, and 50 ml of ion-exchanged water was added.

The plants were then grown for three days without watering in a greenhouse with ventilation turned off. The temperature inside the greenhouse over these three days was a maximum of 45°C and a minimum of 28°C. Water was then added until water began to flow from the bottom of each plastic pot into the bottom water supply tray, the greenhouse's ventilation system was turned on, and the condition of the tomatoes in each pot was observed two days later. The number of surviving seedlings out of a total of 10 seedlings was counted and the survival rate (%) was calculated. The results are shown in Table 3 below.

[Example 2]
The survival rate (%) of tomatoes was determined in the same manner as in Example 1, except that 6 hours after the cellulose acetate and ion-exchanged water were added to the pots, 254 ml of ion-exchanged water was showered onto the pots over a period of 2 hours. The results are shown in Table 3 below.

[Comparative Example 1]
The survival rate (%) of tomatoes was determined in the same manner as in Example 1, except that cellulose acetate was not sprayed. The results are shown in Table 3 below.

[Comparative Example 2]
The survival rate (%) of tomatoes was determined in the same manner as in Example 1, except that 50 ml of an aqueous solution of acetic acid with a concentration of 0.06 vol % was used instead of cellulose acetate and ion-exchanged water. The results are shown in Table 3 below.

[Comparative Example 3]
The survival rate (%) of tomatoes was determined in the same manner as in Comparative Example 2, except that 6 hours after the acetic acid solution was added to the pots, 254 ml of ion-exchanged water was showered onto the pots over a period of 2 hours. The results are shown in Table 3 below.

[Comparative Example 4]
The survival rate (%) of tomatoes was determined in the same manner as in Comparative Example 2, except that 6 hours after the acetic acid solution was added to the pots, 63.5 ml of ion-exchanged water was showered onto the pots over a period of 2 hours. The results are shown in Table 3 below.

Example 2, Comparative Example 3, and Comparative Example 4 are rainfall models, and the amount of additional water in Table 3 corresponds to the amount of rainfall after application of the plant stimulant. Example 2 and Comparative Example 3 correspond to weather conditions in which heavy rain of 20 mm/hr per unit area continued for a pot with a diameter of 9 cm (area of approximately 63.6 cm ² ). Comparative Example 4 corresponds to weather conditions in which light rain of 5 mm/hr per unit area continued.

As shown in Table 3, Examples 1 and 2, which used the plant stimulant of the present disclosure, showed significantly better plant growth conditions than Comparative Example 1, in which no plant stimulant was applied. On the other hand, the results of Comparative Examples 3 and 4 show that while applying an aqueous acetic acid solution improves the drought tolerance of plants, this effect is lost when rain falls after application. These evaluation results clearly demonstrate the superiority of the present disclosure.

The plant stimulants and methods described above can be applied to a variety of plant growth environments.

Claims (13)

The composition contains an acetyl group-containing polymer as a main component,
The flaky acetic acid sustained-release plant stimulant, wherein the acetyl group-containing polymer has a BET specific surface area of 1.0 m ² /g or more and 6.0 m ² /g or less . The acetic acid sustained-release plant stimulant according to claim 1, wherein the acetyl group-containing polymer is one or more selected from the group consisting of cellulose derivatives in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups, vinyl acetate polymers, and modified starches in which some of the hydroxyl groups of glucose have been substituted with acetyl groups. The acetic acid sustained-release plant stimulant according to claim 1 or 2, wherein the acetyl group-containing polymer comprises a cellulose derivative in which some of the hydroxyl groups of cellulose have been substituted with acetyl groups. The acetic acid sustained-release plant stimulant according to claim 3, wherein the cellulose derivative is cellulose acetate. The acetic acid sustained-release plant stimulant according to claim 4, wherein the acetyl substitution degree of the cellulose acetate is 1.3 or more and 2.9 or less. The acetic acid sustained-release plant stimulant according to any one of claims 1 to 5, wherein the content of the acetyl group-containing polymer is 80% by weight or more based on the total weight. further comprising acetic acid,
The acetic acid sustained-release plant stimulator according to any one of claims 1 to 6, wherein the total amount of the acetyl group-containing polymer and acetic acid is 90% by weight or more based on the total weight. further comprising an alkali metal or alkaline earth metal;
The acetic acid sustained-release plant stimulant according to any one of claims 1 to 7, wherein the total content of the alkali metal and alkaline earth metal is 0.001% or more and 0.300% or less based on the total weight. The acetic acid sustained-release plant stimulator according to any one of claims 1 to 8, wherein the acetyl group content of the acetyl group-containing polymer is 25.0 mass% or more in terms of acetic acid. The acetic acid sustained-release plant stimulant according to any one of claims 1 to 9, wherein the weight average molecular weight Mw of the acetyl group-containing polymer is 10,000 or more and 1,000,000 or less. The acetic acid sustained-release plant stimulant according to any one of claims 1 to 10, wherein the molecular weight distribution Mw/Mn of the acetyl group-containing polymer is 1.0 or more and 6.0 or less. Further containing water,
The acetic acid sustained-release plant stimulant according to any one of claims 1 to 11, wherein the water concentration in the acetic acid sustained-release plant stimulant is 1% by weight or more and 10% by weight or less. A method for improving plant resistance to abiotic stress, comprising applying the acetic acid sustained-release plant stimulant according to any one of claims 1 to 12 to the growing environment of a plant.