JP7598145B2 - Plant disease control agent and plant disease control method - Google Patents

Description

The present invention relates to a plant disease control agent and a plant disease control method. The plant disease control agent and the plant disease control method of the present invention have the advantages of being low cost and highly safe.

Once soil-borne plant diseases occur, they are difficult to eradicate, and they can spread not only to the area around the initial outbreak but to the entire production area and surrounding areas. In general, measures to combat soil diseases are taken to reduce damage by using resistant varieties, disinfecting the soil, and improving the physicochemical and biological properties of the soil, but sometimes it is necessary to change the cropping season, switch to crops that have less impact, or leave the land fallow.

Chemically synthesized fumigants have mainly been used to disinfect soil to prevent crop failure caused by soil diseases, but due to factors such as the impact on the target fields and surrounding environment, the burden on workers, and product image strategies, there is a demand for the development of new countermeasure technologies that do not rely on existing soil fumigants.

However, the development of new synthetic chemical pesticides and microbial pesticides requires a large amount of research and development costs, and it is said to take more than 10 years from the discovery of new compounds and useful microorganisms to safety evaluation, residual and effectiveness testing, registration of the pesticide, and launch on the market, so there is a demand for the development of lower-cost countermeasure technologies. Meanwhile, specified pesticides (specified control materials) such as vinegar are defined in Article 2, Paragraph 1 of the revised Agricultural Chemicals Control Act as "pesticides designated by the Minister of Agriculture, Forestry and Fisheries and the Minister of the Environment as those that, in light of their raw materials, are clearly not likely to cause harm to agricultural crops, human livestock, or aquatic animals and plants," and it is expected that they will be further utilized for pest control as low-cost agents that can be used immediately in agricultural production sites.

The use of resistant varieties and rootstocks and various soil disinfections have been introduced as core technologies to combat soil diseases, and the development of control agents is also underway for some soil diseases. Regarding tomato bacterial wilt (pathogen: Ralstonia solanacearum), one of the important soil diseases, prior patents relating to treatment agents for plants include "Disease control microorganisms and disease control method for solanaceae crops" (Patent Document 1) and "Bacterial wilt resistance inducer and bacterial wilt control method" (Patent Document 2).

On the other hand, in the case of using vinegar to control plant diseases, "Control of rice seedling diseases using vinegar" (Non-Patent Document 1) and a method of using vinegar to dilute German Bordeaux A for vegetable seed disinfection (Non-Patent Document 2) have been developed. In addition, pure brown rice black vinegar (manufactured by Kewpie Brewing Co., Ltd.) is sold for general agricultural horticulture use, and the usage method is described as "controlling diseases such as bacterial wilt and root rot in tomatoes by irrigating the soil with a 50-fold diluted solution." In addition, prior patents related to disease control using vinegar include "Post-harvest disease control agent and post-harvest disease control method" (Patent Document 3), "Rice disease control method" (Patent Document 4), "Plant vitalizer and crop cultivation method using said plant vitalizer" (Patent Documents 5 and 6), and "Seaweed disease control agent and seaweed disease control method" (Patent Document 7).

Japanese Patent Application Laid-Open No. 01-090107 Patent No. 6007360 JP 2017-165654 A Patent No. 3990691 JP 2001-061344 A JP 2001-064112 A Patent No. 3629049

Junko Sekihara, Toshiyuki Morikawa, "Control of rice seedling diseases using vinegar", Plant Protection, Vol. 63, No. 11 (2009), pp. 690-694 National Agriculture and Food Research Organization, Vegetable and Tea Research Institute, "Manual for Control of Bacterial Fruit Spot Disease of Cucurbitaceae Vegetables (For Seed Production and Inspection)" (2009), p.1-22. http://www.naro.affrc.go.jp/publicity_report/publication/files/uri-2.pdf

Generally, measures to combat soil-based diseases are being promoted by developing and introducing resistant varieties and rootstocks, but the types of diseases for which varieties and rootstocks with strong resistance can be developed are limited. There are also cases where new races emerge, and multiple races or types of soil diseases occur together in a single field, and responses to these are also required. Furthermore, there are problems such as recontamination of the soil with pathogens from deep soil layers or from the surrounding areas after soil disinfection, and there is a need to develop control methods that can be applied after planting in the field.

Regarding tomato bacterial wilt, new grafting methods and soil reduction disinfection methods (Nakayasu et al., 2019) have been developed, but there is a demand for simpler and lower-cost techniques than conventional techniques. Among these, methods such as immersing tomato seedlings in a solution of non-pathogenic Fusarium bacteria (JP Patent Publication No. 01-090107) and histidine, a type of amino acid (Patent Publication No. 6007360, Seo et al., 2016) have been developed and are considered promising, but there is a need to develop even lower-cost control techniques to expand user options.

The present invention was made against this technical background, and aims to provide a means of controlling plant diseases that is low-cost and can be immediately used in agricultural production sites.

As a result of intensive research to solve the above problems, the inventors have found that tomato bacterial wilt can be controlled by immersing the roots of tomato seedlings in a diluted vinegar solution. The inventors have also found that tomato bacterial wilt can be controlled even at a low concentration of diluted vinegar that does not exhibit antibacterial activity against the bacterial wilt bacterium. Furthermore, the inventors have also found that by immersing the roots of tomato seedlings in a diluted vinegar solution and irrigating the seedlings at the base of the potted plant with the diluted vinegar solution, the control effect is significantly improved compared to when only the roots are immersed. Furthermore, the inventors have found that immersing the roots of komatsuna seedlings in a diluted vinegar solution can also control komatsuna downy mildew. The present invention was completed based on the above findings.

That is, the present invention provides the following (1) to (13).
(1) A plant disease control agent for root dipping, which contains acetic acid.

(2) The plant disease control agent for root dipping according to (1), characterized in that the plant disease is bacterial wilt.

(3) The plant disease control agent for root immersion according to (1), characterized in that the plant is a tomato and the plant disease is tomato bacterial wilt.

(4) A plant disease control agent for root dipping according to (1), characterized in that the plant disease is downy mildew.

(5) The plant disease control agent for root immersion according to (1), characterized in that the plant is komatsuna and the plant disease is komatsuna downy mildew.

(6) A plant disease control agent for root immersion according to any one of (1) to (5), characterized in that the concentration of acetic acid is 0.004 to 0.4 v/v%.

(7) A method for controlling plant diseases, comprising the step of immersing the roots of a plant in an aqueous solution of acetic acid.

(8) The method for controlling a plant disease according to (7), characterized in that the plant disease is bacterial wilt.

(9) The method for controlling a plant disease according to (7), characterized in that the plant is a tomato and the plant disease is tomato bacterial wilt.

(10) The method for controlling a plant disease according to (7), characterized in that the plant disease is downy mildew.

(11) The method for controlling a plant disease according to (7), characterized in that the plant is komatsuna and the plant disease is komatsuna downy mildew.

(12) A plant disease control method according to any one of (7) to (11), characterized in that the concentration of acetic acid is 0.004 to 0.4 v/v%.

(13) The method for controlling plant diseases according to any one of (7) to (12), further comprising a step of irrigating the soil in which the plant, the roots of which have been immersed in the acetic acid solution, is grown.

The present invention provides a novel plant disease control agent and a novel method for controlling plant diseases. The plant disease control agent and the method for controlling plant diseases of the present invention have the advantages of being low cost and highly safe.

A graph showing the disease-reducing effect of tomato bacterial wilt caused by root soaking and irrigation with a diluted grain vinegar solution. In the graph, - indicates the distilled water treatment area, and + indicates the grain vinegar diluted solution (x 1/100) treatment area. FIG. 1 is a graph showing the disease-reducing effect of tomato bacterial wilt caused by root immersion in a mixed solution of acetic acid and amino acids. Only root immersion was performed. A graph showing the effect of various vinegar treatments in reducing the incidence of bacterial wilt in tomatoes. Root soaking and irrigation were used in combination. Graph showing the disease-reducing effect of root immersion treatment with a diluted grain vinegar solution. Only root immersion treatment was performed.

The present invention will be described in detail below.
(1) Plant Disease Control Agent for Root Dipping The plant disease control agent for root dipping of the present invention is characterized by containing acetic acid.

In the present invention, "plant disease control agent for root immersion" means a plant disease control agent used for immersing the roots of a plant to be controlled.

The plant disease control agent of the present invention for root dipping can be used, for example, to drench the roots of a plant seedling before transplanting the seedling into a farm field or the like.

Acetic acid may be commercially available as a reagent, or it may be acetic acid contained in foods such as vinegar (grain vinegar, rice vinegar, fruit vinegar, etc.).

There are no particular limitations on the concentration of acetic acid, so long as it provides a control effect and does not adversely affect the roots of the plant. The specific concentration can be determined according to the type of plant or disease, the immersion time, etc., but it is preferably 0.004 to 0.4 v/v%, more preferably 0.01 to 0.1 v/v%, and even more preferably 0.02 to 0.08 v/v%.

The plant disease control agent for root immersion of the present invention may contain components other than acetic acid. Since the plant disease control agent for root immersion of the present invention can be prepared from vinegar, it may contain components in vinegar other than acetic acid (e.g., various amino acids, organic acids other than acetic acid). In addition, the plant disease control agent for root immersion of the present invention may contain components generally contained in plant disease control agents, such as fertilizer components, plant activators, growth promoters, pH adjusters, surfactants, antifoaming agents, suspending agents, stabilizers, etc.

The plant disease to be controlled is not particularly limited, and for example, soil-borne diseases can be controlled. Specific examples include bacterial wilt and downy mildew. Examples of bacterial wilt include tomato bacterial wilt, eggplant bacterial wilt, potato bacterial wilt, and pepper bacterial wilt, while examples of downy mildew include komatsuna downy mildew, cabbage downy mildew, cucumber downy mildew, onion downy mildew, and grape downy mildew. As shown in the examples described below, the plant disease control agent for root immersion of the present invention is effective not only against bacterial wilt but also against downy mildew, which is a disease completely different from bacterial wilt (bacterial wilt is a disease caused by bacteria, and downy mildew is a disease caused by oomycetes). From this, it is considered that the plant disease control agent for root immersion of the present invention is effective not only against specific diseases but also against a wide range of diseases.

There are no particular limitations on the plants that can be controlled, and include tomato, wolfberry, lycium barbarum, ground cherry, eggplant, potato, chili pepper, tobacco, Datura stramonium, and Tsukubaneagao (Solanaceae), komatsuna, Arabidopsis, rapeseed, cabbage, broccoli, Chinese cabbage, and wasabi (Brassicaule), banana, musa, and Heliconia (Musaceae), mint, such as perilla, basil, and salvia, ginger, myoga, and kuzu (Chinese ginger), and other plants from the Solanaceae family. Examples of plants that can be mentioned include plants of the Zingiberaceae family (such as lucuma), Asteraceae family (such as chrysanthemum, dahlia, sycamore, and sunflower), Rosaceae family (such as strawberry), Fabaceae family (such as peanut and kidney bean), Myrtaceae family (such as clove), Pedaliaceae family (such as sesame), Mulberry family (such as mulberry), Ornithaceae family (such as Strelitzia), Euphorbiaceae family (such as cassava), Plumeriaceae family (such as statice), Gentianaceae family (such as lisianthus), and Cucurbitaceae family (such as cucumber). As shown in the examples described below, the plant disease control agent for root immersion of the present invention is effective not only for tomatoes but also for Japanese mustard spinach (tomatoes belong to the Solanaceae family, and Japanese mustard spinach belongs to the Brassicaceae family), which is not closely related to tomatoes. From this, it is considered that the plant disease control agent for root immersion of the present invention is effective not only for specific plants but also for a wide range of plants.

(2) Plant Disease Control Method The plant disease control method of the present invention is characterized by comprising a step of immersing roots of a plant in an aqueous acetic acid solution.

Acetic acid may be commercially available as a reagent, or it may be acetic acid contained in foods such as vinegar (grain vinegar, rice vinegar, fruit vinegar, etc.).

The concentration of acetic acid in the aqueous acetic acid solution is not particularly limited as long as it is within a range that provides a control effect and does not adversely affect the roots of the plant. The specific concentration can be determined according to the type of plant or disease, the immersion time, etc., but is preferably 0.004 to 0.4 v/v%, more preferably 0.01 to 0.1 v/v%, and even more preferably 0.02 to 0.08 v/v%.

The acetic acid aqueous solution may contain components other than acetic acid. Since the acetic acid aqueous solution can be prepared from vinegar, it may contain components in vinegar other than acetic acid (e.g., various amino acids, organic acids other than acetic acid). In addition, the acetic acid aqueous solution may contain components that are generally contained in plant disease control agents, such as fertilizer components, plant activators, growth promoters, pH adjusters, surfactants, antifoaming agents, suspending agents, and stabilizers.

The time for immersion in the acetic acid aqueous solution is not particularly limited as long as it provides a control effect and does not adversely affect the roots of the plant. The specific time can be determined depending on the type of plant or disease, the acetic acid concentration, etc., but it is preferably 10 to 120 hours, more preferably 20 to 100 hours, and even more preferably 30 to 80 hours.

The plant disease to be controlled is not particularly limited, and for example, soil-borne diseases can be controlled. Specific examples include bacterial wilt and downy mildew. Examples of bacterial wilt include tomato bacterial wilt, eggplant bacterial wilt, potato bacterial wilt, and bell pepper bacterial wilt, while examples of downy mildew include komatsuna downy mildew, cabbage downy mildew, cucumber downy mildew, onion downy mildew, and grape downy mildew. As with the plant disease control agent for root immersion of the present invention, the plant disease control method of the present invention is effective not only against specific diseases but also against a wide range of diseases.

There are no particular limitations on the plants that can be controlled, and include tomato, wolfberry, lycium barbarum, ground cherry, eggplant, potato, chili pepper, tobacco, Datura stramonium, and Tsukubaneagao (Solanaceae), komatsuna, Arabidopsis, rapeseed, cabbage, broccoli, Chinese cabbage, and wasabi (Brassicaule), banana, musa, and Heliconia (Musaceae), mint, such as perilla, basil, and salvia, ginger, myoga, and kuzu (Chinese ginger), and other plants from the Solanaceae family. Examples include plants of the Zingiberaceae family such as lucuma, Asteraceae family such as chrysanthemum, dahlia, sycamore, and sunflower, Rosaceae family such as strawberry, Fabaceae family such as peanut and kidney bean, Myrtaceae family such as clove, Pedaliaceae family such as sesame, Mulberry family such as mulberry, Strelitzia reginae family such as Strelitzia, Euphorbiaceae family such as cassava, Plumeriaceae family such as statice, Gentianaceae family such as lisianthus, and Cucurbitaceae family such as cucumber. As with the plant disease control agent for root immersion of the present invention, the plant disease control method of the present invention is effective not only for specific plants but also for a wide range of plants.

The plant disease control method of the present invention may further include a step of irrigating the soil in which the plant, the roots of which have been immersed in the acetic acid solution, is grown with the acetic acid solution.

The acetic acid solution used for irrigation can be the same as the one used for soaking the roots.

There are no particular limitations on the amount of irrigation, so long as it provides a control effect and does not adversely affect the plant. The specific amount can be determined according to the type of plant or disease, the size of the plant, the acetic acid concentration, etc., but it is preferable to use 1 to 100 ml per plant, more preferably 10 to 80 ml, and even more preferably 20 to 50 ml.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1: Effect of root immersion and irrigation with diluted grain vinegar on the occurrence of bacterial wilt in tomatoes Seedling cell trays (cell size 25 mm square × depth 45 mm, Yanmar Holdings) were filled with seedling soil (organic horticultural soil, Kanto Nosan), tomato "Momotaro" (Takii Seed) was sown, and seedlings were grown in a greenhouse. Starting two weeks after sowing, a 500-fold diluted solution of Hyponex concentrate (Hyponex Japan) was applied once a week instead of irrigation, and after the plants had grown to about two true leaves, they were cultivated by bottom watering. Tomatoes were grown to about three true leaves, and the roots extending from the bottom of the cell tray were cut with scissors. 5 × 5 cells (total of 25 cells) were transferred to a polypropylene tray (320 × 230 × 52 mm, AS ONE) with the seedlings still in the tray. 1 L of grain vinegar (Mizkan Holdings) diluted 100 times (v/v) with distilled water or 1 L of grain vinegar (Mizkan Holdings) diluted 100 times (v/v) with distilled water was poured into the tray to start the root immersion treatment. After the root immersion treatment of the seedlings was performed for a specified period, the roots of the seedlings were immersed for 1 minute in a suspension of the tomato wilt bacteria (strain 8107R) of a specified concentration, and each seedling was potted in a 7.5 cm diameter pot filled with culture soil (Nippi Engei Baido No. 1, Nippon Hyogi). The day after inoculation with the pathogen, 30 ml of grain vinegar diluted 100 times (v/v) with distilled water was irrigated at the base of the tomato. Thereafter, the plants were cultivated with bottom watering, and 21 days after inoculation, the presence or absence of disease (wilting symptoms) in the aboveground parts of the tomatoes was examined. The experiment was conducted three times, and the average percentage of diseased plants in each treatment was calculated. The results are shown in Figure 1. Twelve tomato plants were used for each treatment. The root immersion treatment period for the seedlings was 2 days (first experiment) or 3 days (second and third experiments), and the concentration of the tomato bacterial wilt pathogen was 1.5 x ¹⁰⁷ cfu/ml (first experiment), 1.3 x ¹⁰⁷ cfu/ml (second experiment), or 1.7 x ¹⁰⁷ cfu/ml (third experiment). The average temperatures in the greenhouse after inoculation were 20.9°C (first experiment), 19.9°C (second experiment), and 20.2°C (third experiment).

As shown in Figure 1, the onset of bacterial wilt was suppressed by immersing the roots of tomato seedlings in a diluted grain vinegar solution. In addition, the control effect was further increased by irrigating the base of the seedlings with a diluted grain vinegar solution after potting.

Example 2: pH of grain vinegar and antibacterial activity against bacterial wilt The pH of the original grain vinegar solution or the solution diluted 10 to 10,000 times (v/v) with distilled water was measured with a pH meter (B-712, Horiba, Ltd.). In addition, tomato bacterial wilt was cultured on a Yeast Pepton Agar (hereinafter referred to as YPA, yeast _extract 5g/L, peptone 10g/L, _{Na2HPO4.12H2O} 4g/L, _{KH2PO4 0.5g} /L, _agar 15g/L, distilled water 1L) slant medium for 3 days, and suspended in a small amount of sterile distilled water to obtain a pathogen liquid. After heating and dissolving, the pathogen liquid was added in an amount of 1/100 (v/v) to the YPA medium cooled to about 50°C, stirred, and poured into a sterile petri dish with a diameter of 9 cm, and solidified to prepare a plate. Sterilized paper disks (diameter 8 mm, thin, ADVANTEC) were placed on plates, and 20 μl of undiluted grain vinegar or a solution diluted 10 and 100 times (v/v) with sterile distilled water was dropped onto the paper disks, and the plates were incubated at 30°C in the dark for 2 days. If a growth inhibition zone was visually observed around the paper disk, it was judged that there was antibacterial activity against the pathogen, and if not, there was no antibacterial activity. The results are shown in Table 1.

As shown in Table 1, the 100-fold diluted grain vinegar, which was confirmed to have a preventive effect against tomato bacterial wilt by root immersion treatment, did not show any antibacterial activity. From this, it is speculated that the reason for the preventive effect is due to factors other than direct antibacterial activity.

Example 3 Effect of treatment with acetic acid and amino acid solution on the reduction of tomato bacterial wilt disease occurrence In the same manner as in Example 1, "Momotaro" tomato seedlings were grown in a cell tray until they had about three true leaves. The roots that had grown from the bottom of the cell tray were cut off with scissors. 15 seedlings were transferred to a new cell tray (5 x 5 cells). The seedlings were then placed in a polypropylene tray (320 x 230 x 52 mm, AS ONE). After that, the seedlings were soaked in a solution of distilled water or grain vinegar diluted 100 times (v/v) with distilled water, 0.042 v/v% acetic acid*, amino acid mixture solution** (0.87 mg/L L-leucine, 0.86 mg/L (+)-arginine, 0.37 mg/L L-alanine, 0.36 mg/L L-serine, 0.37 mg/L L-valine), acetic acid/amino acid mixture solution (0.042 v/v% acetic acid, 0.87 mg/L Root immersion treatment was started by pouring 1.5L of a 100% aqueous solution of 0.1 mg/L L-leucine, 0.86 mg/L (+)-arginine, 0.37 mg/L L-alanine, 0.36 mg/L L-serine, and 0.37 mg/L L-valine. After 3 days of root immersion treatment, each seedling was potted in a 7.5 cm diameter pot filled with culture soil, and inoculated by irrigating the base of each seedling with 30 ml of a suspension of the tomato bacterial wilt pathogen at a concentration of 1 x ¹⁰⁸ cfu/ml. After that, the seedlings were managed by bottom watering, and the presence or absence of disease (wilting symptoms) in the above-ground parts of the tomatoes was investigated after a specified period of time had passed since the inoculation.

* We requested Tsukuba Food Evaluation Center to analyze the organic acids contained in grain vinegar (undiluted solution), and found that the main organic acid was acetic acid at 4.23g/100g. Since the specific gravity of vinegar and acetic acid is approximately 1.0g/ml, acetic acid (special reagent grade, Fujifilm Wako Pure Chemical) was adjusted with distilled water to 0.042v/v%, which is the concentration contained in grain vinegar (100 times diluted solution), and used for the test.

※※ We requested Tsukuba Food Evaluation Center to analyze the free amino acids contained in grain vinegar (undiluted solution), and found that the top amino acids in terms of molar concentration were 0.66 mM leucine, 0.49 mM arginine, 0.42 mM alanine, 0.34 mM serine, and 0.32 mM valine. For these five amino acids, an amino acid mixture solution containing 0.87 mg/L L-leucine, 0.37 mg/L L-alanine, 0.36 mg/L L-serine, and 0.37 mg/L L-valine (the above four amino acids are special grade reagents, Fujifilm Wako Pure Chemical Industries), which corresponds to the concentration contained in grain vinegar (100 times diluted solution), and 0.86 mg/L L(+)-arginine (Wako special grade, Fujifilm Wako Pure Chemical Industries), was prepared with distilled water and used for the test.

The test was carried out three times, and the average rate of diseased plants in each treatment area was calculated. The results are shown in Figure 2. Twelve tomato plants were used for each treatment area. The presence or absence of disease was investigated 14 days (first test) or 21 days (second and third tests) after inoculation of the pathogen. The average temperatures in the greenhouse after inoculation of the pathogen were 22.8°C (first test), 19.6°C (second test), and 21.5°C (third test).

As shown in Figure 2, the onset of tomato bacterial wilt was suppressed by immersing the roots of tomato seedlings in a 0.042% acetic acid solution, which is the same concentration as the acetic acid contained in the grain vinegar (100 times diluted solution). This suggests that acetic acid is involved in the control effect of root immersion in the diluted grain vinegar solution.

Example 4: Effect of various food vinegar treatments on the reduction of tomato bacterial wilt disease As in Example 1, tomato "Momotaro" seedlings were grown in cell trays until they had about 3-4 true leaves, and the roots were pruned. They were then placed in a tray and 1L of distilled water or grain vinegar diluted 100 times (v/v) with distilled water, rice vinegar* (Mizkan Holdings) diluted 107 times (v/v), or apple cider vinegar* (Mizkan Holdings) diluted 119 times (v/v) was poured into the tray to start root immersion treatment. After root immersion treatment of the seedlings for 3 days, the roots were immersed in a suspension of tomato bacterial wilt bacteria of a given concentration as in Example 1, and the seedlings were potted up one by one in a 7.5 cm diameter pot filled with culture soil. The day after inoculation with the pathogen, 30ml each of distilled water or grain vinegar, rice vinegar, and apple cider vinegar diluted to the same concentration as above was irrigated at the base of the tomato. Thereafter, the plants were cultivated with bottom watering, and 14 days after inoculation of the pathogen, the presence or absence of disease (wilting symptoms) in the above-ground parts of the tomatoes was examined.

* We requested Tsukuba Food Evaluation Center to analyze the organic acids contained in rice vinegar and apple cider vinegar (both undiluted), and found that the main organic acid was acetic acid at 4.52g/100g and 5.03g/100g, respectively. Since the specific gravity of vinegar and acetic acid is approximately 1.0g/ml, rice vinegar and apple cider vinegar were adjusted with distilled water to the same acetic acid concentration of 0.042v/v% as the grain vinegar (100 times diluted solution) in Example 3, and then used for the test.

The test was carried out three times, and the average percentage of diseased plants in each treatment was calculated. The results are shown in Figure 3. Twelve tomato plants were used for each treatment. The concentration of the tomato bacterial wilt pathogen was 1.8 x ¹⁰⁷ cfu/ml (first test), 1.5 x ¹⁰⁷ cfu/ml (second test), or 1.7 x ¹⁰⁷ cfu/ml (third test). The average temperatures in the greenhouse after inoculation of the pathogen were 22.9°C (first test), 23.6°C (second test), and 28.8°C (third test).

As shown in Figure 3, the onset of tomato bacterial wilt was suppressed when tomato seedlings were dipped in a diluted solution of rice vinegar or apple cider vinegar (acetic acid concentration adjusted to 0.042%).

Example 5: Effect of root immersion in diluted grain vinegar on the occurrence of komatsuna downy mildew Komatsuna "Kuromisugi" (Sakata Seed) was sown using the same seedling cell tray and culture soil as in Figure 1, and seedlings were raised in a greenhouse. The seedlings were grown to the cotyledon stage, and 3 x 5 cells (total of 15 cells) were transferred to a polypropylene tray, and 1 L of distilled water or grain vinegar diluted 100 times (v/v) with distilled water was poured into the tray to start the root immersion treatment. After root immersion treatment for 2 days, the seedlings were transferred to a strawberry pack (M-500A, Minecrone Chemical Industry) thinly filled with tap water while still in the cell tray, and 10 μl of a suspension of Komatsunabe fungus (strain koma-tu1) adjusted to a conidial concentration of 10 ³ /ml was dropped onto the cotyledons for inoculation, and the plants were maintained under moist conditions at 15/15°C, approximately 10,000/0 Lux (12/12 hrs). Seven days after inoculation, the backside of the cotyledons was visually examined for the presence or absence of disease (conidial formation). Thirty plants (60 cotyledons) were used for each treatment group for each test, and the test was performed three times.

As shown in Figure 4, the incidence of komatsuna downy mildew was reduced by immersing the roots of komatsuna seedlings in a diluted grain vinegar solution.

The present invention is expected to be used by tomato producers and agricultural chemical companies. The vinegar used (grain vinegar, rice vinegar, apple vinegar, Mizkan Holdings Co., Ltd.) is available at low cost at general retail stores. Because the treatment is simple and can be carried out at low cost, it is expected to be introduced and used preventively not only in fields where bacterial wilt has already occurred, but also in fields where it has not yet occurred.

In addition, bacterial wilt is distributed throughout the world, mainly in tropical and temperate regions, and causes damage to many crops, including tomatoes. Although it is necessary to confirm the disease control effect and the occurrence of damage for each vinegar product, vinegar is one of the major seasonings produced and used around the world, and it is thought that it is used in a wide range of agricultural situations.

In addition, there is a rice seed-borne bacterial disease control agent (Ecofit, Kumiai Chemical) on the market that uses acetic acid as its active ingredient, but there is potential for the development of a new control agent that uses acetic acid as its active ingredient not only as a seed disinfectant but also targets soil diseases.

Claims (7)

A plant disease control agent containing acetic acid, characterized in that: 1) the plant disease is bacterial wilt or downy mildew; 2) the plant disease control agent is used for immersing the roots of seedlings before transplanting the seedlings into a field; and 3) the concentration of acetic acid is 0.004 to 0.4 v/v%. 2. The plant disease control agent according to claim 1, wherein the plant is tomato, and the plant disease is tomato bacterial wilt. 2. The plant disease control agent according to claim 1, wherein the plant is Komatsuna (rapeseed), and the plant disease is Komatsuna downy mildew. A method for controlling plant diseases, comprising a step of immersing roots of a plant seedling in an aqueous acetic acid solution prior to transplantation into a field, the method being characterized in that 1) the plant disease is bacterial wilt or downy mildew, and 2) the concentration of the acetic acid is 0.004 to 0.4 v/v %. 5. The method for controlling a plant disease according to claim 4 , wherein the plant is a tomato, and the plant disease is tomato bacterial wilt. 5. The method for controlling a plant disease according to claim 4, wherein the plant is Komatsuna (rapeseed), and the plant disease is Komatsuna downy mildew. 7. The method for controlling plant diseases according to claim 4 , further comprising the step of irrigating soil in which seedlings of a plant having roots immersed in the aqueous acetic acid solution are grown with the aqueous acetic acid solution.