Strain and fungicide for preventing and treating corn southern leaf blight and application of strain and fungicide

Abstract

The invention belongs to the field of microorganisms, and relates to a strain and a fungicide for preventing and treating corn southern leaf blight and application of the strain and the fungicide. The bacterial strain for preventing and treating the corn southern leaf blight is bacillus velezensis A122, can resist salt and alkali, and has a relatively good inhibition effect on helminthosporium maydis. The bacterial strain for preventing and treating corn southern leaf blight also has strong capability of producing cellulase, amylase, protease and indole-3-acetic acid (IAA), and has a good growth promoting effect on corn, and the microbial inoculum prepared from the biocontrol bacterium does not cause pollution to the ecological environment in the use process, and is pollution-free. By using the biocontrol bacterium disclosed by the invention, the dosage of other chemical pesticides can be reduced, the prevention and control cost of corn diseases is reduced, the corn growth is promoted, and the biocontrol bacterium has a good popularization value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microorganisms, and particularly relates to a strain, a bacterial agent and application thereof for preventing and treating corn small spot. BACKGROUND

[0002] Corn small spot is a global important disease of corn caused by Bipolaris maydis, which mainly damages leaf, leaf sheath, bract and ear, and can occur in the whole growth period of corn, especially in the tasseling to grain filling period. The prevalence of corn small spot depends on three key factors: large-scale planting of susceptible varieties, sufficient overwintering source of pathogen in the field, and suitable temperature and humidity environment. The pathogen overwinters on the diseased residues in the form of mycelium or conidia, and can survive for 1-2 years. In the following year, it is transmitted by air and rain, and can germinate and infect within 4-8 hours. New spores are produced within 3-4 days to cause repeated infection, and the disease can spread rapidly within a short period of time. In addition, factors such as overlarge planting density, poor ventilation and light, and improper fertilization and irrigation management can further increase the risk of disease occurrence.

[0003] Current prevention and control of corn small spot mainly relies on comprehensive measures, but there are obvious limitations. For example, long-term and large-scale use of chemical control can lead to drug resistance of the pathogen, and the amount of pesticide needs to be increased to form a vicious cycle. At the same time, chemical agents can cause environmental pollution and harm non-target organisms, which is contrary to the development needs of green agriculture. Measures such as crop rotation, removal of diseased residues, and reasonable planting density can reduce the source of the pathogen or improve the field environment, but due to regional and planting mode limitations, the prevention and control effect is limited when used alone to deal with the disease outbreak.

[0004] Biological control has become an important development direction for the prevention and control of corn small spot due to its environmental friendliness and low risk of drug resistance. However, existing biocontrol strains generally have narrow inhibition spectrum, weak environmental adaptability, and unstable control effect. Therefore, it is of great significance to screen new biocontrol strains with strong inhibition activity, wide inhibition spectrum, good environmental adaptability, and good growth promotion effect, in order to improve the prevention and control level of corn small spot and ensure the sustainable development of corn industry. SUMMARY

[0005] The present application aims to provide a strain Bacillus velezensis, a bacterial agent and application thereof for preventing and treating corn small spot. The strain for preventing and treating corn small spot is Bacillus velezensis A122, which is isolated from the soil of a mango plantation in Damao Village, Yazhou District, Sanya City (east longitude 109°12′5″, north latitude 18°24′38″), and is salt-tolerant and capable of inhibiting multiple pathogenic bacteria and corn diseases.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The application further provides a microbial agent for preventing and treating corn small spot, wherein the microbial agent comprises a bacterial suspension of the strain.

[0008] The application further provides a microbial agent for preventing and treating corn small spot, wherein the microbial agent comprises a bacterial suspension of the strain.

[0009] Further, the concentration of the bacteria in the bacterial suspension is 1-9x10 7 CFU / mL.

[0010] The application further provides a preparation method of the microbial agent for preventing and treating corn small spot, wherein the strain for preventing and treating corn small spot is inoculated into a fermentation medium to perform fermentation culture, so as to obtain the microbial agent for preventing and treating corn small spot.

[0011] The application further provides a preparation method of the microbial agent for preventing and treating corn small spot, wherein the fermentation culture is performed at a temperature of 30-40 DEG C, a rotation speed of 180-220 rpm, and a time of 40-50 h.

[0012] The application further provides an application of the strain for preventing and treating corn small spot in promoting the growth of corn.

[0013] Further, the promotion of the growth of corn includes increasing the plant height, root length and stem diameter of corn.

[0014] The application further provides an application of the strain for preventing and treating corn small spot in inhibiting Bipolaris maydis.

[0015] The application further provides an application of the strain for preventing and treating corn small spot in producing extracellular hydrolytic enzymes.

[0016] The application further provides an application of the strain for preventing and treating corn small spot in decomposing cellulose, starch or protein.

[0017] Beneficial effects

[0018] The strain for preventing and treating corn small spot provided by the present application is Bacillus velezensis A122, which can resist salt and alkali, has good inhibitory effect on Bipolaris maydis, and can effectively prevent and treat corn small spot. Bacillus velezensis A122 also has strong abilities of producing cellulase, protease, amylase and indole-3-acetic acid (IAA), and has good growth promoting effect on corn. The biocontrol agent prepared by using the biocontrol fungus does not pollute the ecological environment and has no pollution during use. The use of the biocontrol fungus of the present application can reduce the use amount of other chemical pesticides, reduce the prevention and control cost of corn diseases, promote the growth of corn, and has good popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A phylogenetic tree of Bacillus velezensis A122;

[0020] Figure 2 A whole genome biosynthesis gene cluster of Bacillus velezensis A122;

[0021] Figure 3 An inhibitory effect diagram of Bacillus velezensis A122 on Bipolaris maydis;

[0022] Figure 4 A salt stress resistance ability determination result diagram of Bacillus velezensis A122, which is respectively a salt plate phenotype result diagram of Bacillus velezensis A122 and model strain FZB42;

[0023] Figure 5 A salt stress resistance ability determination result diagram of Bacillus velezensis A122, which is respectively a salt plate phenotype result diagram of Bacillus velezensis A122 and model strain FZB42; Figure 5 The pH of medium A is 2, Figure 5 The pH of medium B is 3, Figure 5 The pH of medium C is 11, Figure 5 The pH of medium D is 12;

[0024] Figure 6 A HPLC analysis diagram of secondary metabolites of Bacillus velezensis A122;

[0025] Figure 7 A secondary metabolite crude extract of Bacillus velezensis A122 inhibitory effect detection result diagram;

[0026] Figure 8 A detection result diagram of Bacillus velezensis A122 producing protease, cellulase, amylase and ACC deaminase; Figure 8 Medium A is for producing protease, Figure 8 Medium B is for producing cellulase, Figure 8 Medium C is for producing amylase, Figure 8 Medium D is for producing ACC deaminase;

[0027] Figure 9 The ability of Bacillus velezensis A122 to produce indole-3-acetic acid (IAA) is determined;

[0028] Figure 10 The disease prevention effect diagram of Bacillus velezensis A122 on small spot of corn plants;

[0029] Figure 11 The promotion effect diagram of Bacillus velezensis A122 on the growth of corn plants; wherein, Figure 11 A is the plant height, Figure 11 B is the root length, Figure 11 C is the fresh weight of the aboveground part, Figure 11 D is the dry weight of the aboveground part, Figure 11 E is the fresh weight of the underground part, Figure 11 F is the dry weight of the underground part, Figure 11 G is the stem diameter.

[0030] Biological preservation instructions

[0031] The Bacillus velezensis A122 provided by the present application is preserved in the Guangdong Microbial Culture Collection Center, with a preservation number of GDMCC No: 66572, a preservation date of June 23, 2025, a classification name of Bacillus velezensis, and a preservation address of the 5th floor of Building 59, 100 Middle Martyrs Road, Guangzhou, Institute of Microbiology, Guangdong Academy of Sciences. DETAILED DESCRIPTION

[0032] The technical solutions provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0033] Example 1

[0034] Classification status analysis of Bacillus velezensis A122 based on core genome

[0035] Bacillus velezensis A122 was inoculated into liquid LB medium and cultured at 200 rpm and 37°C for 12 hours. The bacterial cells were collected by centrifugation, and the genomic DNA was extracted using a bacterial DNA extraction kit (Hunan Aikewei Biological Engineering Co., Ltd.). The 16S rRNA gene was amplified by PCR using the forward primer 27F: 5'-AGAGTTTGATCCTGGCTCAG-3' (SEQ ID No. 3) and the reverse primer 1492R: 5'-GGTTACCTTGTTACGACTT-3' (SEQ ID No. 4). The PCR conditions were as follows: 95°C for 5 min; 95°C for 15 s; 56°C for 1 min; 72°C for 1 min; 32 cycles; 72°C for 10 min; and 4°C storage. The PCR product was sequenced by Shengong Bioengineering (Shanghai) Co., Ltd. The 16S rRNA gene sequence of Bacillus velezensis A122 is shown in SEQ ID No. 1.

[0036] The 16S rRNA gene sequence of Bacillus velezensis A122 is as follows:

[0037]

[0038] PCR amplification and sequencing of the gyrB gene:

[0039] Forward primer gyrB-F:

[0040] 5'-GAAGTCATCATGACCGTTCTGCAYGCNGGNGGNAARTTYGA-3' (SEQ ID No. 5);

[0041] Reverse primer gyrB-R:

[0042] 5'-AGCAGGGTACGGATGTGCGAGCCRTCNACRTCNGCRTCNGTCAT-3' (SEQ ID No. 6); PCR reaction conditions for the gyrB gene were as above.

[0043] The partial gene sequence of the gyrB gene is approximately 1200 bp in length, and the results are shown in the sequence listing SEQ ID No. 2.

[0044] GyrB gene sequence:

[0045]

[0046] 16S rRNA and gyrB identification results show that strain A122 belongs to Bacillus velezensis. Secondly, based on the genomic sequence of A122, 19 strains closest to the species level were selected based on 31 housekeeping genes of all samples, and a phylogenetic tree was constructed by MEGA6.0 software selection method. The results show that the evolutionary distance between strain A122 and Bacillus velezensis is the closest. The above results show that strain A122 belongs to Bacillus velezensis.

[0047] Whole genome sequencing of Bacillus (using Illumina Hiseq 4000 and PacBio SMRT sequencing system) was performed. Online tools (antiSMASH (https: / / dl.secondarymetabolites.org / releases / 4.0.2 / )) were used to predict the biosynthetic gene clusters (BGCs) of Bacillus A122 secondary metabolites. It is predicted that Bacillus A122 chromosome contains three kinds of lipopeptide compounds and three kinds of polyketide BGCs, which are responsible for the biosynthesis of Fengycin, Surfactin, Iturin, Bacillaene, Difficidin and Macrolactin H.

[0048] Example 2

[0049] Antibacterial ability determination of Bacillus velezensis A122

[0050] The antibacterial ability of Bacillus velezensis was preliminarily determined, and the pathogenic fungi selected include Bipolaris maydis.

[0051] Determination of the antibacterial ability of Bacillus velezensis on pathogenic fungi: From the original pathogenic fungus culture plate, a certain number of fungus cakes with a diameter of about 0.6 cm were punched at the outermost edge of the colony with a sterile puncher, and then the fungus cakes (containing mycelium) were transferred to the center of a new potato dextrose agar (PDA) culture plate. After placing the Bacillus velezensis A122 block at the same distance from the fungus cake, it was placed in a 28 ℃ incubator, and the antibacterial effect was observed. The results are shown in Figure 3 , which shows that Bacillus velezensis A122 has a certain inhibitory effect on Bipolaris maydis.

[0052] Example 3

[0053] Determination of stress tolerance of bacillus velezensis a122

[0054] The stress tolerance of Bacillus velezensis is closely related to its disease resistance and growth promotion ability, therefore, the stress tolerance of Bacillus velezensis A122 was determined.

[0055] 1. Determination of salt stress tolerance of Bacillus velezensis A122

[0056] Different salt stresses 1%, 3%, 5%, 7%, 9%, 11%, 13%, 13.1%, 13.2% were simulated to determine the salt stress resistance of strains A122 and FZB42. Single colonies of the test strains were picked into LB liquid medium and cultured overnight at 37°C, 200 rpm for 24 h. When the concentration of the bacterial solution was OD 600 =2.0, 5 μL of the bacterial solution was transferred to LB solid medium with different salt gradients, and then the medium was placed in a 37°C incubator. After 2 days, the colony growth conditions of each strain under different salt gradients were observed, and the results are shown in Figure 4 . The results showed that Bacillus velezensis A122 could grow under salt stress conditions with a salt content of 13.1%, and its growth state was better than that of the model strain FZB42, indicating that it had certain salt stress tolerance.

[0057] 2. Determination of acid and alkali stress tolerance of Bacillus velezensis A122

[0058] Different acid and alkali stresses (pH gradient: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) were simulated to determine the acid and alkali stress resistance of Bacillus velezensis A122 and FZB42. Single colonies of the test strains were picked into LB liquid medium and cultured overnight at 37°C, 200 rpm. 5 μL of the bacterial solution was transferred to LB liquid medium with different pH gradients, and then the medium was placed in a 37°C shaking incubator. After 2 days, 5 μL of the bacterial solution was transferred to LB solid medium to observe the colony growth conditions of each strain under different pH conditions, and each treatment was repeated 3 times. The results are shown in Figure 5 . The results showed that Bacillus velezensis A122 had difficulty growing under acid stress at pH 2 and alkali stress at pH 12.

[0059] Example 4

[0060] Extraction, identification and antibacterial activity determination of secondary metabolites of Bacillus velezensis A122

[0061] 1. Extraction and identification of secondary metabolites of Bacillus velezensis A122

[0062] Bacillus velezensis A122 was activated on LB solid medium and placed in a 37 °C incubator until single colonies grew; single colonies were picked into 20 mL of LB liquid medium and cultured at 37 °C, 200 rpm for 12 h; 1% of the Bacillus velezensis A122 bacterial solution was transferred to 200 mL of LB liquid medium and cultured at 37 °C, 200 rpm for 48 h; 6 mL of resin (XAD-16N) was added to the A122 bacterial solution, and the culture was continued for 24 h; the bacterial solution was centrifuged at 8000 rpm for 10 min, and the bacterial cells were collected; the bacterial cells were dissolved in 30 mL of methanol, and the bacterial suspension was then cultured at 37 °C, 200 rpm for 4 h; the bacterial suspension was centrifuged at 8000 rpm for 10 min, and the supernatant was collected and filtered with filter paper; the supernatant was concentrated to 2 mL using a rotary evaporator, and then the crude extract was filtered with a 0.22 μm filter membrane; the production of lipopeptide compounds was detected by high-performance liquid chromatography (HPLC), and the results are shown in Figure 6 , which show that Bacillus velezensis A122 can produce Fengycin, Surfactin, and Iturin.

[0063] 2. Antifungal effect determination of secondary metabolites of Bacillus velezensis A122

[0064] Bipolaris maydis was selected as the pathogenic fungus, and a certain number of fungus cakes were punched from the outermost edge of the original pathogenic fungus culture plate with a sterile puncher with a diameter of about 0.5 cm, and then the fungus cakes (with mycelium) were transferred to the center of a new potato dextrose agar (PDA) culture plate, and cultured in a suitable temperature incubator. When new mycelium grew around the fungus cake, it was ready for use. Then, at the same distance from the fungus cake, a sterile puncher with a diameter of 0.5 cm was used to punch a hole, 50 μL of secondary metabolites of Bacillus velezensis A122 were added to the center of the hole, and methanol solution was used as a control. After blowing dry, it was placed back in the incubator, and the antifungal effect was observed. The results are shown in Figure 7 . The results of the plate confrontation experiment show that the secondary metabolites of Bacillus velezensis A122 have good antagonistic effect on Bipolaris maydis.

[0065] 3. Determination of the ability of Bacillus velezensis A122 to produce extracellular hydrolytic enzymes

[0066] Qualitative detection of protease production by *Bacillus belyssae* A122 was performed on skim milk agar plates: The ability of *Bacillus belyssae* to produce protease was determined in agar medium containing skim milk powder (20 g skim milk powder, 20 g agar, pH 7.0, sterilized at 115°C for 10 min). Single colonies of *Bacillus belyssae* were picked and incubated in LB broth at 37 °C, 200 r / min overnight for 12 h; 5 μL (OD) of the culture medium was added dropwise to the medium. 600 A bacterial suspension with a concentration of 1.0 g / cm³ was incubated at 37 °C for 24-36 h. Afterward, the presence of a clear zone around the colonies was observed. Results were as follows: Figure 8 As shown in Figure A.

[0067] The cellulase production capacity of *Bacillus belyssiensis* A122 was determined using sodium carboxymethyl cellulose (CMC-Na) medium: Single colonies of *Bacillus belyssiensis* were picked and cultured overnight at 37 °C and 200 rpm for 12 h. 5 μL of the bacterial suspension (OD) was then aspirated onto a CMC-Na agar plate. 600 =1.0), seal the plate and incubate it in a 37 °C incubator; after 2 days, remove the petri dish, pour Gram's iodine stain solution until it submerges the surface of the plate, let it stand for 4 minutes, then pour off the stain solution and observe whether a clear zone forms around the colonies. If a clear hydrolysis zone appears around the bacterial cells, it indicates that the strain can produce the corresponding enzyme; if no clear hydrolysis zone appears, it indicates that the strain cannot produce this type of enzyme. The results are as follows. Figure 8 As shown in B.

[0068] Detection of amylase activity in Bacillus belyssus A122 on starch agar medium: Colonies of Bacillus belyssus were picked and placed in LB broth, incubated at 37 °C and 200 rpm for 12 h, and then 5 μL of bacterial suspension (OD200) was added. 600 =1.0) was added to starch-containing culture medium and incubated in a 37°C incubator; after 2 days, the petri dishes were removed, Gram's iodine stain was poured in to submerge the surface of the plates, and after standing for 4 minutes, the stain was poured off. The experimental results were observed and recorded as follows. Figure 8 As shown in C.

[0069] Colonies of Bacillus belye were picked and placed in LB broth, incubated overnight at 37 °C and 200 rpm for 12 h, and then 5 μL of bacterial suspension (OD) was added. 600=1.0)to DF medium, DF (containing ammonium sulfate) medium, ADF medium, and observe the growth of the strain in the three different media. When the strain grows well in the ADF medium and poorly in the DF medium, it indicates that the strain can grow by relying on 1-aminocyclopropane-1-carboxylic acid (ACC) as the sole nitrogen source, and also indicates that the strain has the ability to produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase. The results are shown in Table 1. Figure 8 Table 1

[0070] The results show that the strain A122 can produce a larger transparent hydrolysis circle in skimmed milk powder medium, sodium carboxymethyl cellulose (CMC-Na) medium, and amylase detection medium, and can grow in ADF medium, which indicates that it can produce cellulase, protease, amylase, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase.

[0071] 4. Determination of the ability of Bacillus velezensis A122 to produce indole-3-acetic acid (IAA)

[0072] Salkowski colorimetric solution: 0.81 g of FeCl3 was weighed into 10 mL of ddH2O, dissolved thoroughly, and mixed uniformly to serve as a 0.5 mol / L stock solution. A 35% concentration of perchloric acid solution was prepared, and then 50 mL of the perchloric acid solution was mixed with 1 mL of the 0.5 mol / L FeCl3 stock solution and mixed uniformly for use.

[0073] First, the strain stock solution was obtained using LB medium at 37°C and 200 rpm. Then, the stock solution was transferred to YMB liquid medium at a ratio of 1%, and cultured at 37°C and 200 rpm for 48 h. 2 mL of the bacterial solution was centrifuged at 12000 rpm to obtain the supernatant. An equal volume of Salkowski colorimetric solution was added to the supernatant, mixed uniformly, and reacted in the dark for 30 min. If the solution turned red, it indicated that the strain could produce indole-3-acetic acid (IAA). The same volume of YMB liquid medium was used as a blank control, and standard solutions with indole-3-acetic acid (IAA) concentrations of 2.5 μg / mL, 5.0 μg / mL, 7.5 μg / mL, 10.0 μg / mL, and 12.5 μg / mL were prepared. The OD values of the standard solutions and the sample solution were measured using a spectrophotometer, and the regression equation = 0.0428x - 0.0257 was obtained. The ability of Bacillus velezensis A122 to produce indole-3-acetic acid (IAA) was calculated to be 7.70 μg / mL, and the ability of the model strain FZB42 was calculated to be 7.59 μg / mL. The results are shown in Table 2. 530 Table 2 Figure 9The results showed that Bacillus velezensis A122 could produce indole-3-acetic acid (IAA), and the ability of strain A122 to produce indole-3-acetic acid (IAA) was higher than that of the model strain FZB42, indicating that it had great potential in promoting plant growth and development, and had the potential to develop into a biocontrol agent.

[0074] Example 5

[0075] Determination of the ability of Bacillus velezensis A122 to control corn small spot

[0076] Complete and full corn seeds were picked and soaked in 30% sodium hypochlorite solution for 120 s, then soaked in 75% ethanol for 30 s, and then repeatedly washed with ddH2O for 5 times until there was no irritating odor left on the surface of the corn seeds. The nutrient soil and vermiculite were mixed in a ratio of 2:1 and sterilized at 121 ℃ for 20 min; then the substrate soil was filled into the flowerpot, and the detoxified corn seeds were planted into the soil, and then covered with a layer of soil on the upper layer. The flowerpot was placed in a tray, and an appropriate amount of water was added to the tray, and placed in a 28 ℃ greenhouse for culture until the corn plants entered the large trumpet stage (4-6 leaf stage). Bacillus velezensis A122 and the model strain FZB42 were activated on LB solid medium. Single colonies were picked with sterile toothpicks and placed in 20 mL of LB liquid medium, and incubated at 37 ℃, 200 rpm overnight. The next day, 1% was transferred and cultured for 48 h, and the OD 600 of the bacterial solution was adjusted to 0.5 (10 7 CFU / mL) for use. Quartz sand was used to rub the corn leaves to create wounds, and corn small spot bacterial discs were inoculated on the leaf wounds, and diluted Bacillus velezensis bacterial suspension was sprayed. The control group was sprayed with water. All treatments were cultured with a film for 3 d, then removed, and the disease incidence was recorded after 1-2 weeks.

[0077] Table 1 Prevention and treatment effect of Bacillus velezensis A122 on corn small spot

[0078]

[0079] The experimental results showed that the spraying of Bacillus velezensis A122 on corn leaves reduced the incidence of corn small spot, and the corn plants treated with Bacillus velezensis A122 had the smallest lesion area, which was 8.19 mm 2 , which was 16.2 mm 2 smaller than the lesion area of the blank control group. The treatment of Bacillus velezensis A122 had good prevention and treatment effect on corn small spot, and the prevention and treatment effect was close to that of the FZB42 treatment group.

[0080] Example 6

[0081] Exploration of the growth-promoting effect of bacillus velezensis A122 on corn plants

[0082] Corn seed disinfection and germination: pick intact and full seeds, immerse in 30% sodium hypochlorite solution for 120 s, then immerse in 75% ethanol for 30 s, and then repeatedly rinse with ddH2O for 5 times until there is no irritating odor left on the surface of the corn seeds; place sterile filter paper pieces in 9 cm sterilized glass culture dishes, add appropriate amount of sterile water with a pipette so that the filter paper in the dish is completely wetted with water; use sterile forceps to pick up the corn seeds and place them on the filter paper, making sure that there is a certain distance between the seeds to facilitate germination;

[0083] Corn seedling planting: mix the nutrient soil and vermiculite in a ratio of 2:1, sterilize at 121 DEG C for 20 min, and then use a puncher with a diameter of about 2-3 cm to punch a hole in the center of a disposable plastic cup, then fill the substrate soil, use forceps to pick up the corn seeds that have grown out of the radicle, and plant them in the soil with the roots facing down, then cover the top layer with soil, place the disposable plastic cup in a tray, add appropriate amount of water in the tray, and place it in a 28 DEG C greenhouse for about 20 days.

[0084] Fermentation broth of bacillus velezensis A122 root irrigation treatment: when the corn seedlings grow to two leaves and one heart, pick plants with consistent growth, dilute the seed liquid of bacillus velezensis A122 and the model strain FZB42 to 10 7 CFU / mL with sterile water, inject 50 mL of the bacterial suspension with a final concentration of 10 7 CFU / mL into each corn root, use sterile water as a blank control, perform the second treatment after 7 days, and count the growth-promoting data after 15 days of culture, and the results are shown in Figure 11 .

[0085] The results show that A122 has good growth-promoting effect on corn plants. Among them, the strain A122 has the best growth-promoting effect on the dry weight and fresh weight of the aboveground part of corn, with a growth-promoting rate of 115.60% and 89.06%; the strain A122 has good growth-promoting effect on the dry weight and fresh weight of the underground part of corn, with a growth-promoting rate of 59.99% and 59.52%; the growth-promoting rate of this strain on corn is higher than that of the model strain FZB42, which shows that bacillus velezensis A122 has good growth-promoting effect and has certain development potential.

[0086] From the above examples, it can be seen that the bacillus velezensis A122 provided by the present application has the ability to resist salt and alkali, and can effectively prevent and control small spot disease, and has very good growth-promoting effect on corn, and has great application potential in biological pesticides.

[0087] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A strain for controlling Gaeumannomyces graminis var. tritici, characterized in that, The strain is Bacillus velezensis A122, which is preserved in Guangdong Microbial Culture Collection Center, with the preservation number of GDMCC No:66572, the preservation date of June 23, 2025, the classification and naming of Bacillus velezensis, and the preservation address of the 5th floor of Building 59, Guangzhou, Guangdong Academy of Sciences, Institute of Microbiology.

2. A fungicide for controlling corn northern leaf blight, characterized by comprising, The microbial agent comprises a bacterial suspension of the strain of claim 1.

3. The agent for preventing or treating of corn small spot according to claim 2, characterized by, The bacteria concentration in the bacteria suspension is 1-9 x 10 7 CFU / mL.

4. The method of claim 2, wherein the fungicide for controlling the corn leaf spot disease is prepared by the steps of: The strain for preventing and treating corn small spot of claim 1 is inoculated into a fermentation medium for fermentation culture to obtain a microbial agent for preventing and treating corn small spot. ​ 5. The method of claim 4, wherein the agent is prepared by the steps of: a) mixing the compound of formula (I) with a carrier; and b) adding a surfactant to the mixture of step a). The fermentation culture temperature is 30-40 DEG C, the rotation speed is 180-220 rpm, and the time is 40-50 h.

6. The strain for preventing and treating corn small spot of claim 1 is applied to promote the growth of corn.

7. Use according to claim 6, characterized in that, The promotion of corn growth includes increasing the plant height, root length and stem diameter of corn.

8. The strain for preventing and treating corn small spot of claim 1 is applied to inhibit Bipolaris maydis.

9. The strain for preventing and treating corn small spot of claim 1 is applied to produce extracellular hydrolytic enzymes.

10. The strain for preventing and treating corn small spot of claim 1 is applied to decompose cellulose, starch or protein.

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