Biological fungicide capable of effectively preventing and controlling rice bacterial blight and the used bacteria

Abstract

The invention belongs to the technical field of rice disease prevention and control, and specifically relates to a biological fungicide for preventing and controlling rice bacterial blight in the field of biological control. The invention discloses a Bacillus velezensis Bv-303, whose deposit number is: CGMCC No.23395. The invention also discloses the application of the Bacillus velezensis Bv-303 in preventing and controlling rice bacterial blight.

Description

Technical Field

[0001] The invention belongs to the technical field of rice disease prevention and control, and in particular relates to a biological fungicide for preventing and controlling rice bacterial blight in the field of biological control. Background Art

[0002] Rice is the main food crop for mankind. The three major diseases of rice are rice blast, bacterial leaf blight and sheath blight. Other important diseases include rice false smut, stripe disease, downy mildew, etc. Bacterial leaf blight (Xanthomonas oryzae pv.oryae, Xoo), also known as white leaf blast, occurs in rice-growing areas in my country, which can lead to a decrease in rice quality and yield, usually causing a 20%-40% reduction in yield, and up to 50%-60% in severe planting areas, or even no harvest, ranking first among rice bacterial diseases in the world. In order to quickly and effectively prevent and control rice diseases, chemical fungicides are often used. Chemical fungicides play a key role in the process of preventing and controlling crop diseases. However, the long-term and uncontrolled use of a large amount of chemical pesticides will lead to pesticide residues on crops, which will endanger human health after human consumption and pollute the environment. Pesticides not only kill pathogens, but also treat beneficial microorganisms in the field soil environment equally, so they will cause damage to the field ecosystem. Therefore, it is imperative to develop efficient, green and environmentally friendly biofungicides.

[0003] The invention of CN114933995A relates to a biocontrol Bacillus velezensis ML21 and its application. Bacillus velezensis ML21 or a microbial preparation has an inhibitory effect on a variety of plant pathogenic bacteria such as mango bacterial angular leaf spot pathogen, rice leaf streak pathogen, rice white leaf blight pathogen, crucifer black rot pathogen, citrus canker pathogen and sugarcane white streak pathogen.

[0004] The invention of CN114736821A discloses that Bacillus Velezii SF305 has good antibacterial activity against plant pathogens such as Colletotrichum gloeosporioides, Colletotrichum oxysporum, Pyricularia oryzae, Fusarium wilt, Phytophthora capsici, Botrytis cinerea, Xanthoceras oryzae and Pseudomonas streak, and can also promote crop growth and increase crop fresh weight.

[0005] The invention of CN114107124A relates to a strain of Bacillus Velezii D-1 and its preparation and application. The strain has significant control effects on three types of Fusarium that cause taro dry rot, and also has good inhibitory effects on a variety of plant pathogenic fungi and pathogenic bacteria such as tea dichaete leaf spot pathogen, kiwi black spot pathogen, kiwi coryneformis leaf spot pathogen, kiwi fruit rot pathogen, kiwi canker pathogen, pepper bacterial spot pathogen, rice white leaf blight pathogen and citrus canker pathogen, showing a broad-spectrum antibacterial activity. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a biological fungicide for preventing and controlling rice bacterial blight.

[0007] In order to solve the above technical problems, the present invention provides a Bacillus velezensis strain, which is Bacillus velezensis Bv-303, and its preservation number is: CGMCC No.23395.

[0008] The invention also provides application of Bacillus velezensis Bv-303 in preventing and controlling rice bacterial leaf blight.

[0009] The present invention also provides a method for preparing a biological fungicide capable of preventing and controlling rice bacterial blight, comprising the following steps:

[0010] 1) Slant strains:

[0011] Cultivate Bacillus velezensis Bv-303 with the accession number of CGMCC No. 23395 on a NA slant at 27.5-28.5° C. for 18-36 h (preferably at 28° C. for 24 h);

[0012] Note: After taking out, store in a refrigerator at 4℃ to prevent contamination by bacteria;

[0013] 2) Plate activation:

[0014] The bacterial strain obtained (preserved) by the above NA slant culture is inoculated onto a plate culture medium, wherein the plate culture medium is a NA culture medium; the culture conditions are 27.5-28.5°C for 18-36h (preferably 28°C for 24h);

[0015] Generally, the subculture is repeated twice under the same conditions (i.e., co-cultured 2 times);

[0016] 3) Liquid fermentation seeds:

[0017] PDB medium was used as seed medium;

[0018] The activated strains are inoculated into a shake flask filled with PDB medium, and cultured in an oscillator at 27.5-28.5°C (preferably 28°C) and 150-250 rpm (preferably 200 rpm) for 22-26 hours (preferably 24 hours) to obtain liquid fermentation seeds;

[0019] 4) Liquid fermentation:

[0020] The liquid fermented seeds are inoculated into a PDB medium at an inoculation rate of 1% (volume %), and cultured in an oscillator at 27.5-28.5° C. (preferably 28° C.) and 150-250 rpm (preferably 200 rpm) for 46-50 h (preferably 48 h) to obtain a fermentation liquid, which is a biofungicide capable of preventing and controlling rice diseases;

[0021] Note: Step 3) and step 4) are both "aerobic sterile culture", that is, they meet the "breathable" condition;

[0022] 5) Centrifugal filtration:

[0023] The fermentation liquid obtained in step 4) is centrifuged at 12,000 to 14,000 rpm for 18 to 22 min (preferably at 13,000 rpm for 20 min), the precipitate is removed to obtain a supernatant, and the supernatant is filtered through a 0.22 μm sterile filter membrane to obtain a sterile fermentation supernatant, which is also the biocide supernatant;

[0024] 6) Resuspend the cells:

[0025] Add sterile water to the precipitate obtained in step 5) above to evenly disperse the bacteria (shortly vortex for 30 seconds) to obtain a bacterial suspension of the biocide.

[0026] The Bacillus velezensis Bv-303 of the present invention has a preservation name of Bacillus velezensis, a preservation number of CGMCC No. 23395, and a preservation date of September 13, 2021; the preservation unit is the General Microbiology Center of China National Microbiological Culture Collection Administration, and the preservation address is No. 3, Yard No. 1, Beichen West Road, Chaoyang District, Beijing.

[0027] The present invention has the following technical advantages:

[0028] 1. Biocides are easy to culture, have a short growth cycle, and are easy to collect;

[0029] 2. The biofungicide obtained by the present invention has the characteristics of good thermal stability, acid and alkali resistance, storage stability and ultraviolet resistance;

[0030] 3. The biofungicide obtained by the present invention has a significant inhibitory effect on various species of bacterial blight.

[0031] 4. The biological fungicide obtained by the present invention can effectively prevent and treat rice diseases (bacterial leaf blight diseases) caused by various bacterial blight species, and the effect is remarkable.

[0032] When the biofungicide capable of preventing and controlling rice diseases of the present invention is actually used, its usage and dosage are as follows: after mixing the biofungicide (fermentation liquid) with sterile water at a volume ratio of 1:10-50, seed treatment: soak the seeds with the biofungicide for 4 hours before sowing, and then keep the seeds in a simmering state for 12 hours, and then germinate after washing. Seedling treatment: spray in July-August each year (generally from the booting stage to the heading stage in the field). Generally speaking, 5-15L of the biofungicide as an active ingredient is used per mu. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0034] Figure 1 The colony and bacterial morphology characteristics of Bacillus Velezii Bv-303 on NA;

[0035] Figure 1 In the figure, A and B are single colony morphologies, C is a Gram staining image, D is a spore staining image, and E is a scanning electron microscope image.

[0036] Figure 2 Phylogenetic tree constructed for the multi-gene sequences of Bacillus velezinsis Bv-303.

[0037] Figure 3 It is the in vitro plate inhibition effect of the supernatant of the biofungicide on various bacterial blight pathogens;

[0038] Figure 3 Figure AE are the inhibition zone diagrams of PXO86, PXO71, PXO99, Zhejiang 173 and C2, and Figure F is the statistical result diagram of the inhibition zone diameter.

[0039] Figure 4 The effect of the supernatant of the biofungicide at different dilution ratios on the bacterial cells of the bacterial blight pathogen;

[0040] Figure 4 In the figure, A is a scanning electron micrograph of bacterial blight pathogen, and BC are scanning electron micrographs of bacteria treated with the supernatant of the biofungicide diluted 50 times and 10 times, respectively.

[0041] Figure 5 The in vitro plate inhibitory effect of the biofungicide supernatant obtained at different culture times on rice bacterial blight pathogen.

[0042] Figure 6 The results are for the in vitro plate inhibition of bacterial blight by the supernatant of the biofungicide under different storage conditions;

[0043] Figure 6 Among them, A is treatment at different temperatures, B is treatment at different pH values, C is treatment at different UV irradiation times, and D is treatment at different storage times.

[0044] Figure 7 For the in vivo control of bacterial blight by biofungicide supernatant, biofungicide suspension and biofungicide;

[0045] Figure 7 In the figure, A and C show the bacterial blight lesions of rice inoculated with PXO86, and B and D show the bacterial blight lesions of rice inoculated with Zhe 173.

[0046] Figure 8 To analyze the effects of biofungicides on rice growth and development;

[0047] Figure 8 In the figure, A is the germination rate, B is the length of the aboveground part, and C is the root length. DETAILED DESCRIPTION

[0048] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0049] In the present invention, NA medium and PDB medium are both conventional mediums. For example, NA medium is: 3g beef extract, 5g peptone, 1g yeast powder, 10g sucrose, 18g agar powder, 1000ml water, pH adjusted to 7.0-7.2, sterilized at 121°C for 20min; PDB medium is: 200g potato, 20g glucose, 1000ml water, sterilized at 121°C for 20min.

[0050] Example 1, Acquisition of Bacillus velezensis Bv-303:

[0051] The antagonistic strain Bv-303 was isolated from healthy leaves of short-stalked cherry in a cherry orchard in Chisong Town, Jinhua City, Zhejiang Province. It was obtained by screening using the dilution separation method and the bacterial blight pathogen Zhejiang 173 as the indicator bacteria. The experimental steps are as follows: Select healthy leaves and draw 2×2 cm 2 Cut into small pieces with scissors, disinfect the surface with 0.1% mercuric chloride and 75% ethanol for 0.5-1min respectively, wash with sterile water for 3 times, grind in a sterile EP tube, add 1mL of sterile water, let the tissue fluid soak in water for 30min, and then dilute with sterile water for 10 minutes. -1 , 10 -2 , 10 -3 , 10 -4, 100 μL of each was spread on NA plates and cultured at 28°C for 1-2 days. Single colonies from each plate were picked and inoculated into shake flasks containing NB medium, cultured in an oscillator at 28°C and 200 rpm for 24 hours, and the resulting fermentation broth was centrifuged at 14 000 rpm for 20 minutes, the precipitate was removed to obtain the supernatant, and the sterile fermentation supernatant was obtained by filtering with a 0.22 μm sterile filter membrane, and Zhe 173 was used as an indicator pathogen to determine the inhibitory activity of the isolated endophytes against bacterial blight.

[0052] Among the isolated strains, Bv-303 has a significant inhibitory effect on bacterial blight pathogen Zhe 173. The characteristics of this bacterium are as follows: the colonies on NA medium are milky white and opaque, with wrinkled surfaces, irregular edges, and are sticky and difficult to pick up ( Figure 1 AB); Gram-stained purple, Gram-positive bacteria ( Figure 1 C); can produce spores, oval, mesophytic ( Figure 1 D). Under electron microscope, the bacteria are long rod-shaped ( Figure 1 E). By constructing a joint evolutionary tree of five genes: 16S rDNA, gyrA, gyrB, rpoB, and purH ( Figure 2 ) and identified the bacterium as Bacillus velez.

[0053] The strain Bv-303 was deposited, and the preservation information is as follows: the preservation name is Bacillus velezensis, the preservation number is CGMCC No.23395, the preservation date is September 13, 2021; the preservation unit is the General Microbiology Center of China Microbiological Culture Collection Administration, and the preservation address is No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing.

[0054] Example 2: A biofungicide for preventing and controlling rice diseases, the preparation method of which is to carry out the following steps in sequence:

[0055] 1) Slant strains:

[0056] Bacillus velezensis Bv-303 with the deposit number of CGMCC No. 23395 was cultured on NA slant for 24 h (culture temperature was 28° C.) and stored in a refrigerator at 4° C. to prevent contamination by foreign bacteria.

[0057] 2) Plate activation:

[0058] The bacterial strains stored on the NA slant were inoculated onto a plate culture medium, which was a NA medium. The culture conditions were culturing at 28° C. for 24 h, and the subculture was repeated twice under the same conditions (ie, co-cultured twice).

[0059] 3) Liquid fermentation seeds:

[0060] PDB medium was used as seed medium;

[0061] One loop of the activated strain was inoculated into a shaking flask containing 50 ml of PDB liquid culture medium, and cultured at 28° C. and 200 rpm for 24 hours to obtain liquid fermentation seeds.

[0062] 4) Liquid fermentation:

[0063] The liquid fermentation seeds were inoculated into PDB medium (in a shaking bottle) at an inoculation rate of 1% (volume %), and cultured in an oscillator at 28°C and 200 rpm for 48 hours to obtain a fermentation liquid (fermentation product). The fermentation liquid is a biological fungicide capable of preventing and controlling rice bacterial blight.

[0064] That is, the volume ratio of the liquid fermentation seeds to the PDB medium was 1%.

[0065] Step 3) and step 4) are both conventional aerobic sterile cultures.

[0066] 5) Centrifugal filtration:

[0067] The fermentation liquid obtained in step 4) is centrifuged (rotation speed is 13000 rpm, time is 20 min), the precipitate is removed to obtain the supernatant, and the supernatant is filtered with a 0.22 μm sterile filter membrane to obtain a sterile fermentation supernatant, which is the biocide supernatant.

[0068] 6) Resuspend the cells:

[0069] Add sterile water to the precipitate obtained by centrifugation in step 5) until the volume is the same as the original fermentation liquid before centrifugation, and vortex for 30 seconds to evenly disperse the bacteria to obtain a biocide bacterial suspension.

[0070] In vitro plate inhibition of the biofungicide supernatant obtained in Experiment 1 and Example 2 against various bacterial blight pathogens

[0071] (1) activating Xanthomonas oryzae pv.oryzae from Chinese physiological races Zhe173 and C2 and Philippine physiological races PXO86, PXO71, and PXO99 according to conventional methods;

[0072] (2) Pour the melted PDA medium into culture dishes to prepare 30 plates; divide them into 5 groups of 6 plates.

[0073] (3) Pick out the activated bacterial blight bacteria and mix them in sterile water to measure their OD 600The value is about 0.3. Pipette 100 μL of the above bacterial solution into the prepared plate, and spread the bacterial solution evenly with a spreading stick; spread 6 plates for each bacterial species.

[0074] For each bacterial species, the following experimental steps were performed:

[0075] (4) Use tweezers to pick up the Oxford cup and insert it vertically into the center of the plate without touching the bottom of the plate (the Oxford cup should not be inserted too deep or too shallow into the culture medium);

[0076] (5) Pipette 200 μL of the biocide supernatant into an Oxford cup and place it on three plates as treatment; Pipette 200 μL of sterile water into an Oxford cup and place it on three plates as control; repeat the operation for five groups.

[0077] (6) Seal the plate and place in a 28°C incubator (aerobic) for 2 days;

[0078] (7) Take photos and measure the diameter of the inhibition zone.

[0079] The results are as follows Figure 3 shown.

[0080] Through in vitro antagonism test of biocide supernatant, it was found that it has a wide range of antibacterial properties ( Figure 3 AE). Although it did not show a certain antibacterial trend against different toxic physiological species, the average diameter of the inhibition zone was 4.8 to 5.3 cm ( Figure 3 F), the antibacterial effect is significant.

[0081] In summary, the biofungicide supernatant of the present invention (which is a microbial fermentation supernatant and does not contain Bacillus Velezii) has a significant antibacterial effect on a variety of bacterial blight species (such as Chinese physiological races Zhe 173, C2 and Philippine physiological races PXO86, PXO71, PXO99), can generally antagonize bacterial blight caused by various physiological races, and is more efficient and targeted.

[0082] Effects of different dilution ratios of the biofungicide supernatant obtained in Experiment 2 and Example 2 on bacterial blight pathogens

[0083] (1) The fermentation supernatant of the biofungicide was diluted 10 times and 50 times, and co-cultured with PXO86 bacterial blight pathogen for 24 h, respectively, to conduct a direct contact antagonism experiment, with sterile water as the control.

[0084] (2) The morphology of Xanthoceras spp. was observed under a scanning electron microscope.

[0085] The results are as follows Figure 4 shown.

[0086] Xanthoceras is a Gram-negative bacterium with a cell membrane composed of membrane lipids and membrane proteins. Under a scanning electron microscope, the bacterial cells of the control bacterial blight pathogen were rod-shaped with blunt ends and smooth, plump and wrinkle-free surfaces. However, the surfaces of the bacterial cells treated with the supernatant of the biofungicide at different dilutions became obviously rough, wrinkled and even damaged, and the bacterial morphology was abnormal. Figure 4 The supernatant of the biofungicide in C) caused more serious damage to the bacterial blight.

[0087] Therefore, according to Figure 4 It can be known that the effective antibacterial substances in the antibacterial agent can have a greater destructive effect on the bacterial cells of the white leaf blight pathogen. The higher the concentration, the stronger the inhibitory effect.

[0088] Experiment 3: In vitro inhibition of bacterial blight pathogens by supernatants of biocides at different culture times

[0089] (1) Pick a loop of activated Bv-303 with an inoculation loop and inoculate it into a flask containing 20 ml of PDB medium, and culture it at 28°C and 200 r / min for 24 hours to obtain a mother solution. Then inoculate it into PDB medium at 1% (mother solution volume / culture medium volume), and culture it at 28°C and 200 r / min. Take the fermentation liquid at 24, 48, 72, 96, 120, and 144 hours of culture, centrifuge it at 13000 r / min for 20 minutes, collect the supernatant, and filter it with a 0.22 μm microporous filter to obtain the supernatant of the biocide at different culture times.

[0090] (2) In view of the results of Experiment 1, a new species of bacterial blight pathogen, Chinese physiological species Zhe 173, was selected for this experiment. The rest of the content was the same as Experiment 1.

[0091] The results are as follows Figure 5 shown.

[0092] The results showed that the antibacterial effect of the supernatant of the 48h biocide on Zhe 173 was the best, and there was a significant difference in the antibacterial effect of the supernatant of the biocide at other culture times. Therefore, 48h was selected as the culture time for culturing Bv-303 strain.

[0093] Experiment 4: In vitro inhibition of bacterial blight by supernatants of biofungicides under different storage conditions

[0094] (1) Using the same culture method as in Experiment 3, take the supernatant of the Bv-303 strain biofungicide at the optimal culture time (48 h).

[0095] (2) Perform the following conditional processing respectively:

[0096] ① Acid and base: Use 1 mol / L HCL or NaOH solution to adjust the pH value to acidic (1-2, 5-6), alkaline (9-10, 11-12, 13-14) or neutral (7-8), and adjust the pH value of the biocide supernatant back to the original pH (6.8) after standing for 24 hours;

[0097] ②Ultraviolet light: irradiate under ultraviolet light (wavelength: 254nm) for 0.5, 1, or 2 hours;

[0098] ③ Heat treatment: constant temperature water bath at 20, 30, 40, 50, 60℃ for 1h;

[0099] ④Storage time: store at 4℃ for 1, 5, 10, 20, 30, 40 days.

[0100] Untreated supernatant was used as control.

[0101] (3) The Oxford cup method was used to determine the inhibitory effect of the above-treated biofungicide supernatants on bacterial blight. A bacterial blight race, Chinese physiological race Zhe 173, was selected for the experiment, and the rest of the methods were the same as those in Experiment 1.

[0102] The results are as follows Figure 6 shown.

[0103] The results showed that the supernatant of Bv-303 biofungicide had good thermal stability and good acid-base tolerance, and had no significant effect on the antibacterial effect of bacterial blight pathogen Zhe 173 within 2 hours of ultraviolet irradiation or 40 days of storage. Specifically, heat treatment at 20-40℃ had no significant effect on the antibacterial effect, and heat treatment at 50-60℃ slightly decreased the antibacterial effect ( Figure 6 A); it has better stability under acidic conditions, that is, the antibacterial effect is stable when the pH is between 5 and 8, while the antibacterial effect decreases significantly under alkaline conditions ( Figure 6 B); there was no significant difference between 0 and 2 hours of ultraviolet irradiation ( Figure 6 C); Different storage time has little effect on the antibacterial effect. Although there is a downward trend after 10 days, the antibacterial zone can still reach about 4.3cm until 40 days ( Figure 6 D, no significant difference).

[0104] Comparative Experiment 1: Bacillus Velez D-1, Bacillus Velez SF305, and Bacillus Velez ML21 were stored at 4°C for 40 days with reference to the above-mentioned embodiments and the methods described in Experiment 4. It was found that the inhibition zone for Chinese physiological species Zhejiang 173 was significantly reduced (inhibition zone <2 cm), and the antibacterial effect was significantly reduced compared with that before storage.

[0105] Experiment 5: In vivo control of bacterial blight disease (caused by PXO86 and Zhe 173 bacterial blight species) by the biofungicide, biofungicide supernatant and biofungicide suspension obtained in Example 2

[0106] (1) Preparation of bacterial solution: Select the activated bacterial blight pathogen PXO86 and mix it in sterile water. Measure the OD 600 The value is about 0.5.

[0107] (2) The rice plants were divided into four groups, namely, a biofungicide group, a biofungicide supernatant group, a biofungicide suspension group, and a water treatment group. Each group had 10 plants, and three leaves were selected from each plant for use.

[0108] (3) Use scissors to dip the bacterial solution of Xanthomonas spp. and cut the rice leaves selected from each group 2 cm from the tip for inoculation. Dip the leaves in the bacterial solution again before cutting each time.

[0109] (4) The four groups of inoculated leaves were sprayed with the corresponding biofungicide, biofungicide supernatant, biofungicide bacterial suspension (obtained from steps 4), 5), and 6) of Example 2) and clean water, respectively, wherein the clean water group was the control (Mock) group, and the spraying was continued until the liquid dripped. The treatment was carried out 5 times a day, with an interval of 1 hour between each treatment; the treatment was continued for 5 days.

[0110] (5) 15 days after inoculation, the length of the lesions was measured and the resistance improvement rate was calculated = (the length of the lesions in the control group - the length of the lesions in the experimental group) / the length of the lesions in the control group × 100%.

[0111] In addition, the bacterial blight pathogen Zhe173 was used instead of the bacterial blight pathogen PXO86. The other operations remained unchanged and steps (1) to (5) were repeated.

[0112] The results are as follows Figure 7 shown.

[0113] The experimental results show that the length of rice leaf spots sprayed with biological fungicides is significantly shortened, and the resistance of rice to bacterial leaf blight can be increased by 53.8% to 62.7%.

[0114] Experiment 6: Analysis of the effects of the biofungicide obtained in Example 2 on rice growth and development

[0115] (1) Preparation of biofungicide: The biofungicide obtained in Example 2.

[0116] (2) Seed soaking: Select Wuyunjing No. 7 and Nanjing 9108 rice seeds with full grains, disinfect their surfaces, and soak them in a biocide for 10 h.

[0117] (3) Germination: The cells were transferred to a culture dish on a filter paper soaked with a biocide and cultured at 28°C for 72 h. The germination rate was then calculated, with clean water treatment as the control.

[0118] (4) Growth: Seeds with consistent germination were selected from the germinated seeds treated with clean water and those treated with biofungicides. The seeds were cultured in clean water or biofungicides in an incubator at 28°C (16 h light / 8 h dark) for 7 days, and the root length and aboveground length of the plants were measured.

[0119] The results are as follows Figure 8 As shown; Mock represents clean water treatment, and CCB represents biocide treatment.

[0120] The experimental results show that the biofungicide has no significant effect on the germination of rice seeds, has no negative impact on the growth of the above-ground and underground parts of the seedlings, and has a significant promoting effect on the root growth of Wuyunjing No. 7.

[0121] Comparative experiment 2:

[0122] Bacillus Velez D-1, Bacillus Velez SF305, and Bacillus Velez ML21 were used to experiment on rice Wuyunjing 7 in the manner described in Experiment 6. It was found that they had no promoting effect on the growth of the above-ground and underground parts of the seedlings.

[0123] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. Bacillus Velez Bacillus velezensis ) Bv-303, characterized by The accession number is: CGMCC No.23395.

2. The Bacillus Velezii as claimed in claim 1 ( Bacillus velezensis ) Application of Bv-303 in the prevention and control of rice white leaf blight.

3. A method for preparing a biological fungicide capable of preventing and controlling rice bacterial blight, characterized in that The following steps are involved: 1) Slant strains: The Bacillus Velezii of claim 1 ( Bacillus velezensis ) Bv-303 was cultured on NA slants at 27.5-28.5°C for 18-36 h; 2) Tablet activation: The bacteria obtained by the NA slant culture are inoculated onto a plate culture medium, wherein the plate culture medium is a NA culture medium; the culture conditions are 27.5-28.5° C. for 18-36 hours; 3) Liquid fermentation seeds: PDB medium was used as seed medium; The activated strains were inoculated into a shake flask filled with PDB medium, and cultured in an oscillator at 27.5-28.5°C and 150-250 rpm for 22-26 hours to obtain liquid fermentation seeds; 4) Liquid fermentation: The liquid fermented seeds are inoculated into a PDB medium at an inoculation rate of 1%, and cultured in an oscillator at 27.5-28.5°C and 150-250 rpm for 46-50 hours to obtain a fermentation liquid, which is a biological fungicide capable of preventing and controlling rice diseases.

4. Use of the biofungicide prepared by the method as claimed in claim 3 in preventing and controlling rice bacterial blight or promoting root growth of Wuyunjing No. 7.

Images