Paenibacillus polymyxa s437 and application thereof

Abstract

The application discloses a Paenibacillus polymyxa S437 and application thereof. The name of the strain is Paenibacillus polymyxa S437, and the preservation number is GDMCC No: 66085. The strain S437 has a good disease prevention effect on banana soft rot, and the disease prevention effect reaches more than 85%. The strain S437 has a wider bacteriostatic spectrum, can effectively inhibit the growth of multiple pathogenic fungi and bacteria such as fusarium and mycosphaerella citri, and has a good bacteriostatic effect on banana soft rot bacteria. The strain S437 can avoid the potential adverse effects of chemical pesticides on the environment and crop safety, and has potential commercial development and application value in the biological control of diseases.

Description

Technical Field

[0001] This invention belongs to the field of plant disease and pest control technology, specifically relating to a polymyxa Bacillus strain S437 and its applications. Background Technology

[0002] Soft rot, root rot, and stem base rot are among the major diseases affecting fruit trees, with the former two also being soil-borne diseases. Once they spread, they can have a devastating impact on the growth of fruit trees. Soft rot manifests as the death of the entire tree; root rot and stem base rot often present as browning and rotting of the roots and stem base, sometimes covered with a white mold layer, ultimately causing the entire tree to wilt and die. Currently reported pathogens causing soft rot include *Dickeya* spp., *Pectobacterium* spp., *Bacillus* spp., *Flavobacterium* spp., *Pseudomonas* spp., and *Klebsiella* spp. Pathogens causing root rot and stem rot include *Ralstonia solanacearum*, *Klebsiella variicola*, *Fusarium oxysorum*, *F. solani*, *Pythium*, *Neofusicoccum parvum*, and *Botryosphaeria dothidea*. These pathogens often infect plants one or more at a time, causing root rot and stem rot. The same pathogen from different plants can also vary in pathogenicity and host range. Because fruit trees are mostly perennial plants, and there is a lack of disease-resistant varieties and effective chemical fungicides, once root rot and stem rot occur, it can lead to the death of one or several plants, or even the complete destruction of the entire orchard.

[0003] Anthracnose is an airborne disease caused by fungi of the genus *Colletotrichum* spp. It has a wide host range and can cause damage during the growing season and post-harvest period. During the growing season, it mainly affects different parts of the plant, such as flowers, leaves, fruits, and stems. When anthracnose affects leaves, it initially invades from the leaf tip or margin, gradually expanding into yellowish-brown, cloud-like lesions, often in a "V" shape, which can cause significant leaf drop in severe cases. When anthracnose affects shoots, it often occurs at the shoot tip, initially appearing as light brown, oval lesions, eventually leading to the death of the entire shoot tip. When anthracnose affects fruits, it initially appears as small white spots, which gradually expand to cover the entire fruit under suitable environmental conditions. Commonly known pathogens include *Colletotrichum gloeosporioides*, *Colletotrichum acutatum*, *Colletotrichum karstii*, *Colletotrichum fructicola*, and *Colletotrichum siamense*.

[0004] Leaf spot diseases can occur in almost all plants throughout their entire growth period, including canker, brown spot, black spot, angular spot, and stripe disease, etc. They can be caused by fungi, bacteria, viruses, etc., affecting plant photosynthesis, leading to reduced yield, and greatly impacting plant productivity and economic value. Common leaf spot diseases in fruit trees are mainly caused by species such as Xanthomonas spp., Pseudomonas spp., Colletotrichum sp., Alternaria sp., Pestalotiopsis sp., and Nigrospora sp. Symptoms caused by fungi of the same genus can vary on different hosts, and they often occur singly or in combination on plants.

[0005] Dragon fruit canker is a major disease affecting dragon fruit production. Its pathogens include *Neoscytalidium dimidiatum* and *Fusarium oxysorum*, among others. *Neoscytalidium dimidiatum* is the primary pathogen in the Guangdong and Guangxi regions, damaging the fleshy stems, flowers, and fruits of dragon fruit. It easily spreads in patches and thrives in warm, rainy weather; its occurrence and spread are lower during the hot summer months. Currently, the main control method for dragon fruit canker is the application of chemical fungicides. However, due to the complexity of the pathogen and the emergence of drug resistance, chemical fungicides have limited effectiveness in controlling the disease, necessitating the search for new control methods.

[0006] *Paenibacillus polymyxa* is a Gram-positive, spore-forming, rod-shaped soil bacterium with nitrogen-fixing, phosphorus-solubilizing, antibiotic-producing, and plant-promoting properties. It is widely used in agricultural biological control, soil improvement, and industrial enzyme production, and is a common species in environmentally friendly microbial agents. Currently, *Paenibacillus polymyxa* is known to have antagonistic effects against pathogens causing citrus Huanglongbing (HLB), mango anthracnose, potato wilt, sweet potato root rot, soybean root rot, alfalfa root rot, and vegetable soft rot, while also exhibiting some plant-promoting effects; however, reports on its effects on other plant diseases are relatively few. Summary of the Invention

[0007] In order to overcome the shortcomings and deficiencies of the prior art, the purpose of this invention is to provide a strain of Bacillus polymyxa S437 and its application in the prevention and control of plant diseases.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] The first objective of this invention is to provide a strain of *Paenibacillus polymyxa*, named *Paenibacillus polymyxa* S437, which was deposited on April 2, 2025, at the Guangdong Provincial Microbial Culture Collection Center of the Institute of Microbiology, Guangdong Academy of Sciences, 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou, Guangdong Province, with accession number GDMCC No: 66085.

[0010] The second objective of this invention is to provide a reagent containing the aforementioned Bacillus polymyxa S437 as an active ingredient.

[0011] Preferably, the reagent is a biocontrol agent, and the Polymyxin Bacillus S437 is at least one of the following: live Polymyxin Bacillus S437 cells, cell fragments, fermentation broth, fermentation supernatant, and its metabolites.

[0012] The third objective of this invention is to provide the application of the above-mentioned polymyxa Bacillus S437 or reagent in the prevention and control of plant diseases.

[0013] Preferably, the plant diseases are bacterial plant diseases, stem rot, wilt, anthracnose, and / or leaf spot, etc.

[0014] Preferably, the pathogens of the bacterial diseases of the plants are *Pseudomonas aeruginosa*, *Pseudomonas citrus*, or *Ralstonia solanacearum*; the pathogens of the stem base rot of the plants are *Pseudomonas lychee*, *Pseudomonas xinhuiensis*, or *Pseudomonas pituitary*; the pathogens of the wilt diseases of the plants are *Pseudomonas aeruginosa*, *Pseudomonas coptis*, *Pseudomonas sibirica*, or *Pseudomonas guava*; the pathogens of the anthracnose diseases of the plants are fungi of the genus *Colletotrichum*; and the pathogens of the leaf spot diseases of the plants are *Xanthomonas* spp., *Pseudomonas* spp., *Ralstonia solanacearum* spp., *Alternaria* sp., *Nigrospora* sp., *Pestalotiopsis* sp., *Diaporthe* sp., or *Fusarium* sp.

[0015] Preferably, the banana soft rot pathogen is Klebsiella variicola, the citrus canker pathogen is Xanthomonas citri and / or Pseudomonas oryzihabitans, and the tomato bacterial wilt pathogen is Ralstonia solanacearum.

[0016] Preferably, the lychee stem rot pathogen is at least one of *Nigrospora sphaerica*, *Lasiodiplodia theobromae*, *Fusarium decemcellulare*, and *Plectosphaerella cucumerina*, the Xinhui citrus foot rot pathogen is *Fusarium oxysporum*, and the dragon fruit canker pathogen is *Neoscytalidium diimidiatum*.

[0017] Preferably, the wilt pathogen of banana is *Fusarium oxysporum* f.sp. Cubense race 4 (FOC4), the wilt pathogen of *Coptis chinensis* is *Plectosphaerella cucumerina*, the wilt pathogen of *Polygonatum sibiricum* is *Fusarium solani*, and the wilt pathogen of guava branches is *Neofusicoccum parvum*.

[0018] Preferably, the pathogen of the plant anthracnose is *C. gloeosporioides*, *C. fructicola*, *C. gloeosporioides*, *C. fructicola*, *C. gloeosporioides*, or *C. gloeosporioides*.

[0019] Preferably, the *Xanthomonas* spp. is *Xanthomonas citri*, the *Pseudomonas* spp. is *Pseudomonas oryzihabitans*, the *Ralstonia* spp. is *Ralstonia solanacearum*, the *Alternaria* sp. is *Alternata*, the *Nigrospora* sp. is *Nigrospora sphaerica*, the *Pestalotiopsis* sp. is *Pestalotiopsis microspora*, the *Diaporthe* sp. is *Diaporthe citri*, and the *Fusarium* sp. is *Fusarium sacchari*.

[0020] The present invention has the following advantages and effects compared with the prior art:

[0021] (1) The newly discovered polymyxa Bacillus S437 has a good disease prevention effect on banana soft rot, with a disease prevention effect of over 85%.

[0022] (2) The *Bacillus polymyxa* S437 provided by this invention has a broader antibacterial spectrum, effectively inhibiting the growth of 17 pathogenic fungi and 4 bacteria, including stem rot fungi or wilt fungi of 7 plant species, anthracnose fungi of 5 plant species, *Alternaria alternata* and *Ulva globosum*, *Melastoma citrus*, and *Fusarium oxysporum*. S437 also has a good inhibitory effect on the pathogen of banana soft rot. These functions have not been reported in the prior art. Since strain S437 was isolated from the rhizosphere soil of plants, its use in controlling soil-borne diseases can be considered. This strain avoids the potential adverse effects of chemical pesticides on the environment and crop safety, and has potential commercial development and application value in the biological control of diseases. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the morphology of strain S437 on PDA medium and NA medium (26℃, 7d).

[0024] Figure 2 Phylogenetic tree of strain S437.

[0025] Figure 3 This is a schematic diagram showing the confrontation culture of strain S437 with banana soft rot fungus, citrus canker fungus, and tomato bacterial wilt fungus.

[0026] Figure 4 This is a schematic diagram showing the confrontation culture (7 days) of strain S437 with anthracnose pathogens of mandarin orange, plum, black tiger, and pomelo.

[0027] Figure 5 This is a schematic diagram showing the confrontation culture (7 days) of strain S437 with wilt pathogens of guava, Coptis chinensis, banana, and Polygonatum sibiricum.

[0028] Figure 6 This is a schematic diagram showing the confrontation culture (7 days) of strain S437 with *Xinhui citrus foot rot* and *Lychee stem rot*.

[0029] Figure 7 This is a schematic diagram showing the confrontation culture (7 days) of strain S437 with dragon fruit canker pathogen, Buddha's hand leaf spot pathogen, guava leaf spot pathogen, and Citrus reticulata leaf spot pathogen.

[0030] Figure 8 This is a schematic diagram showing the results of 18 days of confrontation culture between strain S437 and *Fusarium wiltii*, *Fungiella asiatica*, *Citrus medica*, *Anthracnose spp.*, *Fungiella asiatica*, and *Litchi chinensis*.

[0031] Figure 9 This is a schematic diagram illustrating the disease control effect of strain S437 against banana soft rot. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed under conventional experimental conditions or according to the manufacturer's recommended experimental conditions. Unless otherwise specified, the materials and reagents used are commercially available.

[0033] Example 1: Isolation, Identification and Biological Characteristics Analysis of Paenibacillus polymyxa S437 I. Isolation of Strain S437

[0034] Rhizosphere soil from orchards in Zengcheng, Guangzhou, Guangdong Province was collected. A soil suspension was prepared with sterile water and evenly spread on the surface of PDA agar plates using a gradient dilution separation method. After the surface moisture of the plates was dried, they were incubated at 26°C. Single colonies were picked daily and subjected to confrontation culture with Klebsiella variicola (Kv), the causal agent of banana soft rot. After primary and secondary screening, a strain of Bacillus polymyxa with significant inhibitory effect on Klebsiella variicola was obtained and named S437.

[0035] II. Morphological characteristics of strain S437

[0036] Both strain S437 and PDA (potato dextrose agar powder 39 g / L) medium and NA medium at 26℃ exhibit different morphologies on different media. On PDA medium, the colonies are translucent and viscous; on NA medium, they are milky white and smooth. Figure 1 ).

[0037] III. Identification of the taxonomic attributes of strain S437

[0038] Strain S437 was inoculated into 100 mL of PDB (potato dextrose powder 24 g / L) liquid medium and cultured overnight at 26°C and 180 rpm in a shaker. The cells were collected by centrifugation at 10,000 rpm for 7 min, ground in liquid nitrogen, and genomic DNA was extracted from strain S437 using a standard DNA extraction kit. Using the genomic DNA of strain S437 as a template, PCR amplification and sequencing were performed using the universal 16S rDNA primers 27F (SEQ ID NO. 2, 5'-AGAGTTTGATCMTGGCTCAG-3') and 1492R (SEQ ID NO. 3, 5'-GGTTACCTTGTTACGACTT-3'). The 16S rDNA sequencing results of strain S437 (SEQ ID NO. 1) were compared with BLASTn on NCBI to obtain the sequence information of closely related strains. Phylogenetic trees were constructed by downloading the 16S rDNA sequences of closely related species and related type strains. Figure 2 Using molecular systematics methods, strain S437 was identified as Paenibacillus polymyxa S437.

[0039] Paenibacillus polymyxa S437 was deposited on April 2, 2025, at the Guangdong Provincial Microbial Culture Collection Center (GDMCC), located at the Institute of Microbiology, Guangdong Academy of Sciences, 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou, Guangdong Province, 510070, China. The accession number is GDMCC No. 66085, and the classification name is Paenibacillus polymyxa S437.

[0040] In this invention, Paenibacillus polymyxa S437 is abbreviated as S437.

[0041] Example 2: Cultivation and fermentation of Bacillus polymyxa S437

[0042] I. Cultivation of strain S437

[0043] Using an inoculation loop, scrape an appropriate amount of bacterial cells from the surface of the S437 colony, streak them onto the surface of PDA medium, and incubate overnight at 26°C. Figure 1 ).

[0044] II. Preparation of fermentation broth for strain S437

[0045] Using an inoculation loop, scrape an appropriate amount of bacterial cells from the surface of the S437 colony, inoculate it into PDB liquid medium, and then incubate it overnight at 26°C and 180 rpm as a seed culture.

[0046] Using a sterile 1mL pipette tip, 1mL of seed culture was inoculated into a 250mL sterile Erlenmeyer flask containing 100mL of PDB liquid culture medium. After incubation at 26℃ and 180rpm for 3 days, the fermentation broth was filtered through a single layer of sterile gauze and the filtrate was collected to obtain the fermentation broth of strain S437.

[0047] Example 3: Antagonistic effect of Bacillus polymyxa S437 on plant pathogenic bacteria

[0048] This experiment selected *Klebsiella variicola* (Kv), the causal agent of banana soft rot; *Xanthomonas citri* (Xac), the causal agent of citrus canker; *Pseudomonas oryzihabitans* (Po), the causal agent of citrus canker; and *Ralstonia solanacearum* (Rs), the causal agent of bacterial wilt of tomato, and cultured them in confrontation with S437 to determine the antibacterial activity of S437 against plant pathogenic bacteria. Figure 3 ).

[0049] Banana soft rot pathogen, citrus canker pathogen (Xac), citrus canker pathogen (Po), tomato bacterial wilt pathogen, and biocontrol bacterium S437 were inoculated separately into LB liquid medium (10.0 g / L tryptone, 5.0 g / L yeast extract, 5.0 g / L sodium chloride) using a sterile inoculation loop and cultured overnight at 26°C. The next day, 1% of the above strains incubated overnight were inoculated into fresh LB liquid medium and cultured overnight to obtain bacterial suspensions. Then, the bacterial suspensions of Kv, Xac, Po, and Ps were added separately to sterilized LB solid medium (10.0 g / L tryptone, 5.0 g / L yeast extract, 5.0 g / L sodium chloride, 10 g / L agar) (60 μL / 40 mL), shaken well, and poured into plates. After the plates cooled, sterilized Oxford cups (10×8×6±0.1mm) were placed in the center of the plates, and the shaken biocontrol bacteria S437 (30μL / plate) suspension was injected into the cups. The plates were incubated overnight at 26℃. Each treatment was replicated 5 times. The size of the inhibition zone was observed.

[0050] The results are as follows Figure 3 As shown, strain S437 exhibits strong inhibitory effects against all tested plant pathogenic bacteria. The inhibition zone diameter of strain S437 against *Klebsiella variicola* (Kv), which causes banana soft rot, was 15 mm, and the control efficacy against banana soft rot reached 85% in pot experiments. The inhibition zone diameters against *Xanthomonas citri* (Xac) and *Pseudomonas oryzihabitans* (Po), which cause citrus canker, were 18 mm and 25 mm, respectively. The inhibition zone diameter against *Ralstonia solanacearum* (Rs), which causes tomato bacterial wilt, was 16 mm. Therefore, strain S437 demonstrates good potential for controlling bacterial plant diseases.

[0051] Example 4: Antagonistic effect of Bacillus polymyxa S437 against plant anthracnose pathogens

[0052] This invention used a confrontation culture method to determine the antifungal activity of strain S437 against *Colletotrichum* fungi that cause anthracnose on mandarin oranges, black tiger oranges, Sanhua plums, pomelos, and guavas. The tested fungi were *C. gloeosporioides* from mandarin oranges, black tiger oranges, and guavas, and *C. fructicola* from Sanhua plums and pomelos. Figure 4 and Figure 8 ).

[0053] Five-mm diameter hyphal fragments were collected from the edge of freshly cultured *Colletotrichum* colonies (5 days prior) and inoculated onto fresh PDA agar plates 2 cm from the edge. S437 cells were scraped using an inoculation loop and spread 4.5 cm from the pathogen, serving as a control (no S437 inoculation). Five replicates were performed for each treatment. After incubating the plates at 26°C for 5 days, the width of the inhibition zone was measured, and the inhibition rate was calculated. Inhibition rate (%) = (4.5 - width of inhibition zone in treatment group) / 4.5 × 100.

[0054] The results are as follows Figure 4 As shown, strain S437 exhibits strong antifungal effects against all tested *C. fructicola* fungi. Strain S437 showed the strongest antifungal effect against *C. fructicola*, the anthracnose causal agent of *Prunus triloba*, at 85.32%; and the weakest antifungal effect against *C. gloeosporioides*, the anthracnose causal agent of *C. gloeosporioides*, at 35.24%. Figure 8 As shown, after 18 days of confrontation culture against *C. gloeosporioides*, the causal agent of anthracnose in guava, strain S437 showed an inhibition rate of 53.26%, indicating that the antibacterial activity of S437 against anthracnose has a certain persistence. This demonstrates that strain S437 has good potential for controlling plant anthracnose.

[0055] Example 5: Antagonistic effect of Bacillus polymyxa S437 against plant stem rot / wilt pathogens

[0056] This experiment selected *Neofusicoccum parvum*, *Fusarium solani*, *F. oxysporum FOC4*, *Neoscytalidium diimidiatum*, *Plectosphaerella cucumerina*, *F. oxysporum*, and *Nigrospora sphaerica*, *Lasiodiplodia theobromae*, *Fusarium decemcellulare*, and *Plectosphaerella cucumerina* as pathogens of plant stem rot and wilt, respectively, and cultured them in confrontation with S437 to determine the antibacterial activity of S437 against these pathogens. Figures 5-8 ).

[0057] Guava twig blight, Polygonatum wilt, banana wilt, dragon fruit canker, Coptis chinensis wilt, Citrus citrus foot rot, and litchi stem rot were inoculated onto PDA agar plates and incubated at 26℃ for 5 days. Mycelial blocks with a diameter of 5 mm were then collected from the edge of the colonies and inoculated onto new PDA agar plates 2 cm from the edge. S437 cells were scraped using an inoculation loop and spread 4.5 cm from the pathogen. The treatment without S437 inoculation served as a control. Five replicates were performed for each treatment. After incubating the plates at 26℃ for 7 days, the width of the inhibition zone was measured, and the inhibition rate was calculated. Inhibition rate (%) = (4.5 - width of inhibition zone in treatment group) / 4.5 × 100.

[0058] The results are as follows Figures 5-7 As shown, strain S437 exhibited strong inhibitory effects against all tested pathogens of stem rot / wilt. The inhibition rate against *Fusarium solani* was 25.2%; against *Fusarium canker* of dragon fruit, 38.56%; against *Fusarium wilt* of banana, 58.64%; against *Fusarium solani* of *Polygonatum sibiricum*, 45.23%; against *Fusarium oxysporum* of *Coptis chinensis*, 75.42%; against *Fusarium oxysporum* of *Citrus reticulata*, 48.25%; and against *Fusarium solani* of litchi stem rot (*N. sphaerica* 33.14%, *L. theobromae* 44.12%, *F. decemcellulare* 54.87%, and *P. cucumerina* 28.54%). Figure 8 As shown, after 18 days of confrontation culture against *P. cucumerina*, the causal agent of *Fusarium oxysporum*, and *F. decemcellulare*, strain S437 still maintained inhibition rates of 56.89% and 54.12%, respectively. There was no significant difference in the inhibitory effect of strain S437 against *F. decemcellulare* after 7 days and 18 days of culture. Therefore, strain S437 exhibits long-lasting inhibitory effects against *Fusarium oxysporum* / *Fusarium oxysporum*, demonstrating good biocontrol potential.

[0059] Example 6: Antagonistic effect of Bacillus polymyxa S437 against three important plant pathogenic fungi

[0060] This experiment used a confrontation culture method to determine the antifungal activity of strain S437 against four pathogenic fungi that cause plant diseases. These pathogenic fungi include *Alternaria alternata* (Citrus reticulata var. chinensis), *Pestalotiopsis microspora* (Guava), *Diaporthecitri* (Citrus medica var. sarcodactylis), and *Fusarium sacchari* (Banana), all of which cause leaf spot disease. The assay method was the same as in Example 5.

[0061] The results are as follows Figures 7-8 As shown, strain S437 exhibited strong antifungal effects against all four tested plant pathogenic fungi. The highest inhibition rate (51.35%) was observed against *A. alternata*, the pathogen causing leaf spot disease in citrus red, and the inhibition rates against other pathogens were all above 43.19%. Figure 8 As shown, after 18 days of confrontational culture, strain S437 still maintained a 10.14% inhibition rate against *F. sacchari*, the pathogen of banana leaf spot, and 59.67% and 21.34% inhibition rates against *D. citri*, the pathogen of bergamot leaf spot, and *P. microspora*, the pathogen of guava leaf spot, respectively. This indicates that strain S437 not only has a broad antibacterial spectrum but also exhibits a certain degree of persistence. Therefore, it has good development and application value in the biological control of plant diseases.

[0062] Example 7: The preventive effect of Bacillus polymyxa S437 on banana soft rot

[0063] This experiment used the live root irrigation inoculation method during the banana seedling stage to determine the disease control effect of the fermentation broth of strain S437 on banana soft rot.

[0064] Inoculum preparation: Prepare inoculum solutions with concentrations of OD0.05 and OD0.05. 600 =2.0 of strain S437 bacterial culture and 2×10 6 A fresh suspension of Klebsiella variicola (Kv) spores / mL was used as the stock solution. An equal volume of strain S437 was mixed with the Klebsiella variicola stock solution to prepare the inoculum for the treatment group. The final concentration (OD) of strain S437 in this inoculum was... 600 =1.0 and the final concentration of banana soft rot pathogen is 1×10 6 spores / mL. The banana soft rot pathogen stock solution was prepared by mixing an equal volume of distilled water to a final concentration of 1×10⁻⁶. 6 The inoculum for the positive control group of banana soft rot pathogen was prepared with 1 spore / mL. Sterile distilled water was used as the negative control (CK). All treatments were prepared and used immediately.

[0065] Inoculation: Banana seedlings were planted in 8cm diameter seedling cups in a greenhouse. Two seedlings with uniform growth at the 6-leaf stage were transplanted into one pot. The inoculum solution for the treatment group and the control group was applied to the root zone of the seedlings by drenching, with 35mL per seedling. Two pots of banana seedlings were inoculated for each treatment, and each treatment was repeated three times.

[0066] Disease survey: After inoculation, the disease incidence of the plants was monitored. The disease severity of each plant was investigated at 6 and 8 months after inoculation, and the disease index and disease control effect were calculated. Disease control effect (%) = (Disease index of positive control group - Disease index of treatment group) / Disease index of positive control group × 100.

[0067] The results are as follows Figure 9 As shown, bacterial suspension of strain S437 has a good preventive effect against banana soft rot. Compared with the positive control inoculated only with banana soft rot pathogen, OD at the same time point was significantly higher. 600 Treatment with S437 bacterial suspension at a concentration of 2.0 resulted in greener leaves, better growth, milder soft rot symptoms, and a significantly lower disease index in banana plants. At 6 and 8 months post-inoculation, the disease control efficacy of strain S437 was 79% and 85%, respectively. This indicates that strain S437 provides relatively long-term protection against banana soft rot.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A strain of *Bacillus polymyxa* ( Paenibacillus polymyxa S437, with accession number GDMCC No: 66085.

2. A reagent, characterized in that, It contains the polymyxa S437 as described in claim 1 as an active ingredient.

3. The reagent according to claim 2, characterized in that, The reagent is a biocontrol agent, and the Polymyxin Bacillus S437 is at least one of live Polymyxin Bacillus S437 cells and fermentation broth.

4. The application of the *Bacillus polymyxa* S437 according to claim 1 or the reagent according to any one of claims 2-3 in the prevention and control of plant diseases, characterized in that: The plant diseases mentioned are bacterial plant diseases, stem rot, wilt, anthracnose, and / or leaf spot. The pathogens of the bacterial diseases of the plants are *Bacillus thuringiensis*, *Bacillus canker*, or *Bacillus spp.*; the pathogens of the stem base rot of the plants are *Bacillus lychee* stem rot, *Bacillus xinhuiensis* foot rot, or *Bacillus pituitary*; the pathogens of the wilt diseases of the plants are *Bacillus fusarium*, *Bacillus coptis*, *Bacillus sibiricum*, or *Bacillus guava* branch blight; the pathogens of the leaf spot diseases of the plants are *Alternaria alternata* (…). A. alternata ), Microsporum simulans ( P. microspora ), Citrus intercalation diatoms ( D. citri ) or Fusarium canis ( F. sacchari ); The banana soft rot pathogen is Klebsiella pneumoniae (Klebsiella pneumoniae). Klebsiella variicola The pathogen causing citrus canker is Xanthomonas citrus (…). Xanthomonas citri ) and / or Pseudomonas oryzae ( Pseudomonas oryzihabitans The bacterial wilt pathogen of tomatoes is *Ralstonia solanacearum* (Ralstonia solanacearum). Ralstonia solanacearum ); The pathogen causing lychee stem rot is *Ulva globulus* (…). Nigrospora sphaerica ), Dioscorea opposita ( Lasiodiplodia theobromae Fusarium multiseptum ( Fusarium decemcellulare ) and Cucumber Flocculation ( Plectosphaerella cucumerina At least one of the following, wherein the fungus causing the foot rot of Xinhui citrus is Fusarium oxysporum (… Fusarium oxysporum The pathogen causing dragon fruit canker is *Neocytospora datura* (…). Neoscytalidium dimidiatum ); The fungus causing banana wilt is Fusarium oxysporum, specifically race 4 of the Cuban variant. Fusarium oxysporum f.sp. Cubense race 4), the pathogen causing the wilt of Coptis chinensis is *Schmidtia cucumeris* (race 4). Plectosphaerella cucumerina The pathogen causing the wilt of Polygonatum sibiricum is Fusarium solani (…). Fusarium solani The guava twig blight pathogen is *Clostridium neoformans* (…). Neofusicoccum parvum ); The pathogens causing anthracnose in the plants mentioned are *Anthracnose fungus*, *Anthracnose fungus* of *Prunus triloba*, *Anthracnose fungus* of *Hemiberlesia lataniae*, *Anthracnose fungus* of *Pomelo*, or *Anthracnose fungus* of *Guava*; the *Anthracnose fungus* of *Prunus triloba* is *Colletotrichum gloeosporioides* (…). C. gloeosporioides The anthracnose pathogen of the Sanhua plum is *Colletotrichum oryzae* (…). C. fructicola The anthrax bacterium mentioned is *Colletotrichum gloeosporioides* (also known as *Colletotrichum gloeosporioides*). C. gloeosporioides The anthracnose fungus of the pomelo is *Colletotrichum oryzae* (…). C. fructicola The guava anthrax pathogen is *Colletotrichum gloeosporioides* (Gollum anthrax). C. gloeosporioides ).

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