Firmicutes and their applications

Abstract

The application relates to the field of microbial technology, and discloses a pristinamycetincl strain and application thereof. The preservation number of the strain is CCTCC NO: M 2026288. The pristinamycetincl strain has an excellent prevention and treatment effect on banana wilt, can significantly promote plant growth, has the abilities of phosphorus solubilization and nitrogen fixation, and provides a good foundation for developing and applying the strain in a microbial fertilizer product.

Description

Technical Field

[0001] This invention relates to the field of microbial technology, specifically to a strain of Priestella megaterium and its applications. Background Technology

[0002] Bananas are an important economic crop in tropical and subtropical regions. Fusarium wilt, caused by Fusarium oxysporum caudata, is a devastating soil-borne disease that threatens the banana industry. This pathogen has strong survival capabilities and a wide transmission route. Among its strains, tropical race 4 has the widest pathogenic range and causes the most severe damage, resulting in significant yield reductions or even total crop failure in affected fields, seriously hindering the development of banana cultivation.

[0003] Currently, the main methods for controlling this disease in production include disease-resistant breeding, agricultural management, chemical agents, and biological control, but all have significant shortcomings. Traditional hybrid breeding is limited by the seedless nature of bananas, and disease-resistant varieties generally suffer from poor quality and poor adaptability. Agricultural rotation and soil treatment are slow to take effect and have low land use efficiency, making it difficult to completely eliminate pathogens. Chemical fungicides can only temporarily inhibit pathogens and cannot kill dormant spores in the soil. Long-term use can easily induce drug resistance in pathogens, and it can also damage the soil microecology, posing risks of pesticide residues and environmental pollution.

[0004] Existing biocontrol microbial agents mostly only have antibacterial and disease-preventing effects, with limited functions. They lack the ability to improve soil and enhance nutrients, requiring additional application of chemical fertilizers. At the same time, the strains have weak field colonization ability and unstable control efficacy, making it difficult to meet both disease prevention and crop nutritional needs.

[0005] Therefore, the industry urgently needs to develop microbial resources and preparations that have multiple functions of promoting growth and preventing diseases, so as to combine green disease control with crop growth promotion and soil fertilization. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a strain of *Priestella megaterium* and its applications. This strain exhibits good control efficacy against banana wilt disease, significantly promotes plant growth, and also possesses phosphorus solubilization and nitrogen fixation functions, laying a solid foundation for its development into microbial fertilizers.

[0007] To achieve the above objectives, the first aspect of the present invention provides a strain of Priestella megaterium (… Priestia megaterium The strain has the accession number CCTCC NO: M 2026288.

[0008] A second aspect of the present invention provides a microbial inoculant, the microbial inoculant comprising *Priestella giantiflora* as described in claim 1.

[0009] The third aspect of this invention provides the use of *Priestella megaterium* as described in the first aspect, or the microbial agent as described in the second aspect, in the preparation of a biological agent for the prevention and control of banana wilt disease.

[0010] The fourth aspect of this invention provides the use of *Priestella giantiflora* as described in the first aspect, or the microbial agent as described in the second aspect, in the preparation of a biological agent for inhibiting the growth of the pathogen causing banana wilt.

[0011] The fifth aspect of this invention provides a method for controlling banana wilt disease, which involves applying the *Priestella megaterium* described in the first aspect, or the microbial agent described in the second aspect, to the roots and / or pseudostem of the banana plant.

[0012] The sixth aspect of this invention provides the use of the *Priestella giantiflora* described in the first aspect, or the microbial agent described in the second aspect, in the preparation of a biological agent for promoting the growth of banana plants.

[0013] The seventh aspect of the present invention provides a method for promoting the growth of banana plants by applying the *Priestella megaterium* described in the first aspect or the microbial agent described in the second aspect to the roots and / or pseudostems of the banana plant.

[0014] The eighth aspect of the present invention provides the use of *Priestella giantiflora* as described in the first aspect, or the microbial agent as described in the second aspect, in the decomposition of inorganic phosphorus.

[0015] The ninth aspect of the present invention provides the application of the Priestella giantiflora described in the first aspect, or the microbial agent described in the second aspect, in nitrogen fixation.

[0016] Through the above technical solution, the present invention has at least the following beneficial effects: The *Priestella megaterium* strain of this invention is a high-performance endophytic antagonistic bacterium. This strain exhibits significant control effects against banana wilt disease, effectively inhibiting pathogen damage. Simultaneously, this strain has a marked growth-promoting effect on banana plants, contributing to improved plant vigor. Furthermore, this strain possesses nitrogen-fixing and inorganic phosphorus-solubilizing activities, improving soil nutrient utilization efficiency. The acquisition of this strain effectively expands the biocontrol microbial resource pool for banana wilt disease and has broad application prospects.

[0017] Biological Preservation The *Priestella giantiformis* provided by this invention is classified and named as follows: Priestia megaterium YN2303 was deposited on January 29, 2026, at the China Center for Type Culture Collection (CCTCC), located at 299 Bayi Road, Wuchang District, Wuhan, Hubei Province, China (Wuhan University), with accession number CCTCC NO: M 2026288. Attached Figure Description

[0018] Figure 1This is the phylogenetic tree of *Priestella giantiflora* YN2303 in this invention; Figure 2 The inhibitory effect of *Priestella megaterium* YN2303 on the pathogen of banana wilt in this invention (left: *Priestella megaterium* YN2303 treatment group; right: control group). Figure 3 This is a graph showing the inorganic phosphorus solubilization capacity of *Priestella giantiflora* YN2303 in this invention. Figure 4 This is a diagram showing the nitrogen fixation capacity of *Priestella giantiflora* YN2303 in this invention; Figure 5 The control effect of Priestella giantiflora YN2303 on banana wilt in potted plants in this invention (a: YN2303+TR4; b: CK+TR4). Figure 6 This invention describes the growth-promoting effect of *Priestella giantiflora* YN2303 on banana plants (a: YN2303; b: CK). Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] In this invention, unless otherwise specified, "Priestella megaterium / strain YN2303", "Priestella megaterium / strain of this invention", and "Priestella megaterium / strain CCTCC NO: M 2026288" all refer to the same strain, namely the Priestella megaterium strain with accession number CCTCC NO: M 2026288. The above expressions have the same meaning and can be used interchangeably.

[0021] During their research, the inventors of this invention isolated a strain of *Priscilla megaterium* from the root system of banana plants collected in Lianghe County, Dehong Prefecture, Yunnan Province. Priestia megaterium The study found that it is an endophytic antagonistic bacterium. This strain has excellent control effects on banana wilt disease, can significantly promote the growth of banana plants, and has the ability to fix nitrogen and solubilize inorganic phosphorus, further enriching the biocontrol strain resources for banana wilt disease.

[0022] The first aspect of this invention provides a strain of Priestella megaterium ( Priestia megaterium The strain has the accession number CCTCC NO: M 2026288.

[0023] A second aspect of the present invention provides a microbial inoculant, the microbial inoculant comprising *Priestella giantiflora* as described in claim 1.

[0024] In this invention, preferably, based on the total mass of the bacterial agent, the viable bacterial content of *Priscilla megaterium* is ≥10⁻⁶. 8 CFU / mL, more preferably 1×10⁻⁶ 8 -1×10 9 CFU / mL.

[0025] The third aspect of this invention provides the use of *Priestella giantiflora* as described in the first aspect, or the microbial agent as described in the second aspect, in the preparation of a biological agent for the prevention and control of banana wilt disease.

[0026] The fourth aspect of this invention provides the use of *Priestella giantiflora* as described in the first aspect, or the microbial agent as described in the second aspect, in the preparation of a biological agent for inhibiting the growth of the pathogen causing banana wilt.

[0027] In this invention, preferably, the pathogen causing banana wilt is *Fusarium oxysporum* var. *cubicans* (a specific strain of *Fusarium oxysporum*). Fusarium oxysporum f. sp. cubense More preferably, Fusarium oxysporum Cuban-specific type ( Fusarium oxysporum f. sp. cubense )4 physiological race.

[0028] The fifth aspect of this invention provides a method for controlling banana wilt disease, which involves applying the *Priestella megaterium* described in the first aspect, or the microbial agent described in the second aspect, to the roots and / or pseudostem of the banana plant.

[0029] In this invention, preferably, the *Priestella giantiflora* described in the first aspect or the microbial agent described in the second aspect is applied to the roots of the banana plant.

[0030] In this invention, preferably, the *Priestella megaterium* is applied in the form of a fermentation broth; the fermentation broth is the fermentation broth of *Priestella megaterium* as described in the first aspect, or the supernatant fermentation broth after removing the bacterial cells.

[0031] More preferably, the fermentation broth is the cell-free fermentation broth of *Priestella giantiflora* as described in the first aspect.

[0032] More preferably, the number of viable bacteria in the fermentation broth is 1×10⁻⁶. 8 -1×10 9 CFU / mL, for example, can be 1×10⁻⁶. 8 CFU / mL, 2×10 8 CFU / mL, 5×10 8CFU / mL, 8×10 8 CFU / mL, 9×10 8 CFU / mL, 1×10 9 CFU / mL or any value or range between the above values.

[0033] In this invention, the application includes any one or more methods such as irrigation and root drenching; it can be applied preventively before the disease occurs or applied for treatment after the disease occurs, and can be applied once or at intervals according to actual cultivation needs.

[0034] In this invention, preferably, the dosage of *Priscilla megaterium* is 5 × 10⁻⁶. 9 -5×10 10 CFU / strain.

[0035] The sixth aspect of this invention provides the use of the *Priestella giantiflora* described in the first aspect, or the microbial agent described in the second aspect, in the preparation of a biological agent for promoting the growth of banana plants.

[0036] The seventh aspect of the present invention provides a method for promoting the growth of banana plants by applying the *Priestella megaterium* described in the first aspect or the microbial agent described in the second aspect to the roots and / or pseudostems of the banana plant.

[0037] In this invention, preferably, the *Priestella giantiflora* described in the first aspect or the microbial agent described in the second aspect is applied to the roots of the banana plant.

[0038] In this invention, preferably, the *Priestella megaterium* is applied in the form of a fermentation broth; the fermentation broth is the fermentation broth of *Priestella megaterium* as described in the first aspect, or the supernatant fermentation broth after removing the bacterial cells.

[0039] More preferably, the fermentation broth is the cell-free fermentation broth of *Priestella giantiflora* as described in the first aspect.

[0040] More preferably, the number of viable bacteria in the fermentation broth is 1×10⁻⁶. 8 -1×10 9 CFU / mL, for example, can be 1×10⁻⁶. 8 CFU / mL, 2×10 8 CFU / mL, 5×10 8 CFU / mL, 8×10 8 CFU / mL, 9×10 8 CFU / mL, 1×10 9 CFU / mL or any value or range between the above values.

[0041] In this invention, the application includes any one or more of the following methods: watering, root drenching, foliar spraying, misting, and smearing; it can be applied once or multiple times at certain intervals according to the different growth stages of the banana plant.

[0042] In this invention, preferably, the dosage of *Priscilla megaterium* is 5 × 10⁻⁶. 9 -5×10 10 CFU / strain.

[0043] The eighth aspect of the present invention provides the use of *Priestella giantiflora* as described in the first aspect, or the microbial agent as described in the second aspect, in the decomposition of inorganic phosphorus.

[0044] In this invention, preferably, the *Priestella megaterium* or microbial inoculant is applied to the rhizosphere soil of crops to achieve the decomposition and utilization of inorganic phosphorus.

[0045] The ninth aspect of the present invention provides the application of the Priestella giantiflora described in the first aspect, or the microbial agent described in the second aspect, in nitrogen fixation.

[0046] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0047] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available products purchased from regular chemical / biological reagent or material suppliers, and all reagents are of analytical grade.

[0048] NA medium formula: 10g glucose, 20g agar, 3g beef extract, 1g yeast extract, 10g peptone, 1000mL distilled water, pH 7.0. Liquid NA medium is prepared without agar. PDA medium formula: 200g potato, 20g glucose, 15g agar, 1L water, pH 7.0. Liquid PDA medium is prepared without agar.

[0049] Example 1 This embodiment illustrates the acquisition, identification, and preservation of Priestella megaterium YN2303.

[0050] (I) Isolation and purification of strains A strain of Priestella megaterium was isolated from the root system of banana plants in Lianghe County, Dehong Prefecture, Yunnan Province. Priestia megaterium It was named *Priestella megaterium* YN2303 (accession number CCTCC NO: M 2026288).

[0051] The specific steps are as follows: After rinsing the banana plant roots with sterile water, surface disinfection was performed with 75wt% ethanol for 60 seconds, followed by rinsing with sterile water and air drying. Following root disinfection, the roots were cut into small pieces under sterile conditions using a sterile knife for isolation. Pathogens were isolated using the streak plating method, streaked onto NA medium, and incubated at 30°C for 1 day. Single colonies were picked and purified three times before being stored at 4°C for later use.

[0052] (II) Identification of strains Molecular identification: Genomic DNA was extracted using a bacterial genomic DNA extraction kit. A partial 16S rDNA sequence of the antagonistic bacteria was amplified by PCR using universal primers 27F / 1492R, with upstream primer 5'-AGAGTTTGATCCTGGCTCAG-3' (SEQ ID NO: 1) and downstream primer 5'-GGTTACCTTGTTACGACTT-3' (SEQ ID NO: 2). Primer sequences were synthesized by Shanghai Sangon Biotech Co., Ltd., and the PCR amplification products were sent to Shanghai Sangon Biotech Co., Ltd. for sequencing.

[0053] The total volume of the PCR reaction system was 50 μL, and the formulation of each component was as follows: 0.5 μL TaKaRa LA-Taq enzyme, 2 μL DNA template, 5 μL 10×PCR Buffer, 8 μL dNTP Mixture, 2 μL each of upstream and downstream primers, and 30.5 μL double-distilled water.

[0054] PCR program: 94℃ pre-denaturation for 5 min, 94℃ for 30 s, 54℃ for 30 s, 72℃ for 1 min, 30 cycles; extension at 72℃ for 7 min. The sequenced data were compared with the NCBI database using BLAST homology. Its 16S rDNA sequence, as shown in SEQ ID NO: 3, is similar to that of *Priscilla megaterium* (…). Priestia megaterium The homology between the two species reached 99.79%, and a phylogenetic tree was constructed using MEGA5.0 software. Figure 1 The results showed that the strain was related to *Priscilla megaterium* (…). Priestia megaterium The strain YN2303 was identified as Priestella megaterium because it was closely related to the parent strain and clustered into one line.

[0055] The sequence of SEQ ID NO: 3 is as follows:

[0056] Example 2 This embodiment is used to illustrate the test of the antibacterial activity of *Priestella megaterium* YN2303 against *Fusarium wilt*, the causal agent of banana wilt.

[0057] Fusarium wilt of bananas, race 4 (abbreviated) Foc 4) As an indicator bacterium, the antibacterial activity of strain YN2303 of *Priscilla megaterium* was determined using conventional confrontation culture methods. The pathogen of banana wilt is *Fusarium oxysporum* var. *cubicans*. Fusarium oxysporum f. sp. cubense ( Foc strain No. 4 Foc 15-1 was isolated and preserved by the banana research team of the Institute of Agricultural Environment and Resources, Yunnan Academy of Agricultural Sciences. PDA medium was used for both pathogen culture and antibacterial tests.

[0058] The inhibition rate of the strains was determined using the plate confrontation method. The pathogen of banana wilt was transferred to PDA plates and incubated at 28℃ for 7 days. Using a sterilized punch, 5mm diameter mycelial cakes were collected along the edge of the colony and inoculated into the center of the PDA plate. Then, *Priscilla megaterium* YN2303 was symmetrically inoculated at 25mm from the center of the PDA plate edge, with 4 spots per plate. PDA plates inoculated only with the tested pathogen served as a control group. Each treatment was repeated 3 times. After incubation at 28℃ for 7 days, the inhibition effect was observed, and the cross-hatching method was used to determine the inhibition rate of the pathogen of banana wilt (…). Foc The diameter of 15-1) was measured, and the antibacterial rate was calculated. The results are shown in Table 1 and... Figure 2 As shown.

[0059] Inhibition rate (%) = (Coronavirus colony diameter of control pathogen - Coronavirus colony diameter of treatment pathogen) / Control diameter × 100; Table 1

[0060] From Table 1 and Figure 2 It can be seen that the control group colonies covered the entire surface of the plate (9cm petri dish, with bacterial growth covering the entire surface), while *Priestella megaterium* YN2303 was effective against the pathogen of banana wilt (…). Foc The growth of strain 15-1) showed strong antagonistic effect, with an average inhibition rate of 72.59%, indicating that this strain has a significant inhibitory effect on pathogens.

[0061] Example 3 This embodiment is used to illustrate the determination of the inorganic phosphorus solubilization and nitrogen fixation capabilities of Priestella megaterium YN2303.

[0062] (a) Determination of inorganic phosphorus solubility Inorganic phosphorus solid culture medium: glucose 10g, (NH4)2SO4 0.5g, NaCl 0.3g, KCl 0.3g, MgSO4•7H2O 0.3g, FeSO4•7H2O 0.03g, MnSO4•4H2O 0.03g, Ca3(PO4)2 10g, agar 18g, distilled water 1000mL, pH 7.0-7.5.

[0063] Priestella megaterella YN2303 was inoculated onto inorganic phosphorus solid agar plates, with one colony per plate and three replicates. The plates were incubated at 30°C for 7 days. After 7 days, the phosphorus solubilizing activity was determined by observing whether a clear zone was formed around the colony, and the diameter of the clear zone and the colony diameter were measured.

[0064] The results are as follows Figure 3 As shown, a clear halo forms around the YN2303 colony, indicating that the YN2303 strain has the ability to degrade inorganic phosphorus.

[0065] The diameters (D) of the three solubilization zones were 1.75 cm, 1.8 cm, and 1.7 cm, respectively; the colony diameters (d) were 0.65 cm, 0.7 cm, and 0.6 cm, respectively; and the D / d ratios were 2.69, 2.57, and 2.83, respectively, with an average of 2.70.

[0066] (II) Determination of nitrogen fixation capacity Ashby medium: 0.2g potassium dihydrogen phosphate, 0.2g magnesium sulfate, 0.2g sodium chloride, 5g calcium carbonate, 10g mannitol, 0.1g calcium sulfate, 18g agar, 1000mL distilled water, pH 6.8-7.0.

[0067] The *Priestella megaterium* strain was inoculated onto Assumption agar plates, one colony per plate, with three replicates. The plates were incubated at 30°C for 7 days. After 7 days, the nitrogen-fixing capacity was determined by observing whether a clear zone formed around the colony. Results are as follows: Figure 4 As shown, a clear transparent zone forms around the YN2303 colony, indicating that the YN2303 strain has the ability to fix nitrogen.

[0068] The diameters (D) of the three nitrogen-fixing zones were 2.30 cm, 2.40 cm, and 2.30 cm, respectively; the colony diameters (d) were 1.65 cm, 1.60 cm, and 1.70 cm, respectively; and the D / d ratios were 1.38, 1.50, and 1.35, respectively, with an average value of 1.41.

[0069] The above results indicate that strain YN2303 has the ability to both decompose inorganic phosphorus and fix nitrogen. This strain shows good application potential in promoting plant nutrient absorption, providing excellent strain resources and theoretical basis for the development of efficient compound microbial fertilizers and biocontrol agents.

[0070] Example 4 This example illustrates the control and growth-promoting effects of *Priestella megaterium* YN2303 on banana wilt in potted plants.

[0071] Preparation of experimental banana seedlings: In a plastic greenhouse, tissue-cultured Brazilian banana seedlings (tissue-cultured seedlings from the Banana Research Laboratory of the Institute of Agricultural Environment and Resources, Yunnan Academy of Agricultural Sciences) were removed. After washing the culture medium from the roots, they were transplanted into seedling bags. Once the seedlings had 3-4 leaves (approximately one month), they were transplanted into plastic pots with a diameter of 11cm and a height of 12cm, using vermiculite as the substrate. After transplanting, regular watering was maintained to keep the soil moist. Fertilizer was applied 1-2 times per week (2g of compound fertilizer per plant per application, dissolved in water; the N-P2O5-K2O ratio in the compound fertilizer was 15-15-15 by mass). Once the banana seedlings had 4-5 leaves (approximately one month), they were ready for use.

[0072] Preparation of fermentation broth for *Priestella giantiflora* YN2303: The cryopreserved strain YN2303 was streaked onto solid NA medium plates and activated in a 28℃ incubator for 2 days. The activated YN2303 strain was then inoculated into liquid NA medium and cultured at 28℃ and 250 r / min on a shaker for 5 days. The culture medium was filtered through four layers of sterile gauze to obtain the fermentation broth. A 1×10⁻⁶ concentration was prepared using sterile water. 8 YN2303 strain fermentation broth (CFU / mL) is prepared for use.

[0073] Preparation of banana wilt fungus spore suspension (TR4 spore suspension): The banana wilt fungus (TR4 spore suspension) was prepared by spore suspension of the fungus. Foc 15-1) Streak inoculation was performed on solid PDA medium plates, and the plates were incubated at 28℃ for 5 days to activate the fungus. The activated banana wilt pathogen was then inoculated into liquid PDA medium and incubated at 28℃ and 250 rpm for 7 days. The culture medium was filtered through four layers of sterile gauze to obtain a suspension of pathogen spores. This suspension was then diluted with sterile water to a concentration of 1×10⁻⁶. 6 Prepare a solution of banana wilt spores at CFU / mL.

[0074] (I) Pot experiment on the control of banana wilt disease Control test method: The fermentation broth of *Priscilla megaterium* YN2303 (concentration 1×10⁻⁶) was used to control the bacteria. 8The solution (CFU / mL) was applied to the roots of the potted banana plants with uniform growth, with 50 mL applied to each plant. The control group (CK) received 50 mL of NA liquid culture solution per plant. After 7 days, the roots of the potted banana plants were treated to prevent root damage, and a solution of 1×10⁻⁶ CFU / mL was applied to the roots of each plant. 6 The spores of Fusarium wilt of banana (CFU / mL) were applied to the roots of potted banana plants at a rate of 50 mL per plant. The control group was treated with PDA liquid culture solution.

[0075] Control and investigation methods: Disease index was investigated 45 days after inoculation with TR4 spore solution. External symptoms (leaf samples) and internal symptoms (corona samples) were investigated for each treatment of banana plants. Disease severity was determined based on the degree of browning in the longitudinal sections of banana leaves and corms, and the disease index and control effect were calculated. The disease index grading criteria are shown in Table 2.

[0076] Disease index = [∑(number of diseased plants at each level × relative level value) / (total number of plants surveyed × highest disease level value)] × 100; Prevention and control effect (%) = (CK disease index - treatment disease index) / CK disease index × 100; Table 2 Grading Standards for Banana Fusarium Wilt Disease

[0077] The potted plant control experiment included two treatments, each with three replicates, and ten banana seedlings per replicate. A1: irrigation with NA liquid culture medium + Fusarium wilt spore solution (CK+TR4); A2: irrigation with Priestella megaterium fermentation broth + Fusarium wilt spore solution (YN2303+TR4). Disease incidence was investigated for each treatment, disease index was calculated, and control efficacy was determined. The results are shown in Table 3.

[0078] Through pot experiment, 45 days after inoculation with TR4 spore solution, as Figure 5 As shown, only the TR4-inoculated treatment resulted in withered and yellowed leaves, fewer leaves, and shorter plants. Figure 5 b); while the banana plants treated with YN2303 fermentation broth mostly maintained healthy leaves, had a large number of leaves, and showed good plant growth. Figure 5 a). Furthermore, after dissecting the bulbs, it can be observed that the bulbs inoculated with YN2303 fermentation broth were almost not invaded by TR4 mycelium, with only some bulbs showing a small amount of browning, while the banana bulbs inoculated only with TR4 turned brown and showed more brown mycelium.

[0079] Table 3

[0080] Note: This indicates that the difference is highly significant ( P <0.01).

[0081] As shown in Table 3, the disease index of banana bulbs and leaves was significantly lower in the treatment group irrigated with the fermentation broth of *Priscilla megaterium* YN2303 compared to the control group. The fermentation broth of this strain achieved a control effect of over 75% against banana wilt. These results indicate that *Priscilla megaterium* YN2303 possesses excellent control capabilities against banana wilt.

[0082] (II) Plant growth promotion experiment Plant growth promotion test method: The fermentation broth of *Priscilla megaterium* YN2303 (concentration 1×10⁻⁶) was used to promote plant growth. 8 The solution (CFU / mL) was applied to the roots of potted banana plants with uniform growth, with 50 mL applied to each plant. The control group was treated with 50 mL of NA liquid culture solution per plant.

[0083] Methods for investigating plant growth promotion: On the day of irrigation with *Priscilla megaterium* YN2303 fermentation broth (0 dpi) and 45 days after irrigation with *Priscilla megaterium* fermentation broth (45 dpi), bioinformatics indicators such as plant height, pseudostem diameter, number of leaves, leaf length, and leaf width of all treated banana plants were measured and recorded. In addition, bioinformatics indicators such as fresh weight of aboveground and underground parts of the plants were measured 45 days after irrigation with *Priscilla megaterium* YN2303 fermentation broth.

[0084] The plant growth promotion experiment had two treatments, each with three replicates, and each replicate contained 10 banana seedlings. B1: watering with NA liquid culture medium, serving as the control (CK) for the plant growth promotion experiment; B2: watering with Priestella megaterium fermentation broth (YN2303).

[0085] Measurement and recording methods: Plant height: Measured from the ground to the point where the petioles of the two top leaves intersect; Leaf length: Measured from the tip to the tip of the first leaf at the top of the plant; Leaf width: Measured at the widest point of the first leaf at the top of the plant; Pseudostem diameter: Measured using calipers at the base of the pseudostem approximately 1 cm above the ground; Number of leaves: Recorded number of green leaves per plant; Above-ground fresh weight: Weight of the banana plant above the base of the pseudostem approximately 1 cm above the ground; Below-ground fresh weight: Weight of the banana plant below the base of the pseudostem approximately 1 cm above the ground. Various biological information indicators are shown in Table 4 and... Figure 6 As shown.

[0086] Table 4

[0087] Note: Indicates a significant difference ( P <0.05); different lowercase English letters a, b, c represent significant differences between groups, and the significance level is [not specified].P <0.05; the same letter indicates no significant difference between the two groups, and different letters indicate a significant difference between the two groups.

[0088] Through Table 4 and Figure 6 The results showed that on the initial day of the experiment (0 dpi), banana plants in the treatment group (0 dpi YN2303) and the control group (0 dpi CK) sprayed with Priscilla megaterium fermentation broth were investigated, and five biological indicators, including plant height, pseudostem diameter, number of leaves, leaf length, and leaf width, were measured. The results indicated that there were no significant differences in any of the indicators between the two groups of plants.

[0089] After irrigating banana plants with *Priscilla megaterium* fermentation broth YN2303 for 45 days, various biological indicators of the banana plants were measured. The results showed that the plant height, leaf length, leaf width, pseudostem diameter, and number of leaves in the treatment group (45 dpi YN2303) were significantly improved compared to the control group (45 dpi CK); the fresh weight of both the above-ground and underground parts of the plants was also significantly higher than that of the control group. In conclusion, the YN2303 fermentation broth can effectively promote the growth of banana plants, significantly improving multiple growth indicators, confirming that this fermentation broth has a good growth-promoting effect on bananas.

[0090] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A strain of Priestella megaterium ( Priestia megaterium ), characterized in that, The preservation number of this strain is CCTCC NO: M 2026288.

2. A microbial inoculant, characterized in that, The microbial agent includes *Priestella gianti* as described in claim 1.

3. The microbial agent according to claim 2, wherein, Based on the total mass of the bacterial agent, the viable bacterial content of *Priscilla megaterium* is ≥1×10⁻⁶. 8 CFU / mL, preferably 1×10⁻⁶ 8 -1×10 9 CFU / mL.

4. The use of the *Priestella giantiflora* as described in claim 1, or the microbial agent as described in claim 2 or 3, in the preparation of a biological agent for the prevention and control of banana wilt disease.

5. The use of the *Priestella giantiflora* as described in claim 1, or the microbial agent as described in claim 2 or 3, in the preparation of a biological agent for inhibiting the growth of the pathogen causing banana wilt.

6. A method for controlling banana wilt disease, characterized in that, Apply the *Priestella giantiflora* as described in claim 1, or the microbial agent as described in claim 2 or 3, to the roots and / or pseudostem of the banana plant.

7. The use of the Priestella giantiflora of claim 1, or the microbial agent of claim 2 or 3, in the preparation of a biological agent for promoting the growth of banana plants.

8. A method for promoting the growth of banana plants, characterized in that, Apply the *Priestella giantiflora* as described in claim 1, or the microbial agent as described in claim 2 or 3, to the roots and / or pseudostems of the banana plant.

9. The use of the Priestella giantiflora as described in claim 1, or the microbial agent as described in claim 2 or 3, in the decomposition of inorganic phosphorus.

10. The use of the Priestella giantiflora as described in claim 1, or the microbial agent as described in claim 2 or 3, in nitrogen fixation.

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