Polyangium strain for preventing and treating nematode disease, bacterial agent and application thereof

Abstract

This invention discloses a strain of Aspergillus polypolysaccharide, its inoculant, and its application for controlling nematode diseases. This Aspergillus polypolysaccharide is classified and named Aspergillus polypolysaccharide. Aspergillus sydowii The product, named LD-3 and with the preservation number CGMCC No. 42713, was isolated from wheat rhizosphere soil in Ningxia. The fermentation broth showed a 100% nematicide rate against *Cephalopoda graminea* and *Strombus chinensis* (northern root-knot nematode) within 48 hours, and an inhibition rate of 35.56%–73.33% against nine soil-borne fungi. It reduced the cyst decay rate of greenhouse wheat by 87.50% and significantly promoted growth. It can be formulated as a liquid, powder, or granule for seed soaking, root irrigation, or broadcasting. It possesses triple effects of nematicide, antibacterial activity, and growth promotion, making it green and safe for the green control of soil-borne diseases in crops.

Description

Technical Field

[0001] This invention belongs to the field of microbial inoculants, and mainly relates to a strain of Aspergillus polypolysaccharide for the control of crop nematode diseases. Aspergillus sydowii LD-3 strain, inoculant and its application. Background Technology

[0002] The community composition of soil nematodes can reflect soil health, pollution levels, organic matter input, and the degree of natural and human disturbance. Plant nematodes cause $80 billion in losses worldwide annually, with rice parasitic nematodes accounting for approximately $16 billion. The area affected by soil nematodes in my country's major rice, corn, wheat, and soybean growing areas is expanding year by year, becoming a significant factor seriously affecting food security. Cyst nematodes (… Heterodera ayenae Root-knot nematodes can infect wheat, soybeans, potatoes, and rice, causing slow growth, stunted growth, yellowing leaves, and underdeveloped root systems. They can survive in the soil for years, accumulating over time and causing severe yield losses, generally 10%–20%, but in severe cases reaching 30%–50%, or even total crop failure. Root-knot nematodes can affect plant height, tillering, seedling weight, root weight, and leaf area index, leading to poor plant growth and development. Poaceae root-knot nematodes can cause losses of 16%–20% in dryland rice and 16%–32% in irrigated rice, with yield losses exceeding 70% in severe cases. Weeds and cereal crops such as sorghum and wheat are excellent hosts for root-knot nematodes.

[0003] Currently, planting resistant varieties and applying chemical pesticides are common practices. However, the breeding cycle for resistant varieties is lengthy, and the residues from repeated use of chemical nematicides can easily threaten the ecological environment and human health. Biological control technology, as a safe and effective means, has been widely researched and applied in the control of plant pathogenic nematodes and fungi. The application of microbial agents to control plant nematode diseases provides a guarantee for the high-quality development of modern agriculture.

[0004] Aspergillus polymorpha ( Aspergillus sydowiiAspergillus polyploid, belonging to the genus Aspergillus in the family Aspergillusceae of the order Hylocorales, possesses strong nematicidal activity and can effectively inhibit plant pathogens, exhibiting significant insecticidal and disease-preventing effects. It can also produce plant hormones such as auxin and di-tert-butylphenol, promoting plant growth, making it a biocontrol bacterium with great potential and application prospects. The fermentation broth of Aspergillus polyploid Snef210, screened by Wang Shuai et al., showed strong toxicity against second-instar larvae of the southern root-knot nematode. After 24 hours of treatment with the undiluted broth, the corrected mortality rate reached 90.1%, and after 3 days of treatment, the inhibition rate of egg hatching reached 92.8%. In pot experiments, compared with the control, soil treatment with a 10-fold dilution of the strain's fermentation broth resulted in a 66.7% reduction in root knots in tomato roots. Aspergillus polyploid ZK-2, screened by Wang Peng et al., showed resistance against Rhizoctonia solani (…). Rhizoctonia solani Alternaria ( Alternaria solani ) and Verticillium dahliae ( Verticillium dahliae All three showed significant inhibitory effects, with inhibition band widths of 10.0 mm, 9.00 mm, and 16.5 mm, respectively, achieving control effects of 46.6%–61.2% against potato black scurf.

[0005] However, there are currently few polyaspergillus agents that can effectively control root-knot nematodes and cereal cyst nematodes in northern China, so it is necessary to carry out research on polyaspergillus agents suitable for the control of plant nematode diseases. Summary of the Invention

[0006] This invention addresses the problems existing in agricultural production and the shortcomings of existing technologies by providing a strain of Aspergillus polypolycarbide that has good antibacterial effects against Fusarium and other pathogens and high control efficacy against soil nematode diseases. Another objective of this invention is to provide the application of this Aspergillus polypolycarbide agent.

[0007] The Aspergillus polypolysaccharide of this invention is classified and named as Aspergillus polypolysaccharide (… Aspergillus sydowii The sample was collected from the rhizosphere soil of wheat in Longde County, Ningxia Hui Autonomous Region, and named Aspergillus polypolysaccharide LD-3. It was deposited on May 25, 2026 at the China General Microbiological Culture Collection Center (address: No. 3, No. 1, Beichen West Road, Chaoyang District, Beijing) with accession number CGMCC No. 42713.

[0008] The morphological characteristics of Aspergillus polypolysaccharide LD-3 of the present invention on potato agar medium are as follows ( Figure 1 At 25°C, after 7 days of cultivation, the colony diameter is approximately 22 mm, and can reach 25–40 mm with prolonged growth. Its texture is velvety to fluffy, dense and compact. Initially, the colony color is grayish-blue, gradually turning dark to dark blue-grayish-green over time, with occasional light brown patches.

[0009] The Aspergillus polypolysaccharide LD-3 strain exhibits extremely strong toxic activity against cereal cyst nematodes and northern root-knot nematodes, while also providing broad-spectrum antagonism against various Fusarium, Phytophthora, and fruit and vegetable pathogenic fungi, and can significantly promote the growth of wheat seedlings.

[0010] This strain can be made into a biocontrol agent. The formulation and preparation method of the biocontrol agent are as follows: Liquid fermentation inoculant: Culture medium formulation: Corn flour liquid culture medium; Preparation process: Activate LD-3 single colonies and prepare 1×10⁻⁶ colonies. 6 CFU / mL bacterial suspension was inoculated into corn flour liquid culture medium (50 g corn flour, 1000 mL water, pH 5.6±0.2) at a 1% inoculation rate. The culture was carried out at 28℃ and 180 r / min in the dark with shaking for 3 days. The resulting fermentation broth is the liquid bacterial agent, which should be stored at 4℃ in the dark.

[0011] Application method of microbial agent: Seed soaking treatment: After disinfection, wheat seeds are soaked in 1×10... 6 Soaking in CFU / mL fermentation broth for 1 hour, then air-drying before sowing, is suitable for nematode prevention during the sowing period; Root irrigation: 15 days after wheat seedlings emerge, irrigate each plant with 10 mL of fermented stock solution to inhibit nematode reproduction and prevent root fungal diseases during the growing season. Specifically, this strain has the following effects:

[0012] 1. Extremely high nematicidal activity 1×10 6 CFU / mL fermentation broth was used to treat second-instar larvae of *Corydalis gracilis* and *Strombus chinensis* for 48 h. The survival rate of both nematodes was 0, and the nematode-killing effect was 100%. The survival rates of nematodes in the blank control group were 75.96% and 84.90%, respectively, showing excellent indoor nematode-killing effect. 2. Broad-spectrum antagonism against soil-borne pathogenic fungi

[0013] Plate confrontation tests were conducted to determine the inhibition rates of mycelia of nine common pathogenic fungi: Fusarium wilt of cucumber 73.33%, Tobacco black shank 64.21%, Fusarium oxysporum 61.23%, Fusarium moniliforme 55.40%, Fusarium rotundifolium 55.15%, Fusarium wilt of watermelon 54.52%, Anthracnose of strawberry 42.46%, Alternaria alternata 36.83%, and Fusarium verticillata 35.56%. These results showed significant inhibitory effects on various soil-borne pathogens affecting grains, fruits, and vegetables.

[0014] 3. Significantly promotes the growth of wheat seedlings The greenhouse experiment included two application methods: seed soaking and root irrigation, compared to a control group using only water: (1) Seed soaking treatment: seedling emergence rate increased by 5.26%, plant height increased by 26.87%, and root length increased by 33.57%; (2) Root irrigation treatment: stem diameter increased by 1.45%, plant height increased by 20.45%, and root length increased by 22.88%; It can simultaneously improve wheat emergence rate, above-ground growth and root development, and enhance the plant's resistance to adverse conditions.

[0015] 4. Effectiveness of greenhouse nematode control Soaking wheat seeds in fermented liquid followed by root irrigation during the growing season, and then inoculating them with cereal cyst nematodes for 30 days, showed that the control group had an average of 8 cysts, while the LD-3 treatment group had only 1, with a cyst reduction rate of 87.50%, demonstrating excellent greenhouse control efficacy.

[0016] The beneficial effects of this invention are: The *Aspergillus polypolysaccharide* LD-3 of this invention was collected from the rhizosphere soil of wheat in Longde County, Ningxia Hui Autonomous Region. It exhibits outstanding control efficacy against wheat cyst nematodes and northern root-knot nematodes, and also possesses antibacterial activity against various other plant pathogens, such as *Fusarium oxysporum*. Fusarium oxysporum ), Fusarium verticillata ( F. verticilliodes Fusarium moniliforme () F. moniliforme Fusarium solani () F. solani Tobacco black shank bacterium ( Phytophthora parasitica var.nicotianae ), cucumber wilt pathogen ( F. Oxysporum f.sp. cucumerinum), Fusarium wilt of watermelon ( F. oxyspirum f.sp. niveum), strawberry anthracnose fungus ( Colletotrichum gloeospoioides ) and Alternaria strawberry ( A. alternata This strain has a growth-promoting effect on crops such as wheat and has a very promising application prospect in the development of biological agents for plant diseases. Attached Figure Description

[0017] Figure 1 This is a colony morphology diagram of Aspergillus polypolysaccharide LD-3.

[0018] Figure 2 Phylogenetic tree of Aspergillus polypolysaccharide LD-3.

[0019] Figure 3 The antibacterial effect of Aspergillus polypolysaccharide LD-3 against a variety of pathogens.

[0020] Preservation of biological materials Accession number: CGMCC No. 42713 Name: Aspergillus polypolysaccharide LD-3 Classification and nomenclature: Aspergillus polypolysaccharide Aspergillus sydowii ) Survival status: Survival Preservation period: May 25, 2026 Preservation Institution: China General Microbiological Culture Collection Center, China Microbiological Culture Collection Committee Address: No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing. Detailed Implementation

[0021] Example 1: Isolation and Identification of Aspergillus polypolysaccharide LD-3

[0022] (1) Isolation and purification of Aspergillus polymorpha from wheat rhizosphere soil Rhizosphere soil samples were collected from wheat roots in Longde County, Ningxia Hui Autonomous Region. 10 g of soil was weighed and placed in a 90 mL sterile Erlenmeyer flask. The mixture was shaken and stirred at room temperature for 0.5 h. The samples were then processed at 10, 10... 2 and 10 3 Serial dilutions were performed, and the resulting samples were spread onto potato dextrose agar (PDA) plates and incubated upside down at 28°C for 5 days. Edge hyphae were picked based on the colony characteristics of Aspergillus polypolysaccharide and further purified on PDA plates. The purified strains were then stored in 40% glycerol at –80°C.

[0023] The above isolation method yielded the strain LD-3 of the present invention.

[0024] (2) Nematode killing test of strain LD-3 against wheat cereal cyst nematode and northern root-knot nematode Culture of strain LD-3: A single colony of strain LD-3, which had been activated for 7 days, was inoculated into PSA liquid medium and cultured at 28°C and 180 rpm / min for 5 days to obtain the seed fermentation broth of strain LD-3.

[0025] Preparation of fermentation broth for strain LD-3: 1×10⁻⁶ ppm of the LD-3 fermentation broth was prepared. 6 One mL of the CFU / mL seed fermentation broth of strain LD-3 was inoculated into a 250 mL Erlenmeyer flask containing 100 mL of corn flour liquid medium (50 g corn flour, 1000 mL water, pH 5.6 ± 0.2) and incubated at 37°C with shaking at 200 rpm in the dark for 3 days. The resulting broth was then stored at 4°C for later use as the fermentation stock solution.

[0026] Determination of nematicidal activity of biocontrol bacteria fermentation broth: The biocontrol bacteria fermentation stock broth was prepared with sterile water to a concentration of 1×10⁻⁶. 6CFU / mL, 1 mL of fermentation broth was added to a 24-well cell culture plate, and 100 second-instar larvae of *Corydalis gracilis* and *Strombus chinensis* were added respectively. Uninoculated corn flour liquid medium was set as a blank control. A total of 5 treatments were performed, and each treatment was repeated 5 times. The mortality of nematodes was observed after 48 h. The life and death of nematodes were determined by observing the morphology of the nematodes, and the mortality rate and corrected mortality rate of nematodes were calculated (Table 1).

[0027] Nematode survival rate (%) = (number of surviving nematodes / number of added nematodes) × 100%.

[0028] Nematode killing effect (%) = [(Survival rate of treated nematodes - Survival rate of control nematodes) / (1 - Survival rate of control nematodes)] × 100%.

[0029] Table 1. Nematicidal effects of strain LD-3 against *Corydalis gracilis* and *Strombus chinensis*.

[0030] Indoor nematicide test results showed that strain LD-3 had a strong nematicide effect on wheat gramineous cyst nematode and northern root-knot nematode, and has the potential to be used as a biological nematicide.

[0031] (3) Identification of strain LD-3 Total DNA was extracted from strain LD-3. Using DNA samples meeting the required concentration and quality as templates, amplification was performed using the universal ITS1 / ITS4 primers: ITS1 (5'-TCCGTAGGT-GAACCTGCGG-3') and ITS4 (5'-TCCTCCGCT-TATTGATATGC-3'). The PCR reaction mixture consisted of: 12.8 μL ddH2O; 3 μL Buffer; 2 μL dNTPs; 3 μL Primer1; 3 μL Primer2; 1 μL DNA template; and 0.2 μL enzyme, for a total volume of 30 μL. The amplification program was: 96°C pre-denaturation for 5 min; 95°C denaturation for 45 s, 55°C annealing for 30 s, and 72°C extension for 60 s, for 35 cycles; followed by a 72°C extension for 7 min. The amplified PCR product was sequenced, and the results showed that its ITS sequence is shown in Sequence 1 of the sequence listing. BlastN alignment analysis showed a 99% similarity to *Aspergillus polyploidus* strain CBS 593.65. Based on morphological analysis, it was identified as *Aspergillus polyploidus*. The phylogenetic tree of *Aspergillus polyploidus* LD-3 is as follows: Figure 2 As shown.

[0032] Aspergillus polypolysaccharide LD-3 has been deposited at the China General Microbiological Culture Collection Center (CGMCC, address: No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing) on ​​May 25, 2026, with accession number CGMCC NO. 42713.

[0033] Example 2: Antibacterial test of Aspergillus polypolysaccharide LD-3 against Fusarium and other pathogens. Fusarium oxysporum ( Fusarium oxysporum 295. Fusarium verticillata ( F. verticilliodes 173. Fusarium moniliforme ( F. moniliforme N19-2-2, Fusarium solani ( F. solani N18-1-2, Tobacco Black Shank Bacterium ( Phytophthora parasitica var.nicotianae ), cucumber wilt pathogen ( F. Oxysporum f.sp.cucumerinum), strawberry anthracnose fungus ( Colletotrichum gloeospoioides ), Alternaria strawberry Alternaria alternata Pathogen colony pellets (1 cm) were placed in the center of PDA agar plates. Aspergillus polyploid LD-3 pellets were placed 2 cm from the edge of the pathogen colony. Plates without pellets served as blank controls. All plates were incubated in the dark at 28°C, with four replicates. After 5 days, the diameter of the pathogen colony and the inhibition zone were measured to screen for strains with significant antagonistic effects (Table 2 and...). Figure 3 ).

[0034] Relative mycelial inhibition rate (%) = (control colony diameter - treated colony diameter) / control colony diameter × 100%.

[0035] Table 2. Antagonistic effects of Aspergillus polypolysaccharide LD-3 against various pathogens including Fusarium. Fusarium oxysporum 61.23 Fusarium moniliforme 55.40 Fusarium solani 55.15 Fusarium verticillata 35.56 Tobacco black shank bacterium 64.21 Cucumber wilt pathogen 73.33 Strawberry anthracnose 42.46 Alternaria strawberry 36.83 Fusarium wilt of watermelon 54.52 Antibacterial experiments showed that Aspergillus polypolysaccharide LD-3 of the present invention has antagonistic effects against a variety of pathogens such as Fusarium, and is a very excellent antagonistic strain.

[0036] Example 3: Efficacy test of Aspergillus polypolysaccharide LD-3 against cereal cyst nematode under greenhouse conditions. Seed treatment: Wheat seeds were surface disinfected in a 1% sodium hypochlorite solution for 30 min, then rinsed with sterile water to remove residual sodium hypochlorite. The seeds were dried on a clean bench and then soaked in Aspergillus polypolysaccharide LD-3 fermentation broth (prepared according to the method in Example 1) for 1 h (cell concentration 1×10⁻⁶). 6 (CFU / mL).

[0037] Nematode activity of Aspergillus polypolysaccharide LD-3 fermentation broth on cereal cyst nematodes: Wheat seeds soaked in the broth were planted in a 500 cm³ solution. 3One plant was placed in each 10 cm pot of sterile medium (sand:soil = 3:7) under the following conditions: 26℃ / 20℃, 16 h light / 8 h dark. After 15 days of colonization, the plant was inoculated with 1000 second-instar larvae of the rice cyst nematode at a rate of 1000 larvae per plant. Two days after inoculation, the plant was irrigated with 10 mL of biocontrol bacteria fermentation solution. Uninoculated corn flour liquid medium served as the control (CK). Each treatment was replicated five times. After 30 days, the number of sporangia was counted, and the sporangia reduction rate was calculated (Table 3). The greenhouse experiment was designed with two groups: CK was the blank control; B was strain LD-3.

[0038] Sporangium reduction rate (%) = (number of sporangia in control group - number of sporangia in treatment group) / number of sporangia in control group × 100%.

[0039] Table 3. Greenhouse nematicidal effect of Aspergillus polypolysaccharide LD-3 against *Corydalis gracilis*. CK 8 / Aspergillus polymorpha LD-3 1 87.50 The experimental results are shown in Table 3. Aspergillus polypolysaccharide LD-3 has a good nematicidal effect on cereal cyst nematodes under greenhouse conditions.

[0040] Example 4: Growth-promoting effect of Aspergillus polypolysaccharide LD-3 on wheat seedlings under greenhouse conditions. After the wheat seedlings emerged uniformly in the greenhouse, the emergence rate was investigated: the wheat seeds were placed in a 1% sodium hypochlorite solution for surface disinfection for 30 minutes, then the residual sodium hypochlorite on the seed surface was rinsed off with sterile water, and the surface moisture was dried on a clean bench.

[0041] The growth-promoting effect of Aspergillus polypolysaccharide LD-3 fermentation broth (prepared according to the method of Example 1) on seed soaking: Wheat seeds were surface-sterilized with 1% sodium hypochlorite solution for 30 min, dried on a clean bench, and then soaked in Aspergillus polypolysaccharide LD-3 fermentation broth for 1 h (cell concentration 1×10⁻⁶). 6 CFU / mL), planted in flowerpots, and after uniform emergence (about 10 days after planting), the emergence rate was investigated, and after 30 days, the plant height and root length were investigated (Table 4). The experiment was designed with two groups: CK was the water control; B was the strain LD-3.

[0042] The growth-promoting effect of Aspergillus polypolysaccharide LD-3 fermentation broth on root irrigation: Wheat seeds were surface-sterilized with 1% sodium hypochlorite solution for 30 minutes, dried on a clean bench, and planted in a greenhouse. After 15 days, each pot was irrigated with 50 mL of Aspergillus polypolysaccharide LD-3 fermentation broth (cell concentration 1×10⁻⁶). 6 (CFU / mL); with uninoculated corn flour liquid medium as the CK control, each treatment was replicated 5 times. After 30 days, wheat plant height, root length, and stem diameter were measured (Table 5). The experiment was designed with two groups: CK was the blank control; B was strain LD-3.

[0043] Table 4. Greenhouse growth-promoting effect of Aspergillus polypolysaccharide LD-3 seed soaking on wheat seedlings.

[0044] Table 5. Greenhouse growth-promoting effect of Aspergillus polypolysaccharide LD-3 root irrigation on wheat seedlings

[0045] The experimental results are shown in Tables 4 and 5. The results show that soaking and root irrigation with Aspergillus polypolysaccharide LD-3 has a good growth-promoting effect on wheat seedlings under greenhouse conditions.

[0046] Example 5: Detection and Analysis of Major Toxins in Aspergillus polypolysaccharide LD-3 Sample pretreatment: (1) Place the strain in PDA medium and incubate at 28℃ and 200 rpm for 72 h. Then centrifuge the fermentation broth at 12000 rpm for 10 min. (2) Add 20 mL of acetonitrile / water (80 / 20, V / V) to 20 mL of supernatant and vortex the sample for 2 min. Add the extraction pack (Agilent QuECHERS Extract Pouch, 5982-5650) and vortex for 2 min. Centrifuge at 8000 rpm / min for 5 min. (3) Take 8 mL of supernatant and add it to the purification pack (Agilent QuECHERS Extract Pouch, 5982-0029), then shake and mix for 1 min. (4) Centrifuge the sample at 8000 rpm / min for 5 min, take 2 mL of supernatant, filter it through a 0.22 μm microporous membrane, and test.

[0047] Instrumentation: Acquity UPLC I-Class liquid chromatograph (Waters Corporation, USA), QTRAP 5500 triple quadrupole mass spectrometer (AB SCIEX Corporation, USA).

[0048] Instrument conditions: (1) Chromatographic conditions ① Chromatographic column: ACQUITY BEH C18 column (100 mm × 2.1 mm, particle size 1.7 μm), flow rate 0.3 mL / min, injection volume 3 μL, column temperature 40℃. ② Mobile phase: Phase A was 0.1% formic acid-water solution, Phase B was methanol solution, and the elution gradient is shown in Table 6. Table 6 Gradient elution conditions of mobile phase 0 0.3 90 10 1 0.3 90 10 2 0.3 70 30 4 0.3 40 60 6 0.3 10 90 8 0.3 10 90 8.1 0.3 90 10 10 0.3 90 10 (2) Mass spectrometry conditions Ion source: Electrospray ionization (ESI); ion source temperature: 550℃; ion spray voltage: 5500 V (positive mode) / -4500 V (negative mode); curtain gas: 35 psi; gas 1: 50 psi; gas 2: 55 psi; detection was performed using multiple reaction monitoring (MRM) mode. The results of Aspergillus polypolysaccharide LD-3 toxin detection are shown in Table 7.

[0049] Table 7 Results of Aspergillus polypolysaccharide LD-3 toxin detection Aflatoxin B1 (AFB1) 5.825 1596.710533 0.026599057 <0 Aflatoxin B2 (AFB2) 5.698 1792.002357 0.006735762 <0 Aflatoxin G1 (AFG1) 5.491 2337.530341 0.044998502 <0 Aflatoxin G2 (AFG2) 5.354 573.1922237 0.099179851 <0 Table 7 shows that Aspergillus polypolysaccharide LD-3 does not produce aflatoxins B1, B2, G1, and G2.

Claims

1. A strain of Aspergillus polymorpha, characterized in that, The name is Aspergillus polypolysaccharide LD-3, and the classification name is Aspergillus polypolysaccharide ( Aspergillus sydowii It was deposited on May 25, 2026 at the China General Microbiological Culture Collection Center, with accession number CGMCC No. 42713.

2. The application of Aspergillus polypolysaccharide LD-3 according to claim 1 in at least one of the following: killing plant parasitic nematodes, inhibiting plant pathogenic fungi, and promoting crop growth.

3. The application according to claim 2, characterized in that, The plant parasitic nematode is one or a combination of two of the following: *Corydalis gracilis* and *Northern Root-knot Nematode*.

4. The application according to claim 2, characterized in that, The plant pathogenic fungus was selected from: Fusarium oxysporum (… Fusarium oxysporum ), Fusarium verticillata ( F. verticilliodes Fusarium moniliforme () F. moniliforme Fusarium solani () F. solani Tobacco black shank bacterium ( Phytophthora parasitica var.nicotianae ), cucumber wilt pathogen ( F. Oxysporum f.sp. cucumerinum), Fusarium wilt of watermelon ( F. oxyspirum f.sp. niveum), strawberry anthracnose fungus ( Colletotrichum gloeospoioides ), Alternaria strawberry A. alternata Any one or more combinations of ).

5. The application according to claim 2, characterized in that, The crop in question is wheat.

6. A biocontrol agent for controlling soil-borne diseases and nematodes, characterized in that, The active ingredient is the Aspergillus polypolysaccharide LD-3 cell, fermentation broth, or fermentation metabolites as described in claim 1.

7. The biocontrol agent according to claim 6, characterized in that, The inoculant formulation can be liquid fermentation inoculant, powder, or granules.

8. A method for applying the Aspergillus polypolysaccharide LD-3 of claim 1 or the biocontrol agent of claim 6 or 7, characterized in that, The application methods include one or more combinations of seed soaking, root irrigation, and soil application.

9. The use of Aspergillus polypolysaccharide LD-3 according to claim 1 in the preparation of microbial nematicides, agricultural antibacterial agents, or bio-fertilizers.

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