Endophytic Beauveria bassiana SDQD-1 and its application in controlling serendipita stercoraria

Abstract

This invention discloses an endophytic Beauveria bassiana strain ( Beauveria bassiana SDQD-1 and its application in disease control. This strain is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 41845. This strain exhibits high sporulation, rapid growth, and strong UV resistance, and can colonize cowpeas endophytically through root irrigation or seed soaking. Experiments show that this strain is effective against common thrips (…). Megalurothrips usitatus Time to death (LT) 50 The colonization period was 2.34 days. After 7 and 14 days of colonization, the cumulative corrected mortality rate of common thrips after 9 days reached 74.57%–78.49% and 64.80%–66.58%, respectively. This invention utilizes excellent endogenous characteristics to solve the problem of the concealed damage caused by thrips, and provides a highly efficient microbial resource for the green control of common thrips in cowpeas.

Description

Technical Field

[0001] This invention relates to the field of biological pest control, specifically to an endophytic strain of Beauveria bassiana (Beauveria bassiana). Beauveria bassiana SDQD-1 also relates to the culture method of the strain, the biocontrol agent containing the strain, the application of the strain in the control of common thrips in cowpea, and the cowpea-microbial symbiosis with resistance to common thrips formed by the strain. Background Technology

[0002] Thrips belong to the order Thysanoptera and the family Thripidae. They are among the most difficult-to-control small pests in vegetable production. They are tiny, reproduce rapidly, and live in secluded places, often hiding in the crevices of crop shoots and bean pods to feed and cause damage. Among them, the common thrips... Megalurothrips usitatus The bean thrips, also known as the cowpea thrips, is a major pest of vegetable crops in tropical regions such as Hainan, especially dominating the local cowpea crop. Benefiting from the high accumulated temperature and simultaneous rainfall and heat conditions, its population multiplies extremely rapidly. It severely damages cowpea shoots, flowers, and pods, leading to reduced yields and lower quality, and has become a core issue hindering the green development of the cowpea industry.

[0003] Currently, the control of common thrips in cowpeas in agricultural production still relies mainly on chemical control. However, the long-term use of chemical pesticides has not only led to a significant increase in the resistance of common thrips and a continuous decline in control effectiveness, but has also resulted in excessive pesticide residues in cowpea fruits, which violates the requirements of agricultural product quality and safety and green agricultural development. The limitations of traditional chemical control methods are becoming increasingly apparent.

[0004] Beauveria bassiana ( Beauveria bassiana Beauveria bassiana is a widely used entomopathogenic fungus with advantages such as environmental friendliness, safety to non-target organisms, and low risk of drug resistance. Some strains also possess endophytic colonization capabilities, surviving within plant roots, stems, and leaves, effectively addressing the problem of pesticide inaccessibility caused by thrips' concealed habitat. It is a preferred microbial resource for thrips biological control. However, currently, there is a shortage of highly pathogenic Beauveria bassiana strains targeting common cowpea thrips. Existing reported strains suffer from low lethality, weak resistance, and low colonization rates in cowpeas, making it difficult to meet actual field control needs.

[0005] Therefore, screening new endophytic Beauveria bassiana strains with high lethality, strong resistance, and high endophytic colonization ability, improving their supporting culture methods and biocontrol agent preparation technology, and clarifying their endophytic colonization and control application schemes on cowpea are of great practical significance for enriching the biocontrol resource bank of common cowpea thrips and realizing the green control of this pest. Summary of the Invention

[0006] The purpose of this invention is to overcome the deficiencies of existing technologies and provide an endophytic Beauveria bassiana strain SDQD-1 that is highly toxic to common thrips in cowpeas, has strong resistance, and can stably colonize within cowpeas. Simultaneously, this invention provides a cultivation method for this strain, a biocontrol agent containing this strain, the application of this strain in controlling common thrips in cowpeas, and a cowpea-microbial symbiosis formed by this strain, providing a complete, efficient, and scalable microbial control solution for the green control of common thrips in cowpeas.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an endophytic Beauveria bassiana strain SDQD-1, whose taxonomic name is Beauveria bassiana. Beauveria bassiana Latin name Beauveria bassiana This strain is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 41845, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, on March 21, 2025.

[0009] Furthermore, the ITS nucleotide sequence of the SDQD-1 strain is shown in SEQ ID NO: 1. Its morphological characteristics are as follows: the colonies are round with a raised center, white and cottony in appearance, with neat edges and no obvious pigmentation; the conidia are spherical and colorless, producing septate, slender germ tubes upon germination; the hyphae are slender, colorless, septate, and well-branched.

[0010] Secondly, the present invention provides a biocontrol agent containing the aforementioned endophytic Beauveria bassiana SDQD-1 strain, wherein the biocontrol agent is a conidial suspension with a conidial concentration of 1× spores / mL.

[0011] Furthermore, the biocontrol agent also includes the surfactant Tween-80, which has a mass-volume concentration of 0.01%.

[0012] Thirdly, the present invention provides a method for culturing the above-mentioned Beauveria bassiana SDQD-1.

[0013] Further, the culture medium is either Goettel sporulation medium or PDA solid medium. The Goettel sporulation medium, by weight percentage, consists of 2% corn flour, 1% wheat bran, 0.5% peptone, 0.3% potassium dihydrogen phosphate, 0.1% magnesium sulfate heptahydrate, 0.1% ammonium nitrate, 2% agar, 0.5% cicada molting, and the balance being distilled water. The PDA solid medium, by weight percentage, consists of 0.5% potato starch, 2% glucose, 2% agar, 0.01% chloramphenicol, and the balance being distilled water. Both media are autoclaved at 121°C for 15 minutes before use.

[0014] Preferably, the cultivation conditions are: temperature 26±5℃, photoperiod 12L:12D, and relative humidity 75±5%.

[0015] Fourthly, the present invention provides a method for constructing endophytic colonization of the above-mentioned endophytic Beauveria bassiana SDQD-1 on cowpea. The method uses the conidial suspension described in the second aspect and applies it to cowpea by root irrigation or seed soaking.

[0016] Furthermore, the root irrigation method is as follows: 7 days after the cowpea seedlings emerge, irrigate the conidial suspension along the roots of the seedlings at a rate of 30 mL / plant, once a day, for 3 consecutive days.

[0017] Furthermore, the soaking method is as follows: cowpea seeds are treated with 70% ethanol for 2 min, treated with 2% sodium hypochlorite solution containing 0.05% Triton X-100 for 3 min, rinsed with sterile water 3 times for surface disinfection, and then soaked in the conidial suspension for 12 hours before sowing.

[0018] Fifthly, the present invention provides a cowpea-microorganism symbiotic with pest resistance, which is formed by the above-mentioned endophytic Beauveria bassiana SDQD-1 colonizing inside cowpea tissue through the root irrigation method or seed soaking method described in the fourth aspect.

[0019] In a sixth aspect, the present invention provides the application of endophytic Beauveria bassiana SDQD-1, its conidia obtained by the method described in the third aspect, the biocontrol agent described in the second aspect, or the symbiotic described in the fifth aspect in the control of common thrips in cowpea, wherein the thrips is preferably common thrips; the application method includes direct spraying on the surface of the pest, or indirect action on the pest after endophytic colonization by the method described in the fourth aspect.

[0020] Beneficial effects

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Excellent strain characteristics and high sporulation quality: Strain SDQD-1 has high sporulation and high germination activity, and outstanding UV resistance (it still retains more than 60% of its activity after 48 h of irradiation), which solves the problem of short field efficacy of conventional strains. The accompanying culture medium containing cicada molting components further ensures the large-scale and high-quality production of the strain.

[0023] (2) Fast pest control and significant efficacy: This strain has extremely high pathogenicity against common thrips (deadly time is only 2.34 days), which can rapidly reduce the pest population and shorten the window period for cowpea to be affected.

[0024] (3) Overcoming the problem of the hidden harm of thrips: By establishing an efficient root irrigation and seed soaking endophytic colonization system, the strains entered the cowpea tissue to form a symbiotic organism. The endophytic nature of the strains was used to achieve long-term indirect control of thrips hidden in the tender shoots, pod crevices and other hidden parts, making up for the technical shortcomings of traditional agents that are difficult to reach.

[0025] (4) Achieves multiple control measures that address both internal and external factors: This invention combines direct contact (spraying) with long-term endogenous control, establishing a complete green control technology chain. There is no risk of chemical pesticide residues throughout the entire process, which meets the ecological protection needs of the modern vegetable industry. Attached Figure Description

[0026] Figure 1 Morphological characteristics of Beauveria bassiana SDQD-1: A: Colony morphology (PDA medium, 7 days); B: Conidial germination morphology (showing slender germ tubes); C: Conidiophore morphology (showing branching structure).

[0027] Figure 2 Phylogenetic tree of Beauveria bassiana SDQD-1.

[0028] Figure 3 Cumulative corrected mortality curve of common thrips adults against Beauveria bassiana SDQD-1 spore suspension.

[0029] Figure 4 Symptoms of Beauveria bassiana SDQD-1 infection in adult common thrips.

[0030] Figure 5 Corrected mortality rate of common thrips adults by cowpea-Beauveria bassiana SDQD-1 symbiont after 7 days of colonization.

[0031] Figure 6 Corrected mortality rate of common thrips adults by cowpea-Beauveria bassiana SDQD-1 symbiont after 14 days of colonization. Detailed Implementation

[0032] The present invention will be further illustrated below through specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art should understand that various changes, modifications, substitutions, and improvements can be made to these embodiments without departing from the principles and core tenets of the present invention. The scope of protection of the present invention is defined by the claims and their equivalents.

[0033] Materials and General Methods

[0034] Test insect: Common thrips ( Megalurothrips usitatus Adults were collected in 2024 from cowpea fields in Lingao Village, Yazhou District, Sanya City, Hainan Province, and were reared in cowpea pods in an artificial climate chamber (temperature 26±5℃, light intensity 12 L:12 D, relative humidity 75±5%).

[0035] Preparation of spore suspension: Scrape mature spore powder, place it in a sterile solution containing 0.01% Tween-80, grind, shake to mix, filter and collect, determine the spore concentration using a hemocytometer, and dilute to the required concentration with a sterile solution containing 0.01% Tween-80.

[0036] Data analysis: Data were organized using Excel 2019 and plotted using OriginPro 2021 software. Experimental results for each embodiment are expressed as mean ± standard deviation (Mean ± SD). Significant differences among multiple groups were tested using two-way ANOVA, supplemented by Tukey's HSD test for pairwise comparisons between groups.

[0037] P < 0.05 was used as the criterion for statistical significance. In the figures (Figures 5 and 6), the asterisks above the data at the same treatment time point indicate the significance level between different treatments, where "***" indicates P < 0.001 and "****" indicates P < 0.0001.

[0038] Example 1: Isolation, Culture and Identification of Strains

[0039] 1.1 Collection of bacterial strains

[0040] Whiteflies infected with white fungal hyphae were collected in a cowpea field in Jimo District, Qingdao City, Shandong Province in 2024. Bemisia tabaci ) Insect body.

[0041] 1.2 Isolation and culture of strains

[0042] White mycelia were collected from the surface of diseased insects and inoculated onto Goettel sporulation medium (formula shown in 1.3). The medium was then cultured in an artificial climate chamber (temperature 26±5℃, light intensity 12 L:12 D, relative humidity 75±5%). After sporulation, the target strain was isolated and purified using the streak plate method.

[0043] 1.3 Culture medium formulation

[0044] Goettel sporulation medium (by weight): corn flour 2%, wheat bran 1%, peptone 0.5%, potassium dihydrogen phosphate 0.3%, magnesium sulfate heptahydrate 0.1%, ammonium nitrate 0.1%, agar 2%, cicada molts 0.5%, balance distilled water. Autoclave at 121°C for 15 min.

[0045] 1.4 Strain Identification

[0046] Morphological identification: The purified strain was inoculated into PDA medium and cultured at 26±5℃ for 7 days. Colonies were round, centrally raised, white and cottony, with neat edges and no pigmentation. Conidia were spherical, colorless, and produced septate, slender germ tubes upon germination; hyphae were slender, colorless, septate, and well-branched. Figure 1 ).

[0047] Molecular identification: SDQD-1 DNA extracted using a fungal genomic DNA extraction kit was used as a template for PCR amplification using universal primers ITS1 and ITS4 (Table 1). PCR system (25 μL): Mix 12.5 μL, primers 1 μL each, DNA 2 μL, ddH2O 8.5 μL. Amplification conditions: 98℃ pre-denaturation for 30 s; 94℃ denaturation for 10 s, 55℃ annealing for 15 s, 72℃ extension for 15 s, 35 cycles; final extension at 72℃ for 1 min. The amplified product was sequenced, and the obtained ITS sequence is shown in SEQ ID NO: 1. After comparison with NCBIBLAST, it was found to be similar to *Beauveria bassiana* (…). Beauveria bassiana The similarity reached 99%, and the phylogenetic tree showed aggregation with Beauveria bassiana. Figure 2 Based on morphological characteristics, strain SDQD-1 was identified as... Beauveria bassiana .

[0048] Table 1 Primer sequence listing

[0049]

[0050] Example 2: Pathogenicity of SDQD-1 strain against common thrips

[0051] 2.1 Preparation of SDQD-1 spore suspension

[0052] Mature SDQD-1 spore powder was scraped from the sporulation medium and placed in a sterile solution containing 0.01% Tween-80. The mixture was then thoroughly ground using a glass tissue homogenizer and vortexed. The filtered suspension was collected using gauze, and the conidia content was determined using a 25-square × 16-square hemocytometer. The count was repeated three times, and the average value was calculated. Finally, the suspension was diluted to the desired concentration using a sterile solution containing 0.01% Tween-80 for later use.

[0053] 2.2 Comparison of the indoor pathogenicity of different Beauveria bassiana strains against common thrips

[0054] Test strains: The newly isolated SDQD-1 strain and eight Beauveria bassiana strains preserved in the applicant's laboratory were used in this experiment. They were numbered Bb01, Bb324, Bb04, Bb06, Bb07, Bb1317, GZGY-1, and E, respectively. All of the above strains were isolated from naturally infected insects, purified and cultured, and then preserved in PDA slant medium at 4°C.

[0055] All nine strains were prepared to a concentration of 1× A spore suspension of 1 spore / mL was evenly sprayed onto the surface of healthy, active adult common thrips (35 thrips per dish, 4 replicates), with 0.01% Tween-80 sterile water as a control. Fresh cowpea fragments were added to each dish, sealed with film, and incubated in a climate chamber (26±5℃, 75±5% RH). Starting 24 hours after treatment, the number of dead thrips was recorded daily, and fresh cowpea slices were replaced. Observation continued for 7 days. Dead individuals were transferred to petri dishes for observation; those with a white mycelial layer growing on their surface were considered to have died from infection by the strain. Figure 4 Data was collected and processed using Excel 2019. The mortality rate was calculated using the formula: Mortality rate (%) = Number of dead insects ÷ Total number of insects × 100%. The cumulative corrected mortality rate was then calculated using the formula: Corrected mortality rate (%) = (Morality rate of treatment group - Mortality rate of control group) ÷ (1 - Mortality rate of control group) × 100%. OriginPro 2021 software was used for plotting.

[0056] The results showed that the newly isolated SDQD-1 strain exhibited extremely high virulence against adult common thrips, with a cumulative corrected mortality rate of (97.01±4.22)% after 7 days, significantly higher than the other 8 tested strains. Among the remaining strains, strain E had the highest corrected mortality rate, at only (77.68±7.36)%, while the corrected mortality rates of the other strains ranged from 27.68% to 69.64%, all far lower than that of strain SDQD-1, fully demonstrating the virulence advantage of SDQD-1 (Table 2). From day 1 to day 7 post-inoculation, the cumulative corrected mortality rates of adult common thrips were 4.67±4.55%, 37.16±4.61%, 74.14±8.46%, 84.02±10.49%, 91.49±4.63%, 95.59±2.94%, and 97.01±4.22%, respectively, with a median time to death (LT). 50 It is 2.34 days. Figure 3 White mycelial layers grew to varying degrees on the surface of the dead insects. Figure 4 In summary, the results indicate that the Beauveria bassiana SDQD-1 strain exhibits good infective and lethal activity against common thrips.

[0057] Table 2. Cumulative corrected mortality rate of adult common thrips over 7 days for spore suspensions of different Beauveria bassiana strains.

[0058]

[0059] Note: Tukey's HSD test was used for multiple comparisons between groups (P < 0.05). The range of treatments with the same letter was not significant, while the difference between treatments with different letters was significant.

[0060] Example 3 Bioactivity assay of SDQD-1 strain

[0061] 3.1 Determination of bacterial germination rate

[0062] Take 1× One spore / mL spore suspension was added to 1 mL of sterile spore germination medium (4% glucose, 1% yeast powder), and the mixture was shaken and incubated at 25℃ and 120 r / min for 16 h. Spores were counted under a microscope; those with a germ tube length exceeding the spore radius were considered germinated. Spore germination rate (%) = (number of germinating spores ÷ number of spores detected) × 100%, with 5 replicates. The results showed that the average spore germination rate of *Beauveria bassiana* SDQD-1 strain at 25℃ and 120 r / min was 91.13 ± 0.95%, indicating that this strain has excellent conidial germination activity.

[0063] 3.2 Determination of Sporulation Yield of Strains

[0064] Beauveria bassiana SDQD-1 inoculated on PDA medium was cultured for 15 days. Five mycelial cakes were collected from the center to halfway along the edge of the colony using a 1 cm diameter punch and placed in test tubes. A 1× concentration was prepared using an aqueous solution containing 0.01% Tween-80. A spore suspension of 1 spore / mL was prepared by shaking on a constant-temperature shaker for 10 min to mix thoroughly. The spore count was then determined under an optical microscope using a hemocytometer, and the results were repeated 5 times. The spore yield was calculated using the formula: Spore yield (spores / cm²) 2 = (Total number of spores on the hemocytometer × dilution factor) ÷ 5, where 5 is the total number of mycelial cakes.

[0065] The results showed that the sporulation yield of Beauveria bassiana SDQD-1 strain after 15 days of culture on PDA medium was (5.96±1.71)× pcs / cm 2 This shows that the strain has a relatively good sporulation ability.

[0066] 3.3 Determination of bacterial growth rate

[0067] Beauveria bassiana SDQD-1, inoculated into PDA medium, was cultured for 15 days. Mycelial cakes were created on colonies where mycelial growth was uniform using a 1 cm diameter circular punch. These cakes were then inoculated into the center of PDA plates. Colony diameters were measured using the cross-sectional method on days 3, 5, 7, 9, 11, 13, and 15. The growth rate (cm / d) was calculated as growth distance (cm) ÷ growth time (d). The results are shown in Table 3. The growth rate of strain SDQD-1 on PDA medium was 0.13±0.06 cm / d after 3 days, increasing to 0.24±0.05 cm / d after 5 days, and entering a stable growth phase at 0.27±0.02 cm / d after 7 days. It reached its peak growth rate of 0.29±0.02 cm / d at 13 days, and maintained a stable growth rate between 0.26 and 0.29 cm / d from 7 to 15 days without significant decline, indicating stable and efficient overall growth.

[0068] Table 3. Growth rate of Beauveria bassiana SDQD-1 on PDA medium at different culture times.

[0069]

[0070] 3.4 Determination of UV resistance of the strain

[0071] Take 1× Ten mL of spore suspension (1 spore / mL) was spread evenly in a 90 mm sterile petri dish and placed under a 15°C WUV-B UV lamp (315 nm wavelength). The vertical distance between the petri dish surface and the lamp tube was 30 cm. Irradiation was performed for 12, 24, and 48 h, and the number of ungerminated spores was determined according to method 3.1. Spore inactivation rate (%) = (number of ungerminated spores ÷ number of spores detected) × 100%, with 5 replicates. The results showed that after 12, 24, and 48 h of irradiation, the spore inactivation rates were 25.27±12.29%, 26.70±6.85%, and 35.28±12.38%, respectively. Even after 48 h of irradiation, more than 60% of the spores still had good activity, indicating that the strain has strong UV resistance.

[0072] Example 4: Construction and colonization rate determination of SDQD-1 strain-cowpea symbiont

[0073] 4.1 Construction of the strain-cowpea symbiosis

[0074] Root irrigation method: 7 days after cowpea emergence, slowly irrigate the base of the seedlings with 30 mL of 1× [amount not specified]. SDQD-1 spore suspension was prepared at 1 spore / mL for 3 consecutive days, and seedlings were then transferred to an artificial climate chamber for cultivation.

[0075] Seed soaking method: Cowpea seeds are treated with 70% ethanol for 2 min, 2% sodium hypochlorite (containing 0.05% Triton X-100) for 3 min, and rinsed 3 times with sterile water to complete surface disinfection. Then, they are placed in a 1× After soaking in a spore suspension of 1 spores / mL for 12 h, the seedlings were sown and then transferred to an artificial climate chamber for cultivation.

[0076] 4.2 Determination of colonization rate

[0077] Root, stem (upper and lower), and leaf (upper and lower) tissues from cowpea seedlings with consistent growth status were collected on days 7, 14, and 21 after root irrigation treatment and on days 7, 14, and 21 after emergence from seed soaking. After surface sterilization (roots: pre-washed with 0.05% Triton X-100 for 3 min, soaked in 2% NaOCl for 3 min, rinsed with 75% ethanol for 1 min, and rinsed 3 times with sterile water; stems and leaves: each step time was halved), the samples were placed in petri dishes containing 75% diluted PDA medium (containing 0.1 g / L penicillin, 0.2 g / L streptomycin, and 0.05 g / L tetracycline) and incubated in the dark at 26±1℃ for 10 days to observe the growth of the bacterial strain. Untreated cowpea seedlings were used as a control group. All treatments and controls were replicated in triplicate. Colonization rate (%) = (number of plants with detected SDQD-1 strain colonization ÷ total number of plants) × 100%.

[0078] The results showed that *Beauveria bassiana* SDQD-1 could effectively colonize the roots, stems, and leaves of cowpea plants via root drenching and seed soaking. The highest colonization rate was observed 7 days after treatment, with the root drenching treatment achieving a root colonization rate of 86.67±11.54%, while the rates for lower leaves and lower stems were 83.33±5.77% and 73.33±5.77%, respectively. The colonization rate decreased over time, but at 21 days, the root drenching treatment still achieved a root colonization rate of 33.33±5.77%. Overall, the colonization rate at each stage followed the pattern of root > lower leaf > lower stem > upper leaf > upper stem (Table 4).

[0079] Table 4. Colonization rate of SDQD-1 in different tissue parts of cowpea

[0080]

[0081] Note: Upper leaves and lower leaves refer to the newly emerging leaves above the cotyledons and the basal leaves below the cotyledons of cowpea seedlings, respectively; upper stem and lower stem refer to the newly emerging stem segments above the cotyledons and the basal stem segments below the cotyledons of cowpea seedlings, respectively.

[0082] Example 5: Determination of the lethality of SDQD-1 strain-cowpea symbiont against common thrips.

[0083] Symbionts were constructed using root drenching and seed soaking methods, respectively. Cowpea leaves were collected on days 7 and 14 after root drenching and on days 7 and 14 after emergence from seed soaking. Thirty healthy, active adult common thrips were inoculated into each dish (three replicates), with untreated leaves serving as a control. The dishes were sealed with plastic wrap (with fine pinholes) and cultured in an artificial climate chamber (26±5℃, 12 L:12 D light intensity, 75±5% relative humidity), maintaining humidity daily. The number of dead thrips was checked daily for 9 consecutive days, starting 24 hours after inoculation. The cumulative corrected mortality rate was calculated (using the same formula as in Example 2).

[0084] The results showed that *Beauveria bassiana* SDQD-1, after being used to propagate cowpeas via root drenching or seed soaking, exhibited significant infection and lethality against *Thrips simonii* (P < 0.05). At 7 days post-planting, the cumulative corrected mortality rates at 9 days were 74.57±5.65% and 78.49±3.39% for the root drenching and seed soaking treatments, respectively; at 14 days post-planting, they were 64.80±12.19% and 66.58±7.70%, respectively. At 7 days post-planting, the corrected mortality rate in the root drenching treatment group was significantly higher than that in the seed soaking group from day 6 to day 8 (P < 0.05); at 14 days post-planting, there were no significant differences between the two groups at any time point (P > 0.05). Figure 5 , Figure 6 In summary, the symbiotic relationship established by root irrigation is more lethal to common thrips than that established by seed soaking.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An endophytic Beauveria bassiana strain ( Beauveria bassiana SDQD-1, characterized in that, The strain is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 41845 and deposit date of March 21, 2025. The ITS sequence of the strain is shown in SEQ ID NO:

1.

2. A method for culturing the endophytic Beauveria bassiana SDQD-1 as described in claim 1, characterized in that, The cells were cultured using Goettel sporulation medium or PDA solid medium. The Goettel sporulation medium consisted of the following components by weight percentage: 2% corn flour, 1% wheat bran, 0.5% peptone, 0.3% potassium dihydrogen phosphate, 0.1% magnesium sulfate heptahydrate, 0.1% ammonium nitrate, 2% agar, 0.5% cicada molting, and the remainder being sterile water. Both the Goettel sporulation medium and the PDA solid medium were sterilized by autoclaving at 121°C for 15 minutes before use.

3. The cultivation method according to claim 2, characterized in that, The cultivation conditions were: temperature 26±5℃, photoperiod 12L:12D, and relative humidity 75±5%.

4. A biocontrol agent for controlling common thrips, characterized in that, Its active ingredient includes conidia of the endophytic Beauveria bassiana SDQD-1 as described in claim 1, wherein the biocontrol agent is a conidia suspension, and the concentration of conidia is 1× spores / mL.

5. The biocontrol agent according to claim 4, characterized in that, The biocontrol agent also includes a surfactant; the surfactant is a wetting and dispersing agent Tween-80, and the mass-volume concentration of Tween-80 in the biocontrol agent is 0.01%.

6. The application of the endophytic Beauveria bassiana SDQD-1 as described in claim 1, or its conidia obtained by culturing according to the methods described in claims 2-3, in the control of common thrips in cowpea, characterized in that, The common thrips is Megalurothrips usitatus .

7. The application according to claim 6, characterized in that, The application method includes colonizing the endophytic Beauveria bassiana SDQD-1 in the cowpea tissue by root irrigation or seed soaking, forming a cowpea-microbe symbiosis with resistance to common thrips.

8. The application according to claim 7, characterized in that, The specific steps of the root irrigation method are as follows: Seven days after the cowpea seedlings emerge, irrigate the biocontrol agent described in claim 4 along the roots of the seedlings, with an irrigation volume of 30 mL / plant, once a day, for three consecutive days.

9. The application according to claim 7, characterized in that, The specific steps of the soaking method are as follows: after surface disinfection, cowpea seeds are soaked in the conidial suspension described in claim 5 for 12 hours before sowing.

10. A cowpea-microbial symbiont with resistance to common thrips, characterized in that, The endophytic Beauveria bassiana SDQD-1 described in claim 1 is colonized within cowpea tissue using the root irrigation method or seed soaking method described in claim 7.

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