Streptomyces griseoviridis strain qs2-7 and its use

Abstract

The application discloses a Streptomyces caniferus QS2-7 and application thereof, and belongs to the technical field of microorganisms. The application separates and obtains a Streptomyces caniferus QS2-7 with a preservation number of CGMCC No.32328. Experiments show that the strain QS2-7 has a strong inhibiting effect on various plant pathogenic bacteria, and has superior biocontrol potential. The strain has the functions of nitrogen fixation, phosphorus solubilization and protease production, can effectively degrade autotoxic substances generated in the process of planting plants, and can relieve autotoxicity. The strain can significantly promote the growth of plant plants, effectively reduce the incidence of diseases, and has high application value in green control of plant diseases and continuous cropping production.

Description

Technical Field

[0001] This invention relates to the field of microbial technology, and in particular to a strain of Streptomyces simulans QS2-7 and its applications. Background Technology

[0002] Cucumber cultivation accounts for approximately 60% of the total area of ​​greenhouse vegetable cultivation, making it a major vegetable variety. In recent years, with the adjustment of the agricultural industrial structure, land resources have become scarce. As planting years have accumulated, the excessive use of chemical fertilizers and pesticides in pursuit of maximum economic output, coupled with the continuous planting of the same crop on the same land, has led to continuous cropping obstacles, which are particularly serious among cucurbitaceous crops. This has resulted in a series of problems, including declining soil quality, increased soil-borne diseases, and reduced cucumber yields.

[0003] Soil degradation caused by continuous cropping has various causes, but essentially stems from two abnormal changes in the soil's micro-ecosystem caused by continuous cropping: an imbalance in the soil's microbial flora and abnormal chemical substances. In cucumbers grown continuously for three years or more, the rhizosphere soil microbial ratio becomes imbalanced, with a significant decrease in beneficial bacteria and actinomycetes, and an increase in pathogenic fungi such as Fusarium oxysporum and Verticillium sp. Fusarium oxysporum f.sp. cucumerinum is a common fungal disease in greenhouse cucumber production, occurring throughout the entire growth period, but most prevalent during flowering and fruiting. The pathogen infects the roots or rootstock of cucumbers, damaging the vascular tissue of the stem and causing symptoms such as yellowing leaves, wilting, and stunted growth.

[0004] The accumulation of autotoxic substances is a significant factor exacerbating soil degradation caused by continuous cropping. During its growth, cucumbers release metabolites such as aldehydes, ketones, phenols, and acids, affecting physiological and biochemical processes like nutrient absorption, thereby reducing root activity and inhibiting root and cucumber growth. Common autotoxic substances in cucumber root exudates include p-hydroxybenzoic acid, ferulic acid, gallic acid, and cinnamic acid, which are major factors causing continuous cropping obstacles.

[0005] The widespread existence of soil degradation due to continuous cropping has led to a series of significant problems, including environmental pollution and agricultural product quality and safety. Adding antagonistic bacteria can effectively prevent continuous cropping obstacles caused by autotoxicity and soil-borne diseases. Currently, existing microbial agents are not very effective in controlling continuous cropping obstacles in cucumber production, mainly because existing biocontrol bacteria lack broad-spectrum biocontrol potential and the ability to degrade autotoxic substances. Furthermore, many antagonistic bacteria have poor field colonization capabilities. Many strains in nature possess the ability to degrade phenolic acids; therefore, alleviating continuous cropping obstacles through microbial degradation of autotoxic substances is a safe and environmentally friendly approach. Thus, screening strains that are highly effective in controlling cucumber diseases and also possess the ability to degrade autotoxic substances is a crucial issue that needs to be addressed in the research and application of biological control of cucumber diseases and the alleviation of continuous cropping obstacles. This is of great significance for enriching biocontrol microbial resources and promoting green control of plant diseases. Summary of the Invention

[0006] The purpose of this invention is to provide a strain of *Streptomyces caniferus* QS2-7 and its applications to solve the problems existing in the prior art. This invention isolates and obtains a strain of *Streptomyces caniferus* QS2-7. Experiments show that this strain QS2-7 has a strong inhibitory effect on a variety of plant pathogens, demonstrating superior potential as a biocontrol agent. Furthermore, this strain possesses nitrogen-fixing, phosphorus-solubilizing, and protease-producing functions, effectively degrading autotoxic substances produced during plant cultivation and alleviating autotoxic effects. This strain can significantly promote plant growth and effectively reduce disease incidence, demonstrating high application value in green control of plant diseases and continuous cropping production.

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

[0008] In the first aspect, the present invention provides a rhizosphere growth-promoting bacterium, Streptomyces caniferus QS2-7, which is deposited at the China General Microbiological Culture Collection Center (CGMCC) at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 32328.

[0009] Secondly, the present invention also provides the application of the aforementioned Streptomyces grayi QS2-7 in the preparation of microbial inoculants.

[0010] Thirdly, the present invention also provides a microbial inoculant containing the aforementioned Streptomyces griseus QS2-7 and / or its fermentation products.

[0011] Fourthly, the present invention also provides the application of the aforementioned Streptomyces globosum QS2-7 or the aforementioned microbial agent in promoting plant growth.

[0012] Fifthly, the present invention also provides the application of the aforementioned Streptomyces hygroscopicus QS2-7 or the aforementioned microbial agent in inhibiting the growth of plant pathogens, the plant diseases including cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizomatous fruit rot, melon vine blight, tomato late blight and / or pepper damping-off.

[0013] In a sixth aspect, the present invention also provides the application of the aforementioned *Streptomyces hygroscopicus* QS2-7 or the aforementioned microbial agent in the preparation of products for the prevention and control of plant diseases, the plant diseases including cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizopus fruit rot pathogens, melon vine blight pathogens, tomato late blight pathogens and / or pepper damping-off pathogens.

[0014] In a seventh aspect, the present invention also provides a product for preventing and controlling plant diseases, the product comprising the aforementioned Streptomyces globosum QS2-7 or the aforementioned microbial agent.

[0015] Preferably, the plant diseases include cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizomatous fruit rot, melon vine blight, tomato late blight, and / or pepper damping-off.

[0016] In an eighth aspect, the present invention also provides a method for preventing and controlling plant diseases, comprising the step of applying the aforementioned Streptomyces globosum QS2-7, the aforementioned microbial agent, or the aforementioned product to plants.

[0017] Preferably, the plant diseases include cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizomatous fruit rot, melon vine blight, tomato late blight, and / or pepper damping-off.

[0018] The present invention discloses the following technical effects:

[0019] This invention isolated a strain of *Streptomyces caniferus* QS2-7 from the root soil of *Magnolia officinalis* plants in Qianshan Scenic Area, Anshan City, Liaoning Province. Experiments showed that this strain QS2-7 exhibited strong inhibitory effects against nine pathogens (fusarium wilt pathogen of cucumber, root rot pathogen of eggplant, early blight pathogen of tomato, gray mold pathogen of tomato, blight pathogen of pepper, rhizopus fruit rot pathogen of pepper, vine blight pathogen of melon, late blight pathogen of tomato, and damping-off pathogen of pepper), demonstrating superior biocontrol potential. Furthermore, this strain possesses certain nitrogen-fixing, phosphorus-solubilizing, and protease-producing abilities, and has the capacity to degrade the autotoxic substances ferulic acid, p-hydroxybenzoic acid, and gallic acid. The *Streptomyces caniferus* QS2-7 of this invention is easy to cultivate, has a short fermentation time, and high stability, making it suitable for production and widespread application in agricultural environments. It has high application value in green control of plant diseases and soil remediation in continuous cropping.

[0020] Preservation Information: Streptomyces caniferus QS2-7 was deposited on October 24, 2024, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 32328. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The images show the colony morphology of strain QS2-7; where A represents the colony morphology in ISP-2 medium and B represents the colony morphology in Gao's No. 1 medium.

[0023] Figure 2 A phylogenetic tree of strain QS2-7 based on 16S rDNA;

[0024] Figure 3 The growth curves of strain QS2-7 in TSBY medium are shown; 1E1-1E8 are 8 parallel data.

[0025] Figure 4 The image shows the inhibitory effect of strain QS2-7 on pathogens (Cucumber wilt pathogen, Tomato gray mold pathogen, Eggplant root rot pathogen, Tomato early blight pathogen, Pepper blight pathogen, Pepper rhizopus fruit rot pathogen, Melon vine blight pathogen, Tomato late blight pathogen, and Pepper damping-off pathogen).

[0026] Figure 5 The graph shows the results of nitrogen fixation capacity determination for strain QS2-7;

[0027] Figure 6 The graph shows the results of phosphorus solubilization ability determination for strain QS2-7; where A represents the result of inorganic phosphorus solubilization and B represents the result of organic phosphorus solubilization. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] The pathogens of cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizopus fruit rot, melon vine blight, tomato late blight, and pepper damping-off were purchased from Shanghai Boko Biotechnology Co., Ltd.

[0034] PDA solid culture medium: 200 g / L potato, 20 g / L glucose, 20 g / L agar.

[0035] Gao's No. 1 solid culture medium: soluble starch 20g / L, potassium nitrate 1g / L, dipotassium hydrogen phosphate 0.5g / L, magnesium sulfate heptahydrate 0.5g / L, sodium chloride 0.5g / L, ferrous sulfate heptahydrate 0.01g / L, potassium dichromate 0.1g / L, agar 20g / L, pH 7.2-7.4.

[0036] ISP-2 medium: yeast extract 4 g / L, malt extract 10 g / L, glucose 4 g / L, agar 20 g / L, pH 7.2-7.4.

[0037] TSBY liquid medium: tryptone 17g / L, soybean peptone 3g / L, sodium chloride 5g / L, yeast extract 5g / L, dipotassium hydrogen phosphate 2.5g / L, glucose 2.5g / L, pH 7.2-7.4.

[0038] Example 1: Isolation and Identification of Streptomyces caniferus QS2-7

[0039] 1. Isolation and preservation of bacterial strains

[0040] Soil samples from the root system of Magnolia plants were collected from Qianshan, Anshan City, Liaoning Province (123.7°E, 41.1°N). 1g of soil sample was added to 99mL of sterile water and incubated on a shaker at 180rpm for 30min. The sample was then serially diluted 10-fold, with 100μL of each diluted sample taken from each volume. -3 10 -4 10 -5 The samples were evenly spread on 0.1×TSB solid plates using a pipette and incubated in a 30℃ constant temperature incubator. After 5 days, single colonies were picked and the purified strains were inoculated into Gao's No. 1 medium for storage.

[0041] Using *Fusarium oxysporum*, the pathogen causing cucumber wilt, as an indicator bacterium, a 6 mm agar block containing the pathogen was inoculated in the center of a PDA medium plate. Then, single colonies of the isolated bacteria were inoculated at equal intervals 2.5 cm away from the pathogen, with 4 strains inoculated per plate and 5 replicates. After incubation at 28℃ for 5-7 days, the size of the inhibition zone was observed, the inhibition band was measured, and the strain with the best antagonistic effect was selected and named QS2-7.

[0042] 2. Identification of strains

[0043] 2.1 Morphological identification

[0044] Morphological identification was performed according to the *Streptomyces Identification Manual*. The results showed that strain QS2-7 grew well on both Gao's No. 1 and ISP-2 media, exhibiting typical characteristics of the *Streptomyces* genus. Colonies were nearly circular, white to grayish-white, opaque, wrinkled, and dry. Spores were elliptical, with curved or spiral spore filaments and a smooth surface. Figure 1 As shown.

[0045] 2.2 Identification of Physiological and Biochemical Characteristics

[0046] Strain QS2-7 can utilize glucose, sucrose, maltose, rhamnose, D-mannitol, and inositol, but cannot utilize L-arabinose, D-xylose, D-fructose, raffinose, or lactose. Strain QS2-7 can hydrolyze starch, but exhibits weak coagulation and peptonization of milk.

[0047] 2.3 DNA extraction and molecular biological identification

[0048] After culturing strain QS2-7 in Gao's No. 1 medium at 30℃ for 5 days, genomic DNA was extracted using the Qingke DNA Extraction Kit (TSP701-50). 16S rDNA of strain QS2-7 was amplified by PCR. The total PCR reaction volume was 20.0 μL, including 2.0 μL each of forward and reverse primers, 1.0 μL of DNA template, and 15.0 μL of ddH2O. The PCR reaction program was: 98℃ for 2 min; 98℃ for 10 s, 57℃ for 10 s, 72℃ for 45 s, 35 cycles; 72℃ for 5 min. The amplified PCR product was subjected to agarose gel electrophoresis (2 μL sample + 6 μL bromophenol blue) at 300V for 12 min. A single band was obtained and sent to Beijing Qingke Biotechnology Co., Ltd. for purification and sequencing. The nucleotide sequences of the PCR amplification primers are as follows:

[0049] 27F: 5'-AGTTTGATCMTGGCTCAG-3' (SEQ ID NO. 1);

[0050] 1492R: 5'-GGTTACCTTGTTACGACTT-3' (SEQ ID NO. 2).

[0051] The sequences of the obtained amplification products are as follows:

[0052] ACGACGCTGGCGGCGTGCTTAACACATGCAAGTCGAACGATGAACCTCCTTCGGGA

[0053] GGGGATTAGTGGCGAACGGGTGAGTAACACGTGGGCAATCTGCCCTTCACTCTGGGAC

[0054] AAGCCCTGGAAACGGGGTCTAATACCGGATACGACCACCGACCGCATGGTCTGGTGGTG

[0055] GAAAGCTCCGGCGGTGAAGGATGAGCCCGCGGCCTATCAGCTTGTTGGTGGGGTGATG

[0056] GCCTACCAAGGCGACGACGGGTAGCCGGCCTGAGAGGGCGACCGGCCACACTGGGACT

[0057] GAGACACGGCCCAGACTCCTACGGGAGGCAGCAGTGGGGAATATTGCACAATGGGCGA

[0058] AAGCCTGATGCAGCGACGCCGCGTGAGGGATGACGGCCTTCGGGTTGTAAACCTCTTTC

[0059] AGCAGGGAAGAAGCGAGAGTGACGGTACCTGCAGAAGAAGCGCCGGCTAACTACGTG

[0060] CCAGCAGCCGCGGTAATACGTAGGGCGCAAGCGTTGTCCGGAATTATTGGGCGTAAAGA

[0061] GCTCGTAGGCGGCTTGTCACGTCGGATGTGAAAGCCCGGGGCTTAACCCCGGGTCTGCA

[0062] TTCGATACGGGCAGGCTAGAGTTCGGTAGGGGAGATCGGAATTCCTGGTGTAGCGGTGA

[0063] AATGCGCAGATATCAGGAGGAACACCGGTGGCGAAGGCGGATCTCTGGGCCGATACTG

[0064] ACGCTGAGGAGCGAAAGCGTGGGGAGCGAACAGGATTAGATACCCTGGTAGTCCACGC

[0065] CGTAAACGTTGGGAACTAGGTGTGGGCGACATTCCACGTCGTCCGTGCCGCAGCTAACG

[0066] CATTAAGTTCCCCGCCTGGGGAGTACGGCCGCAAGGCTAAAACTCAAAGGAATTGACG

[0067] GGGGCCCGCACAAGCAGCGGAGCATGTGGCTTAATTCGACGCAACGCGAAGAACCTTA

[0068] CCAAGGCTTGACATACACCGGAAACGTCTGGAGACAGGCGCCCCCTTGTGGTCGGTGT

[0069] ACAGGTGGTGCATGGCTGTCGTCAGCTCGTGTCGTGAGATGTTGGGTTAAGTCCCGCAA

[0070] CGAGCGCAACCCTTGTTCTGTGTTGCCAGCATGCCCTTCGGGGTGATGGGGACTCACAG

[0071] GAGACTGCCGGGGTCAACTCGGAGGAAGGTGGGGACGACGTCAAGTCATCATGCCCCT

[0072] TATGTCTTGGGCTGCACACGTGCTACAATGGCCGGTACAATGAGCTGCGATACCGCGAG

[0073] GTGGAGCGAATCTCAAAAAGCCGGTCTCAGTTCGGATTGGGGTCTGCAACTCGACCCCA

[0074] TGAAGTCGGAGTTGCTAGTAATCGCAGATCAGCATTGCTGCGGTGAATACGTTCCCGGG

[0075] CCTTGTACACACCGCCCGTCACGTCACGAAAGTCGGTAACACCCGAAGCCGGTGGCCC

[0076] AACCCCTTGTGGGAGGGAATCGTCGAAGGTGGGACTGGCGATTGGGACGAAGTCGTAA

[0077] CAGGGTAGCCGTA(SEQ ID NO.3)。

[0078] The 16S rDNA sequence of this strain was determined to be 1471 bp and submitted to EzBioCloud (https: / / www.ezbiocloud.net / ) for alignment. The alignment results showed that the 16S rDNA sequence similarity between strain QS2-7 and *Streptomyces caniferus* reached 99.8%. Based on the homology comparison results, bacteria QS2-7 can be preliminarily confirmed as *Streptomyces caniferus* (see...). Figure 2 ).

[0079] 2.4 Growth curve determination of strain QS2-7

[0080] The turbidimetric method was used to determine the spore suspension of QS2-7 (10% inoculum) in 100 mL of TSBY liquid medium. The medium was incubated at 30°C. Under constant culture conditions, the OD value of the bacterial suspension was measured every 60 minutes using the MicroScreen high-throughput real-time microbial growth analysis system (Jieling), at a wavelength of 600 nm. 600 The growth curve of *Streptomyces griseus* QS2-7 was plotted with OD value on the ordinate and incubation time on the abscissa to determine the optimal incubation time.

[0081] The results are as follows Figure 3 As shown, QS2-7 spore suspension requires a period of adjustment and adaptation to a new environment; therefore, the cells are in a lag phase (delayed growth phase) during the initial 0-14 hours. From 14-20 hours, the cells begin to grow at a constant geometric progression, entering the logarithmic growth phase. During this stage, the morphology, staining properties, and physiological activity of the cells are relatively typical, and they are sensitive to external environmental factors. After 20 hours, cell growth tends to stabilize.

[0082] Example 2: Determination of the biocontrol effect of Streptomyces glaucus QS2-7

[0083] Using the plate confrontation method, mycelial cakes of *Fusarium oxysporum* (cucumber wilt pathogen), *Fungi Imperficti* (eggplant root rot pathogen), *Alternaria solani* (tomato early blight pathogen), *Botrytis cinerea* (tomato gray mold pathogen), *Phytophthora capsici* (pepper blight pathogen), *Rhizopus stolonifer* (pepper rhizopus fruit rot pathogen), *Mycosphaerella melonis* (melon vine blight pathogen), *Phytophthora infestans* (tomato late blight pathogen), and *Rhizoctonia solani* (pepper damping-off pathogen) with a diameter of 5 mm were inoculated into the center of PDA solid medium plates. Activated strain QS2-7 was inoculated at equal intervals 2.5 cm from the center. A blank control was included. The plates were incubated at 28℃ for 7 days, and the growth of the pathogens was observed, and the inhibition rate was calculated. The formula for calculating the inhibition rate is: Inhibition rate (%) = (Coronavirus colony diameter of control pathogen - Coronavirus colony diameter of treatment pathogen) / Coronavirus colony diameter of control pathogen × 100%.

[0084] The results are as follows Figure 4 As shown, strain QS2-7 exhibited the best inhibitory effect against early blight of tomato, with a band width of 9 mm. The inhibition zone remained transparent throughout the incubation period, indicating stable antibacterial performance of this antagonistic bacterium. The inhibition rates and effects of QS2-7 against various pathogens are shown in Table 1.

[0085] Table 1. Inhibition rate and inhibitory effect of Streptomyces grayi QS2-7 against 9 pathogens.

[0086]

[0087] Example 3: Determination of the function and autotoxicity degradation effect of Streptomyces glaucus QS2-7

[0088] 1. Multifunctional testing

[0089] ① Nitrogen fixation: *Streptomyces glaucus* QS2-7 mycelial pellets cultured on Gao's No. 1 medium for 5 days were inoculated onto Ashby solid medium and cultured at 30℃ for 5 days. Growth was observed, with each strain inoculated three times. Results showed that QS2-7 could grow normally on Ashby medium, indicating that the QS2-7 strain has nitrogen-fixing ability (see...). Figure 5 ).

[0090] ② Phosphorus solubilization: *Streptomyces glaucus* QS2-7 mycelial pellets cultured on Gao's No. 1 medium for 5 days were inoculated onto inorganic and organic phosphorus solid culture plates and incubated at 28℃ for 5 days. The results showed that QS2-7 produced a clear zone on the culture medium, indicating its phosphorus solubilization ability (see...). Figure 6 ).

[0091] ③ Protease production: *Streptomyces griseus* QS2-7 mycelial pellets cultured on Gao's No. 1 medium for 5 days were inoculated onto milk agar plates and incubated at 28℃ for 5 days. The results showed that QS2-7 exhibited a clear zone on the milk agar plate, indicating its protease hydrolytic ability.

[0092] The results showed that *Streptomyces glaucus* QS2-7 has certain nitrogen-fixing, protease-producing, and phosphorus-solubilizing abilities.

[0093] 2. Degradation test of autotoxic substances

[0094] Determination of the maximum absorption wavelength of autotoxic substances: Ferulic acid, p-hydroxybenzoic acid, cinnamic acid, and gallic acid (accurate to 0.001 g each) were weighed separately, dissolved in an appropriate amount of distilled water, and diluted to 100 mL with water. The solutions were then scanned across the entire wavelength range using a UV spectrophotometer to determine their characteristic absorption wavelengths. The maximum absorption wavelengths were found to be 310 nm for ferulic acid, 248 nm for p-hydroxybenzoic acid, 270 nm for cinnamic acid, and 273 nm for gallic acid.

[0095] Take the preserved QS2-7 strain slant and inoculate the QS2-7 spore suspension into TSBY liquid medium at an inoculation amount of 10%. Incubate at 30℃ for 20 hours in a constant temperature shaker at 180 rpm until the logarithmic growth phase. Centrifuge the bacterial suspension at 8000 rpm for 10 minutes, discard the supernatant, and resuspend the bacterial cells in sterile water for later use.

[0096] A culture medium containing four autotoxic substances (ferulic acid, p-hydroxybenzoic acid, cinnamic acid, and gallic acid) at a concentration of 1 mg / mL was prepared using an inorganic salt basal culture medium. The medium was then sterilized in 100 mL Erlenmeyer flasks for 25 min. The bacterial suspension was inoculated into the corresponding culture medium and cultured at 30°C with shaking at 180 rpm for 7 days, with samples taken every 24 hours. After centrifugation at 10000 rpm for 10 min, the supernatant was collected, and the bacterial cells were filtered through a 0.22 μm filter. Finally, the OD value was measured using a microplate reader at the appropriate wavelength. The inorganic salt basal culture medium formulation was: ammonium chloride 0.5 g / L, magnesium sulfate heptahydrate 0.4 g / L, sodium chloride 1.0 g / L, dipotassium hydrogen phosphate 1.3 g / L, pH 7.2.

[0097] Calculate the degradation rate using the following formula:

[0098] Degradation rate = (Absorbance of uninoculated culture medium - Absorbance of inoculated culture medium) / Absorbance of uninoculated culture medium × 100%.

[0099] Table 2 shows that *Streptomyces glaucus* QS2-7 exhibits some degradation ability for three of the autotoxic substances, but cannot degrade cinnamic acid. QS2-7 shows the best degradation ability for p-hydroxybenzoic acid, reaching a degradation rate of 78.5% after 7 days of cultivation. The degradation rates for ferulic acid and gallic acid are 50.77% and 53.94%, respectively. Therefore, QS2-7 demonstrates a good degradation ability for some cucumber autotoxic substances.

[0100] Table 2. Inhibition rate (%) of Streptomyces glaucus QS2-7 on four cucumber autotoxins.

[0101]

[0102] Example 4: Pot Experiment with *Streptomyces glaucus* QS2-7

[0103] 1. Disease prevention and growth promotion effects

[0104] Activated QS2-7 bacteria were inoculated into TSBY liquid fermentation medium, and approximately 10 glass beads were added. The culture was incubated at 30℃ and 180 rpm for 5 days to obtain a bacterial suspension with a concentration of 10. 8 CFU / mL. The mycelia of the cucumber wilt pathogen, cultured for 5 days, were washed with deionized water, filtered through 6 layers of gauze, centrifuged at 10000 rpm for 5 min, the supernatant was discarded, and the spores were collected. A spore suspension was prepared with deionized water and adjusted to 10 CFU / mL. 6 Prepare a spore suspension of Q2-7 at a concentration of 1 spore per mL. Using cucumber seeds (Jinyan No. 4), at the one-true-leaf stage, make 5 holes 2 cm away from the seedling, and inoculate each hole with 2 mL of Q2-7 bacterial suspension. After 7 days, inoculate with 10 mL of pathogen spore suspension. The negative control is 10 mL of sterile water instead of QS2-7 bacterial suspension. Each treatment consists of 8 pots, replicated 3 times. After inoculation, manage the plants normally. Four weeks later, investigate the disease incidence on the cucumber plants and measure plant height and stem diameter.

[0105] The results are shown in Table 3. The results showed that, compared with the control, the treatment with QS2-7 bacterial suspension could effectively increase the plant height and stem diameter of cucumber seedlings, with a plant height increase of 25.4% and a stem diameter increase of 11.2%, and significantly reduce the incidence of cucumber wilt disease.

[0106] Table 3. Control efficacy of Streptomyces simonii QS2-7 against cucumber wilt in potted plants.

[0107]

[0108] Note: Different letters in Table 3 indicate significant differences (P < 0.05), as in the table below.

[0109] 2. To mitigate the toxic effects of autotoxic substances on potted cucumbers.

[0110] The activated QS2-7 strain was inoculated into TSBY liquid fermentation medium, and about 10 glass beads were added. The culture was carried out at 30℃ and 180 rpm for 5 days to obtain a bacterial suspension with a concentration of 10. 8 CFU / mL. Cucumber seeds were disinfected and then placed in a room temperature incubator to promote germination. Seedlings with two true leaves were then sown in seedling pots. Seedlings of uniform size were transplanted into 10cm plastic pots, each containing 50g of substrate. Three autotoxic substances were dissolved and then evenly mixed into the substrate at a concentration of 10mg / g. Eight treatments were set up: four with bacterial solution and four without. A sterile water treatment served as the control group. Each treatment was replicated in eight pots. After 30 days of cultivation, various indicators (plant height, stem diameter, number of true leaves) were measured.

[0111] Table 4 shows that after 30 days of treatment with the three autotoxic substances, the growth of cucumbers was significantly lower than that of the control group (CK) and the QS2-7 bacterial solution treatment group. The QS2-7 strain treatment group showed better stem diameter and plant height than the control group, with plant height increasing by 22.8% and stem diameter by 11.8%. The growth, stem diameter, and plant height of the groups treated with both the QS2-7 strain and the three autotoxic substances were also significantly higher than those treated with the autotoxic substances. In the p-hydroxybenzoic acid treatment group, the addition of QS2-7 bacterial solution resulted in a 15.3% increase in plant height and an 11.4% increase in stem diameter. These results indicate that the QS2-7 strain can significantly improve the growth and development of cucumbers, significantly increasing stem diameter, plant height, and the number of true leaves, and can effectively alleviate the toxic effects of autotoxic substances on cucumbers.

[0112] Table 4. Effects of Streptomyces globosum QS2-7 and its autotoxins on cucumber plant height, stem diameter, and number of true leaves.

[0113]

[0114]

[0115] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A rhizosphere growth-promoting bacterium was found to be infected with Streptomyces glaucus. Streptomyces caniferus QS2-7, characterized in that, The aforementioned *Streptomyces glaucus* QS2-7 is deposited at the China General Microbiological Culture Collection Center (CGMCC), with accession number CGMCC No. 32328.

2. The application of the *Streptomyces glaucus* QS2-7 as described in claim 1 in the preparation of microbial inoculants.

3. A microbial inoculant, characterized in that, The microbial agent contains *Streptomyces glaucus* QS2-7 as described in claim 1.

4. The application of the *Streptomyces glaucus* QS2-7 as described in claim 1 or the microbial agent as described in claim 3 in promoting cucumber growth.

5. The application of *Streptomyces glaucus* QS2-7 as described in claim 1 or the microbial agent as described in claim 3 in inhibiting the growth of plant pathogens, characterized in that... The plant pathogens mentioned are the pathogens of cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizopus fruit rot, melon vine blight, tomato late blight, and / or pepper damping-off.

6. The *Streptomyces glaucus* QS2-7 as described in claim 1 or the microbial agent as described in claim 3, used in the preparation of products for the prevention and control of plant diseases. The application of this is characterized by, The plant diseases mentioned are cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizomatous fruit rot, melon vine blight, tomato late blight, and / or pepper damping-off.

7. A product for preventing and controlling plant diseases, characterized in that, The product contains either the *Streptomyces grayi* QS2-7 as described in claim 1 or the microbial agent as described in claim 3.

8. The product according to claim 7, characterized in that, The plant diseases mentioned are cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizomatous fruit rot, melon vine blight, tomato late blight, and / or pepper damping-off.

9. A method for preventing and controlling plant diseases, characterized in that, The steps include applying the *Streptomyces glaucus* QS2-7 of claim 1, the microbial agent of claim 3, or the product of claim 7 to plants; The plant diseases mentioned are cucumber wilt, eggplant root rot, tomato early blight, tomato gray mold, pepper blight, pepper rhizomatous fruit rot, melon vine blight, tomato late blight, and / or pepper damping-off.

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