Amorpha fruticosa rhizosphere probiotic sdqb6 and application thereof

Abstract

The application relates to the field of microbial technology, and particularly discloses a root zone probiotic SDQB6 of ammodendron and application thereof; the root zone probiotic SDQB6 of ammodendron is Alcaligenes faecalis SDQB6, which was preserved in the China General Microbiological Culture Collection Center on May 19, 2025, is located at No. 1, Xibei Road, No. 3, Chaoyang District, Beijing, is preserved in the Institute of Microbiology, Chinese Academy of Sciences, and has a preservation number of CGMCC No. 34588 and a classification name of Alcaligenes faecalis; the inhibition rate of the strain SDQB6 of the application to 10 kinds of pathogenic bacteria such as Valsa mali reaches 30.17-91.04%, the D / d values of the phosphorus solubilizing ability and the iron complexing ability are 1.28 and 2.37 respectively, the strain can grow on a culture medium containing 15% NaCl or 10% PEG, and has significant growth promotion effects on peppers and melons.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microorganisms, more particularly, it relates to a root zone probiotic SDQB6 of Ammopiptanthus mongolicus and application thereof. BACKGROUND

[0002] Soil salinization is a major threat to global agricultural sustainable development and ecological security, and its essence is the functional degradation caused by excessive accumulation of soil salt. This process is driven by both natural factors (such as salt accumulation in arid regions) and human activities (such as unreasonable irrigation). The high osmotic pressure of salinized soil can disrupt plant water balance, hinder nutrient absorption, trigger a chain reaction of vegetation degradation, reduced biodiversity, and ultimately lead to decreased productivity of arable land, weakened ecological function of grassland, and reduced survival rate of trees.

[0003] Plant growth-promoting rhizobacteria (PGPR) are of great concern due to their growth-promoting and stress-resistant functions. Their mechanisms of action include the secretion of growth regulators (such as IAA and ACC deaminase), the activation of soil nutrients, and the inhibition of pathogenic microorganisms. However, most of the PGPR strains reported so far have limited growth-promoting effects under combined salt and drought stress, and have problems such as insufficient salt tolerance and unstable drought resistance, which leads to poor field application results. In addition, most of the existing strains are derived from the rhizosphere of ordinary crops and have poor adaptability to extreme environments, making it difficult for them to colonize and function efficiently in saline-alkali soils. Therefore, screening PGPR strains with high growth-promoting activity and multiple stress resistance from the rhizosphere of stress-tolerant plants has become an important direction to break through the technical bottleneck of biological improvement of saline-alkali soils.

[0004] Ammopiptanthus mongolicus, as a key constructive species in the northwest desert of China, has strong salt tolerance and drought resistance. Its rhizosphere microbial community has long-term co-evolution, which may contain unique growth-promoting and stress-resistant functional strains. However, the exploration of Ammopiptanthus mongolicus rhizosphere microbial resources is still insufficient. Based on the above statements, the present application provides a root zone probiotic SDQB6 of Ammopiptanthus mongolicus and application thereof. SUMMARY

[0005] In order to solve the problems of weak growth-promoting effect, weak salt tolerance, and weak drought resistance of existing root zone probiotics in actual application, the present application provides a root zone probiotic SDQB6 of Ammopiptanthus mongolicus and application thereof.

[0006] In a first aspect, the present application provides a root zone probiotic SDQB6 of Ammopiptanthus mongolicus, which adopts the following technical solution:

[0007] The sand persimmon rhizosphere probiotic SDQB6 is Alcaligenes faecalis, which was preserved in the China General Microbiological Culture Collection Center on May 19, 2025, at the address of No. 1, Beichen West Road, Haidian District, Beijing, China, and the preservation number is CGMCC No. 34588, and the classification name is Alcaligenes faecalis.

[0008] In a second aspect, the present application provides a microbial biocontrol agent, which adopts the following technical solution:

[0009] The microbial biocontrol agent contains the sand persimmon rhizosphere probiotic SDQB6.

[0010] Preferably, the sand persimmon rhizosphere probiotic SDQB6 exists in the form of cultured live bacteria, fermentation broth or bacterial suspension in the microbial biocontrol agent.

[0011] Preferably, the dosage form of the microbial biocontrol agent is wettable powder, water dispersible agent, water suspending agent or dispersible oil suspending agent.

[0012] In a third aspect, the present application provides an application of the sand persimmon rhizosphere probiotic SDQB6 or a microbial biocontrol agent, which adopts the following technical solution:

[0013] The sand persimmon rhizosphere probiotic SDQB6 in the first aspect or the microbial biocontrol agent in the second aspect is applied to inhibit plant pathogenic bacteria, promote plant growth and enhance stress resistance.

[0014] Preferably, the plant pathogenic bacteria include Cytospora chrysosperma QH2, Fusarium sambucinum GQGF3, Botryosphaeria berengeriana LLW, Botrytis cinerea LHM, Monilinia fructigena LHF, Acrostalagmus luteoalbus CMGF-A, Dactylonectria macrodidyma CMGF-D, Rhizoctonia solani MLS, Cytospora chrysosperma YSFL4-2, Colletotrichu scovillei LJ1 and the like.

[0015] Preferably, the application mode comprises seed soaking, root irrigation after seedling planting, or plant spraying of the microbial biocontrol agent on the plants to be treated.

[0016] Preferably, the plants are apples, medlar, pears, strawberries, potatoes, poplars, peppers, etc.

[0017] In summary, the present application has the following beneficial effects:

[0018] (1) Multifunctional and significant growth promotion effect: Strain SDQB6 has the abilities of phosphorus solubilization (D / d value 1.28) and iron chelation (D / d value 2.37), which can effectively activate soil nutrients. Experiments show that after application, the plant height, stem diameter, leaf number, fresh weight, and dry weight can be improved, which is significantly better than conventional growth-promoting strains.

[0019] (2) Outstanding stress resistance: Strain SDQB6 can tolerate 15% NaCl salt stress and 10% PEG simulated drought conditions, and still maintains the activity of promoting growth under saline / drought stress, providing a new solution to the planting problems in the arid and saline areas of Northwest China.

[0020] (3) Broad-spectrum disease resistance: It shows inhibitory effect on 10 common plant pathogenic bacteria, especially the inhibition rate of Valsa mali reaches 91.04%, and the inhibition rates of medlar root rot fungus and pear brown rot fungus are 77.74% and 81.01% respectively, which can reduce the use of chemical pesticides and has ecological and economic benefits.

[0021] (4) Flexible application form: It can be made into liquid fermentation agent, solid bacterial agent, or wettable powder (viable bacterial count ≥1×10 8 CFU / g), which is suitable for seed treatment, soil application, or foliar spraying, and can meet the needs of different crops and planting scenarios.

[0022] (5) Environment-friendly solution: By using microorganisms to replace part of chemical fertilizers and pesticides, the risk of soil degradation can be reduced, which is especially suitable for use in ecologically fragile areas and meets the requirements of sustainable agricultural development. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Fig. 1 is the in-vitro culture characteristics and scanning electron microscope morphology of strain SDQB6 in Example 1 of the present application, wherein A is the front colony characteristics of strain SDQB6 on LBA medium, and B is the scanning electron microscope observation result of the bacterial morphology of strain SDQB6;

[0024] Figure 2 Fig. 2 is the 16S rRNA sequence and whole genome sequence phylogenetic tree of strain SDQB6 in Example 1 of the present application, wherein A is the phylogenetic tree constructed based on the 16S rRNA gene sequence, and B is the phylogenetic tree constructed based on the whole genome sequence.

[0025] Figure 3 Figure 1 is a functional characterization chart of strain SDQB6 in Example 2 of the present application, wherein A is the growth of strain SDQB6 on Ashby nitrogen-fixing medium, B is the growth of strain SDQB6 on Mengina phosphorus-dissolving medium, C is the growth of strain SDQB6 on CAS medium, D is the blank control of strain SDQB6 under 0% PEG condition, E is the growth of strain SDQB6 under 5% PEG condition, F is the growth of strain SDQB6 under 10% PEG condition, G is the growth of strain SDQB6 under 10% NaCl condition, H is the growth of strain SDQB6 under 12% NaCl condition, and I is the growth of strain SDQB6 under 15% NaCl condition;

[0026] Figure 4 Figure 2 is a comparison chart of the growth-promoting and salt-tolerant effects of strain SDQB6 on melons and peppers in Example 3 of the present application, wherein A is a comparison chart of melon plant growth, B is a comparison chart of pepper plant growth, and C is a comparison chart of whole pepper plant growth, and from left to right in the chart are: CK; SDQB6 treatment group; CK+salt stress group; SDQB6+salt stress group;

[0027] Figure 5 Figure 3 is an effect chart of the improvement of the drought resistance of melons by strain SDQB6 in Example 3 of the present application, and from left to right are: growth state of the melon in the mild drought control group, growth state of the melon in the mild drought treatment group, growth state of the melon in the moderate drought control group, growth state of the melon in the moderate drought treatment group, growth state of the melon in the severe drought control group, and growth state of the melon in the severe drought treatment group;

[0028] Figure 6 Figure 4 is an inhibition effect chart of strain SDQB6 on 10 kinds of plant pathogenic fungi in Example 4 of the present application. DETAILED DESCRIPTION

[0029] The present application will be further described in detail below in combination with the drawings and specific examples in the specification, and the examples are only used to explain the present application and are not used to limit the scope of the present application. The test methods used in the following examples are conventional methods unless otherwise specified, and the materials, reagents, etc. used are commercially available reagents and materials unless otherwise specified.

[0030] The test materials involved in the examples of the present application are as follows:

[0031] 1. Test pathogenic fungi:

[0032] Cytospora mali QH2, Fusarium solani, Colletotrichu scovillei LJ1, Acrostalagmus luteoalbus CMGF-A, Dactylonectria macrodidyma CMGF-D, Cytospora chrysosperma YSFL4-2 were isolated and identified by the laboratory (Ma et al., 2020; Sun et al., 2023; Zhang, 2024; Jia et al., 2022);

[0033] Botrytis cinerea LHM, Botryosphaeria berengeriana LLW, Monilinia fructigena LHF were isolated and identified by the Institute of Pomology, Chinese Academy of Agricultural Sciences (Sun et al., 2017; Sun et al., 2018);

[0034] Rhizoctonia solani MLS was provided by Henan Agricultural University.

[0035] 2. Test medium:

[0036] (1) Potato dextrose agar (PDA medium): potato extract 200 g, glucose 20 g, agar powder 20 g, add deionized water to 1 L, pH 7.2.

[0037] (2) LBA medium: tryptone 10 g, yeast extract 5 g, NaCl 10 g, agar powder 20 g, add deionized water to 1 L.

[0038] (3) LB medium: same as LBA medium, without agar powder.

[0039] (4) Monna's phosphate-free medium: glucose 10 g, (NH4)2SO4 0.5 g, NaCl 0.3 g, KCl 0.3 g, MgSO4·7H2O 0.3 g, FeSO4·7H2O 0.03 g, MnSO4·7H2O 0.03 g, Ca3(PO4)2 2.5 g, yeast paste 0.4 g, add deionized water to 1 L, pH 7.0.

[0040] (5) CAS solid medium: chrome azurol S 60.5 mg, cetyltrimethylammonium bromide 72.9 mg, FeCl3·6H2O 2.645mg, NaH2PO4·2H2O 295.25mg, Na2HPO4·12H2O 1213.5mg, NH4Cl 125mg, KH2PO437.5mg, NaCl 62.5mg, agar 9g, add deionized water to 1L, heat to boil to completely dissolve, pH 6.8.

[0041] (6) Ashby nitrogen fixation medium: KH2PO4 0.2g, NaCl 0.2g, MgSO4·7H2O 0.2g, K2SO4·2H2O 0.2g, CaCO3 5g, glucose 5g, mannitol 5g, add deionized water to 1L, pH 7.0.

[0042] 3. Test instrument:

[0043] Constant temperature incubator (HPX-9162MBE, Shanghai Bo Xun Industry Co., Ltd.);

[0044] Clean bench (SW-CJ-1FD);

[0045] Microscope (LEICA ICC50W, Germany Leica Instrument Co., Ltd.);

[0046] Electrophoresis instrument (BG-Power 600K450W, Beijing Baijing Biotechnology Co., Ltd.);

[0047] PCR instrument (624BR47696, USA Bio-Rad Company).

[0048] Example 1

[0049] Isolation and screening and identification of Alcaligenes faecalis SDQB6

[0050] 1. Isolation and screening of strains

[0051] Collect the rhizosphere soil samples of A. mongolica Maxim in Inner Mongolia region. In the collection process, remove the surface soil of 5cm, collect the rhizosphere soil of 25cm, wrap with cowhide paper, and store at 4℃.

[0052] Dilution and coating plate method is used to separate various bacteria in the soil. The specific separation and screening method is as follows: 10g of dry soil sample is ground and placed in 100mL of sterile water, 4℃, 180rpm shaking for 30min, the soil sample is gradient diluted with sterile water to 10 -6, 100 μL of the dilution was taken and evenly spread on LBA medium, and incubated at 28°C for 48 h. Single bacterial colonies with different morphologies and colors were picked and streaked for purification. After purification, strain SDQB6 was obtained. The purified colonies were transferred into LB medium and incubated at 28°C and 180 rpm for 24 h. An equal volume of 50% glycerol was mixed with the culture (final concentration 25%), and the mixture was stored in a preservation tube at -80°C for later use.

[0053] 2. Morphological characteristics of the strain

[0054] Strain SDQB6 was spread on LBA medium and incubated at 28°C for 48 h. The morphological characteristics of the colonies in the dish were observed, and the bacterial morphology was observed under a scanning electron microscope. As shown in Figure 1 , strain SDQB6 showed uniform coloration on LBA medium, and the colonies were yellow. The bacterial morphology was observed under a scanning electron microscope, and the results are shown in Figure 1 A is the front view of the colony characteristics of strain SDQB6 on LBA medium, Figure 1 B is the result of scanning electron microscopy observation of the bacterial morphology of strain SDQB6.

[0055] 3. Molecular biology identification

[0056] Genomic DNA of strain SDQB6 was extracted, and Pacbio Sequel II was used for whole genome sequencing. The read obtained by sequencing was assembled using SMARTLink 10.1.0 software. The evolutionary distance between different strain genomes was calculated using the genome alignment distance evolution method in the Type Strain Genome Server online program (https: / / tygs.dsmz.de). The approximate species were screened using the minimum evolutionary distance between the genomes obtained. The 16S rRNA and whole genome sequence phylogenetic trees of the strains screened in this test and the 13 strains were constructed using FASTME 2.1.6.1 software. The numbers in each branch represent the confidence rate of 1000 self-exhibitions (bootstrap test). The results are shown in Figure 2 . The 16S rRNA and whole genome sequences of strain SDQB6 and the strains of the genus Alcaligenes were clustered into one large branch. Among them, they were clustered into a branch with Alcaligenes faecalis NBRC13111 and were identified as the same species. The method of combining morphological observation, physiological and biochemical characteristics, and gene sequence determination was used to determine that strain SDQB6 was Alcaligenes faecalis.

[0057] The obtained Amorpha fruticosa rhizosphere probiotic SDQB6 is preserved in the China General Microbiological Culture Collection Center, located at No. 1, Huayuancun, Beijing Economic-Technological Development Area, Beijing, on May 19, 2025, and has a preservation number of CGMCC No. 34588, and is classified and named as Alcaligenes faecalis.

[0058] Example 2

[0059] Verification of the growth promotion and stress resistance functions of the strain SDQB6

[0060] 1. Phosphorus solubilization ability determination

[0061] Experimental method: The strain SDQB6 was inoculated on LBA medium, and incubated in a 28°C constant temperature incubator for 48 hours. The SDQB6 colonies were picked up with a sterile cotton swab and spotted on the Mengjina phosphorus solubilization medium, with three replicates. After incubation in a 28°C constant temperature incubator for 48 hours, the colony diameter (d) and the surrounding transparent circle diameter (D) were measured, and the D / d ratio was calculated.

[0062] Experimental results: The SDQB6 formed a clear transparent circle (such as Figure 3 B); the measured colony diameter d = 5.12 ± 0.23 mm, the transparent circle diameter D = 6.55 ± 0.31 mm, and the D / d ratio was 1.28 ± 0.05, indicating that the strain SDQB6 had significant phosphorus solubilization ability.

[0063] 2. Iron chelation ability determination

[0064] Experimental method: The strain SDQB6 was inoculated on LBA medium, and incubated in a 28°C constant temperature incubator for 48 hours. The SDQB6 colonies were picked up with a sterile cotton swab and spotted on the CAS solid medium, with three replicates. After incubation in a 28°C constant temperature incubator for 48 hours, the formation of orange halos was observed, and the colony diameter (d) and the surrounding transparent circle diameter (D) were measured, and the D / d ratio was calculated.

[0065] Experimental results: The SDQB6 colonies appeared obvious orange halos (such as Figure 3 C); the colony diameter d = 4.87 ± 0.15 mm, the halo diameter D = 11.53 ± 0.42 mm, and the D / d ratio was 2.37 ± 0.08, indicating that the strain SDQB6 had significant iron chelation ability.

[0066] 3. Drought resistance determination

[0067] Experimental method: the strain SDQB6 was inoculated in LB medium, 28℃, 180rpm shaking culture for 24h, SDQB6 bacterial liquid was obtained; LBA medium containing different concentrations of PEG-6000 (0%, 5%, 10%) was prepared, and the LBA medium containing 0% PEG-6000 was used as blank control (CK, such as Figure 3 D); 5μL SDQB6 bacterial liquid (OD 600 =1.0) was spotted on LBA medium, and three replicates were set; after 48h incubation in 28℃ constant temperature incubator, the survival state of the colonies was observed.

[0068] Experimental results: SDQB6 can still grow under the condition of 10% PEG (such as Figure 3 F), which indicates that SDQB6 has strong drought resistance.

[0069] 4. Salt tolerance determination

[0070] Experimental method: the strain SDQB6 was inoculated in LB medium, 28℃, 180rpm shaking culture for 24h, SDQB6 bacterial liquid was obtained; LBA medium containing different concentrations of NaCl (10%, 12%, 15%) was prepared, 5μL SDQB6 bacterial suspension (OD 600 =1.0) was spotted on LBA medium, and three replicates were set; after 48h incubation in 28℃ constant temperature incubator, the survival state of the colonies was observed.

[0071] Experimental results: SDQB6 can still grow under the condition of 15% NaCl (such as Figure 3 I), which indicates that SDQB6 has strong salt tolerance.

[0072] 5. Nitrogen fixation ability determination

[0073] Experimental method: the strain SDQB6 was inoculated in LBA medium, 28℃ constant temperature incubator for 48h, SDQB6 colonies were picked up with sterile cotton swab and spotted on Ashby nitrogen fixation medium, and three replicates were set; after 48h incubation in 28℃ constant temperature incubator, the colony diameter (d) and the transparent circle diameter (D) around the colony were measured, and the D / d ratio was calculated.

[0074] Experimental results: SDQB6 did not form obvious transparent circle on Ashby nitrogen fixation medium (such as Figure 3 A), which indicates that the nitrogen fixation ability of the strain SDQB6 is weak or has no nitrogen fixation ability.

[0075] Example 3

[0076] Promoting growth and stress resistance effect of SDQB6 on plants

[0077] 1. Promoting growth and salt tolerance experiments of melon and pepper

[0078] The strain SDQB6 was inoculated in LB medium and cultured at 28°C with 180 rpm shaking for 24 h. The bacterial solution was adjusted to OD 600 = 1.0 (about 10 8 CFU / mL) with sterile water for standby.

[0079] The melon (Jinmi No. 6) and pepper (Xiangla No. 5) seeds were selected and sowed in the seedling pots mixed with fine sand and vermiculite at a ratio of 1:2. The following treatment groups were set up:

[0080] ① SDQB6 treatment group (inoculation + normal growth conditions): After the seeds of melon / pepper were sowed, the treatment was started when the seeds germinated and broke the soil. 50 mL of SDQB6 bacterial solution was added to each pot. 50 mL of SDQB6 bacterial solution was added to each pot again 14 days after the first addition of bacterial solution. The water content of the sand-vermiculite mixed substrate was maintained at 65% every day.

[0081] Objective: To test the promoting growth effect of strain SDQB6 on plants.

[0082] ② SDQB6 + salt stress group (inoculation + salt stress): After the seeds of melon / pepper were sowed, the treatment was started when the seeds germinated and broke the soil. 50 mL of SDQB6 bacterial solution was added to each pot. 50 mL of SDQB6 bacterial solution was added to each pot again 14 days after the first addition of bacterial solution. 50 mL of 1% NaCl solution was added 2 days after the first addition of bacterial solution. The water content of the sand-vermiculite mixed substrate was maintained at 65% every day.

[0083] Objective: To test the promoting growth and salt tolerance of strain SDQB6 under salt stress.

[0084] ③ Blank control group (CK, no inoculation + normal conditions): After the seeds of melon / pepper were sowed, the treatment was started when the seeds germinated and broke the soil. 50 mL of LB medium was added to each pot. 50 mL of LB medium was added to each pot again 14 days after the first addition of LB medium. The water content of the sand-vermiculite mixed substrate was maintained at 65% every day.

[0085] Objective: To serve as a blank control to compare the promoting growth effect of strain SDQB6.

[0086] ④ Blank control + salt stress group (no inoculation + salt stress): After the seeds of melon / pepper were sowed, the treatment was started when the seeds germinated and broke the soil. 50 mL of LB medium was added to each pot. 50 mL of LB medium was added to each pot again 14 days after the first addition of LB medium. 50 mL of 1% NaCl solution was added 2 days after the first addition of LB medium. The water content of the sand-vermiculite mixed substrate was maintained at 65% every day.

[0087] Objective: To serve as a stress control to compare the protection effect of strain SDQB6 under salt stress.

[0088] After 30 days of treatment, plants from each group were harvested, and various growth indicators of the plants were measured and recorded, including the following indicators:

[0089] ① Plant height (cm): Measured from the base of the stem to the top;

[0090] ② Stem diameter (mm): Measure the diameter at the cotyledon node using vernier calipers;

[0091] ③Fresh weight (g): After washing the roots, let them air dry naturally and weigh the whole plant;

[0092] ④ Dry weight (g): Blanch at 105℃ for 10 minutes, dry at 60℃ to constant weight, and weigh the whole plant.

[0093] The recorded data were analyzed using SPSS 26.0 using one-way ANOVA, and the significance of differences was determined using Duncan's multiple comparisons (*p<0.05). The results are shown in Table 1 below. Figure 4 .

[0094] Table 1. Effects of different treatments on growth promotion and salt tolerance of melon / pepper

[0095]

[0096] Note: Different letters in the same column indicate significant differences between the control group and the treatment group at the P<0.05 level; the quality of the melons was not measured, but the growth chart clearly showed that SDQB6 had a significant growth-promoting effect.

[0097] Combining Table 1 and Figure 4 The results show that strain SDQB6 can significantly improve plant growth and salt tolerance. Figure 4 A is a comparison chart of melon plant growth; Figure 4 B is a comparison chart of chili plant growth; Figure 4 C is a comparison of the growth of the entire chili plant; from left to right in the figure are: CK; SDQB6 treatment group; CK + salt stress group; SDQB6 + salt stress group.

[0098] Under no stress conditions, the plant height, stem diameter, and number of leaves of melons treated with strain SDQB6 were significantly higher than those of the control, increasing by 193.91%, 47.18%, and 88.23%, respectively, compared to the control. Under stress conditions containing 1% NaCl, the plant height, stem diameter, and number of leaves of melons treated with strain SDQB6 were also significantly higher than those of the control, increasing by 134.15%, 33.99%, and 89.47%, respectively, compared to the control.

[0099] Under non-stress conditions, the plant height, stem diameter, leaf number, fresh weight and dry weight of pepper treated with strain SDQB6 were significantly higher than those of the control, which were increased by 49.19%, 32.14%, 61.11%, 122.69% and 256.25% respectively compared with the control. Under 1% NaCl stress conditions, the plant height, fresh weight and dry weight of pepper treated with strain SDQB6 were also significantly higher than those of the control, which were increased by 34.77%, 36.18%, 40.91%, 46.15% and 81.82% respectively compared with the control.

[0100] According to the above data, it can be seen that strain SDQB6 not only can promote plant growth under normal conditions, but also can maintain high growth indicators of plants under salt stress environment, indicating that it has dual functions of growth promotion and stress resistance.

[0101] 2. Drought resistance experiment of melon

[0102] To evaluate the role of strain SDQB6 in improving the drought resistance of melon, different gradient drought stress treatments were set up for the treatment experiment, which were specifically grouped as follows:

[0103] T0 (mild drought control group): water every day, keep the soil water content at 65% of the maximum field water holding capacity, 2 weeks after seed germination, add 50 mL LB medium to each pot, and then add another 50 mL LB medium after another 2 weeks;

[0104] T1 (moderate drought control group): water every 3 days, keep the soil water content at 45% of the maximum field water holding capacity, 2 weeks after seed germination, add 50 mL LB medium to each pot, and then add another 50 mL LB medium after another 2 weeks;

[0105] T2 (severe drought control group): water every 5 days, keep the soil water content at 25% of the maximum field water holding capacity, 2 weeks after seed germination, add 50 mL LB medium to each pot, and then add another 50 mL LB medium after another 2 weeks;

[0106] T3 (mild drought treatment group): water every day, keep the soil water content at 65% of the maximum field water holding capacity, 2 weeks after seed germination, add 50 mL SDQB6 bacterial solution (1×10 8 CFU / mL) to each pot, and then add another 50 mL SDQB6 bacterial solution (1×10 8 CFU / mL) after another 2 weeks;

[0107] T4 (moderate drought treatment group): water every 3 days, keep the soil water content at 45% of the maximum field water holding capacity, 2 weeks after seed germination, add 50 mL SDQB6 bacterial solution (1×10 8CFU / mL) and 50 mL of SDQB6 bacterial liquid (1 x 10 8 CFU / mL) was added to each pot after 2 weeks.

[0108] T5 (severe drought treatment group): water every 5 days to keep the soil water content at 25% of the field maximum water holding capacity, 50 mL of SDQB6 bacterial liquid (1 x 10 8 CFU / mL) was added to each pot after 2 weeks. 8 CFU / mL) was added to each pot after 2 weeks.

[0109] The recorded data was analyzed by one-way ANOVA (ANOVA) using SPSS 26.0, and the significant difference was analyzed by Duncan's multiple comparison (*p < 0.05). The results are shown in Table 2 and Figure 5 Figure 5 The growth status of melons from left to right is as follows: mild drought control group, mild drought treatment group, moderate drought control group, moderate drought treatment group, severe drought control group, and severe drought treatment group.

[0110] Table 2 Effect of strain SDQB6 on the drought resistance of melons

[0111]

[0112] Note: Different letters in the same column indicate significant differences between the control group and the treatment group at the P < 0.05 level

[0113] According to the data in the above table, strain SDQB6 can significantly enhance the drought resistance of melons and show stable growth-promoting effects under mild, moderate, and severe drought conditions. Among them, the plant height, stem diameter, leaf number, fresh weight, and dry weight of the SDQB6 treatment group are better than those of the control group, especially under severe drought conditions, with a 77.09% increase in plant height and a 105.98% increase in fresh weight, showing a significant "stress-enhancing effect". The strain has the most stable promoting effect on the development of melon leaves (increasing by 26-28%), and can maintain the growth of dry matter accumulation, indicating that it may enhance plant drought resistance by regulating water use efficiency and protecting photosynthetic organs. These results fully prove that strain SDQB6 can effectively enhance the drought tolerance of melons and significantly alleviate the inhibitory effect of drought stress on plant growth.

[0114] Example 4

[0115] Antibacterial spectrum determination of Alcaligenes faecalis SDQB6

[0116] ​The antagonistic effect of SDQB6 on 10 important tree and crop plant pathogenic fungi, including Cytospora chrysosperma QH2, Fusarium sambucinum GQGF3, Botryosphaeria berengeriana LLW, Botrytis cinerea LHM, Monilinia fructigena LHF, Acrostalagmus luteoalbus CMGF-A, Dactylonectria macrodidyma CMGF-D, Rhizoctonia solani MLS, Cytospora chrysosperma YSFL4-2, and Colletotrichu scovillei LJ1, was determined by in-dish antagonism method.

[0117] The specific test process is as follows: the SDQB6 bacterial body is picked up with a sterile cotton swab, and is inoculated on both sides of a PDA plate, and 10 kinds of pathogenic fungi cakes (6 mm in diameter) are inoculated in the center of the plate respectively; only the pathogenic fungi are inoculated in the center of the plate as a control, and each treatment is repeated three times, and the culture is placed in a 28℃ constant temperature incubator. When the control colony grows on the plate, the lesion diameter is observed and recorded, and the inhibition rate is calculated.

[0118] Inhibition rate (%) = (1-antagonistic treatment lesion diameter / control lesion diameter) x 100.

[0119] The specific results are shown in Table 3 and Figure 6

[0120] Table 3 Detection results of the effect of strain SDQB6 on 10 kinds of pathogenic fungi

[0121]

[0122] The results show that strain SDQB6 has significant inhibition effect on the above-mentioned 10 kinds of pathogenic fungi Figure 6 ), the inhibition zone is between 1.9-12.15 mm, and the inhibition rate is between 30.17-91.04%, among which the inhibition effect on Cytospora chrysosperma reaches 91.04%, indicating that strain SDQB6 has a wide inhibition spectrum and good inhibition effect.

[0123] ​The specific embodiments are only an explanation of the present application, which is not a limitation to the present application, and the person skilled in the art can make a modification to the present embodiments without creative contribution according to the need after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A rhizosphere probiotic SDQB6 of *Ilex chinensis*, characterized in that, The rhizosphere probiotic SDQB6 of *Ilex serrata* is *Alcaligenes faecalis* SDQB6, which was deposited on May 19, 2025, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, with accession number CGMCC No. 34588, and classified as *Alcaligenes faecalis* (…). Alcaligenes faecalis ).

2. A microbial biocontrol agent, characterized in that, The microbial biocontrol agent contains the rhizosphere probiotic SDQB6 of *Ilex pubescens* as described in claim 1.

3. The microbial biocontrol agent according to claim 2, characterized in that, In the aforementioned microbial biocontrol agent, the rhizosphere probiotic SDQB6 of *Ilex pubescens* exists in the form of cultured live bacteria, fermentation broth, or bacterial suspension.

4. The microbial biocontrol agent according to claim 2, characterized in that, The formulation of the microbial biocontrol agent is a wettable powder, a water dispersible agent, an aqueous suspension, or a dispersible oil suspension.

5. The application of the microbial biocontrol agent according to any one of claims 2-4 in inhibiting plant pathogens and promoting plant growth, wherein the plant pathogen is *Phyllostachys edulis* (the causal agent of apple rot). Cytospora chrysosperma ), Lycium barbarum root rot fungus ( Fusarium sambucinum ), pear ring rot fungus ( Botryosphaeria berengeriana ), pear gray mold ( Botrytis cinerea ), pear brown rot fungus ( Monilinia fructigena Strawberry root rot pathogen ( Acrostalagmus luteoalbus Strawberry root rot pathogen ( Dactylonectria macrodidyma ), potato black scurf ( Rhizoctonia solani Poplar rot pathogen ( Cytospora chrysosperma Anthracnose of pepper ( Colletotrichu scovillei ).

6. The application of the microbial biocontrol agent according to any one of claims 2-4 in enhancing plant stress resistance, wherein the stress resistance is salt tolerance or drought resistance, and the plant is melon or pepper.

7. The application of the microbial biocontrol agent according to claim 5 in inhibiting plant pathogens and promoting plant growth, characterized in that, The application methods include soaking the plants to be treated with the microbial biocontrol agent, irrigating the roots or spraying the plants after transplanting the seedlings.

8. The application of the microbial biocontrol agent according to claim 5 in inhibiting plant pathogens and promoting plant growth, characterized in that, The plants mentioned are apples, goji berries, pears, strawberries, potatoes, poplars, and chili peppers.

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