Ammopiptanthus mongolicus rhizosphere probiotic SDQB6 and application thereof

Abstract

The invention relates to the technical field of microorganisms, and particularly discloses ammopiptanthus mongolicus rhizosphere probiotics SDQB6 and application thereof. The ammopiptanthus mongolicus rhizosphere probiotic SDQB6 is alcaligenes faecalis SDQB6 and is preserved in the China General Microbiological Culture Collection Center on May 19, 2025, the address is Institute of Microbiology, Chinese Academy of Sciences, No.3, Beichen West Road, Chaoyang District, Beijing, the preservation number is CGMCC No.34588, and the classification name is alcaligenes faecalis; the inhibition rate of the strain SDQB6 to 10 pathogenic bacteria such as valsa mali reaches 30.17-91.04%, the D / d values of the phosphate solubilizing capacity and the iron complexing capacity of the strain SDQB6 are 1.28 and 2.37 respectively, the strain SDQB6 can still grow on a culture medium containing 15% of NaCl or 10% of PEG, and the strain SDQB6 has a remarkable growth promoting effect on hot peppers and muskmelons.

Description

Technical Field

[0001] This application relates to the field of microbial technology, and more specifically, to a rhizosphere probiotic SDQB6 of *Ilex pubescens* and its application. Background Technology

[0002] Soil salinization is a major threat to global agricultural sustainable development and ecological security. Its essence is functional degradation caused by excessive accumulation of soil salt. This process is driven by natural factors (such as salt accumulation on the surface in arid regions) and can be exacerbated by human activities (such as improper irrigation). The high osmotic pressure of salinized soils disrupts plant water balance, hinders nutrient absorption, and triggers a chain reaction of vegetation degradation and reduced biodiversity, ultimately leading to decreased arable land productivity, weakened grassland ecological functions, and reduced tree survival rates.

[0003] Plant rhizosphere growth-promoting bacteria (PGPRs) have attracted much attention due to their growth-promoting and stress-resistance functions. Their mechanisms of action include secreting growth regulators (such as IAA and ACC deaminases), activating soil nutrients, and inhibiting pathogenic microorganisms. However, most reported PGPR strains have limited growth-promoting effects under combined saline-alkali and drought stress, exhibiting insufficient salt tolerance and unstable drought resistance, leading to poor field application results. Furthermore, existing strains are mostly derived from the rhizosphere of common crops, exhibiting poor adaptability to extreme environments and difficulty in efficiently colonizing and functioning in saline-alkali soils. Therefore, screening PGPR strains from the rhizosphere of stress-tolerant plants that possess both high growth-promoting properties and multiple stress resistances has become an important direction for overcoming the bottlenecks in biological improvement technology for saline-alkali land.

[0004] As a key dominant species in the deserts of Northwest my country, *Ammopiptanthus mongolicus* possesses extremely strong salt and drought tolerance. Its rhizosphere microbial community has undergone long-term co-evolution, potentially harboring unique strains with growth-promoting and stress-resistance functions. However, the exploration of *Ammopiptanthus mongolicus* rhizosphere microbial resources remains insufficient. Based on the above, this application provides a rhizosphere probiotic, SDQB6, for *Ammopiptanthus mongolicus* and its applications. Summary of the Invention

[0005] To address the common problems of weak growth-promoting effects, poor salt tolerance, and weak drought resistance in the practical application of existing rhizosphere probiotics, this application provides a rhizosphere probiotic SDQB6 of *Ilex pubescens* and its application.

[0006] In the first aspect, this application provides a rhizosphere probiotic SDQB6 from *Ilex pubescens*, employing the following technical solution:

[0007] A rhizosphere probiotic SDQB6 of *Ilex serratus*, wherein the rhizosphere probiotic SDQB6 is *Alcaligenes faecalis* SDQB6, 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*.

[0008] Secondly, this application provides a microbial biocontrol agent, which adopts the following technical solution:

[0009] A microbial biocontrol agent, wherein the microbial biocontrol agent contains the above-mentioned rhizosphere probiotic SDQB6 of Ilex chinensis.

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

[0011] Preferably, the formulation of the microbial biocontrol agent is a wettable powder, a water dispersible agent, an aqueous suspension, or a dispersible oil suspension.

[0012] Thirdly, this application provides an application of the rhizosphere probiotic SDQB6 of *Ilex pubescens* or a microbial biocontrol agent, employing the following technical solution:

[0013] The application of the rhizosphere probiotic SDQB6 of *Ilex pubescens* described in the first aspect or the microbial biocontrol agent described in the second aspect in inhibiting plant pathogens, promoting plant growth, and enhancing stress resistance.

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

[0015] Preferably, the application method includes soaking the plants to be treated with the microbial biocontrol agent, or irrigating the roots or spraying the plants after transplanting the seedlings.

[0016] Preferably, the plant is an apple, goji berry, pear, strawberry, potato, poplar, chili pepper, etc.

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

[0018] (1) Significant multifunctional growth-promoting effect: Strain SDQB6 has both phosphorus solubilization (D / d value 1.28) and iron chelation (D / d value 2.37) capabilities, which can effectively activate soil nutrients. Experiments show that after application, it can increase plant height, stem diameter, number of leaves, fresh weight and dry weight, which is significantly better than conventional growth-promoting strains.

[0019] (2) Outstanding stress resistance: The strain SDQB6 can tolerate 15% NaCl salt stress and 10% PEG simulated drought conditions. It still maintains its vitality under saline-alkali / drought stress, providing a new solution to the planting problem in arid and saline-alkali areas in Northwest China.

[0020] (3) Broad-spectrum disease resistance: It shows inhibitory effects on 10 common plant pathogens, especially the inhibition rate of apple rot fungus reaching 91.04%, and the inhibition rates of wolfberry root rot fungus and pear ring rot fungus reaching 77.74% and 81.01% respectively. It can reduce the amount of chemical pesticides used and has both ecological and economic benefits.

[0021] (4) Flexible application: It can be made into liquid fermentation agent, solid agent or wettable powder (live count ≥1×10⁻⁶). 8 (CFU / g), suitable for seed treatment, soil application or foliar spraying, and can meet the needs of different crops and planting scenarios.

[0022] (5) Environmentally friendly solutions: By replacing some chemical fertilizers and pesticides through microbial regulation, the risk of soil degradation can be reduced. It is particularly suitable for promotion and use in ecologically fragile areas and meets the requirements of sustainable agricultural development. Attached Figure Description

[0023] Figure 1 The images show the in-plate culture characteristics and scanning electron microscope morphology of strain SDQB6 in Example 1 of this application. A is a frontal colony feature of strain SDQB6 on LBA medium, and B is a scanning electron microscope image of the cell morphology of strain SDQB6.

[0024] Figure 2 Phylogenetic trees were constructed for the 16S rRNA sequence and whole genome sequence of strain SDQB6 in Example 1 of this application, where A is a phylogenetic tree constructed based on the 16S rRNA gene sequence and B is a phylogenetic tree constructed based on the whole genome sequence.

[0025] Figure 3 This diagram shows the functional characteristics verification of strain SDQB6 in Example 2 of this application. A represents the growth of strain SDQB6 on Ashby nitrogen-fixing medium, B represents the growth of strain SDQB6 on Monkina phosphorus-solubilizing medium, C represents the growth of strain SDQB6 on CAS medium, D represents the blank control of strain SDQB6 under 0% PEG conditions, E represents the growth of strain SDQB6 under 5% PEG conditions, F represents the growth of strain SDQB6 under 10% PEG conditions, G represents the growth of strain SDQB6 under 10% NaCl conditions, H represents the growth of strain SDQB6 under 12% NaCl conditions, and I represents the growth of strain SDQB6 under 15% NaCl conditions.

[0026] Figure 4 This is a comparison of the growth-promoting and salt-tolerance effects of strain SDQB6 in Example 3 of this application on melon and pepper. In the figure, A is a comparison of melon plant growth, B is a comparison of pepper plant growth, and C is a comparison of pepper plant growth. From left to right in the figure, they are: CK; SDQB6 treatment group; CK + salt stress group; SDQB6 + salt stress group.

[0027] Figure 5 The image shows the effect of strain SDQB6 in Example 3 of this application on improving the drought resistance of melon. From left to right, the images show the growth status of melon in the mild drought control group, the mild drought treatment group, the moderate drought control group, the moderate drought treatment group, the severe drought control group, and the severe drought treatment group.

[0028] Figure 6 This is a diagram showing the antibacterial effect of strain SDQB6 in Example 4 of this application against 10 plant pathogens. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0030] The test materials involved in the embodiments of this application are as follows:

[0031] 1. Test pathogen:

[0032] The following fungi were isolated and identified in our laboratory: *Cytospora mali* QH2 (apple rot), *Fusarium solani* (goji berry root rot), *Colletotrichu scovillei* LJ1 (pepper anthracnose), *Acrostalagmus luteoalbus* CMGF-A (strawberry root rot), *Dactylonectria macrodidyma* CMGF-D (strawberry root rot), and *Cytospora chrysosperma* YSFL4-2 (poplar rot) (Ma Qiang et al., 2020; Sun Pingping et al., 2023; Zhang Hongling, 2024; Jia Wei et al., 2022).

[0033] The fungi causing pear gray mold (Botrytis cinerea LHM), pear ring rot (Botryosphaeriaberengeriana LLW), and pear brown rot (Monilinia fructigena LHF) were isolated and identified by the Institute of Fruit Trees, Chinese Academy of Agricultural Sciences (Sun et al. 2017; Sun Pingping et al., 2018).

[0034] The Rhizoctonia solani MLS fungus for potato black scurvy was provided by Henan Agricultural University.

[0035] 2. Test culture medium:

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

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

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

[0039] (4) Mongkina phosphorus-solubilizing medium: 10g glucose, 0.5g (NH4)2SO4, 0.3g NaCl, 0.3g KCl, 0.3g MgSO4·7H2O, 0.03g FeSO4·7H2O, 0.03g MnSO4·7H2O, 2.5g Ca3(PO4)2, 0.4g yeast extract, add deionized water to make up to 1L, pH 7.0.

[0040] (5) CAS solid culture medium: Chromium azurite S 60.5 mg, hexadecyltrimethylammonium bromide 72.9 mg, FeCl3·6H2O 2.645 mg of NaH2PO4·2H2O, 295.25 mg of Na2HPO4·12H2O, 1213.5 mg of NH4Cl, 125 mg of KH2PO4, 37.5 mg of NaCl, and 9 g of agar were added to a final volume of 1 L with deionized water. The mixture was heated to boiling until completely dissolved, and the pH was adjusted to 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 make up to 1L, pH 7.0.

[0042] 3. Testing instruments:

[0043] Incubator (HPX-9162MBE, Shanghai Boxun Industrial Co., Ltd.);

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

[0045] Microscope (LEICA ICC50W, Leica Instruments GmbH, Germany);

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

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

[0048] Example 1

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

[0050] 1. Isolation and screening of strains

[0051] Rhizosphere soil samples of *Ilex sabina* were collected from Inner Mongolia. During the collection process, 5cm of topsoil was removed, and 25cm of rhizosphere soil was collected. The samples were wrapped in kraft paper and stored at 4℃.

[0052] Various bacteria in soil were isolated using the dilution-spread plate method. The specific isolation and screening methods are as follows: 10g of dried soil sample was ground and placed in 100mL of sterile water, shaken at 4℃ and 180rpm for 30min, and then serially diluted with sterile water to 100mL. -6Take 100 μL of the dilution solution and spread it evenly on LBA medium. Incubate at 28°C for 48 h. Select individual bacterial colonies with different morphologies and colors and streak them for purification. After purification, strain SDQB6 is obtained. Select purified colonies and transfer them to LB medium. Incubate at 28°C with shaking at 180 rpm for 24 h. Mix thoroughly with an equal volume of 50% glycerol (final concentration 25%), and store in a preservation tube at -80°C for later use.

[0053] 2. Identification of the morphological characteristics of the strain

[0054] Strain strain SDQB6 was plated on LBA medium and incubated statically at 28°C for 48 hours. Colony morphology was observed, and colonies were picked for scanning electron microscopy. Results are as follows: Figure 1 As shown, strain SDQB6 showed uniform staining in LBA medium, with yellow colonies; scanning electron microscopy revealed that the bacterial cells were coccoid, with spores, and their size was 0.74-1.33 μm long and 0.28-0.36 μm wide. Figure 1 A shows the frontal colony characteristics of strain SDQB6 on LBA medium. Figure 1 Image B shows the morphological results of the SDQB6 strain observed by scanning electron microscopy.

[0055] 3. Molecular biological identification

[0056] Genomic DNA was extracted from strain SDQB6, and its whole genome was sequenced using PacbioSequel II. The sequenced reads were assembled using SMARTLink 10.1.0 software. The evolutionary distance between the genomes of different strains was calculated using the genome alignment distance method in the Type Strain Genome Server online program (https: / / tygs.dsmz.de). Approximate species were screened using the minimum evolutionary distance between genomes. A phylogenetic tree of the selected strains and the 13 strains was constructed using FASTME 2.1.6.1 software, with the numbers in each branch representing the confidence rate of 1000 bootstrap tests. Results are as follows: Figure 2 As shown, the 16S rRNA and full genome sequence of strain SDQB6 clustered with strains of the genus *Alcaligenes* in a large clade. It clustered with *Alcaligenes faecalis* NBRC13111 and was identified as the same species. Using a combination of morphological observation, physiological and biochemical characteristics, and gene sequencing, strain SDQB6 was confirmed to be *Alcaligenes faecalis*.

[0057] The rhizosphere probiotic SDQB6 obtained in this application was deposited on May 19, 2025, at the China General Microbiological Culture Collection Center, Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, with accession number CGMCC No. 34588, and its classification name is Alcaligenes faecalis.

[0058] Example 2

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

[0060] 1. Determination of phosphorus solubility

[0061] Experimental method: The strain SDQB6 was spread on LBA medium and incubated at 28℃ for 48 h. SDQB6 colonies were picked with sterile cotton swabs and inoculated onto Monkina phosphate-solubilizing medium, with 3 replicates. After incubation at 28℃ for 48 h, the colony diameter (d) and the diameter of the surrounding transparent zone (D) were measured, and the D / d ratio was calculated.

[0062] Experimental results: SDQB6 formed a clear transparent zone on Monkina agar medium (e.g., Figure 3 B); The colony diameter was measured to be d=5.12±0.23mm, the transparent zone diameter was D=6.55±0.31mm, and the D / d ratio was 1.28±0.05, indicating that strain SDQB6 has significant phosphate solubilization ability.

[0063] 2. Determination of iron complexation capacity

[0064] Experimental method: The SDQB6 strain was spread on LBA medium and incubated at 28℃ for 48 h. SDQB6 colonies were picked with sterile cotton swabs and inoculated onto CAS solid medium, with 3 replicates. After incubation at 28℃ for 48 h, the formation of the orange halo was observed and the colony diameter (d) and the diameter of the surrounding transparent zone (D) were measured. The D / d ratio was calculated.

[0065] Experimental results: SDQB6 colonies showed a distinct orange halo around them (e.g., Figure 3 C); the colony diameter d=4.87±0.15mm, the halo diameter D=11.53±0.42mm, and the D / d ratio reached 2.37±0.08, indicating that strain SDQB6 has a significant iron complexing ability.

[0066] 3. Drought resistance performance test

[0067] Experimental methods: SDQB6 strain was inoculated into LB medium and cultured at 28℃ with shaking at 180 rpm for 24 h to obtain SDQB6 bacterial suspension; LBA medium containing different concentrations of PEG-6000 (0%, 5%, 10%) was prepared, with LBA medium containing 0% PEG-6000 serving as the blank control (CK). Figure 3 D); Take 5 μL of SDQB6 bacterial suspension (adjust OD with sterile water). 600 =1.0) was spot-inoculated onto LBA medium, with 3 replicates; after static incubation at 28℃ for 48h, the survival status of the colonies was observed.

[0068] Experimental results: SDQB6 can still grow under 10% PEG conditions (e.g., Figure 3 F) indicates that SDQB6 has strong drought resistance.

[0069] 4. Salt tolerance test

[0070] Experimental methods: SDQB6 strain was inoculated into LB medium and cultured at 28℃ with shaking at 180 rpm for 24 h to obtain SDQB6 bacterial suspension; LBA medium containing different concentrations of NaCl (10%, 12%, 15%) was prepared, and 5 μL of SDQB6 bacterial suspension (adjusted with sterile water to OD) was taken. 600 =1.0) was spot-inoculated onto LBA medium, with 3 replicates; after static incubation at 28℃ for 48h, the survival status of the colonies was observed.

[0071] Experimental results: SDQB6 can still grow under 15% NaCl conditions (e.g., Figure 3 (I) indicates that SDQB6 has strong salt tolerance.

[0072] 5. Nitrogen fixation capacity determination

[0073] Experimental method: The SDQB6 strain was spread on LBA medium and incubated at 28℃ for 48 h. SDQB6 colonies were picked with sterile cotton swabs and inoculated onto Ashby nitrogen-fixing medium, with 3 replicates. After incubation at 28℃ for 48 h, the colony diameter (d) and the diameter of the surrounding transparent zone (D) were measured, and the D / d ratio was calculated.

[0074] Experimental results: SDQB6 did not form a clear zone on Ashby nitrogen-fixing medium (e.g., Figure 3 A) indicates that strain SDQB6 has weak or no nitrogen-fixing ability.

[0075] Example 3

[0076] The effects of SDQB6 on plant growth promotion and stress resistance

[0077] 1. Experiments on growth promotion and salt tolerance of melons and peppers

[0078] Strain strain SDQB6 was inoculated into LB medium and cultured at 28°C with shaking at 180 rpm for 24 h. The bacterial culture was then adjusted to OD using sterile water. 600 =1.0 (approximately 10) 8 (CFU / mL) for later use.

[0079] Seeds of melon (Jinmi No. 6) and chili pepper (Xiangla No. 5) were sown in seedling pots containing a 1:2 mixture of fine sand and vermiculite. The following treatment groups were established:

[0080] ①SDQB6 treatment group (inoculation + normal growth conditions): After sowing melon / pepper seeds, treatment began when the seeds germinated and broke through the soil; 50mL of SDQB6 bacterial solution was added to each pot, and another 50mL of SDQB6 bacterial solution was added to each pot 14 days after the first addition, and the moisture content of the leech mixed substrate was maintained at 65% daily;

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

[0082] ②SDQB6 + Salt Stress Group (Inoculation + Salt Stress): After sowing melon / pepper seeds, treatment began when the seeds germinated and broke through the soil; 50mL of SDQB6 bacterial solution was added to each pot. 14 days after the first addition of bacterial solution, another 50mL of SDQB6 bacterial solution was added to each pot. 2 days after the first addition of bacterial solution, 50mL of 1% NaCl solution was added. The moisture content of the leech mixed substrate was maintained at 65% daily.

[0083] Objective: To test the growth-promoting and salt-tolerant effects of strain SDQB6 on plants under salt stress.

[0084] ③ Blank control group (CK, no inoculation + normal conditions): After sowing melon / pepper seeds, treatment began when the seeds germinated and broke through the soil; 50mL LB medium was added to each pot, and another 50mL LB medium was added to each pot 14 days after the first addition of LB medium, and the moisture content of the leech mixed substrate was maintained at 65% daily;

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

[0086] ④ Blank control + salt stress group (no inoculation + salt stress): After sowing melon / pepper seeds, treatment began when the seeds germinated and broke through the soil; 50 mL of LB medium was added to each pot. 14 days after the first addition of LB medium, another 50 mL of LB medium was added to each pot. 2 days after the first addition of LB medium, 50 mL of 1% NaCl solution was added. The moisture content of the leech mixed substrate was maintained at 65% daily.

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

[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 no stress conditions, the plant height, stem diameter, number of leaves, fresh weight, and dry weight of peppers treated with strain SDQB6 were significantly higher than those of the control, increasing by 49.19%, 32.14%, 61.11%, 122.69%, and 256.25% respectively compared to the control. Under stress conditions containing 1% NaCl, the plant height, fresh weight, and dry weight of peppers treated with strain SDQB6 were also significantly higher than those of the control, increasing by 34.77%, 36.18%, 40.91%, 46.15%, and 81.82% respectively compared to the control.

[0100] Based on the above data, it can be seen that the SDQB6 strain can not only promote plant growth under normal conditions, but also maintain high growth indicators in plants under salt stress, indicating that it has dual functions of promoting growth and resisting stress.

[0101] 2. Drought resistance experiment of melon

[0102] To evaluate the effect of strain SDQB6 on improving the drought resistance of melon, this study set up different gradients of drought stress treatments and conducted treatment experiments. The specific groups are as follows:

[0103] T0 (mild drought control group): Water daily to maintain soil moisture content at 65% of field capacity. Two weeks after seed germination, add 50 mL of LB medium to each pot, and then add another 50 mL of LB medium to each pot after another two weeks.

[0104] T1 (moderate drought control group): Water every 3 days to maintain soil moisture content at 45% of field capacity. Two weeks after seed germination, add 50 mL of LB medium to each pot, and then add another 50 mL of LB medium to each pot after another two weeks.

[0105] T2 (severe drought control group): Water every 5 days to maintain soil moisture content at 25% of field capacity. Two weeks after seed germination, add 50 mL of LB medium to each pot, and then add another 50 mL of LB medium to each pot after another two weeks.

[0106] T3 (Mild Drought Treatment Group): Water daily to maintain soil moisture content at 65% of field capacity. Two weeks after seed germination, add 50 mL of SDQB6 bacterial solution (1×10⁻⁶) to each pot. 8 CFU / mL), and after another 2 weeks, add 50mL of SDQB6 bacterial solution (1×10⁻⁶) to each pot. 8 (CFU / mL)

[0107] T4 (Moderate drought treatment group): Water every 3 days, maintaining soil moisture content at 45% of field capacity. Two weeks after seed germination, add 50 mL of SDQB6 bacterial solution (1×10⁻⁶) to each pot. 8CFU / mL), and after another 2 weeks, add 50mL of SDQB6 bacterial solution (1×10⁻⁶) to each pot. 8 (CFU / mL)

[0108] T5 (severe drought treatment group): Water every 5 days, maintaining soil moisture content at 25% of field capacity. Two weeks after seed germination, add 50mL of SDQB6 bacterial solution (1×10⁻⁶) to each pot. 8 CFU / mL), and after another 2 weeks, add 50mL of SDQB6 bacterial solution (1×10⁻⁶) to each pot. 8 (CFU / mL).

[0109] 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 2 and... Figure 5 As shown. Figure 5 From left to right, the images show the growth status of melons in the 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. Effects of strain SDQB6 on drought resistance in melon.

[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] The data in the table above show that strain SDQB6 significantly enhances the drought resistance of melons, exhibiting stable growth-promoting effects under mild, moderate, and severe drought conditions. Specifically, the SDQB6 treatment group showed superior results compared to the control group in terms of plant height, stem diameter, number of leaves, fresh weight, and dry weight. Particularly under severe drought conditions, plant height increased by 77.09%, and fresh weight increased by 105.98%, demonstrating a significant "stress-enhancing effect." This strain showed the most stable promoting effect on melon leaf development (increasing by 26-28%), while also maintaining 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 demonstrate 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 assay of Alcaligenes faecalis SDQB6

[0116] The antagonistic effects of SDQB6 on 10 important tree and crop pathogens were determined using the in-plate antagonism method: Cytospora chrysosperma QH2 (apple rot), Fusarium sambucinum GQGF3 (goji berry root rot), Botryosphaeria berengeriana LLW (pear ring rot), Botrytis cinerea LHM (pear gray mold), Monilinia fructigena LHF (pear brown rot), Acrostalagmus luteoalbus CMGF-A (strawberry root rot), Dactylonectriamacrodidyma CMGF-D (strawberry root rot), Rhizoctonia solani MLS (potato black spore), Cytospora chrysosperma YSFL4-2 (poplar rot), and Colletotrichu scovillei LJ1 (pepper anthracnose).

[0117] The specific testing procedure is as follows: SDQB6 bacterial cells were picked up with a sterile cotton swab and spotted onto both sides of a PDA plate. Ten pathogenic bacterial colonies (6 mm in diameter) were inoculated in the center of the plate. The treatment with pathogens inoculated only in the center of the plate served as a control. Each treatment was repeated three times, and the plates were incubated statically at 28°C. Once the control colonies had completely covered the plate, the diameter of the lesions was observed and recorded, and the inhibition rate was calculated.

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

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

[0120] Table 3. Results of the efficacy test of strain SDQB6 against 10 pathogens.

[0121]

[0122] The results showed that strain SDQB6 had a significant inhibitory effect on all 10 pathogens mentioned above. Figure 6 The inhibition zone ranged from 1.9 to 12.15 mm, and the inhibition rate ranged from 30.17% to 91.04%. Among them, the inhibition effect against apple rot pathogens reached 91.04%, indicating that strain SDQB6 has a broad antibacterial spectrum and good antibacterial effect.

[0123] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A rhizosphere probiotic SDQB6 of *Ilex chinensis*, characterized in that, The rhizosphere probiotic SDQB6 of *Ilex sambac* 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 CGMCCNo. 34588 and classified as *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 use of a microbial biocontrol agent according to any one of claims 2-4 in inhibiting plant pathogens, promoting plant growth, and enhancing stress resistance.

6. The application of the microbial biocontrol agent according to claim 5 in inhibiting plant pathogens, promoting plant growth, and enhancing stress resistance, characterized in that, The plant pathogens mentioned include *Cytospora chrysosperma* QH2 (apple rot), *Fusarium sambucinum* GQGF3 (goji berry root rot), *Botryosphaeria berengeriana* LLW (pear ring rot), *Botrytis cinerea* LHM (pear gray mold), *Monilinia fructigena* LHF (pear brown rot), *Acrostalagmus luteoalbus* CMGF-A (strawberry root rot), *Dactylonectria macrodidyma* CMGF-D (strawberry root rot), *Rhizoctonia solani* MLS (potato black spore rot), *Cytospora chrysosperma* YSFL4-2 (poplar rot), and *Colletotrichuscovillei* LJ1 (pepper anthracnose rot).

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

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