Cotton Verticillium wilt is a disease that significantly impacts the cotton industry, severely affecting cotton quality and the economic well-being of farmers. Bacillus atrophaeus YL84 is a biocontrol bacterium with broad-spectrum antagonistic and growth-promoting characteristics, previously isolated by our laboratory. This study aimed to elucidate the antagonistic effects of sterilized fermentation filtrate from Bacillus atrophaeus YL84 on cotton Verticillium wilt pathogen Verticillium dahliae and its growth-promoting effects on cotton. The experiments were conducted in vitro and in vivo to assess these effects comprehensively. Using the dual culture method, it was found that Bacillus atrophaeus YL84 exhibited a high inhibition rate on mycelial growth of V. dahliae, with an inhibition rate of 84.11%. The undiluted YL84 sterilized fermentation filtrate and its 10% volume fraction dilution (fermentation filtrate diluted to 10%) exhibited inhibition rates of 80.25% and 72.16% for conidial germination and mycelial growth of V. dahliae, respectively. Scanning electron microscopy showed increased branching, swelling, and shortened internodes in the antagonized mycelia. Conductivity measurements revealed a significant enhancement caused by the YL84 filtrate, with conductivity increasing by 8.94 times compared to the control at a 250 μg/mL concentration. Similarly, protein leakage peaked at 9.47 times the control level at 250 μg/mL, demonstrating the filtrate’s potent impact on mycelial cell membrane permeability. The enzymatic activities of polygalacturonase (PG), cellulase (CL), and β-glucosidase (β-GC) were significantly reduced following treatment with YL84 sterilized fermentation filtrate, with reductions from control levels of 15.78, 10.11, and 5.01 U/mL to treatment levels of 11.81, 6.96, and 1.44 U/mL, respectively. Indoor pot experiments demonstrated that different concentrations of YL84 sterilized fermentation filtrate significantly suppressed the occurrence of cotton Verticillium wilt while promoting plant growth. Compared to the control group, application of 250 μg/mL YL84 sterilized fermentation filtrate resulted in a control efficacy of 66.69% for cotton Verticillium wilt, with increases in plant height, root length, fresh weight, and dry weight of 9.36–33.85%, 17.33–29.49%, 16.79–28.24%, and 25–58.33%, respectively. These findings underscore the potential of the YL84 filtrate as both a biocontrol agent and a promoter of cotton plant growth in agricultural settings. These results indicate that Bacillus atrophaeus YL84 sterilized fermentation filtrate possesses both disease-suppressing and growth-promoting activities, making it a promising candidate for development and use as a biocontrol agent and plant growth promoter.

To identify the primary pathogen responsible for brown rot in mature Korla fragrant pears and to screen for effective biocontrol bacterial strains, a research team collected 30 samples of brown rot-infected fruits and 84 samples from healthy trees (including branches, leaves, and fruits) from three Korla pear cultivation areas in Korla, Aksu, and Kashgar between September and October 2024. Investigation into the severity of the disease revealed the local field incidence rate of brown rot ranged from 17% to 31%. From the 30 disease samples, 23 morphologically identical fungal strains were isolated, with 13 strains isolated from Korla City (56.5%), 6 from Aksu City (26.1%), and 4 from Tumushuk (17.4%), all detected in infected fruits. Pathogenicity tests were conducted using both inoculation by wounding with mycelium and spray inoculation experiments to study the pathogens’ effect on brown rot in Korla fragrant pears. From the 84 samples of healthy trees, 55 bacterial strains were isolated, and the antagonistic bacteria’s inhibitory effect on the isolated pathogens was determined using the dual-culture method. The pathogen was identified by morphological characteristics and phylogenetic analysis based on multi-locus sequencing (ITS-TUB2-Lcc2). Antagonistic bacterial strains were identified through morphological observation and 16S rDNA sequencing. The results demonstrated that the pathogen isolated from the diseased Korla fragrant pear tissues was identified as Monilinia yunnanensis. Among the biocontrol antagonistic bacteria isolated from the branches, bark, and leaves of healthy Korla fragrant pear trees, Bacillus siamensis exhibited significant inhibitory effects against the pathogen, with an in vitro inhibition rate of (88.18 ± 3.43)%.

Bacillus atrophaeus has considerable potential for development as a microbial pesticide. Optimization of fermentation conditions and the wettable powder (WP) formulation is critical for its industrialization and application in sustainable agriculture. In this study, the fermentation of B. atrophaeus YL84 was optimized using single-factor experiments and response surface methodology. Based on these results, a WP formulation was developed and further optimized. The optimal carbon, nitrogen, and inorganic salt sources were sucrose (13.9 g·L⁻¹), tryptone (11.8 g·L⁻¹), and MgSO₄ (5.9 g·L⁻¹), respectively; optimal fermentation conditions were pH 7.0, 32 °C, and 210 r·min⁻¹. After optimization, the inhibition rate and OD₆₀₀ reached 83.71% and 1.758, respectively. The optimized formulation comprised attapulgite-based powder (79%, as carrier), sodium alkyl naphthalene sulfonate (5.4%) as a wetting agent, PEG-6000 (12.6%), CaCO₃ (2%), and vitamin C (1%). The resulting WP exhibited a spore viability of 2.63 × 10⁹ CFU·g⁻¹, and its 50-fold dilution demonstrated antagonistic activity in vitro against Cytospora pyri (Korla pear valsa canker agent) and biocontrol efficacy in vivo on detached-branch assays. These findings demonstrate that the YL84 WP is a promising candidate for the biological control of Korla pear valsa canker.

The occurrence of pear Valsa canker caused by Cytospora pyri poses a serious threat to the healthy and sustainable development of the Korla fragrant pear industry. To effectively control the disease, endophytic strains were isolated from the bark of Korla fragrant pear trees and screened for strong antagonistic activity against the pathogen. The selected strain was identified based on morphological characteristics and 16S rRNA phylogenetic analysis. Its biocontrol potential and functional traits were further evaluated, along with its growth-promoting ability assessed through in vitro tests and preliminary tomato pot experiments. Results showed that a total of 264 endophytic isolates were obtained from 200 pear tissue samples using dilution plating and tissue separation methods. Among them, strain FB-4 exhibited significant inhibition against C. pyri. Morphological observations and phylogenetic analysis identified the strain as Bacillus velezensis, named FB-4. The cell-free supernatant inhibited conidial germination and mycelial growth of the pathogen by 88.21% and 85.51%, respectively, and showed preventive and curative efficacies of 74.49% and 58.97% against pear Valsa canker. In vitro assays indicated that FB-4 could produce indole-3-acetic acid, protease, amylase, and cellulase, and demonstrated abilities to solubilize inorganic phosphate and synthesize siderophores. Inoculation with FB-4 bacterial suspension promoted the growth of tomato seedlings, with higher concentrations yielding more pronounced effects. In conclusion, strain FB-4 represents a dual-functional biocontrol agent with both antagonistic and plant-growth-promoting properties.