Optimization of the Fermentation and Preparation of the Wettable Powder Formulation of Bacillus velezensis F0b

<i>Bacillus velezensis</i> is an effective biocontrol bacterium, with its microbial pesticides showing promise in biological control. In this study, we optimized the medium and conditions for fermenting strain F0b, developed a wettable powder formulation, and assessed its efficacy against <i>Botrytis cinerea</i>. We screened carriers, wetting agents, dispersants, and UV protectants compatible with F0b, determining the optimal ratio and dosage. The best medium for F0b fermentation included rice flour (3.472%), ammonium chloride (4.898%), and disodium phosphate (1.871%). The ideal fermentation conditions were a 20% inoculum volume, 40 °C temperature, 80% sterile water, and a 72 h fermentation time, yielding a viable count of 1.33 × 10¹⁰ CFU/mL. The final formulation contained 54.7% <i>Bacillus velezensis</i> dried powder, 27.3% kaolinite carrier, 16% wetting agent (3:7 ratio of sodium dodecyl sulfate to sodium lignin sulfonate), and 2% ascorbic acid as a UV protectant. All quality indicators met national standards, with a viable bacteria concentration of 7 billion CFU/g. Field trials showed that the F0b wettable powder effectively controlled <i>Botrytis cinerea</i>, with a disease index significantly lower than the control group. Control efficacy ranged from 50.58% to 73.14% over 7 to 14 days, demonstrating the commercial potential of this formulation.