Abstract: To explore novel biocontrol microbial resources, a strain of Bacillus velezensis, designated as EEAM 10B, was isolated and identified from the surface of black soldier fly (Hermetia illucens) eggs. This study investigated its antagonistic effects and mechanisms against Sclerotium rolfsii Sacc, the pathogen of peanut southern blight. Peanut southern blight is a serious soil-borne fungal disease caused by Sclerotium rolfsii Sacc.Antagonism assays demonstrated that the fermentation broth, supernatant, and volatile organic compounds (VOCs) of EEAM 10B significantly inhibited the mycelial growth of peanut southern blight with the fermentation broth exhibiting the strongest suppression. Pot experiments revealed that EEAM 10B treatment notably reduced the disease index of infected peanut seedlings and exhibited plant growth-promoting effects. The optimal biocontrol efficacy (65.80%) was achieved when peanut plants were sprayed with EEAM 10B fermentation broth two days prior to pathogen inoculation. Whole-genome sequencing of EEAM 10B revealed a genome size of 3,929,786 bp with 1089.2×sequencing depth and a GC content of 46.5%. Functional annotation identified key genes encoding enzymes for fungal cell wall degradation (e.g., chitinases and β-1,3-glucanases) and secondary metabolite gene clusters responsible for antifungal compounds (e.g., surfactin, fengycin, and bacillibactin). Additionally, genes associated with plant growth promotion (e.g., indole-3-acetic acid synthesis) and pathogen antagonism were detected, suggesting their critical roles in suppressing peanut southern blight. These findings highlight the potential of EEAM 10B as a biocontrol agent and provide a foundation for developing novel antimicrobial formulations.

Key words: peanut southern blight, Bacillus velezensis, antibacterial, biological control, whole genome sequencing