From genome to field: Bacillus halotolerans BJ-3 as a novel biocontrol solution for grapevine Botryosphaeria dieback

Grapevine trunk diseases (GTD), particularly Botryosphaeria dieback caused by <i>Lasiodiplodia theobromae</i>, pose a significant threat to global viticulture. Current study aimed to develop a biocontrol solution using the locally isolated BJ-3 bacterial strain. We assessed the genomic biocontrol potential of BJ-3 through genome mining, evaluated its efficacy against 19 fungal pathogenic strains <i>in vitro</i>, and validated its efficiency against <i>L. theobromae</i> through spore inhibition assay, grapevine shoot inoculation and field experiments. Based on morphological characteristics and phylogenomic analysis, BJ-3 was identified as <i>Bacillus halotolerans</i>. Genome mining revealed eleven antimicrobial biosynthesis gene clusters, encoding secondary metabolites including bacillibactin, bacilysin, bacillaene, fengycin, subtilosin, aurantinin, thailanstatin, and laterocidine; many of which are associated with biocontrol activities. <i>In vitro</i> assays demonstrated BJ-3's broad-spectrum antagonistic capacity, with inhibition rates ranging from 55.56 % to 91.62 % against economically important GTD pathogens, including <i>Botryosphaeria dothidea</i> (76.18 %), <i>Neofusicoccum parvum</i> (70.59 %), <i>Diaporthe sojae</i> (91.62 %), <i>D. eres</i> (81.31 %), and <i>L. theobromae</i> (69.89 %). In the spore germination assay, BJ-3 achieved 98.47 % inhibition at 4 × 10⁷ CFU/mL after 10-12 h of incubation. Preventive treatments with BJ-3 at a concentration of 1.08 × 10⁸ CFU/mL resulted in 74.39 % control efficiency against <i>L. theobromae</i>. In the field experiment, BJ-3 effectively controlled Botryosphaeria dieback disease, with an inhibition rate of 71.94 %. These findings highlight the potential of the <i>B. halotolerans</i> BJ-3 strain as a biofungicide for managing Botryosphaeria dieback disease in grapevine, providing a foundation for developing <i>B. halotolerans</i> BJ-3-based antimicrobial secondary metabolites in future studies.