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 Lasiodiplodia theobromae, 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 in vitro, and validated its efficiency against L. theobromae through spore inhibition assay, grapevine shoot inoculation and field experiments. Based on morphological characteristics and phylogenomic analysis, BJ-3 was identified as Bacillus halotolerans. 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. In vitro 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 Botryosphaeria dothidea (76.18 %), Neofusicoccum parvum (70.59 %), Diaporthe sojae (91.62 %), D. eres (81.31 %), and L. theobromae (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 L. theobromae. 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 B. halotolerans BJ-3 strain as a biofungicide for managing Botryosphaeria dieback disease in grapevine, providing a foundation for developing B. halotolerans BJ-3-based antimicrobial secondary metabolites in future studies.