Biocontrol of chili anthracnose and Fusarium wilt by Bacillus velezensis S141 through lipopeptide gene induction and plant growth promotion

Bacillus velezensis S141 was evaluated as a biocontrol agent against two economically important chili pathogens: Colletotrichum gloeosporioides and Fusarium oxysporum. The evaluations included in vitro , molecular, and in vivo approaches. Dual-culture and cell-free culture filtrate assays demonstrated that both direct bacterial contact and secreted metabolites suppressed mycelial growth and spore germination in a species-specific and concentration-dependent manner, with maximum mycelial inhibition of 51.75% for C. gloeosporioides and 44.02% for F. oxysporum . Scanning electron microscopy of the treated fungi revealed marked surface deformation and hyphal collapse consistent with cell-wall damage. Interestingly, in liquid co-culture, S141 suppressed early mycelial growth in both fungal species. However, F. oxysporum recovered and resumed spore production, indicating tolerance of sublethal metabolite concentrations, whereas C. gloeosporioides remained completely suppressed. Gene-expression analysis showed pathogen-responsive upregulation of biosynthetic genes encoding cell-wall-degrading enzymes during fungal co-culture. These findings provide direct transcriptional evidence consistent with activation of lipopeptide and hydrolytic-enzyme biosynthetic pathways. In vivo bioassays confirmed that S141 significantly reduced anthracnose severity on chili fruits regardless of ripeness stage, achieving reductions of 66–79% and suppression of both anthracnose and Fusarium wilt in seedlings. Furthermore, S141 promoted the chili seedlings growth by 28% through direct inoculation and by 45% through the emission of volatile organic compounds (VOCs). The results show that B. velezensis S141 a promising candidate for the integrated management of chili anthracnose and Fusarium wilt while concurrently promoting plant growth.