Biocontrol potential of an endophytic Bacillus sp. against strawberry anthracnose through antifungal activity, defense priming, and metabolic reprogramming

An endophytic bacterial strain, ABN14, was isolated from the peduncle of a symptomless strawberry plant ( Fragaria × ananassa ) growing in a field heavily infested with Colletotrichum nymphaeae , the causal agent of strawberry anthracnose. Based on phenotypic, biochemical, and molecular characterization, the isolate was identified as Bacillus sp. In dual-culture assays, ABN14 exhibited strong antagonistic activity, reducing mycelial growth of C. nymphaeae by more than 50%. Cell-free non-volatile metabolites completely inhibited fungal mycelial growth and substantially suppressed conidial germination, whereas volatile organic compounds exhibited only limited antifungal activity. The biocontrol efficacy of ABN14 was further confirmed under both postharvest and greenhouse conditions, where applications of live Bacillus sp. ABN14 cellssignificantly reduced anthracnose severity on strawberry fruits and plants following foliar spray and soil-drench treatments. Furthermore, ABN14 modulated the expression of key defense-related genes (PR5, PR10, and FaWRKY-1) and increased the activities of antioxidant and phenylpropanoid-associated enzymes, indicating activation of host defense pathways. In addition, metabolomic analyses revealed treatment-dependent changes in fruit secondary metabolite profiles, suggesting that bacterial colonization influences defense-related metabolic processes. These findings demonstrate that Bacillus sp. ABN14 represents a promising candidate for the development of sustainable biological control strategies for strawberry anthracnose management.