Inhibitory effects of non-volatiles lipopeptides and volatiles ketones metabolites secreted by Bacillus velezensis C16 against Alternaria solani

Alternaria solani, the causal agent of early blight, is a major threat to global potato production. In recent years, Bacillus species have been widely used for biological control of a wide range of plant pathogens. However, limited knowledge is about the antifungal mechanisms of Bacillus strains against A. solani. Further, the specific antifungal activities of different types of secondary metabolites produced by Bacillus species have not been evaluated comprehensively. In this study, we isolated a Bacillus strain with strong antifungal activity and identified it as B. velezensis C16. The antagonistic mechanisms of non-volatile lipopeptides (LPs) and volatile organic compounds (VOCs) produced by strain C16 against A. solani were studied. The results indicated that LPs and VOCs showed considerable antagonistic activities to A. solani, with reduced colony diameter and significantly inhibited conidia germination. Hyphae treated with antagonistic compounds from C16 exhibited serious structural destruction, with thin or gapped structures and swollen sacs. Active compounds in culture supernatant and volatiles produced by C16 significantly reduced the lesion areas and growth of A. solani in vivo. High-performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS) analysis revealed iturins and volatile compounds of C16 that exhibit strong antagonistic activity on mycelia. This study comprehensively investigated the antifungal effects of LPs and VOCs released by strain C16 on the air-borne pathogen A. solani. The results suggest that these compounds exhibit a synergistic effect to resist early blight in potato.