Antagonistic Mechanisms of Iturin A-4 Derived from Bacillus velezensis ZC2–4 against Sporisorium scitamineum

Sugarcane smut, caused by Sporisorium scitamineum, is a globally destructive disease that severely threatens sugarcane production. In this study, we isolated an endophytic bacterium, Bacillus velezensis ZC2–4, which exhibits inhibitory activity against the mycelial and haploid growth of S. scitamineum . Whole-genome sequencing and bioinformatics analysis predicted 13 secondary metabolite biosynthetic gene clusters, and the antifungal compound was subsequently identified as Iturin A-4 through high-performance liquid chromatography and nuclear magnetic resonance spectroscopy. Transcriptomic analysis and physiological assays revealed antagonistic mechanisms of Iturin A-4 against haploid growth including induction of oxidative stress and interference with cell-cycle progression. Scanning and transmission electron microscopy observations further demonstrated that Iturin A-4 inhibits teliospore germination. Remarkably, Iturin A-4 exhibits broad-spectrum antifungal activity against various fungal pathogens. Collectively, this study identifies B. velezensis ZC2–4 as a promising biocontrol agent and elucidates the antifungal mechanisms of Iturin A-4, providing a foundation for sustainable management of sugarcane smut.