Bacillus velezensis BV3 Suppresses Leaf Spot Pathogens via Two Antifungal Metabolites and Promotes Maize Growth

Southern corn leaf blight (SCLB), caused by Bipolaris maydis, poses a serious threat to maize production worldwide. In our previous study, Bacillus velezensis BV3 was isolated and demonstrated strong antagonistic activity against maize leaf spot pathogens and effective disease control in greenhouse experiments. In this study, we evaluated the plant growth-promoting effects of BV3 on two maize cultivars through root application in pot experiments, and investigated the underlying molecular mechanisms using transcriptomic and metabolomic analyses. Inoculation with BV3 significantly promoted maize growth. Moreover, BV3 treatment induced extensive transcriptional and metabolic reprogramming in maize. Transcriptomic analysis identified numerous differentially expressed genes (DEGs) mainly enriched in plant–pathogen interaction, plant hormone signal transduction, MAPK signaling pathway, and phenylpropanoid biosynthesis pathways. Metabolomic analysis revealed substantial changes in metabolite accumulation, particularly in lipids, amino acids, sugars, organic acids, and polyphenols, with enriched pathways including secondary metabolite biosynthesis, phenylpropanoid biosynthesis, and flavonoid biosynthesis. LC/MS and GC/MS analyses further revealed that BV3 produced diverse bioactive compounds. 2,4-DTBP and surfactin exhibited strong antifungal activities, particularly against B. maydis and Exserohilum turcicum. Overall, Bacillus sp. BV3 exhibits strong biocontrol efficacy against maize leaf spot pathogens and significant plant growth-promoting activity, highlighting its potential as an eco-friendly biocontrol agent for the management of southern corn leaf blight.