Molecular insights into the antifungal activity of Bacillus velezensis JLU-53 against Cochliobolus heterostrophus in maize.

Maize (Zea mays L.), a globally cultivated staple grain and economically significant crop, is highly susceptible to Southern corn leaf blight (SCLB), a disease caused by Cochliobolus heterostrophus. This pathogen can lead to substantial losses in both yield and grain quality during the growing season. In this study, Bacillus velezensis strain JLU-53 was identified as a promising biocontrol agent against C. heterostrophus. JLU-53 exhibited broad-spectrum antifungal activity against several phytopathogens, including C. heterostrophus, Setosphaeria turcica, Rhizoctonia solani, Fusarium graminearum, Botrytis cinerea and Sclerotinia sclerotiorum. Genomic analysis revealed the presence of genes encoding diverse carbohydrate-active enzymes (CAZymes), and phenotypic assays confirmed the strain's capacity to produce hydrolytic enzymes such as cellulase, protease, and amylase, as well as indole-3-acetic acid (IAA). Whole-genome sequencing of JLU-53 identified 13 putative biosynthetic gene clusters responsible for the synthesis of antimicrobial peptides (AMPs). Further analysis of secondary metabolites confirmed the production of bacillomycin, macrolactin, and amicoumacin. In vitro experiments demonstrated that JLU-53 significantly inhibited mycelial growth, conidial germination, and appressorium formation of C. heterostrophus, thereby suppressing lesion development of maize leaves. In planta application of JLU-53 activated key defense-related genes in maize, enhanced host resistance, and markedly reduced disease symptoms. These findings indicate that B. velezensis JLU-53 exerts its biocontrol activity through dual mechanisms-direct antagonism and induction of systemic resistance-highlighting its potential as a sustainable and effective biocontrol agent for managing SCLB.