Antifungal mechanism of Bacillus velezensis JLU-55 against maize pathogen Cochliobolus heterostrophus.

Southern corn leaf blight (SCLB), caused by Cochliobolus heterostrophus, is a major disease that severely affects maize production globally, especially in tropical and subtropical regions. Conventional control strategies, such as chemical fungicides and resistant cultivars, are limited due to environmental and health concerns. This study explores Bacillus velezensis JLU-55 as a potential biological control agent against C. heterostrophus. The bacterial strain was isolated from the rhizosphere of maize and systematically evaluated for its antagonistic activity, plant growth-promoting traits, and underlying biocontrol mechanisms. Dual culture assays revealed that JLU-55 exhibited broad-spectrum antifungal activity against C. heterostrophus and other phytopathogens, including Setosphaeria turcica and Fusarium graminearum. The strain produces various hydrolytic enzymes - such as cellulase, protease, and amylase - as well as indole-3-acetic acid, which collectively enhance its biocontrol capabilities. Additionally, in vivo assays demonstrated that JLU-55 significantly reduces lesion development on maize leaves, functioning effectively both as a protective and curative treatment. Genome sequencing identified 11 gene clusters responsible for the synthesis of secondary metabolites, two of which were successfully characterized from JLU-55 extracts. Moreover, JLU-55 was found to induce the expression of key disease resistance genes in maize, indicating its capacity to activate host immune responses. These findings suggest that Bacillus velezensis JLU-55 holds significant promise as a sustainable and environmental-friendly biocontrol agent for managing SCLB in maize production systems.