Characterization of Two Potential Biocontrol Bacillus Strains Against Maize Stalk Rot

Maize stalk rot (MSR) is one of the most devastating fungal diseases affecting maize worldwide. In recent years, biological control agents have emerged as an environmentally friendly and highly attractive strategy for managing MSR. In this study, two Bacillus strains-B. subtilis KP3P9 and B. siamensis K13C-were shown to effectively inhibit the growth of the MSR pathogen Fusarium graminearum in vitro. Pot experiments showed that inoculation with KP3P9 significantly increased plant height, stem width, above-ground part fresh weight, and total plant fresh weight, whereas K13C significantly improved the stem width and under-ground part fresh weight of maize seedlings (p < 0.05), demonstrating their plant-growth-promoting potential. Moreover, both strains markedly reduced the disease severity indices (DSIs) of maize seedlings, indicating that they can enhance maize resistance to the pathogen. Whole-genome sequencing using Oxford Nanopore (ONT) and Illumina technologies showed that the complete genomes of KP3P9 and K13C contained biosynthetic gene clusters involved in the biosynthesis of antimicrobial secondary metabolites, including fengycin, bacillibactin, subtilin, pulcherriminic acid, subtilosin A, bacilysin, and others. Moreover, both strains exhibited strong antagonistic activity against F. solani (the causal pathogen of apple replant disease), as well as F. oxysporum f. sp. cubense race 1 (Foc1) and tropical race 4 (FocTR4) (pathogens responsible for banana wilt disease), with inhibition rates exceeding 70% in vitro. These results indicate that KP3P9 and K13C are promising biocontrol agents for MSR and other devastating Fusarium diseases.