Biocontrol Potential of <i>Bacillus subtilis</i> A3 Against Corn Stalk Rot and Its Impact on Root-Associated Microbial Communities

<i>Fusarium</i> stalk rot (FSR), a devastating soil-borne disease caused by <i>Fusarium</i> species, severely threatens global maize production through yield losses and mycotoxin contamination. <i>Bacillus subtilis</i>, a plant growth-promoting rhizobacterium (PGPR), has shown potential as a biocontrol agent against soil-borne pathogens, but its efficacy and mechanisms against maize FSR remain poorly understood. In this study, an identified strain of <i>B. subtilis</i> A3 was introduced to study its biological control potential against corn stalk rot. The bacteriostatic stability of the biocontrol strain was assessed, revealing that its inhibitory activity against <i>F. graminearum</i> remained consistent over five consecutive generations, indicating robust bacteriostatic stability. The strain also exhibited inhibitory effects on <i>F. verticilliodes</i>, <i>F. proliferalum</i>, and other pathogenic fungi, demonstrating it has broad-spectrum antibacterial activity. Indoor experiments showed that treatment with the biocontrol strain significantly increased plant height, stem diameter, and fresh weight, indicating a positive impact on corn growth. Additionally, the biocontrol strain A3 markedly reduced the lesion length of corn stalk rot, confirming its efficacy in controlling the disease. Field trials demonstrated that the growth of the A3-coated corn seeds was better than the control seeds, the control effect of FSR disease was 45.75%, and the yield increase was 3.6%. Microscopic observations revealed that the biocontrol strain A3 caused the hyphal tips of <i>F. graminearum</i> to swell and exhibit a beaded morphology, inhibiting normal growth. The volatile substances produced by A3 also showed significant antibacterial activity, with the antibacterial spectrum aligning with that of the biocontrol strain. Using headspace solid-phase microextraction and GC-MS, various antibacterial compounds were identified in the volatile substances. Analysis of root-associated microorganisms indicated that A3 significantly changed the microbial community composition. Co-occurrence network analysis revealed that A3-treated plants had fewer edges and lower negative correlations among bacterial communities. This study establishes the strong biocontrol potential of <i>B. subtilis</i> A3 against <i>Fusarium</i> stalk rot in corn, demonstrating its robust bacteriostatic stability, broad-spectrum antibacterial activity, positive impact on plant growth, and significant disease control efficacy, while also revealing its ability to alter root-associated microbial communities. These findings provide a foundation for further research into the mechanism of <i>B. subtilis</i> and its application in field biological control.