<i>Bacillus subtilis</i> 0618A Volatiles Inhibit <i>Sclerotium rolfsii</i> and Enhance Soil Health in the Biocontrol of Peanut Southern Blight

Peanut southern blight, caused by <i>Sclerotium rolfsii</i>, is a severe soil-borne disease. Given the adverse effects associated with chemical fungicides, this study investigated the biocontrol potential of volatile organic compounds (VOCs) from <i>Bacillus subtilis</i> 0618A. VOCs produced by <i>B. subtilis</i> 0618A at 1 × 10⁸ CFU/mL almost completely inhibited mycelial growth and sclerotia germination. Compared to common fungicides, the VOCs (1 × 10⁸ CFU/mL) effectively penetrated soil (up to 2 cm depth) to inhibit sclerotia germination and enhance key peanut defense enzyme activities (SOD, POD, and PPO). The indoor efficacy of VOCs was 75.28%, which was significantly higher than those of 100 mg/L tebuconazole (62.92%) and 300 mg/L polyoxin (46.07%). VOCs also significantly increased soil bacteria and actinomycetes populations and improved sucrase activity. Furthermore, 2,4-di-<i>tert</i>-butylphenol (2,4-DTBP) was identified as the primary active VOC against <i>S. rolfsii</i> (EC₅₀ = 0.23 μL/L). Both VOCs and 2,4-DTBP could destroy the integrity of the cell wall and cell membrane, reduce mitochondrial membrane potential, block ATP synthesis, and ultimately lead to fungal death.