Evaluation of Bacillus subtilis Volatile Compounds in Suppressing Mycelial Growth of Soil-Borne Pathogens

Abstract

Soil-borne fungal pathogens cause substantial yield losses in agricultural systems, and their management remains challenging due to their persistence in soil and resistance to chemical control measures. The present study evaluated the antifungal potential of volatile organic compounds (VOCs) produced by Bacillus subtilis in suppressing the mycelial growth of selected soil-borne pathogens under in vitro conditions. Dual-chamber assay systems were employed to assess the inhibitory effects of bacterial volatiles without direct physical contact between the antagonist and target fungi. Mycelial growth rate, radial expansion, and morphological alterations of fungal colonies were recorded and compared with untreated controls. The results demonstrated that VOCs emitted by B. subtilis significantly inhibited the growth of tested pathogens, with varying degrees of suppression depending on fungal species sensitivity. Exposure to bacterial volatiles resulted in reduced hyphal extension, abnormal mycelial branching, pigmentation changes, and overall growth retardation. The inhibitory effect was attributed to the production of biologically active volatile metabolites capable of disrupting fungal cell metabolism and structural integrity. Certain pathogen species exhibited higher susceptibility, indicating differential sensitivity to bacterial VOC profiles. The study highlights the role of airborne microbial metabolites in inter-kingdom interactions and their potential application in biological control strategies. The findings suggest that B. subtilis VOCs can serve as an effective eco-friendly tool for managing soil-borne fungal diseases in sustainable agriculture. This research contributes valuable insights into volatile-mediated biocontrol mechanisms and supports the development of innovative strategies for reducing reliance on synthetic fungicides in crop protection systems.