Antagonistic Activity of Bacillus amyloliquefaciens Volatile Compounds Against Alternaria alternata Causing Fruit Rot

Abstract

Fruit rot caused by Alternaria alternata is a major postharvest and field disease affecting a wide range of horticultural crops, leading to significant quality deterioration and economic losses. The present study evaluated the antagonistic potential of volatile organic compounds (VOCs) produced by Bacillus amyloliquefaciens against A. alternata under in vitro conditions. Dual-compartment Petri plate assays were used to assess the inhibitory effects of bacterial VOCs on mycelial growth, sporulation, and morphological development of the pathogen without direct physical contact. Results demonstrated strong inhibition of A. alternata mycelial growth in the presence of bacterial VOCs, with marked reductions in colony expansion and sporulation compared with untreated controls. Morphological alterations such as hyphal distortion, reduced branching, and abnormal conidial development were observed in treated fungal cultures, indicating disruption of normal fungal growth processes. The intensity of antifungal activity was dependent on exposure duration, with prolonged exposure leading to higher levels of inhibition. The VOC-mediated suppression suggests the involvement of bioactive compounds such as alcohols, ketones, and other secondary metabolites produced by B. amyloliquefaciens. These compounds likely interfere with fungal cell membrane integrity and metabolic activity, resulting in reduced pathogen viability. The findings highlight the potential of bacterial VOCs as a non-contact biological control mechanism for managing A. alternata-induced fruit rot. Such volatile-mediated interactions offer advantages in postharvest storage environments where direct microbial application may be limited.