Screening of a broad-spectrum antagonist-Bacillus siamensis, and its possible mechanisms to control postharvest disease in tropical fruits

Abstract

Broad-spectrum antagonist Bacillus siamensis (B. siamensis) was screened from ten biocontrol strains because of its excellent antifungal activity on 21 tested pathogens in vitro. In this study, the biological control capability of B. siamensis and its possible action mechanisms on pathogens in postharvest tropical fruits were investigated. Results showed that the volatile organic compounds (VOCs) produced by B. siamensis exhibited significant inhibition to the tested fungi in co-culture. The gas chromatography-mass spectrometry (GC-MS) equipped with solid-phase microextraction (SPME) was adopted for component identification of VOCs, and fifteen diffusible compounds were detected, with properties of inhibiting the growths of hyphae and conidial germinations of fungi proved. Moreover, through Ultra performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-QQQ-MS) analysis, the possible existence of surfactin lipopeptide was speculated. The extracellular lytic enzymes, including β-1,3-glucanase, cellulase and protease released by B. siamensis were detected. In vivo, the results of biological control efficacy test showed that B. siamensis suppressed the occurrence of diseases and browning of tropical fruits during storage. Compared with the control, the physiological qualities of postharvest tropical fruits in the treatment were maintained well. The combination of different mechanisms of action led to the broad-spectrum capacity of B. siamensis to defense and attack the pathogens whether in vivo or in vitro. Findings above indicate that broad-spectrum antagonist B. siamensis has great biocontrol potential and could be applied in controlling postharvest diseases in tropical fruits.