Antifungal Activity of Endophytic Bacillus K1 Against Botrytis cinerea

Abstract

Gray mold caused by <i>Botrytis cinerea</i> is detrimental to plants and fruits. Endophytes have been shown to modify plant disease severity in functional assays. We conducted this study to investigate the endophytic strain <i>Bacillus</i> K1 with excellently antagonistic <i>B. cinerea</i> from the wild grape endosphere. We identified a wild grape endophytic strain K1 with high antifungal activity against <i>B. cinerea</i> both <i>in vitro</i> and <i>in vivo</i>. Combining the phylogenetic results based on 16S rDNA and genome sequencing, K1 was assigned as <i>Bacillus subtilis</i>. The <i>in vitro</i> results displayed that K1 and its volatile substances could significantly inhibit the mycelia growth of <i>B. cinerea</i>. Grape fruit inoculated with <i>Bacillus</i> K1 showed lower gray mold during treatment. The higher levels of defense-related enzymes, including peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase, were induced in grapes after inoculation. Scanning electron microscopy (SEM) suggested that K1 inhibited mycelial growth <i>via</i> bacterial colonization and antibiosis in grapes. The gas chromatography-mass spectrometry analysis identified 33 volatiles in which dibutyl phthalate was the major compound accounting for 74.28%. Dibutyl phthalate demonstrated strong activity in suppressing the mycelia growth of <i>B. cinerea</i>. Genome bioinformatics analysis revealed that the K1 chromosome harbored many known biosynthesis gene clusters encoding subtilosin, bacillaene, bacillibactin, bacilysin, and fengycin. This study provides a potential biological agent to control diseases of post-harvest grape fruit and improves our understanding of the possible biocontrol mechanisms of the <i>Bacillus</i> strain.