Biocontrol potential of vermicompost through antifungal volatiles produced by indigenous bacteria

As a practical manner for improving soil quality, controlling pathogens and pests, and promoting plant growth, vermicompost is increasingly used in agriculture during these decades. Compared with chemical fungicides, vermicompost exhibits a promising potential for controlling fungal plant pathogens for its effectiveness and environmental friendliness. While as a hotspot for isolating beneficial microorganisms, little is known about the mechanisms underlying the interactions between indigenous beneficial microbes and phytopathogenic fungi. In this study, ten plant pathogenic fungi were used to screen antagonistic bacteria from vermicompost. Then, the antagonistic bacteria were identified based on its morphological, physiological and biochemical characteristics, and 16S rDNA gene sequence analysis, the strain M29 which belongs to Bacillus subtilis showed the broadest spectrum of antifungal ability was selected. The antagonistic effect of the mixed volatile organic compounds (VOCs) released by M29 showed significant inhibitory activity against Botrytis cinerea (BC). Based on the GC-MS analysis, eleven VOCs including alcohols, acids, ketones, esters, ethers and hydrocarbons were identified, and the antifungal activity of purified compounds was tested against BC in different concentrations. 1-butanol, acetic acid butyl ester, 1-heptylene-4-alcohol and 3-methyl-3-hexanol completely inhibited the mycelia growth in vitro at a low concentration of 50 μL per dish, while furan-tetrahydro-2,5-dimethyl completely inhibited mycelia growth only at a high concentration of 100 μL per dish. Although 2,6-diisocyanato-1-methyl-benzene, 1-propoxy-2-propanol and benzophenone had limited antagonistic effects on suppressing mycelial growth, they could destroy normal hyphae morphology and induce mycelial fragmentation and crumpling as other prominent compounds. Through this study, we demonstrated that as a biocontrol agent, vermicompost can inhibited the development of fungal pathogens through the VOCs released by symbiotic microbes, which may promote more reasonable and effective utilizations of vermicompost in the future.