Antifungal Effect of Volatile Organic Compounds from Bacillus velezensis CT32 against Verticillium dahliae and Fusarium oxysporum

The present study focuses on the inhibitory effect of volatile metabolites released by Bacillus velezensis CT32 on Verticillium dahliae and Fusarium oxysporum, the causal agents of strawberry vascular wilt. The CT32 strain was isolated from maize straw compost tea and identified as B. velezensis based on 16S rRNA gene sequence analysis. Bioassays conducted in sealed plates revealed that the volatile organic compounds (VOCs) produced by the strain CT32 possessed broad-spectrum antifungal activity against eight phytopathogenic fungi. The volatile profile of strain CT32 was obtained by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). A total of 30 volatile compounds were identified, six of which have not previously been detected in bacteria or fungi: (Z)-5-undecene, decyl formate, 2,4-dimethyl-6-tert-butylphenol, dodecanenitrile, 2-methylpentadecane and 2,2’,5,5’-tetramethyl-1,1’-biphenyl. Pure compounds were tested in vitro for their inhibitory effect on the mycelial growth of V. dahliae and F. oxysporum. Decanal, benzothiazole, 3-undecanone, 2-undecanone, 2-undecanol, undecanal and 2,4-dimethyl-6-tert-butylphenol showed high antifungal activity, with benzothiazole and 2,4-dimethyl-6-tert-butylphenol being the most potent compounds. These results indicate that the VOCs produced by B. velezensis CT32 have the potential to be used as a biofumigant for management of vascular wilt pathogens.