Black spot disease caused by Ceratocystis fimbriata is destructive to the production, transportation, and storage of sweet potato. The antifungal effects of Bacillus tequilensis XK29 against C. fimbriata through volatile organic compounds (VOCs) were evaluated in this study. The activated carbon assay proved that XK29 could exert antibiotic effects through volatiles. By optimizing the wheat seed weight, inoculation method, concentration, volume, and time, the antifungal activity of XK29 was significantly improved. XK29 fumigation inhibited spore formation and germination and changed the cell morphology of C. fimbriata. During the storage of sweet potato tuber roots, XK29 effectively controlled black spot disease and reduced the weight loss and malondialdehyde content. Metabolomic analysis revealed that 21 volatile compounds were released from XK29. Isovaleric acid, isobutyric acid, and 2-methylbutanoic acid effectively inhibited the growth of C. fimbriata. These results indicate that B. tequilensis XK29 has a good potential to be developed as a microbial fumigation agent.
Botrytis cinerea is a necrotrophic fungal pathogen that causes gray mold disease in more than 1400 plant species. The biocontrol effect of microbial volatile compounds on postharvest diseases has become a research hotspot. This study revealed the biocontrol effects of volatiles released by Bacillus tequilensis XK29 on B. cinerea in vitro and in vivo . The results showed that the strain XK29 volatiles inhibited the mycelial growth of B. cinerea . The inhibition effect of strain XK29 volatiles against B. cinerea was increased by optimizing the wheat seeds weight, suspension concentration and inoculation volume of strain XK29, and the pre-culture time. The volatiles of strain XK29 affected the mycelial development, the formation of conidia , and the metabolic activity of B. cinerea . Selected individual monomers and artificial mixtures showed strong antifungal activity against B. cinerea. The volatiles of strain XK29 reduced the lesion diameter and disease severity of cherry tomatoes after inoculation with B. cinerea. These results indicate that the fumigation with B. tequilensis XK29 volatiles is a promising approach to protect cherry tomatoes from gray mold disease. This is also the first study to prove the antifungal effect of B. tequilensis on B. cinerea and its biocontrol effect on postharvest cherry tomatoes.
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