Abstract
The dynamic changes of the levels of volatile organic compounds (VOCs) produced by Bacillus subtilis CF-3 and their biocontrol effects on common fungal pathogens were researched in this study. The results showed that the VOCs in 24-h fermentation liquid (24hFL) of B. subtilis CF-3 inhibited mycelial growth of Botrytis cinerea, Colletotrichum gloeosporioides, Penicillium expansum, Monilinia fructicola, and Alternaria alternata, with a mean inhibition rate of 59.97%. The inhibitory effect on M. fructicola and C. gloeosporioides was the highest; they were therefore selected as target fungal pathogens for further experiments. Based on headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), 74 potential VOCs were identified during the fermentation: 15 alcohols, 18 ketones, 4 pyrazines, 4 esters, 10 acids, 5 phenols, 3 hydrocarbons, 3 amines, 2 aldehydes, 5 ethers, and 5 other components. At different fermentation times, the type and content of VOCs were different. Most of the potential VOCs (62 VOCs) were identified in the 48hFL. The inhibition rates of all VOCs reached their peaks (73.46% on M. fructicola and 63.63% on C. gloeosporioides) in the 24hFL. Among the identified VOCs, 2,4-di-tert-butylphenol, 1-octanol, and benzothiazole showed significant positive correlations with the rates of M. fructicola and C. gloeosporioides inhibition. Benzoic acid and benzaldehyde showed a significant positive correlation with the rates of M. fructicola inhibition, and anisole and 3-methylbutanal showed a significant positive correlation with the rates of C. gloeosporioides inhibition. In vitro, 2,4-di-tert-butylphenol showed a strong inhibitory effect on both M. fructicola and C. gloeosporioides. In vivo, benzothiazole showed the strongest inhibitory effect on the mycelial extensions of both M. fructicola and C. gloeosporioides, which also led to an increased rate of healthy fruit. The results of the present study clarified that 2,4-di-tert-butylthiophenol and benzothiazole are key inhibitory VOCs produced by B. subtilis CF-3.
Highlights
Postharvest decay caused by fungal pathogens is one of the main factors limiting the storage life of fruit, and it results in substantial economic losses, especially in the fruit market supply chain (Prusky, 2011)
To explore the biocontrol effects of volatile organic compounds (VOCs) produced by B. subtilis CF-3 on different common fungal pathogens, the inhibition rate of VOCs was evaluated in three different fractions: the 24-h fermentation liquid (24hFL), cell-free filtrate (CFF) of the 24hFL, and bacterial suspension (BS) of the 24hFL
Almost all collected fungal pathogens were inhibited, indicating that B. subtilis CF-3 has a relatively broad antifungal spectrum; it is necessary to identify the key inhibitory VOCs produced by B. subtilis CF-3
Summary
Postharvest decay caused by fungal pathogens is one of the main factors limiting the storage life of fruit, and it results in substantial economic losses, especially in the fruit market supply chain (Prusky, 2011). Fungicides are widely used to limit postharvest decay and extend the shelflife of fruit. They are becoming less effective, owing to the development of pathogen resistance, which results in the overuse and misuse of fungicides and causes a public health risk (Schreinemachers and Tipraqsa, 2012). Despite these problems, fungicides are currently essential for ensuring that the food supply meets the demands of the increasing global population (Wang and Liu, 2007).
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