Abstract
In this study, we investigated the effects of volatile organic compounds (VOCs) produced by Bacillus subtilis CF-3 on the growth and development of Colletotrichum gloeosporioides and evaluated the elicitation of active defense responses in harvested litchi fruits. In vitro experiments were conducted to explore the bacteriostatic effect of VOCs in inhibiting pathogenic fungi by means of plate enthalpy test, scanning electron microscopy, transmission electron microscopy, and gas chromatography–mass spectrometry (GC–MS). The results showed that 2,4-di-tert-butylphenol and CF-3 24-h fermentation broth (24hFB) can significantly inhibit the germination of fungal spores, disrupt hyphal and cell morphology, and decrease cell membrane fluidity and integrity, resulting in the changes of indexes. In addition, the bacteriostasis of VOCs in the defensive ability of litchi fruits to C. gloeosporioides was studied, and it was shown that 2,4-di-tert-butylphenol and CF-3 24hFB can inhibit the activity of the pathogenic enzymes (pectinase and cellulase) secreted by C. gloeosporioides to reduce the decomposition of plant tissues, activate antioxidant enzymes (peroxidase, polyphenol oxidase, catalase, and superoxide dismutase) in the fruit to eliminate excessive reactive oxygen species in fruits in order to reduce plant cell damage and activate disease resistance enzymes (phenylalanineammonialyase, chitinases, β-1,3-glucanase) to enhance the resistance of litchi fruits to C. gloeosporioides and inhibit its growth. This study investigated the bacteriostasis of VOCs in inhibiting C. gloeosporioides and inducing the resistance of litchi fruits, providing a theoretical basis for future applications.
Highlights
Litchi anthracnose is a common disease of litchi that mainly affects young leaves, flower spikes, and mature or close to mature fruits, resulting in rotten flower and fruit (Liu 2006)
We demonstrated that the antibacterial protein and volatile substances produced by the biocontrol bacteria have good antibacterial effects against various plant pathogenic bacteria (Gao et al 2016)
During the whole storage process, the MDA content in the litchi fruits of the two treatment groups increased with the storage time, but the inhibiting effects of the 2,4-ditert-butylphenol and CF-3 24-h fermentation broth (24hFB) treatments were significantly better than the control treatment
Summary
Litchi anthracnose is a common disease of litchi that mainly affects young leaves, flower spikes, and mature or close to mature fruits, resulting in rotten flower and fruit (Liu 2006). B. subtilis is a mesophilic aerobic or facultative anaerobic gram-positive rod-shaped bacterium (Sonenshein and Losick 1994) It is widely distributed in nature, nontoxic and harmless to humans, easy to isolate and cultivate, and has broad-spectrum antibacterial activity. The VOCs of B. subtilis are composed of a variety of chemical substances, which have strong antibacterial effects and can inhibit the growth of different kinds of pathogens. The mechanism by which the volatile substances produced by B. subtilis inhibit the growth of C. gloeosporioides is not clear. Physical experiments were conducted to explore the mechanism of VOCs-induced defensive reaction in litchi fruits after harvest It provides an effective basis for the production of biological preservatives for effectively controlling C. gloeosporioides and, for updating the biological preservation technology
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