Abstract
In this study, we evaluated the effects of volatile organic compounds (VOCs) produced by Bacillus subtilis CF-3 in inhibiting Monilinia fructicola in vitro and in vivo. In the in vitro experiments, the effect of VOCs on the growth of the pathogenic fungi was explored by using plate enthalpy test; mycelial morphology was studied by scanning electron and transmission electron microscopy; and fatty acid contents in the cell membrane were assessed by gas chromatography-mass spectrometry (GC-MS). The results indicated that treatment with benzothiazole and CF-3 for 24 h, in the form of a fermentation broth (24hFB), significantly inhibited the germination of fungal spores, modified hyphal and cell morphology, and decreased the cell membrane fluidity and integrity. In the in vivo experiments, the effect of VOCs on the defense mechanism of peach fruit toward M. fructicola was studied, and we found that benzothiazole and CF-3 24hFB inhibited the activity of the pathogenic enzymes (pectinase, cellulase) secreted by M. fructicola to reduce the decomposition of plant tissues, activate the antioxidant enzymes (peroxidase, polyphenol oxidase, catalase, and superoxide dismutase) in the fruit to eliminate excessive reactive oxygen species in order to reduce plant cell damage, and trigger the disease-resistant enzymes (phenylalanine ammonia-lyase, chitinases, and β-1,3-glucanase) to enhance the resistance of peach fruit to M. fructicola and inhibit its growth. This study suggests that CF-3 VOCs could activate disease-resistant enzymes to prevent the invasion of pathogenic fungi and induce resistance in peach, thereby providing a theoretical basis for future applications.
Highlights
Due to the inadequate treatment in each production step, Monilinia fructicola infested on the peach fruit causes decay, resulting in large economic losses worldwide (Liu et al, 2008; Hu et al, 2011)
We previously reported by using both physical and flat-panel experiments that volatile organic compounds (VOCs) produced by B. subtilis CF-3 can prevent the decay of peaches and significantly inhibit the growth of pathogenic fungi as well as spore germination (Gao et al, 2018)
It is further indicated that VOCs can destroy fungal cells in vitro and induce disease resistance in postharvest peaches
Summary
Due to the inadequate treatment in each production step, Monilinia fructicola infested on the peach fruit causes decay, resulting in large economic losses worldwide (Liu et al, 2008; Hu et al, 2011). Bacillus subtilis is widely studied for fruit preservation due to its rich physiological characteristics and strong environmental adaptability, which has broad application prospects in the control of plant diseases as an extremely important bio-control resource (Ongena et al, 2005). B. subtilis antagonizes more than 30 types of plant pathogens (Moyne et al, 2004). It is widely distributed in nature and is nontoxic and harmless to humans and children, easy to isolate and cultivate, and has broad-spectrum antifungal activity and strong antireverse ability to produce antibiotics and enzymes such as peptides, lipopeptides, polyenes, and amino acids (Ahimou and Deleu, 1999), being extremely beneficial in biological control and fruit preservation
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