Postharvest biological control of melon pathogens using Bacillus subtilis EXWB1

Melon (Cucumis melo L.) is a widely used fruit which suffers from postharvest decay resulting in large economic losses. In this work we investigated the biological control of melon postharvest diseases using Bacillus subtilis EXWB1, which we had previously isolated and identified from melon in lab experiments. We found that this bacterium excretes a bio-surfactant in Luria- Bertani broth (pH 5-8) that helps it to stick to the hydrophobic melon skin, and spreads at a speed of 125 μm per h over the surface at room temperature and high humidity. During storage time we found that the peak of respiration of melon fruits increased on day 6, and was reduced by 26.1% and 71.9%, respectively in the presence of B. subtilis EXWB1 in inoculated and uninoculated treatments. The ethylene production peak was delayed by about 2 days and reduced by 72.3% and 61.6% on day 4. Growth of one of the main fungal pathogens of melon, Alternaria alternata, was limited around inoculated sites on the fruit surface, and necrotic lesions induced by this pathogen were significantly reduced by 77.2% after coinoculation with B. subtilis EXWB1. Treated fruits retained high levels of sugar and vitamin C, and low levels of organic acids, and maintained water content and turgidity at room temperature. Our findings provide an alternative and promising biological control agent, B. subtilis EXWB1, which can suppress postharvest diseases caused by A. alternata, and may effectively control postharvest physiological changes caused by fungal pathogens.