Journal of Plant Pathology & Microbiology

Abstract

Natural Products to Control Postharvest Gray Mold of Tomato Fruit- Possible Mechanisms

Firas Ali Ahmed, Brent S Sipes and Anne M Alvarez

Grey mold is the one of most important postharvest disease of tomato fruit worldwide. Treatments with edible, natural products are needed to reduce losses and contribute to food sustainability. Based on the hypothesis that inhibition of Botrytis spore germination will significantly reduce postharvest losses, botanicals were tested for their effects on conidia. Ten Botrytis isolates from rotting tomato fruit collected at seventeen different sites in Hawaii were identified morphologically and confirmed by DNA sequence analysis. Effects of plant extracts on spore germination were assessed at several dilutions. Leaves of candidate biocontrol plants were frozen at -20°C and plant fluids were sterilized by passing through a 0.22 μm millipore. The effect of plant extracts on germination of Botrytis spores (106/ml) in sterile malt extract broth was evaluated in multi-well microplates using preparations ranging from 10 to 40%. Changes in absorbance measured at 6, 12, and 24 hours after inoculation were analyzed with Gen5 software. Capsicum chinense cultivars Datil and C. annuum Carnival completely inhibited fungal germination at all evaluation times. Extracts from Capsicum species were superior to all other extracts tested. Treatments with 40% extracts increased the generation of intercellular reactive oxygen species in the fungal conidia. Plasma membrane damage was shown with fluorescence microscopy when extract-treated conidia were stained with propidium iodide. Loss of integrity in the spore plasma membrane appears to account for the inhibition of Botrytis spore germination. Extracts from the two pepper cultivars, Datil and Carnival, showed promise as pre-harvest sprays in the greenhouse and as edible coatings on tomato fruit postharvest to reduce grey mold.