Photodynamic control of fungicide-resistant Penicillium digitatum by vitamin K3 water-soluble analogue

Penicillium digitatum, the fungal pathogen that causes green mold, is responsible for substantial postharvest losses of citrus worldwide. Photodynamic technology is a promising alternative to fungicides to control postharvest fungal decay. In this study, we investigated the antifungal activity of menadione sodium bisulfite (MSB), which is a water-soluble form of vitamin K3, with and without light activation against a fungicide-resistant P. digitatum isolate 3189. Results showed that MSB alone effectively inhibited P. digitatum spore germination and mycelium growth at concentrations of 5 and 40 mg mL−1, respectively, but did not reduce the viability of the ungerminated spores. When light was applied in addition to MSB, the treatment of 30 mg mL−1 of MSB and 30-min light irradiation resulted in a 5-log reduction of ungerminated spores regardless of the light type. In addition, light exposure decreased the required MSB concentrations for the control of spore germination and mycelium growth. Artificially-inoculated oranges with 3189 spores treated with 40 mg mL−1 of MSB and exposed to 30-min of simulated sunlight had no disease symptoms of green mold up to 14 days later compared to controls. In summary, this study illustrates the promising antifungal effect of MSB both with and without light exposure. The in vivo study using oranges as model fruit demonstrates the application potential of MSB for the citrus produce industry.