Melatonin increases the competitive ability of Debaryomyces hansenii in wounded kiwifruit and enhances postharvest decay biocontrol

The ability of a biocontrol agent to survive on or in a host and compete against pathogenic fungi is an important attribute, especially when used on fruit. Enhancing the oxidative stress tolerance of some yeast antagonists increases their fitness in the microenvironment of fruit wounds and improves biocontrol efficacy. In the present study, the effect of melatonin (ML) on the ability of the biocontrol yeast Debaryomyces hansenii to survive and inhibit pathogenic fungi in wounds of kiwifruit were investigated. An application of 5 µM ML pretreatment to D. hansenii increased its survival and growth rate in kiwifruit wounds, relative to the control. Compared to the non-ML-treated (NML) D. hansenii cells, ML cells recovered from kiwifruit wounds exhibited lower levels of oxidative injury, an indicator of increased adaptability to the wound environment, which would have enhanced their competitive ability. Notably, ML yeast exhibited a faster growth in fruit wounds and enhanced control of the fungal pathogens, Botrytis cinerea , Penicillium expansum , and Alternaria alternata , compared to NML yeast. ML induced the expression of several genes in D. hansenii associated with stress tolerance, including catalase 1 , copper-zinc superoxide dismutase , and mitogen-activated protein kinase HOG1 . The ability of ML to enhance the antioxidant capacity of D. hansenii may contribute to its enhanced competitive ability in kiwifruit wounds, which was reflected by its faster growth rate and increased ability to control postharvest fungal decays.