Exogenous Melatonin Treatment Induces Disease Resistance against on Post-Harvest Grapes by Activating Defence Responses.

seriously affects the value of post-harvest grapes. Melatonin can act as an exogenous regulator in the resistance of exogenous pathogens due to its antioxidant activity. An artificial inoculation trial was conducted to research the induced resistance mechanism of melatonin treatment using the table grape "Muscat Hamburg" ( L. cv). Grapes were immersed with 0.02, 0.2, and 2 mmol/L melatonin, followed by suspension injections after 48 h. The results showed that the mycelial growth and spore germination of was not significantly inhibited by melatonin at different concentrations (0.02-2 mmol/L). However, post-harvest melatonin treatment inhibited the increase of disease incidence and severity of grey mould, induced the synthesis and accumulation of total phenols and flavonoids, reduced malondialdehyde generation, and inhibited an increase in cell membrane permeability. Meanwhile, defensive enzyme activities, including superoxide dismutase (SOD), peroxidize (POD), catalase (CAT), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), chitinase (CHI), and β-1,3-glucanase, were significantly increased in fruits treated with exogenous melatonin. These results suggested that exogenous melatonin treatment could activate defence responses to combat the infection of in post-harvest grapes.