Combined treatment with hot water and UV-C elicits disease resistance against anthracnose and improves the quality of harvested mangoes

This research investigated the effects of hot water, UV-C irradiation and their combination on the induction of resistance to anthracnose disease and on quality improvement in harvested mangoes. Naturally infected mango fruits were harvested, surface-disinfested with a solution of 100 ppm sodium hypochlorite and air dried. The fruits were then treated with UV-C irradiation at a dose 6.16 kJ m−2, with hot water at 55 °C for 5 min or with hot water followed by UV-C irradiation. Untreated fruits served as the control. All fruit samples were kept at 13 °C for 12 days. The combined treatment significantly suppressed the severity of anthracnose symptoms compared with either single treatment. Additionally, the specific activities of key plant defense-related enzymes, such as phenylalanine ammonia lyase (PAL), peroxidase (POD), chitinase (CHI) and β-1,3-glucanase (GLU), increased in both the peel and the pulp of the mango fruits. The expressions of the MI-PAL, MI-POD, MI-CHI and MI-GLU genes in the mango peel were markedly enhanced in the fruits treated with the combined treatment in comparison with those treated with hot water or UV-C alone, while the control fruits showed the lowest expression of these genes. The combined treatment or UV-C treatment alone significantly delayed fruit ripening by maintaining fruit firmness, retarding the progressive increase of total soluble solids (TSS) and delaying the decrease in titratable acidity (TA). Weight loss was not significantly different among the treatments. The results suggested that the combination of hot water and UV-C treatment may be used as a tool not only for suppressing anthracnose disease but also for improving the quality of harvested mangoes by inducing the expression of plant defense-related genes.