Postharvest hot water dipping reduces decay by inducing disease resistance and maintaining firmness in muskmelon (Cucumis melo L.) fruit

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Muskmelons (Cucumis melo L.) are major economic crops in the northwestern part of China, and postharvest decay of fruit is serious. In order to reduce postharvest decay and prolong the storage time, the effect of hot water dipping (HWD) on nature decay and mechanisms involved were studied when muskmelon fruit (cv. Yujinxiang) were dipped in hot water at 53°C for 3min. The results showed that postharvest HWD effectively (p<0.01) reduced the decay incidence, 18.9% lower than that in control fruit after 18 days of storage. HWD noticeably enhanced the activities of phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), 4-Coumarate: CoA ligase (4CL), polyphenoloxidase (PPO) and peroxidase (POD), and accumulated phenolic compounds, flavonoid, lignin and hydroxyproline-rich glycoproteins (HRGPs). The treatment effectively maintained fruit firmness by suppressing the activities of endo-1,4-β-d-glucanase (EGase), β-glucosidase (β-Glu), polygalacturonase (PG) and pectinesterase (PME), and promoting the accumulation of suberin and callose. And the data showed a higher correlation between fruit firmness and decay incidence (R2=0.8933). Furthermore, HWD could clean the surface of fruits, melt the epicuticular waxes, cover and seal the stomata. These results indicated that postharvest HWD reduced decay incidence by inducing disease resistance and maintaining the firmness in muskmelon fruit. Our data suggest that HWD has the potential to reduce or/and substitute chemical fungicides to control postharvest decay of muskmelon fruits.