Hot water treatment (HWT) has been demonstrated to be a safe and effective method to control postharvest diseases. In the present study, the effect of HWT (45 °C for 10 min) was investigated on the response of apple fruit against Botrytis cinerea, Colletotrichum acutatum and Neofabraea vagabunda infections. In vivo experiments were conducted with apples treated with HW and then inoculated with pathogen spore suspensions 0, 3, 6 and 24 h after the treatment. In vitro experiments were carried out in order to investigate the HWT effect on the pathogenesis enzyme activities of the three pathogens. These assays were conducted with the crude protein extracts (CPEs) derived from the hot water treated apples. A significant reduction of rot incidence was observed in fruit inoculated at 6 h (B. cinerea 22.7% and C. acutatum 11.0%) and 3 h (N. vagabunda 68.8%) after HWT with respect to the controls (22.0, 18.5 and 19.67 mm, respectively). CPEs extracted from hot water treated fruit inoculated at 6 h and 3 h showed the highest conidia germination inhibition (B. cinerea 85.6%; C. acutatum 52.7% and N. vagabunda 83.1%) with respect to the controls (74.0, 71.0 and 90.3% of conidia germination, respectively). A significant reduction of pathogenesis enzyme activities of the three pathogens was detected when pathogens were exposed to CPEs derived from hot water treated apples. The results showed that HWT can stimulate a defense response on apple against some postharvest pathogens.
