| The effect of hormic dosage of ultraviolet radiation on delaying the senescence of sweet cherry was investigated. "Hong Deng" sweet cherries were irradiated with low dose ultraviolet light-C (UV-C,254nm ) corresponding to 0, 0.25, 0.5 and 1.0KJ.m-2, and were stored at 0 and 25 in a dark room respectively. "Hong Deng" sweet cherry was inoculated artificially with Penicillium expansum after UV-C illumination in order to determine the germicidal and hermetic effects on reducing the postharvest rot.The dose of 0.25 and 0.5KJ.m"2 UV-C were found to be beneficial in delaying ripening and reducing the rot percentage. While the 1 .0KJ.m-2 UV-C aggravated the rot and destroyed the normal physiological process of sweet cherry.The activity of phenylalanine ammonia-lyase and polyphenol oxidase in irradiated fruits were increased, and UV-C also declined of the activity of peroxidase. In addition, the total phenol compounds and the lignin content were increased at the same time.The artificial inoculation ( Penicillium expansum ) test indicated that the rot percentage and the infection index were reduced after UV-C irradiation. Significantly lower numbers of infected fruits and lesion diameter were found in sweet cherries treated with UV-C doses ranging from 0.25 to 0.5 KJ.m-2. There was also a significantly lower level of disease in sweet cherries inoculated at 24~48h than in other times after irradiation. Thus, sweet cherry inoculated with Penicillium expansum followed by UV irradiation could reduce green mold, which suggested the resistance to the disease was induced.Low dose ultraviolet light-C not only delayed the senescence of sweet cherry, but also induced the resistance to the disease and reduced the postharvest rot.
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