Application of Hormetic UV-C for Delayed Ripening and Reduction of Rhizopus Soft Rot in Tomatoes: the Effect of Tomatine on Storage Rot Development

The application of ultraviolet-light C (UV-C, 254 nm) hormesis on tomato fruits to stimulate beneficial responses is a new method of inducing host resistance to Rhizopus soft rot, with maximum protection at 72 h following artificial inoculation with Rhizopus stolonifer and delay fruit ripening. In the tomato-Rhizopus soft rot pathosystem, UV-C induced resistance of tomatoes to soft rot was reversed by fluorescent light, and not by storage under dark condition. The present study was aimed at finding a possible fungal toxic mechanism that was involved in the control of Rhizopus soft rot. The development of carotenoids, loss of chlorophyll and ethylene production were significantly retarded during storage after treatment with hormetic doses of UV-C. The delayed ripening of UV-C treated fruits was attributed in part to the high level of putrescine and spermine polyamines. In a time-control study, it was found that the resistance of UV-C-treated tomatoes artificially inoculated with R. stolonifer correlated with a high concentration of tomatine which accumulated up to 72 h after UV-C treatment. However, there was a higher tomatine content in UV-C-treated fruits compared to untreated fruits where it was transitory at 96 h after treatment in the time-course study.