The germicidal and hormetic effects of UV-C light on reducing brown rot disease and yeast microflora of peaches

Abstract

The application of ultraviolet light-C doses (254 nm, UV-C) was used to determine the germicidal and hormetic effects on reducing brown rot of 'Elberta' peaches which were naturally and artificially inoculated with Monilinia fructicola. The results showed that a negative relationship existed between UV-C doses, colony forming units of the fungus, and the number of brown rot lesions. Also, the results of our study showed that the hormetic (beneficial) effect of low UV-C dose of 7.5 kJ m-2 induced host resistance by controlling latent brown rot infection. The hormetic effects of UV-C on peaches was photoreversed with visible light and resulted in the reduction of host resistance to brown rot. Furthermore, the results indicated that UV-C doses increased phenylalanine ammonia-lyase activity, delayed ripening and suppressed ethylene production. Additionally, the population of epiphytic yeast (Debaryomyces hansenii) increased curvilinearly on peach surfaces following UV-C irradiation up to 7.5 kJ m-2. Evaluation of the yeast population on the peach surfaces showed an antagonistic activity against M. fructicola. The possibility of the host peripheral defense by UV-C stimulation of the antagonist activity of a yeast is discussed.