UV-C Irradiation Reduces Gray Mold Decay and Enhances the Accumulation of Scoparone in Some Citrus Species

Abstract

We examined the effect of UV-C irradiation on the reduction of decay caused by gray mold (Botrytis cinerea Persoon), as well as on the accumulation of scoparone, an important defensive secondary metabolite, in the flavedo (exocarp) of four different Citrus species. Fruits were inoculated with gray mold 4 days after UV-C irradiation. In irradiated Satsuma mandarin and Hyuganatsu fruits let to a delay of disease incidence, and the reduction of the decay radius in Satsuma mandarin, ‘Kiyomi’ tangor, and Hyuganatsu fruits. In contrast, control fruits of Satsuma mandarin, ‘Kiyomi’ tangor, and Hyuganatsu, which had been inoculated with gray mold but had not been subjected to irradiation, showed a pronounced fungal penetration at 7 days post-inoculation. The amount of scoparone accumulation in the inoculated flavedo varied among species and with the irradiation treatment. Scoparone accumulated more rapidly and reached higher levels in irradiated ‘Kiyomi’ tangor and Hyuganatsu than in the control fruits. Interestingly, the disease incidence in the irradiated ‘Eureka’ lemon fruits was considerably lower than that in the other species. However the average radius of decay in the lemon fruits showed no decease and the levels of scoparone were far lower in both irradiated and non-irradiated fruits. We concluded that UV-C irradiation enhanced the accumulation of scoparone and increased resistance to gray mold in the other three Citrus species. These findings contribute to the decrease of the post-harvest disease caused by the fungus in some Citrus species.