Effect of Ultraviolet-B Irradiation on Disease Development Caused by Penicillium italicum in Satsuma Mandarin Fruit

Abstract

Blue mold (Penicillium italicum) is the primary postharvest pathogen affecting citrus fruit. In the present study, we investigated the effect of ultraviolet (UV-B) irradiation on blue mold, and the influence of UV-B on the internal fruit quality and peel color of satsuma mandarin. All UV-B doses examined (15, 30, 60, and 120 kJ·m⁻²) had inhibitory effects on P. italicum growth in vitro (reduction of spore germination > 99%). Additionally, we examined the disease incidence, the soft rot (water soaked) area diameter, and the mycelium (mycelial growth inside soft rot area) area diameter of Citrus unshiu Marc. ‘Aoshima unshu’, which was treated by UV-B irradiation 24 h before or after inoculation at two different harvest periods．The diameter and incidence of soft rot areas were not significantly reduced by UV-B irradiation at 5 days after inoculation. However, a UV-B dose of 60 kJ·m⁻² reduced the diameter of mycelial growth on fruit for 5 days after inoculation, at both early and commercial harvests. At early harvest, UV-B irradiation at doses of 30 kJ·m⁻² and 60 kJ·m⁻² was effective at reducing the incidence of mycelial growths, regardless of whether irradiation occurred 24 h before inoculation or whether inoculation occurred immediately prior to UV-B irradiation. UV-B irradiation did not affect fruit quality with respect to soluble solid concentration, titratable acidity, or peel color. Although UV-B irradiation did not significantly control disease development in inoculated fruit, our results indicate that it might be effective by directly inactivating fungi and inducing an antifungal response in satsuma mandarin fruit.