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The antifungal effect of blue LED (light emitting diode: maximum emission wavelength 465 nm, 80 µmol・m -2 ・s -1 ) irradiation on the blue mold, Penicillium italicum, in satsuma mandarin (Citrus unshiu Marc.) fruits after harvesting was investigated. Blue LED irradiation for 6 days after inoculation with Penicillium italicum significantly reduced symptom development in the fruits compared to that observed with dark treatment. The sporulation and mycelium area were markedly reduced by blue LED irradiation. On the other hand, blue LED irradiation for 6 days before inoculation reduced symptom development when the inoculum dose was low. Blue LED irradiation did not affect the fruit quality, except for the citric acid concentration and moisture loss. These results indicate that blue light irradiation could directly inhibit fungal growth in satsuma mandarin fruits and induce an antifungal response against the blue mold.

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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

the most pronounced inhibitory effect was exerted on P. italicum sporulation. These results show that treatment with low-intensity blue LED irradiation is sufficient to reduce blue mold symptom development and is a promising safe approach to control postharvest spoilage in mandarin fruit.