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.

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.

In the present study, we examined the effect of blue LED irradiation on production of phytoalexin scoparone in wounded satsuma mandarin fruit as a result of fungal infections, as well as the effect of tape-type blue LED on fruit decay during long-term storage (from December to April) in an actual storage room. The blue LED treatment reduced the rate of fruit decay compared to that of dark treatment in wounded fruits. The decay rate of LED irradiated fruit was 13.3%, while that of non-irradiated fruit was 51.1%. In wounded fruits, blue LED treatment resulted in significantly higher scoparone contents than dark treatment. Intact (non-wounded) fruits had low scoparone contents, irrespective of blue LED irradiation. In an examination of changes in total fruit decay rate during storage using tape type-blue LED, the total decay rate was not significantly different between the LED-treated and untreated fruits until 64 days after storage (36 days after starting LED irradiation). On the other hand, at 92 and 120 days after the start of storage, total fruit decay under blue LED treatment was significantly lower compared to the untreated control. The tape-type blue LED (10 μmol·m −2 ·s −1 ) did not affect either the fruit quality analyzed (soluble solid content, titratable acidity, specific gravity, percentage of flesh) or the rind color. These results indicate that blue light induces scoparone production in wounded satsuma mandarin, and because of this, along with other putative factors, tape-type blue LED irradiation reduces mandarin fruit decay during long-term storage.

Here, we investigated the effect of irradiation by a low-intensity red light-emitting diode (LED) (photon flux μmol•m_ 2 •s _ 1 ) on rind color development in Satsuma mandarins after harvesting at two different periods. In the early harvest fruit, the a* value for Satsuma mandarin peel treated by red LED irradiation was 2.7 and 2.4 times higher than that for the dark treatment fruit at 4 and 8 days irradiation, respectively. In the commercial harvest fruit, the a* value of the peel treated by red LED irradiation was 1.2 and 1.4 times higher than for dark treatment at 4 and 8 days irradiation, respectively. Additionally, we examined the influence of red LED irradiation on the internal fruit quality of Satsuma mandarins from the two harvest periods. Low-intensity red LED irradiation did not affect fruit quality. We elucidated the effect of intermittent red LED irradiation on the change in a* value of mandarin fruits. These results indicated that treatment with low-intensity red LED irradiation is sufficient to develop a degree of rind color in mandarins without affecting the internal fruit quality.Keywords: citrus, fruit quality, postharvest, rind color, red light, storage IntroductionThe peel color of Satsuma mandarin fruits is an important factor in customer satisfaction. In recent years, fruits with a low level of coloration despite the degree of flesh maturation have been shipped; this type of fruit development occurred because high fall temperatures caused the flesh to ripen while some green coloration remained in the peel.Satsuma mandarin production is faced with challenges due to global warming (Sugiura and Yokozawa, 2004;Sugiura et al., 2007). One impact of global warming on fruit cultivation is the occurrence of rind puffing. Therefore, it has become increasingly common for growers to treat fruit with gibberellic acid and prohydrojasmon mixtures (hereafter, GP solutions) three months before harvesting, as a method to reduce rind puffing (Makita and Yamaga, 2006;Nakatani et al., 2014). However, treatment with GP solutions is problematic, as gibberellin delays coloration (Porat et al., 2001), and interested parties are keen to find a method that simultaneously solves issues related to both rind puffing and coloration delay. The ability to improve coloration through some type of fruit processing would increase its marketability. In Japanese citrus fruit production areas, mulching the ground with light-reflective, non-woven fabric sheets during cultivation has been embraced as a means of improving coloration and increasing sugar content (Morinaga et al., 2004;Muramatsu et al., 2005). In addition, in the past there have been many studies on methods of improving fruit coloration during post-harvest storage. High-temperature pretreatment, in which the fruit is maintained at 15 _ 20℃ for a week, has been brought into practical use (Murata and Yamawaki, 1992). However, this treatment involves the extended use of heaters (at least 8 days), and improved technology is being sought to reduce costs. In addition, severa...