2019 Volume 63 Issue 4 Pages 204-209
We studied the use of ultraviolet (UV-C) irradiation to suppress blue mold and promote accumulation of scoparone, which is associated with decay resistance in satsuma mandarin (Citrus unshiu Marc.) ‘Aoshima unshu’ fruit. UV-C irradiation (3.6 kJ∙m-2 and 6.0 kJ∙m-2) at 24 h prior to inoculation of fruits with blue mold reduced the incidence of soft rot and sporulation at 4 days after inoculation. Further, UV-C irradiation at 6.0 kJ∙m-2 reduced mycelium and sporulation areas at 4 and 5 days after inoculation. Concomitantly, UV-C irradiation at 6.0 kJ∙m-2 induced the accumulation of scoparone in flavedo tissue (98.8 μg∙g-1 FW) at 8 days after irradiation, and even at 20 days after irradiation, the concentration of scoparone was 87.8 μg∙g-1 FW. Finally, using uninoculated fruits, we tested the efficacy of UV-C irradiation for control of fruit decay caused by naturally occurring infections. Total disease incidence of blue and green molds under UV-C treatment was lower than that in controls at 8 and 17 days after irradiation. In the latter case, total disease incidence of blue and green molds among controls was 27.1%—about twice the incidence observed under UV-C treatment. This indicated that UV-C irradiation induced the production of scoparone as a defensive measure against fungal development in the flavedo tissue of satsuma mandarin fruits, while UV-C at 6.0 kJ∙m-2 effectively suppressed the rate of decay caused by natural fungal infections.
