Effects of delay between harvest and irradiation and of storage temperatures on the sprout-inhibition of onions by gamma irradiation

Senshu-ki onions were irradiated at the ranges of 1-15 Krad. Gamma irradiation at the doses of 7 and 15 Krad inhibited almost completely the sprouting of onions which were irradiated on the 20th day after harvest and after 11/8 months of storage at 0°C before irradiation. In onions which were irradiated at the doses of 7 and 15 Krad after 31/3 months of storage at room tem- perature, there was found considerable sprouting, showing approximately 50% of sprouting. Even when irradiation was carried out about 2 months after harvest, a dose of 5 Krad was sufficient to prevent sprouting during subsequent storage at room temperature. Onions irradiated at a dose of 1 Krad and stored at room temperature sprouted during the storage but showing thin sprouts, whereas in the onions of 1 Krad stored at 6°C after irradiation subsequent sprouting was prevented sufficiently. Irradiation up to 15 Krad did not affect the rates of weight loss and rotting of onions until the unirradiated onions sprouted. There were found the dead cells (darkened area) in both inner buds and disks in early stage of the injury of irradiated onions. The inner buds (or internal sprouts) in sprout-inhibited onions by irradiation darkened during subsequent storage.