Abstract
We investigated the effect of total irradiation dose and dose rate on flower color mutation and nuclear DNA content as an index of radiation damage in chrysanthemum. Chrysanthemum morifolium cv. ‘Taihei’ plants grown by in vitro culture were gamma-irradiated with a total dose of 15, 30 and 60 Gy at a rate of 0.5, 1, 2 and 5 Gy/h. Leaf explants cut from the irradiated plants were tissue cultured, and the regeneration rates and frequency of flower color mutation were investigated. Nuclear DNA content was measured by flow cytometric analysis. The regeneration rate decreased with increase in the total dose and dose rate of irradiation. Mutation frequency did not differ significantly among dose rates, indicating that mutation frequency was independent of dose rate and was dependent mainly on total dose. Comparison of the average of the nuclear DNA content with each treatment revealed that it was influenced by both dose rate and total dose, and that the reduction in nuclear DNA content was less at low dose rates, even when total doses were high. It appears that same mutation frequencies were obtained without large reduction in nuclear DNA content by 0.5 Gy/h, when compared with 2 Gy/h. Consequently, we conclude that gamma ray irradiations of high total doses at low dose rates efficiently induce mutations with less radiation damage in chrysanthemum.
