Effects of gamma ray dose rate and sucrose treatment on mutation induction in chrysanthemum

Gamma rays are useful to develop new cultivars for mutation breeding, in which the total dose and dose rate are important. On two chrysanthemum cultivars, 'Noble Wine' and 'Pinky, were tested the effect of the dose rate. Four weeks after irradiation, their survival rate and plant height were significantly decreased at the dose rate 30 Gy/1 h. The dose rate 30 Gy/4 h produced the highest mutation frequency in both cultivars, with a wide mutation spectrum. Moreover, sucrose is known as stimulus of anthocyanin biosynthesis. For the induction of anthocyanin related flower-color mutants, we pre-treated 4-week-old plants with 100, 200 and 300 mM sucrose before gamma irradiation. The cultivar 'Pinky' showed a high survival rate in all treatments; while almost all 'Noble Wine' plants treated with 200 and 300 mM sucrose died. A number of mutated branches were identified at 100 mM sucrose + 30 Gy/24 h of irradiation in the cultivar 'Noble Wine. Thus, a proper dose rate of gamma rays and sucrose pre-treatment could induce flower color mutation in chrysanthemum.