Studies on the Radiation Breeding in the genus Mentha : (IX) Effective Irradiation Techniques to induce Mutation in Mint

1) The irradiation techniques to induce mutations in mint effectively were checked using chlorophyll mutants as an indicator after acute irradiation of air-dried dormant seeds, and after chronic irradiation of developing a seeds and growing buds. 2) In acute irradiation of dormant seeds, the low mutation rate and the saturation effect of the mutations at high exposure were observed showing less effectiveness of the dormant seeds irradiation. 3) In chronic irradiation of growing plants, the mutation rate per R unit was nearly constant and neither threshold exposure nor saturation effect of the mutations was observed. 4) In irradiation of developing seeds, only limited exposure may be delivered owing to severe radiation damage ; the actual number of mutants was low in comparison with those of the developing bud irradiation. 5) For increasing the number of the mutants in the X2 generation, irradiation of the developing buds was the most effective ; irradiation of the developing seeds was less effectve; and irradiation of the dormant seeds resulted in the lowest rate of mutation.