Effect of Gamma Irradiation on Growth and Determine Optimum Dose in Order to Induce Genetic Variation in landrace Rice (Oryza sativa L.) Cultivars

Mutation breeding as an alternative to conventional breeding, is commonly used to improve current varieties and to generate new varieties. Genetic variation in rice is very low, because of its self-pollination. This study, carried out to determine the GR50 dosage for an irradiation mutagenesis study on the rice and to determine the effects of gamma irradiation on germination and growth rate of rice seedlings. The elite seeds of landrace rice CVs. Anbarbo and Gerdeh after moisture regulation (11-13%) were exposed to 100, 200, 250, 300, and 350 Gy doses of gamma irradiation from 60Co and then grown under greenhouse and laboratory conditions. In both conditions, the experiment was a factorial design laid out in a completely randomized design with four replications. The results showed that the lowest values of germination parameters were observed under 350 Gy gamma irradiation. Also, the results showed that with an increase in gamma irradiation dose, the growth rate of both cultivars of rice decreased. In this respect, the decrease of growth rate has a linear relationship with the gamma irradiation dose. Results demonstrated that with increasing of gamma irradiation dose the plantlet height, survival percentage, the number and length of root and leaf in the both conditions were decreased. Gerdeh variety showed a greater degree of sensitivity to gamma irradiation than the Anbarbo variety. Based on our results, 327 and 287 Gy doses of gamma irradiation were selected for the maximum mutation in Anbarbo and Gerdeh, respectively. Finally, in both cultivars, dosages ranging from 250 to 350 Gy are recommended as the appropriate dose of irradiation to create genetic variation for mutation breeding programs.