Effect of Gamma Rays on Seed Germination, Seedling Height, Survival Percentage and Tiller Production in Some Rice Varieties Cultivated in Sierra Leone

Thirteen rice varieties cultivated in Sierra Leone were used to examine varietal differences in radiosensitivity to gamma radiation during the wet season of 2006 in the lowland ecology. Dry seeds of rice varieties were exposed to gamma radiation ranging from 50 to 800 Gy to determine their responses to radiation and the effective radiation dose for mutation breeding. Percentage germination, percentage survival (field condition), seedling height and tiller production were the traits measured on the M1 generation. The results indicated that increasing doses of gamma irradiation had no effect on germination for the first seven days under laboratory conditions. Percentage survival of germinated seedlings from the 8th to 14th day under laboratory conditions decreased significantly with increase in radiation dose up to 600 Gy. With increase in radiation above 300 Gy a reduction in seedling height and percentage survival under field conditions was observed in irradiated plants of M1 generation. Increase in gamma ray doses from 50 to 300 Gy had little or no effect on tiller production as there were no significant differences in tiller number of irradiated seeds and non-irradiated (control) for all the varieties evaluated. The LD50 values determined from regression analysis based on percentage field survival ranged from 345 Gy for ROK18 to 423 Gy for ROK22. These ranges of LD50 values determined for the different rice varieties could be useful in rice varietal improvement programmes in Sierra Leone.