Radio-sensitivity test informs the optimal irradiation dose for use in mutation breeding. In this study, four rice varieties (Basmati 217, Basmati 370, ITA310, and Komboka) were irradiated with gamma-ray doses ranging from 0 to 500 Gy, to examine their morphological responses at the seedling stage, and estimate their optimal doses. Two experiments were carried out at varied time points between March and May 2022. In the first experiment, the irradiated seeds were pre-germinated before sowing in soil premixed with base fertilizer, while in the second experiment, irradiated seeds were imbibed by soaking in water for 24 h followed by direct sowing in soil. Observations were made on germination percentage, rate of seedling emergence, survival, and seedling height. The results indicated that sensitivity to gamma irradiation varied across varieties. Basmati 370 and Komboka were the most sensitive, ITA310 was moderate, while Basmati 217 was the least sensitive. At low doses of 50, 100, and 150 Gy, gamma irradiation enhanced seedling survival and height, but at higher doses above 300 Gy, they were significantly reduced. LD50 values ranged from 354 to 556 Gy, reduction dose 30 (RD30) ranged from 267 to 426 Gy, while reduction dose 50 (RD50) ranged from 335 to 531 Gy.
Key words: Mutation breeding, radio-sensitivity, LD50, RD30, RD50, gamma irradiation.
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