Appraising LD50 dosage for physical mutagen (Gamma rays) in CR1009 and CR1009 sub1 rice varieties

Present study was aimed to identify the early heading plant types for late maturing rice varieties viz., CR1009 and CR1009 sub1 in order to save resources like irrigation water, fertilizer, labour cost. Mutation breeding was selected as an appropriate breeding methodology to alter the late heading types in CR1009 and CR1009 sub1 rice varieties besides keeping intact of original characteristics. To carry out the successful mutation programme in any of the crop, standardisation of LD50 (Lethal Dosage) is the necessary first step. The LD50 was estimated using probit analysis based on seedling germination of control and their treated ones (100 Gy, 200 Gy, 300 Gy and 400 Gy). Results revealed that the rice variety CR1009 was sensitive to radioactivity exposure with LD50 value 152.52 gray compared to CR1009 sub1 (284.77 Gray). There was a definite relationship for both shoot length and root length in M1 population in relation to dosage. In the variety CR1009, the dosage 200 gray exhibited highest value for both shoot (18.84cm) and root length (5.68 cm) among other treatments. Similarly, the dosage 400 gray recorded lowest value for shoot (7.42 cm) and root length (2.84 cm) in CR1009. Whereas in CR1009 sub1 variety, the highest and lowest value for shoot and root length was noticed in the dosage of 100 gray and 300 gray respectively.