Comparative study of radio-sensitivity and relative biological effectiveness of gamma rays, x-rays, electron beam and proton beam in short grain aromatic rice

Knowledge about the type of mutagen used and its optimized dose are of paramount importance to design and implement any plant mutation breeding programme. Present study was first time carried out to evaluate the comparative effectiveness, radio-sensitivity behavior and relative biological effectiveness of four physical mutagens viz., gamma rays, X-rays, electron beam and proton beam on two short grain aromatic rice landraces viz., Samundchini and Vishnubhog. The seeds of these two varieties were treated with 15 different doses of all four mutagens, ranging from 50Gy to 750Gy with an interval of 50Gy. Germination percentage and seedling growth parameters were recorded at seven and 15 days after sowing, respectively in two replications. It was observed that germination percentage, shoot and root length of the seedling gradually declined with the increase in doses of all the physical mutagens. On the basis of these observations, LD50 and GR50 doses were calculated. The present study reports the optimum range of doses for gamma ray (280 to 350 Gy); electron beam (290 to 330Gy); X-ray (200 to 250 Gy) and proton beam (150 to 200Gy). GR50 doses were observed higher than LD50 doses for all the mutagens in both landraces. However, Samundchini showed higher LD50 and GR50 doses than Vishnubhog indicating later to be more radio-sensitive. Furthermore, both the genotypes were highly radio-sensitive for proton beam and least for gamma rays. Similarly, high relative biological effectiveness was observed for proton beam followed by X-ray, electron beam and gamma rays indicating their decreasing trend of penetration capacity and lethality. Results of present study will be useful for plant breeders to use the above mutagens in an appropriate dose for mutation breeding in rice.