Genotype-specific radiosensitivity and optimization of gamma irradiation dose in diverse rice germplasm using LD₅₀, GR₅₀ and multivariate analyses

Mutation breeding is an effective approach for generating genetic variability in rice, yet its success relies on determining genotype-specific radiosensitivity to avoid the dual risks of excessive lethality or insufficient mutation induction. This study evaluated the radiosensitivity and early-stage morphological responses of 21 rice germplasms representing diverse grain types, including aromatic, biofortified red-pericarp, and high-yielding varieties, under seven irradiation doses (0-600 Gy) using a ⁶⁰Cobalt gamma source. Irradiated seeds were pre-soaked and germinated under controlled polyhouse conditions in a factorial RCBD, and germination, survivability, shoot and root length, leaf number, and fresh and dry biomass were recorded. Two-way ANOVA revealed highly significant effects (p < 0.001) for dose, germplasm, and their interaction across most of the recorded traits. Radiosensitivity varied widely among germplasms, with LD₅₀ values ranging from 234.7 Gy in Rod Minikit to 790.8 Gy in Rataboro and shoot length GR₅₀ ranging from 349.7 Gy to 581.9 Gy. Tulshimala and Rataboro exhibited the highest tolerance, whereas Rod Minikit and BRAC dhan2 were the most sensitive. Dose-response curves were fitted using the four-parameter log-logistic (LL.4) model to estimate LD₅₀ and GR₅₀, highlighting genotype-specific sensitivity to irradiation. Principal component analysis illustrated clear dose-dependent separation and genotype-specific responses, with the first two components explaining 93.6% of total variance. These results highlight the importance of genotype specific radiosensitivity assessment in rice, enabling the selection of optimal irradiation doses that maximize genetic variation and seedling survival, thereby improving the efficiency of mutation breeding and providing a practical reference for future rice improvement programs.