Broadening the genetic horizon of rice: comparative insights from gamma radiation and EMS-induced mutagenesis

BACKGROUND: Genetic uniformity in elite Basmati rice cultivars limits yield improvement and adaptation to changing agro-climatic conditions. Induced mutagenesis using physical and chemical agents provides an effective strategy to generate novel heritable variation. This study the efficiency of gamma irradiation (137Cs) and ethyl methanesulfonate (EMS) in inducing genetic variability and improving yield-related traits in rice. RESULTS: Seeds of Super Basmati and Noor Basmati were treated with gamma rays (150-300 Gy) and EMS (0.25-1.25%) and evaluated across M₁-M₄ generations. Both mutagens caused dose-dependent reductions in germination, seedling growth, and panicle fertility, with Noor Basmati exhibiting higher sensitivity. Root length was reduced by 45.17% at 200 Gy and 52.96% at 0.50% EMS in Noor Basmati. Estimated LD₅₀ values for panicle fertility were 267 Gy (Noor) and 274 Gy (Super) under gamma irradiation, and 0.68% and 0.70% under EMS, respectively. Large-scale selection from M₂ resulted in 4,157 promising mutants, which were progressively narrowed to 753 stable M₄ progenies. Mean grain yield per plant increased by 23.63% in M₄ compared with M₃, with the highest gain (32.5 g plant⁻¹) observed in Noor Basmati treated with 0.25% EMS. 1000-grain weight and tillers per plant increased by 27.19% and 10.38%, respectively. High heritability (>90%) with substantial genetic advance was recorded for tillers per plant and 1000-grain weight. Multivariate analyses identified these traits as the primary contributors to yield enhancement, and Cluster analysis grouped M₄ mutants into three clusters, with 406 progenies as high-yielding. CONCLUSIONS: Gamma irradiation and EMS effectively broadened the genetic base of Basmati rice and enabled significant, stable yield improvement through targeted selection. The identified high-yielding mutant lines represent valuable genetic resources for rice improvement and future functional and genomic studies.