Appraisal of variability for agro-morphological traits in M2 and M3 generation of Nigella sativa L. induced through gamma irradiation

Nigella sativa L. (kalonji or black cumin) is an economically and medicinally important seed spice in which genetic improvement is constrained by limited variability in cultivated germplasm. The present investigation aimed to broaden the genetic base of N. sativa through gamma-ray-induced mutagenesis and to characterize the resulting variability for yield and associated agro-morphological traits. Seeds of the variety Ajmer Nigella-20 (AN-20) were exposed to different doses of gamma irradiation, resulting in a progressive, dose-dependent reduction in seed germination of 6.7–78.2% relative to the untreated control. Based on germination response, 125–150 Gy was identified as the approximate LD₅₀ range and was considered suitable for generating useful mutational variability. Evaluation of the M₃ generation revealed substantial enhancement in the mean performance of major yield-contributing traits, with increases of 4.6% for plant height, 13.8% for total branches plant⁻¹, 16.8% for capsules plant⁻¹, 35.8% for locules capsule⁻¹, 21.5% for seeds capsule⁻¹, 14.8% for seed yield plant⁻¹, and 28.9% for 1000-seed weight over the untreated control. The coefficient of variation ranged from 14.7% for 1000-seed weight to 24.6% for locules capsule⁻¹, confirming considerable induced variability and the potential for effective selection. A distinct macro-mutant, AN-20/150/126, was identified in the M₂ generation, exhibiting complete absence of the gynoecium and a marked floral phenotype with numerous greenish-yellow petals, in contrast to the five white petals of the parental type. Further evaluation of 45 selected M₄ progenies demonstrated substantial variation for yield-associated traits. Correlation analysis revealed significant positive associations of seeds capsule⁻¹ with locules capsule⁻¹ (r = 0.69) and seed weight capsule⁻¹ (r = 0.52), while 1000-seed weight exhibited a significant negative association with locules capsule⁻¹ (r = −0.66). Seeds locule⁻¹ also showed a significant negative association with locules capsule⁻¹ (r = −0.55). Collectively, these relationships indicated that 6–7 locules capsule⁻¹ may represent an optimum phenotypic range for achieving a favourable balance between seed number and seed weight. The findings demonstrate that gamma-ray mutagenesis is an effective approach for broadening genetic variability in N. sativa and provide promising mutant material and selection criteria for the development of high-yielding genotypes.