Genetic Variability, Diversity and Oil Yield Performance of Indian Mustard Genotypes under Timely and Late Sowing in Doon Valley

Background: Indian mustard (Brassica juncea L.) is a major oilseed crop of India, contributing over one-third of the nation’s total oilseed production and playing a crucial role in edible oil security, particularly across northern agro-climatic regions. However, increasing temperature variability and terminal heat stress under delayed sowing conditions pose serious threats to seed yield and oil content, necessitating comprehensive evaluation of genetic variability and diversity for developing high-yielding, heat-tolerant cultivars. Aim: The present study was conducted to assess the significance of genetic variability and diversity among genotypes of Indian mustard (Brassica juncea L.) under timely and late-sowing environments in the Doon Valley, Uttarakhand, India. Study Design: Randomized block design with 3 replications of 30 genotypes of Indian mustard. Place and Duration of Study: The field experiments were conducted at Jigyasa University during the rabi season of 2024-25. Thirty genotypes of Indian mustard (Brassica juncea L.) were sown on different dates of sowing, i.e., timely sowing on 30th October 2024 and late sowing on 30th November 2024. Methodology: Thirty genotypes were grown under uniform agronomic practices with a spacing of 70 × 30 cm. Five representative plants per genotype per replication were selected to record data on growth, phenology, physiological indices (RWC, MSI, PELWL), leaf area index at different stages, and yield attributes, including seed and oil yields, ANOVA, genetic variability analysis (PCV, GCV, ECV, hBS, GAM), and diversity analysis through cluster analysis and intra- and inter-cluster distance. Results: Analysis of variance indicated highly significant differences among genotypes for most of the traits under both sowing environments, indicating the presence of significant genetic variability. Oil content and oil yield per plant were higher with timely sowing, whereas late sowing resulted in significant reductions due to exposure to terminal heat stress during the flowering and seed-filling stages. Genotypes such as Varuna, RGN-48, RB-50, and Shivalik maintained comparatively higher oil content under late sowing, indicating relative tolerance to heat stress. Genetic variability analysis showed that phenotypic coefficients of variation were generally higher than genotypic coefficients, highlighting the influence of environmental factors, particularly under late sowing. High heritability coupled with moderate to high genetic advance was observed for several yield-contributing and physiological traits, suggesting significant gene action and the opportunity for effective selection. Genetic diversity analysis grouped genotypes into six clusters in both sowing environments, with a change in cluster composition under late sowing, suggesting interaction between genotype and environment. High inter-cluster distances indicated substantial genetic divergence, suggesting the potential use of genetically distant genotypes in hybridization programs. Conclusion: The study confirmed that timely sowing provides a more favourable environment for growth, yield, and oil accumulation in Indian mustard, whereas late sowing induces terminal heat stress that adversely affects crop performance. The identified genetically diverse and heat-tolerant genotypes offer valuable breeding material for developing high-yielding, oil-rich, and temperature-resilient mustard cultivars for stress-prone environments.