Journal of Advances in Biology & Biotechnology

Brassica juncea L. (Indian mustard) is a major rabi oilseed crop with a pivotal role in India’s edible oil economy, necessitating continuous genetic improvement for higher yield and quality traits. Therefore, the present study employs Line × Tester analysis to evaluate combining ability and gene action, aiming to identify superior parents and cross combinations for the development of high-yielding and resilient mustard cultivars. The study was conducted during the rabi season of 2025–26 at the Agricultural Research Farm of the Department of Genetics and Plant Breeding, Lovely Professional University, Phagwara, Punjab, India. A total of 40 genotypes comprising 12 parents (9 lines and 3 testers), 27 F₁ hybrids, and one check were evaluated in a randomized block design. Analysis of variance revealed significant differences among genotypes, parents, and crosses for all traits, revealing substantial genetic variability and heterotic potential. Combining ability analysis revealed that both general combining ability (GCA) and specific combining ability (SCA) variances were significant for most traits, suggesting the involvement of both additive and non-additive gene actions. Additive gene action was predominated for traits such as days to 50% flowering, plant height, and siliqua-related characters, while non-additive gene action was more important for biological yield, seed yield, and harvest index. Among the parents, JD 6 and 45 S 46 emerged as superior general combiners among lines, while RK GOLD was identified as the best tester for yield and its components. Crosses such as HYOLA ADV 40 × RK GOLD, 45 S 46 × RK GOLD, JD 6 × RK GOLD, and NRCH-B1 × GSC 07 exhibited high SCA effects and were identified as promising hybrids. High heritability and predictability ratios for several traits indicated the effectiveness of selection, whereas traits governed by non-additive effects can be exploited through heterosis breeding.