Combining ability, gene action and heterosis studies for yield improvement in rapeseed (Brassica napus L.)

Rapeseed (Brassica napus L.) is a key oilseed crop in Bangladesh, yet its yield remains below the global average. This study investigated combining ability, gene action, and heterosis for yield and related traits using a 5 × 5 full diallel among five parental lines. Significant genotypic variation was observed across all seven traits, confirming broad genetic diversity. Specific combining ability variance (σ2sca) exceeded general combining ability variance (σ2gca) for all traits, with σ2A/σ2D ratios below unity, confirming the predomination of dominance effects. Among the parents, NAP-0721-1 and BD-10109 emerged as strong general combiners for yield and its components. The hybrids BD-6951 × BD-7118 and NAP-0724-2 × NAP-0721-1 showed favorable GCA of parents, strong SCA effects, and superior per se performance for seed yield per plant (SY/P). Heterosis breeding proved effective, with crosses such as NAP-0724-2 × NAP-0721-1, NAP-0724-2 × BD-7118, and BD-10109 × NAP-0724–2 exhibiting significant positive heterosis over mid-parent, better-parent, and check variety means for SY/P. Overall, the findings provide critical insights into the genetic control of yield-related traits in B. napus, supporting targeted breeding strategies for yield enhancement and hybrid development.