QUANTITATIVE GENETIC EVALUATION OF PARENTAL LINES THROUGH COMBINING ABILITY AND HYBRID VIGOUR IN BRASSICA NAPUS

Background: Rapeseed (Brassica napus L.) remains a vital oilseed crop globally, yet local production in many regions, including Pakistan, falls short of rising edible oil demand. Hybrid breeding offers an effective pathway to improve yield and related agronomic traits, but its success relies on understanding the genetic contributions of parental lines. Combining ability and heterosis analyses provide essential insights into additive and non-additive genetic effects, enabling breeders to identify superior parents and productive cross combinations. Objective: To evaluate the general combining ability (GCA), specific combining ability (SCA), and heterosis of Brassica napus genotypes for plant height, primary and secondary branches, 1000-seed weight, and seed yield per plant using a structured line × tester approach. Methods: Five female lines and three male testers were crossed during the 2022–23 season to generate fifteen F₁ hybrids. These hybrids, along with their eight parents, were evaluated the following season under a randomized complete block design with three replications. Data from five quantitative traits were subjected to analysis of variance, followed by estimation of GCA and SCA based on established line × tester procedures. Mid-parent and better-parent heterosis were calculated to assess hybrid vigor. Results: Highly significant differences were observed among treatments for all traits, confirming substantial genetic variability. Parent vs. cross differences were significant for all traits except plant height. The line × tester interaction was significant for all traits. Additive genetic effects predominated for plant height, branching traits, and 1000-seed weight, whereas seed yield was more strongly influenced by non-additive effects. Several hybrids displayed strong positive SCA and expressed significant positive heterosis over the better parent for seed yield, indicating strong hybrid potential. Conclusion: The study identified valuable parental lines and promising hybrid combinations suitable for future rapeseed improvement. The results highlight the effectiveness of line × tester analysis in distinguishing superior combiners and support the development of high-yielding Brassica napus hybrids.