Linked epistasis for six quantitative traits in Indian mustard (Brassica juncea (L.) Czern & Coss)

Gene effects, and interactions, and associations between days-to-flower initiation and maturity, number of secondary branches and siliquae per plant, and 1,000-seed weight and yield per plant were studied in a cross of Indian mustard (Brassica juncea (L.) Czern & Coss) using the parents and F1, F2, F3, B1, B2, B11, B12, B21, B22, B1S, B2S, B1F1, B2F1, B1bip, B2bip, F2P1, F2F1, and F2bip generations. A linked digenic model was adequate for all characters studied. According to this model, the main effects, additive and interactions between linked pairs of genes, were present in varying proportions for days-to-flower initiation and maturity and number of siliquae per plant. The contribution of linked epistatic effects, however, was much greater than that of additive effects. Dominance effects contributed significantly to the inheritance of days-to-flower initiation. Duplicate epistasis was observed for all traits except 1,000-seed weight where epistasis was of the complementary type. A complete association among the genes of similar effect (increasing or decreasing) was observed for number of secondary branches and siliquae, and yield per plant. Coupling phase linkage was observed for days-to-flower initiation whereas repulsion phase linkage was observed for daysto-maturity and 1,000-seed weight.