Combining ability of yield attributes traits, oil and protein contents in oil seed rape (Brassica napus) under normal and restricted nitrogen application

Abstract

Combining ability of yield associated traits has been studied quite frequently in oilseed rape (Brassica napus L.) but it was hardly ever studied based on nitrogen levels variations. Six parents along with their 15 F2 half diallel crosses were evaluated in two nitrogen (N) levels including N0 and N+. Analysis of variance revealed significant mean squares of general and specific combining abilities (GCA and SCA) for all the traits studied. The high narrow-sense heritability estimates were found for seed yield and harvest index, implying the more importance of additive genetic effects for and consequently high selection efficiency for improving these traits. Due to low narrow-sense heritability estimates for oil and protein contents and therefore more importance of non-additive genetic effects, selection for improving these traits should be done in later segregating generations. The GCA × N level interaction was significant only for oil content which is indicating of more differences of GCA effect of this trait at two nitrogen levels. Significant N × SCA effect mean squares for harvest index and oil content, revealed significant variation of SCA effects of these traits in nitrogen levels application. Most of the crosses with high seed yield at N0 and N+ had at least one parent with positive GCA effect at both N levels. Among the six parents, PF7045/91 appeared to be the best combiner for seed yield at the N0. This variety also showed high GCA at the N+ but its low oil content at the N+ is certainly disadvantageous as the quality of the hybrid is often intermediate between the two parents.