Response of Performance and Combining Ability of Wheat Parents and Their F2 Progenies for N Efficiency Traits to Reducing N-Fertilizer Level

Because of high production cost of nitrogen (N) fertilizer and prevention of environmental pollution, it is important to improve N use efficiency (NUE) of wheat (Triticum aestivum L.).The objective of this study was to evaluate NUE traits of 6 x 6 diallel wheat F 2 progenies and parents at low (LN, no N fertilizer) and high (HN,75 kg N/fed) N levels.Two experiments were conducted during two seasons, the 1 st under HN and the 2 nd under LN using RCBD in three replications.Data analyzed across seasons indicated that L25, L26 and L27 showed high values of nitrogen use (NUE) and uptake (NUPE) efficiency and the best general combining ability (GCA) effects for these traits.The best F 2 crosses in per se performance and specific combining ability (SCA) effects were L26 x Gz168, L27 x Gem7, L26 x L27 and L25 x Gz168).Mean squares due to both GCA and SCA were significant under both low-N and high-N for all NUE components, but the magnitude of GCA was greater than SCA, indicating that additive is more important than non-additive genetic variance in controlling the inheritance of NUE, NUPE, nitrogen utilization efficiency (NUTE) and nitrogen harvest index (NHI) traits.The results indicated that under low-N and high-N, the mean performance of a given parent is an indication of its general combining ability and the mean performance of a given F 2 cross is an indication of its specific combining ability effects for all studied NUE components.