American Research Journal of Agriculture

Breeding wheat (Triticum aestivum L.) cultivars with improved adaptation to low-N fertilization has gained importance worldwide. This study aimed at investigating the per se performance of nitrogen use efficiency traits, the relative importance of general (GCA) and specific (SCA) combining ability in a set of wheat cultivars and promising lines and their F1 diallel crosses. Parents (6) and F1's (15) were evaluated in in two seasons in two separate experiments using randomized complete block design with three replications; each experiment under one level of N ( 0 or 75 kg N/fed). Results across seasons showed that the rank of crosses in F1 generation for most studied traits was changed from one environment (N-level) to another, indicating a significant G x N interaction. In general, means of NUE, and NUPE of the three parents L25 , L26 and L27 were higher in magnitude than those of the three other parents Gem 7, Gem 9 and Giza 168 under both high-N and low-N levels. Both GCA and SCA mean squares were significant, but the magnitude of GCA was higher than SCA, for all studied traits under the two levels of N, except GPC under low-N, suggesting the existence of a greater portion of additive than that of non additive genetic variance in controlling the inheritance of these traits under the two levels of nitrogen. In general, the best general combiners in F1's for NUE and NUPE were L26 followed by L27 and L25 parents under both high-N and low-N. Under low–N conditions, the best SCA effects were shown the by F1's L25 x Gz168 for NUE and NUPE, L2 x Gem9 and L27 x Gem9 for NUPE and L25 x L 26, L25 x L27 and L27 x Gem9 for NUTE trait. Results indicate that under both N-levels, the best performing parents for grain yield and nitrogen use efficiency and their components are also the best general combiners and vice versa. But under high-N only, the mean performance of a given F1 cross could be considered an indication of its SCA effects.