ABSTRACT
Breeding wheat cultivars with improved adaptation to low soil-N, has gained importance worldwide in order to decrease N fertilizer consumption and overcome the ecological and economic problems of the misuse of this fertilizer. Identification of wheat crosses that show useful heterosis (heterobeltiosis) is an important issue in breeding programs. The main objective of the present investigation was to estimate heterobeltiosis for nitrogen use efficiency and other studied traits of F1 diallel crosses among six wheat parents in order to identify the superior ones for future use in breeding programs. Genetic materials were evaluated at two seasons (2007/2008 and 2008/2009) in a split-plot design with randomized complete block arrangement, using three replications. Main plots were assigned to N levels (0 and 75 kg N/fed), while sub plots were devoted to genotypes. Data combined across the two seasons were presented. In general, low N caused a significant reduction in 9 out of 14 studied traits. These reductions were relatively high in magnitude for number of spikes/ plant (SPP) for parents (23.65%) and F1's (23.99%). On the contrary, low–N caused increases in the averages of nitrogen use efficiency (NUE) by 89.5 and 97.60% for parents and F1's, respectively. Averages of heterobeltiosis for all studied characters were either nonsignificant or significant but non favorable, except for plant height under both low and high N, NUPE under high N and GPS under low N. However, some crosses for each trait showed significant and favorable heterobeltiosis. Under low–N, the highest favorable and significant heterobeltiosis estimate was shown by L27 x Gem 7 for GYPP (14.94%), NUTE (44.81%) and GPS (25.82%), L25 x L26 for 100 GW (13.87%), L 25 x L 27 for SPP (12.53%), L 27 x Gem 9 for GPS (26.19%) and Gem 7 x Gem 9 for BYPP (28.99%).