In order to study the inheritance of nitrogen use efficiency (NUE) traits as indicators of low-N tolerance in bread wheat, plants from a six-parental diallel cross, excluding reciprocals, were grown in the field for two seasons using a randomized complete block design with three replications in two separate experiments; the first under no N fertilization, i.e. 0 kg N/fed (low-N) and the second under fertilization rate of 75 kg N/fed (high-N). Results across seasons showed that variances due to both general (GCA) and specific (SCA) combining ability were significant for all studied nitrogen use efficiency traits, except nitrogen harvest index (NHI) under low-N. The best general combiners for improvement of NUE and nitrogen uptake efficiency (NUPE) under low and high N were L26, L27 and L25 inbreds. Under low–N conditions, the best specific combinations for improvement of low-N tolerance were the F1’s L25 x Gz168 for NUE and NUPE, L2 x Gem9 and L27 x Gem9 for NUPE and L25x L 26, L25 x L27 and L27 x Gem9 for nitrogen utilization efficiency(NUTE) trait. Hayman’s analysis indicated that NUE, NUPE, NHI and NUTE are controlled by additive and non-additive types of gene action. The magnitude of dominance was much greater than additive (D) component for all studied traits in F1’s under both high-N and low-N, except for NUE trait under low-N, where the opposite was true. High narrow-sense heritability estimate was observed for NUE (66.90%) and NUPE (46.36%) under low-N. Expected genetic advance from selection under low-N was much higher than under high-N for all NUE traits, especially for NUPE. Under low-N, the inbreds L25, L26 and L27 had more than 75% dominant genes of NUPE.
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