Mode of Inheritance of Nitrogen Efficiency Traits in Wheat (Triticum aestivum L.) F2 Diallel Crosses under Contrasting Nitrogen Environments

Abstract

There is an increased interest worldwide in developing wheat cultivars that are more efficient in utilizing nitrogen (N) and better fitted to N limitations. The objective of this investigation was to study the effects of contrasting soil N levels on the genetic parameters controlling the nitrogen use efficiency (NUE) components in bread wheat. Parents of contrasting low-N tolerance and their diallel F2 hybrids were evaluated in two seasons under varying levels of soil N, i.e. low-N (0 kg N/fed) and high-N (75 kg N/fed) using a randomized complete block design in three replications. Results of analysis of combining ability across seasons showed that variances due to both general (GCA) and specific (SCA) combining ability were significant for all studied nitrogen efficiency traits. Under low-N, the best general combiners were L25 and L26 for NUE and nitrogen uptake efficiency (NUPE) and L27 for NUE and the best F2 cross for SCA effects was L25 x Gem 7 for two traits (NUE and NUPE), L25 x L27 and L26 x Gem 9 for NUPE. The magnitude of dominance in F2's was much greater than that of additive variance for all studied traits under both high N and low N, suggesting that selection methods that eliminate masking non-additive effects and take advantage of the additive variance should be employed to improve NUE traits under low-N and high-N environments. The average degree of dominance in F2's was in the range of partial dominance for all studied traits under the two levels of nitrogen, except for NUTE and nitrogen harvest index (NHI) under high N, which indicated over dominance and NHI under low-N, which indicated no dominance. Narrow-sense heritability (h2n) in F2's ranged from 2.11% (NHI) to 42.64% (NUE) under high-N and from 6.80% (NHI) to 85.00% (NUE) under low-N, suggesting that it is better to practice selection for studied nitrogen efficiency traits under low-N conditions to obtain higher values of selection gain.