Mode of inheritance of low-N tolerance adaptive traits in wheat (Triticum aestivum L.) under contrasting nitrogen environments

Because of essential economic and ecological concerns, there is increased interest worldwide in developing wheat cultivars that are more efficient in utilizing nitrogen (N) and better suited to N limitations. The objective of the present investigation was to get information on the type of gene action controlling the inheritance of wheat low-N tolerance traits in order to start a breeding program for improving such traits. Six parents of contrasting low-N tolerance were crossed in a diallel fashion. Evaluation of 6 parents, 15 F(1)crosses and 15 F-2 crosses was done using a randomized complete block design with three replications under two levels of soil N, i.e. low-N (0 kg N/ha) and high-N (180 kg N/ha). The magnitude of dominance variance in F-2's for all studied traits was much greater than that of additive variance under both high N and low N, suggesting that selection should be postponed to later segregating generations in order to eliminate masking effects of dominance variance and take advantage of the additive variance for the improvement of nitrogen use efficiency and grain yield traits. Narrow-sense heritability (h(2)n) in F-2's was generally of higher magnitude under low-N than high-N, suggesting that it is better to practice selection for studied nitrogen efficiency and grain yield traits under low-N conditions to obtain higher values of selection gain.