Response of the Gene Actions Governing Grain Yield and Quality Traits in Wheat Parents and Their F1 Progenies to Decreasing Soil-N Rate

To start an accurate wheat breeding program for improving low-N tolerance, information on the type of gene action controlling the inheritance of grain yield and quality traits under contrasting N environments should be available, which is the objective of the present investigation. The diallel crosses (except reciprocals) among six divergent parents in low-N tolerance were made. Parents and F1 crosses were evaluated in two seasons under two N environments; namely 0 kg N/fed (low-N) and 75 kg N/fed (high-N) in two separate experiments using a randomized complete block design with 3 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 yield and quality traits, indicating the involvement of additive and non-additive types of genes in controlling these traits. Parents and F1 crosses thus have different GCA and SCA effects, respectively. The best general combiners with positive effects for improvement of low-N tolerance were L26, L27 and L25 parents. Under low–N conditions, the best specific combinations for improvement of low-N tolerance were L25 x Gz168, Gem9 x Gz168 and Gem7 x Gem 9. Hayman analysis of variance indicated that spikes/plant (SPP), grains/spike (GPS), harvest index (HI) and grain yield/plant (GYPP) were controlled by additive and non-additive types of gene action, while 100 grain weight (100 GW) was controlled by an additive type of gene action. A high narrow sense heritability estimate was observed for GYPP (66.32%), SPP (42.52%), 100 GW (33.11%) and GPS (21.80%) under low-N.