Genetic analysis of agronomic and physiological traits of bread wheat (Triticum aestivum L.) using generation mean analysis under drought stress conditions and spring planting in the cold climate

Study of heritability and gene action to improve agronomic and physiological traits, especially under drought stress conditions, are very important. The objectives of this study were to investigate heritability for important agronomic traits and some physiological characters in a cross between two spring wheat cultivars. The experiment was carried out using different generations (BC1, BC2, F3, RF3) derived from crosses between two cultivars, Arg (tolerant to salinity and drought) and Moghan3, under drought stress conditions using randomized complete block design with two replications in 2014 cropping season at the University of Tabriz research station, Iran. In all plots, irrigation was withheld after antesis until the end of season. Generation mean and generation variance analyses were used to estimate gene action and genetic variance components, respectively, for agronomic and physiological traits of wheat under water deficit conditions. Based on the analysis of variance, significant differences were observed between generations for peduncle length, spike length, flag leaf width, flag leaf area, number of fertile tillers, leaf chlorophyll content, days to heading, spike weight, straw weight, biomass, grain yield and harvest index which revealed the presence of genetic differences between two parents. The generation mean analysis for the flag leaf width and flag leaf area showed that the three-parameter model was the best fit. However, for other traits chi-square of the three parameter model was significant, indicating the presence of non-allelic interactions in the inheritance of these traits. Although both types of additive and dominance effects were significant in control of the studied traits, but dominance component was larger than the additive effect. The dominance × dominance epistasis was also more important than other epistasis components for the studied traits. The broad-sense and narrow-sense heritability of the traits ranged from 0.754 to 0.941 and from 0.144 to 0.579, respectively. Estimates of variance components revealed that dominance variance was greater than additive variance for peduncle length, spike weight, straw weight, biomass, grain yield and harvest index. While, the additive genetic variance was higher than the dominance genetic variance for spike length, flag leaf width, flag leaf area, fertile tiller number, chlorophyll content and days to heading. The average degree of dominance was more than one for all of the traits which indicated the presence of over-dominance gene action in controlling these traits. Presence of non-additive genetic effects in controlling the traits showed the necessity of selection in advanced segregating generations, when populations are relatively fixed line, using bulk-pedigree method or for development of hybrid varieties in wheat, should the pollination and male sterility barriers will be overcome.