Estimation of Genetic Components and Inheritance of Bread Wheat Agronomic Traits Using Regression Method Through Generation Mean Analysis

Studying the genetic structure of crops, including wheat, has always been one of the research priorities to increase the efficiency of breeding methods. In order to genetic analysis of some agronomic traits of bread wheat using generation mean analysis (GMA), all produced generations along with relevant parents of the two populations (Marvdasht × Rasoul and Marvdasht × Shahpasand) were evaluated in a randomized complete block design with three replicates under normal and terminal drought stress conditions in Razi University during 2015-2016 cropping season. Weighted analysis of variance showed the significant differences among generations for the most of the traits in two conditions. The results of GMA revealed that although the mode of inheritance differed in the crosses for the most of the traits, but additive, dominance gene effects and different types of epistasis had the roles in the heritability of the most traits. Among these gene effects, the role of dominance gene effect was higher and therefore, selection should be delayed to later generations. However, the role of fixable gene effects in the heritability of the traits such as stem diameter, awn length and number of spikelets per spike (both crosses), plant height and peduncle length (Marvdasht × Shahpasand), was almost equal or more than dominance gene effect indicating the usefulness of selection in early generations for these traits. The broad-sense heritability for kernel yield was estimated as nearly moderate for both crosses under both conditions, but the narrow-sense heritability was low under both conditions. Results of analysis of variance obtained from regression method showed that fixable-gene effects had higher relative contribution of generation sum of squares for most of the traits than non fixable-gene effects at both crosses under both conditions. The model of genetic control for the most of the traits was similar under both conditions for both crosses and it has not been widely affected by drought stress.