Introduction: The first step in the breeding of agricultural traits is to have sufficient information about genetic parameters such as the mode of inheritance and the way genes work for traits. One of the most suitable methods for calculating genetic parameters is the method of analyzing the average of generations due to the low error calculation. The interpretation of the method of analysis of the average of generations determines the gene effects, which are actually the result of all the gene loci that are diverging. This means that the additive effects as well as the reciprocal effects in connection with these effects are a function of the degree of dispersion of the genes increasing the traits between the parents in the Study, if the dominance parameters result in the direction of dominance in each gene locus. Therefore, the effects of genes in different directions may cause the estimate to be lower than the actual amount. On the other hand, the genetic variance is calculated from the sum of squares of each gene locus.
Materials and Methods: Therefore, in order to study the type of gene action for some quantitatively important traits in safflower plant, crossing between 93 and American cultivars (resistant and sensitive to drought stress, respectively) was done and then F2, BC1.1 and BC1.2 generations were obtained. The parents along with the F1, F2, BC1.1 and BC1.2 generations were studied under drought stress conditions in the research farm of Plant Production Technology Research Institute of Shahid Bahonar University in 2020-2021. The research was conducted in the form of a randomized complete block design with two replications. Dry stress was applied at the 10% Heading stage and up to the full ripening stage. 8 traits including plant height, SPAD, number of sub-branches, number of bolls, single plant yield, days to 5% tillering and number of days to 50% flowering were evaluated.
Results and Discussion: The results of analysis of variance of this research showed that the mean square of the generations for all studied traits in the cross was significant. Therefore, the best genetic model was made for all investigated traits. The interaction effect of generation × location was significant for the studied traits. To evaluate the best genetic model, Meter and Jenkins method and individual scale test (A, B, C and D) were used, and the results of these tests indicate the existence of additive and dominant effects, as well as non-additive parameters (incremental × additive (i), additive × dominance (j) and dominance × dominance (l)) also played a role in the genetic control of all traits. In the irrigation conditions of no stress, most of the traits except the number of sub-branches and the number of bolls were not significant by chi-square and individual scale test and were under the genetic control of the three-parameter additive-dominance model. Also, in the condition of drought stress, it was significant in controlling the inheritance of all chi-square traits and their scale test (A, B, C and D). The opposite sign of h and l in the characteristics of plant height, number of sub-branches and number of bolls under drought stress indicates epistasis of double type. This type of epistasis causes disruption in the selection process by reducing diversity in the F2 generation and subsequent generations and shows the complexity of the inheritance of these traits.
Conclusion: Based on the results of this research, the importance of non-additive effects (epistasis parameters) in the control of investigated traits under conditions of moisture stress, the necessity of selection in segregating generations (after reaching purity and relative homozygosity) and the use of bulk-pedigree method or production Hybrid cultivars show in safflower plant. The different results in the experiments can be attributed to differences in genetic material, sample size, and experimental environment.