Genetic analysis of cotton (Gossypium hirsutum L.) yield and fiber quality by full diallel method under full and deficit irrigation conditions

Objective: In this study, six cotton genotypes, including three drought stress tolerant and three sensitive to drought stress, were crossed using complete full diallel cross method, obtaining F1 and F2 generations; to determine the genetic structure and quantitative heritability of cotton yield, yield components and fiber quality parameters under well watered (100%) and deficit (50%) irrigation conditions. This study was carried out to determine the effect of well watered and deficit irrigation conditions on genotypic variation and the maternal effect on the examined traits to support further breeding studies. Materials and Methods: In the first year of the study, Gloria, Nazilli 84-S, NP Ege, Nazilli M-503, DAK 66:3, NIAB 999 varieties were crossed with full diallelmethod and F1 generations were obtained. At the same time, F2 generation seeds were obtained from the seeds of the F1 generation in the Field Crops Department of ADU Faculty of Agriculture. In the second year of the study, parents, F1 and F2 generations were planted with an inter-row spacing of 70 cm and intra-row spacing of 12 cm, in Randomized Complete Block Design with four replications under the well watered (100%) and deficit (50%) irrigation conditions. Selected agronomic and fiber quality characteristics of the Parents, F1 and F2 generations were measured. The data obtained as a result of the agronomic and fiber quality characteristics measured in the study were evaluated by Griffing Method I, Model I adaptability analysis, full diallel table variance analysis, Jinks-Hayman diallel hybrid analysis and heterosis-heterobeltiosis ratios. Findings: For all populations and traits in Jinks- Hayman analysis of variance; The dominant effects were found more important in the inheritance of all traits, because the negative value of the difference between the additive variance and the dominance variance (D-H1). Also it denotes the overdominance type of gene action predominant for inheritance, because of the fact that the average degree of dominance (H1/D)1/2 was greater than 1. When the Wr/Vr graphs were examined, it was determined that the dominant gene effects (over-dominance, partial dominance, complete dominance) were important for all populations and traits. In the Griffing type analysis method, It was determined that the ratio of GCA/SCA was greater than 1 for ginning percentage, boll weight, number of bolls, sympodial branch, fiber length, fiber fineness, fiber strength, fiber elongation, water use efficiency, intrinsic water use efficiency and cotton yield value. It was thus concluded that the inheritance of traits is under the influence of additive genes. However, in the analysis of variance in combination abilities, both SCI indicating additive gene effects and SCA representing non-additive gene effects were found to be significant for all populations. Conclusion: It is concluded that the beginning of selection in the F5-F6 generation is appropriate in drought-resistant cotton breeding studies. Drought-resistant cotton breeding should be carried out under drought conditions due to the difference in gene movements in crosses between well watered irrigation and drought stress conditions. The selection of the population to which the method will be applied, the environmental factor, the obtaining of the values and interpretation of the analysis are important. The Griffing diallel analysis method would be appropriate in studies on hybrid variety breeding, while Jinks-Hayman type analysis method would be appropriate in researching genetic structures of populations. Keywords: Cotton, Diallel analysis, Maternal effect, Drought resistance/tolerant