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Abstract:Several genetic parameters such as average degree of dominance, proportion and distribution of dominant and recessive alleles in all parents and dominance direction were evaluated in 10 cultivars of bread wheat, using a half diallel design. All 10 cultivars were intercrossed in the first year and these parents and their hybrids were separately planted in a randomized complete block design under normal and moisture stress conditions in the second year. Results of analysis of variance in normal moisture condition showed that there is genetic variation among genotypes for most of the traits except for tiller and fertile tiller number, awn length and 50% heading date. In stress condition there was no significant difference for awn length, 50% heading date, dry weight of root and flag leaf area. Results showed that, there was over-dominance for number of spikelet per spike, number of kernel per spike, 1000-kernel weight, biomass, weight grain yield and harvest index, complete dominance for stomata number per unit of leaf area, and partial dominance for peduncle length, spike length and dry weight of root in normal moisture condition. Also the result in normal moisture condition showed that all traits other than stomate density were controlled by dominant alleles; stomate density was controlled by recessive alleles. In stress condition there were over dominance effect for number of spikelets per spike, spike length and number of kernels per spike, complete dominance for stomate density and partial dominance for peduncle length, 1000-kernel weight, biomass, weight grain yield and harvest index. In stress conditions, all traits were controlled by dominant alleles except 1000-kernel weight which was controlled by recessive alleles.

Abstract:Ten bread wheat cultivars were crossed in a half-diallel scheme in spring 2000. Parents and their 45 F 1 hybrids were planted in field and greenhouse, in a randomized complete block design with 6 replications, in 2001. Both in the field and in greenhouse, two moisture schemes were applied: three of the replications in each set were under normal irrigation condition, and three of then were under moisture stress. Several quantitative traits were studied in the field; however, in the greenhouse experiment only root dry weight was measured. Analysis of variance of the data revealed significant differences between genotypes for majority of traits. Additive and non-additive gene effects were found for the traits under study. Heritabilities of various traits were calculated. General combining ability (GCA) for parents and specific combining ability (SCA) for the F 1 hybrids, as well as the ratio of GCA variance to SCA variance, were estimated. In the normal moisture conditions, non-additive gene effects were observed for number of spikelets, biomass, seeds per spike, seed yield, seed weight, 50% heading date, flag leaf area, number of stomata and harvest index. However, for other traits, namely peduncle length, spike length and root weight, additive gene effects play a good role. In the moisture stress condition, non-additive gene actions were found for most traits except for peduncle length, which showed additive gene effect. One aim of this research was evaluation of the genetics control of the related traits to drought resistance and calculating of the ratio of GSA to SCA variation in normal and moisture condition.