This study was aimed to evaluation the yield stability of twenty bread wheat genotypes that cultivated at two locations (fields of the College of Agricultural Engineering Sciences of Duhok and Zenawa district) during the 2019 - 2020 with two planting dates in each location using randomized complete block design with three replications. The results of the combined analysis of variance showed that the mean square for each of the environments, genotypes and their interactions were highly significant for all studied traits, and the variations due to the environments were greater than those of each of the genotypes and the interactions for most of the studied traits. The values of broad sense heritability ranged between 44.44% for spike length and 93.27% for grain weight per spike. The results of the stability parameters showed that the genotype Apst-12-85578 was highly stable for grains weight per spike and final grain yield followed by each of Adana, Bora, and Apst-6-85576 genotypes which showed high stability for the grain yield.
Eight upland cotton varieties (Iranian, Bulgarian Grrd26, Lachata, French CA22, Syrian strain106, Pima, Bulgarian Chirpam 539 and Coker 310) were crossed in a half diallel mating system to assess the genetic of plant height, number of fruiting branches, number of bolls per plant, boll weight, earliness, ginning outturn and seed cotton yield per plant utilizing Mather and Jinks (1982) The results showed highly significant differences between genotypes for all the characters. Adequacy tests of additive dominance model revealed that data of all the characters were partially adequate for genetic interpretation except for ginning outturn. Additive component (D) was significant from zero for plant height, number of fruiting branches, ginning outturn and seed cotton yield per plant and was lower in magnitude than dominant components (H 1 and H 2) of variation for all traits. This was firmly supported by the value of (H 1 /D) 0.5. Asymmetrical distribution of dominant and recessive genes in parents was found for number of fruiting branches, boll weight, ginning outturn and seed cotton yield per plant due to unequal estimates of dominant components (H 1 and H 2). This was confirmed by the value of H 2 /4H 1. Graphical representation of Wr/Vr demonstrated that additive gene action plays a role in controlling the inheritance of plant height, number of bolls per plant, boll weight and seed cotton yield per plant, while the traits number of fruiting branches, earliness and ginning outturn was under the influence of over dominance. Low narrow sense heritability was exhibited by number of fruiting branches and boll weight, moderate for remaining traits, and its values ranged between 16.95% for number of fruiting branches and 53.18% for ginning outturn. This indicates that all the traits were under the control of dominant gene action, therefore breeding hybrids were useful for these traits.
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