Abstract
Cotton varieties (Coker310, SP8886, Lachata, Montana, Halab33, AC22 and Cord26) and all their F1 half diallel crosses were planted at Al-Hawija (Kirkuk Governorate) using randomized complete block design with three replications. The data analyzed according to method 2 of Griffing (1956) to study heterosis (as deviation of F1 from mid and better parents), variances and effects of general and specific combining abilities for characters:plant height, number of nodes to first flowering branch, number of vegetative and fruiting branches per plant, number of bolls per plant, boll weight, lint and seed indices, earliness and seed cotton yield.
The results showed that the hybrids (Coker310 x Halab33), (SP8886 x Halab 33), (Montana x Cord26), (Halab33 x AC22) and (Halab33 x Cord26) charac- terized by significant desirable heterosis for larger number of characters (as comared with mid and better parents) and gave higher effects of specific comb- ining ability for most cases. The variety Lachatacharacrized as a good general combinor for most characters (number of nodes to first flowering branch, number of vegetative branches per plant, boll weight, lint and seed indices and earliness). It was shown from cluster analysis that the less genetic diversity among parental genotypes is (0.219) between Montana and AC22 in spite of that they are from different sources, while the higher genetic diversity is (0.859) between SP8886 and Halab33 and they are from different sources. The comparision (of values of genetic diversity between parental genotypes for each hybrid with values of average performance of the hybrid, heterosis and specific combining ability for seed cotton yield per plant in single crosses) indicate that higher genetic diversity was between genotypes located in different main groups, and the hybrids resulted from crosses between such genotypes gave higher values of hybrid performance and heterosis of its two kinds, and correlation between genetic diversity and hybrid performance and heterosis and specific combining ability was positive, and this results refer to the possibility of using the mans of parents characters be classifying it to different groups through cluster analysis and introduced it in efficient hybridization programs.