| Abstrakt: |
To estimate the general combining ability (GCA) of the parents, and specific combining ability (SCA)for seed cotton yield and fiber quality traits, and the magnitude of genetic diversity of cotton under water deficit condition 7x7half diallel mating design were used. The results showed that the mean squares of genotypes, parents, and crosses were highly significant for all studied characteristics. The mean squares of general combining and specific combining ability were highly significant for all characteristics under water deficit which indicated the importance of both additive and dominance effect on the inheritance of these characteristics. The ratio of the GCA and SCA was higher than unity for all the characteristics indicating the prevalence of additive gene effect in the inheritance of the investigated traits. The parental genotype Giza 94 recorded significant (desirable) GCA for most yield component characteristics under stress condition. However, the promising cross (Giza 89 x Kar) x Giza 86 x Giza 94) followed by the newest extra-long variety Giza 96 showed significant (desirable) GCA for lint percentage under deficit condition. Giza 93 was the best combiner for all studied fiber properties, and recorded significant desirable GCA values followed by Giza 96 under stress condition. On the basic of SCA, effects revealed that, most of the combinations having significant SCA effects were between genetically diverse parents. Five combinations recorded significant positive SCA values for seed cotton yield. These combinations contained the parental genotype Giza 94 or Suven as a common parent. The cross combination G.92 x G.93 recorded the best SCA effects for most fiber characters. Cluster analysis sequestrated seven parental genotypes of cotton into four major groups based on dissimilarity among them, and 20 contributed characters. The 28 genotypes, 7 parents and 21 Fl hybrids, were grouped into 10 major clusters based on relative dissimilarity among the genotype and the studied contributed characters. The highest inter cluster distance (110.117) was observed between cluster 8 and 9 followed by cluster 1 and 8 (105.604), and cluster 6 and 8 (97.076) indicating wider genetic divergence between these clusters. The lowest inter cluster distance were observed between clusters 1 and 6(11.188) followed by 4 and 7 clusters, and at last 2 and 6 clusters suggesting a close relationship between members of them and narrow genetic divergence among the genotypes. The magnitude of heterosis largely depends on degree of genetic diversity among parents and hence, selection of parents from these clusters should be avoided for combination breeding. [ABSTRACT FROM AUTHOR] |
