الفهرس 
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Abstract
This study was carried out during three successive growing seasons (2006, 2007 and 2008).Thirty triallel crosses were developed among five cotton parental cultivars of Gossypium barbadense L. The triallel crosses and the commercial check cultivar Giza-80 were evaluated at the Experimental Station, Faculty of Agriculture, Cairo University, Giza, Egypt to estimate general and specific combining abilities for yield, yield components and some fiber quality traits. The nature of gene action that controls the inheritance of the studied characters was also estimated. The results indicate that partitioning the mean squares due to the three-way crosses into their components predicted the significant contribution of additive, dominance and epistatic variances to the genetic expression of studied traits.Giza-70 (P1) was the best general combiner among this group of cultivars for all studied traits, except for seed index (S I), lint percentage (L%), lint index (L I), pressely index (P I) and uniformity ratio (U R.%). Cultivar Giza-89 (P2) was the best for lint cotton yield per plant (L C Y /P), cultivar Giza-90 (P3) was the best for boll weight (B W) and the cultivar Giza-88 (P5) was the best for fiber length (F L). These cultivars were good combiners when used as the third parent in the three-way crosses. The crosses P1xP4xP5, P2xP3xP5, P1xP3xP5, P2xP4xP5 and P2xP5xP4 appeared to be the most promising three-way crosses for breeding toward improving most studied yield and fiber traits. The results also showed that the magnitude of additive (σ2A) was positive and larger than that of dominance genetic variance (σ2D), with respect to all the studied traits. The results indicated that the additive by dominance (σ2AD) type of epistasis variance played a secondary role in controlling the inheritance of studied characters of the triallel crosses. Estimates of broad-sense heritability (h2b %) varied from 93.38% for L% to 99.11% for F L and estimates of narrow-sense heritability (h2n %) varied from 3.59 % for U R% to 45.11% for S I. It was concluded that yield and its components and the studied fiber properties were mainly controlled by additive gene effects in addition to additive by dominance epistatic interactions, suggesting that selection practiced in the advanced generations of superior three-way crosses in this study may be effective for improving these traits. Highest estimates of relative precision were detected for simple lattices, while the lowest ones were detected for partially balanced lattices. Path – coefficient analysis showed that N O B/ P had the greatest direct effect on S C Y/ P while N F B/P had the greatest indirect effect on S C Y/ P via N O B/ P