YIELD AND FIBER QUALITY POTENTIAL FOR TRIALLEL CROSSES IN COTTON: 1- NATURE OF GENE ACTION.

This investigation carried out to determine combining ability and gene action estimates for yield and yield components traits with some fiber properties in cotton . The genetic materials in this investigation included five cotton varieties i.e. Suvin  (P₁) ; TNB ( P₂) ; Pima S6 (P₃); G.88 (P₄) and G.89 (P₅) and their 30  three way crosses . All these varieties belong to the species Gossypium Barbadense L.  In 2008 growing season these all genotypes were evaluated in experimental Agriculture Research Station at Sakha, the following traits were estimated : boll weight , seed cotton yield per plant , lint cotton yield per plant , lint percentage , number of bolls per plant , seed index , lint index , number of seeds per boll, lint per seed , fiber strength , fiber fineness, span length at 50%, span length at 2.5% and uniformity ratio % .
   The results indicated that the mean squares of genotypes were highly significant for all studied traits . The results also showed that the three way crosses ( P₃ x P₅ ) x P₂ cleaned the highest mean performance  for boll weight and the combinations ( P₃ x P₄ ) x P₁ ,      ( P₂ x P₅ ) x P₄ and ( P₄ x P₅ ) x P₂ showed the best promising for seed cotton yield per plant , lint cotton yield per plant and lint percentage , respectively .Meanwhile the combinations ( P₃ x P₄ ) x P₁ , ( P₂ x P₃ ) x P₁ and ( P₁ x P₂ ) x P₅ were the superior combinations for number of bolls per plant , seed index and lint index . On the other hand,  the highest mean for number of seeds per boll and lint per seed were observed for the crosses ( P₄ x P₅ )x P₃ and ( P₁ x P₂ ) x P₅ . The results also cleared that the hybrids ( P2 x P₃ ) x P₅ , ( P₁ x P₄ ) x P₃ and ( P₂ x P₃ x P₄ appeared to be the best promising for fiber traits .
From the analysis of triallel crosses the results illustrated that the variety Pima S₆ was the best combiner for yield traits ,While G.88 and Suvin were the best combiner for fiber traits and the results also cleared that these parental varieties could be utilized in a breeding programs to improve these traits through the selection in segregating generations.
  The results indicated that the yield and yield components as well as fiber traits were mainly controlled by additive variance and additive x dominance epistatic variances . These results also revealed that the calculated values of heritability in broad sense ranged from 91.92 % for seed index to 98.36% for seed cotton yield per plant . In the same time the heritability in narrow sense ranged from 1.64% for seed cotton yield per plant to 43.53% for number of seeds per boll.