Estimates of hetrosis, general and specific combining ability for yield, lint percentage and %2.5 span fiber length obtained from a diallel cross of seven cotton cultivars using method 2, model 1 of Griffing. significant(0.01- level) genotype mean squares, general combining ability(GCA) and specific combining ability(SCA) estimates indicated useful variability for the studied characters. Comparisons of GCA mean squares with the SCA mean squares indicated that greater additive genetic variability was available for the lint percentage than for yield and %2.5 span length. The results showed that the cultivars G. hirsutum had good general combining ability for yield and lint percentage but the GCA was negative for %2.5 span length.The GCA estimates for the cultivars of G. barbadens were negative for yield and lint percentage and positive for %2.5 span length. positive and significat SCA estimates were observed for some parental combinations for yield and lint percentage. Therefore, the cultivars are not suitable as parents for impproving the %2.5 span length. Heterosis, expressed as the deviation of Fl hybrids from mid-parent values was significant for yield and lint percentage for some crosses.
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