Combining ability and heterosis of yield components in half diallel crosses of cotton

Combining ability and heterosis estimates were made in seven cotton cultivars and one prospective variety, and their 28 F1 hybrids in half diallel analysis for days to 50% flowering, boll opening, and boll maturity, plant height, first sympodial node, number of sympodia and bools per plant, boll size, 100 seed weight, lint indes, ginning out-turn, seed cotton yield, fiber length, fineness and strength. The experiment was carried out using randomized complete block design with three replications in 2000/01 and 2001/02 seasons at Gezira Research Station (GRS), Wad Medani, Sudan. Four of the cultivars, Albar(57)12, Barac(67)B, Acaka(93)H and Shambat-B were G. hirsutum and the other four Barakat-90, Huda, Barakat-S and B-Pima were G. barbadense. Analysis of variance mean squares revea;ed highly significant variability for all of the measured characters. Shambat-B gave the highest mean seed cotton yield and the two best interspecific hybrids [Acala(93)H X B-Pima and Acala(93)H X Barakat-S] out-yield Shambat-B by 127.6 and 111.6 and 111.6%; and 116.2 and 144.4%, in the two seaons, respectively. Combining ability analysis showed the importance of both additive and non-additive types of gene action in the measured traits. Additive gene action was predominant for days to 50% flowering, and boll opening, firts sympodial node, boll size, lint index and fiber strength. Non-additive gene action predominated for the remaining traits. General combining ability (GCA) effects were significant in either direction for all measured traits and Albar(57)12, Barac(67)B, Acala(93)H, Barakat-S and B-Pima were the best combiners. Barakat-90 was the least combiner. Specific combining ability (SCA) effects were considerable but inconsistent across seasons with the exception of number of bolls per plant. The interspecific hybrids, Acala(93)H X B-pima, Acala(93))H X Barakat-90, Acala(93)H X Barakat-S, Shambat-B X B-Pima, Albar(57)12 X Barakat-90 and Acala(93)H X Huda exhibited significant SCA for number of bolls per plant, seed cotton yield, fiber length and fiber fineness. These hybrids also showed maximum heterosis for the same traits in addition to number of sympodia per plant and plant height. Seed cotton yield was highly and positively correlated with plant height, number of sympodia per plant, boll size, 100 seed weight and lint index, and negatively associated with the components of earliness. Significant GCA effects obtained by the best combiners in a favorable direction suggested the use of these parents in recurrent selection to incorporate their desirable characters. Significant SCA effects coupled with maximum heterosis in the superior crosses suggested their utilization in heterosis breeding