Abstract:
A diallel cross of nine cultivars of Gossypium hirsutum L. (race latifolium), grouped on a basis of origin and staple characteristics into African uplands and American high quality and ordinary quality uplands, was used to examine heterosis and combining ability effects. Heterosis associated with the African cultivars, in combination either with the American cultivars or with each other, at an average of 22 % was approximately double that associated with either American group of cultivars. A number of hybrids significantly outyielded the standard commercial cultivar of the region, Stoneville 7A. The best hybrid yielded 271 kg lint/ha more than Stoneville's yield of 1622 kg lint/ha. This increase was brought about by heterosis in the three yield components: number of bolls, boll weight, and lint percentage. Heterosis was also marked for early height with all groups but was absent or only slight for mature height. No significant heterotic effects were demonstrated for micronaire value or Pressley strength index. Variation due to general combining ability predominated in all traits, particularly for lint yield, number of bolls, boll weight, and mature height. Even when significant, the specific combining ability component of variance was much less than the general combining ability component. All three African cultivars and the ordinary quality American type Stoneville 7A had high general combining ability for lint yield and number of bolls and should be valuable parents for use in a breeding programme. Lint yield in the F1 population was strongly genetically correlated with number of bolls but negatively correlated with boll weight, not associated with lint percentage, and slightly negatively associated with micronaire value and Pressley strength index.