GENETIC DIVERSITY OF US UPLAND COTTON CULTIVARS RELEASED BETWEEN 1980AND 1990

Sustained genetic advances requires that genetically diverse parents b e mated to form segregating populations for selection. Genetic diversi ty of U.S. cotton (Gossypium hirsutum L.) cultivars has not been exten sively quantified. We assessed diversity among 126 Upland cotton culti vars release between 1980 and 1990 by use of coefficient of parentage (CP). In computing CP, we utilized assumptions appropriate for self-po llinated crops. Mean CP among the 126 cultivars was 0.07, implying a g enetically diverse group. However, cluster analysis revealed 12 distin ct gene pools, with mean within-cluster CP = 0.25 and between-cluster origin. The CP analysis indicates that Acala-type cultivars are more d iverse that those bred in the Mississippi Delta or southeastern USA. A trend in germplasm usage in the late 1980s was the repeated mating of genetically related material, or reselection within germplasm, to dev elop proprietary cultivars. To ensure continued progress in cotton imp rovement, we suggest that cotton breeders consider the pedigree of par ents prior to population synthesis.