Genetic Diversity of U.S. Upland Cotton Cultivars Released between 1980 and 1990

Sustained genetic advance requires that genetically diverse parents be mated to form segregating populations for selection. Genetic diversity of U.S. cotton (Gossypium hirsutum L.) cultivars has not been extensively quantified. We assessed diversity among 126 Upland cotton cultivars released between 1980 and 1990 by use of coefficient of parentage (CP). In computing CP, we utilized assumptions appropriate for self‐pollinated crops. Mean CP among the 126 cultivars was 0.07, implying a genetically diverse group. However, cluster analysis revealed 12 distinct gene pools, with mean within‐cluster CP = 0.25 and between‐cluster CP = 0.04. Overall, clusters corresponded to area of cultivar origin. The CP analysis indicates that Acala‐type cultivars are more diverse than 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 develop proprietary cultivars. To ensure continued progress in cotton improvement, we suggest that cotton breeders consider the pedigree of parents prior to population synthesis.