LEVELS AND PATTERNS OF GENETIC DIVERSITY IN AMERICAN UPLAND COTTON

¹ University of Georgia, PO Box 748, Tifton, GA 31793

² Texas Ag. Experiment Station, Route 3 Box 219, Lubbock, TX 79403

³ Texas Tech University, Box 42122, Lubbock, TX 79409

⁴ Texas A&M University, Mail Stop 2474, College Station, TX 77843

⁵ University of Georgia, 111 Riverbend Road, Athens, GA 30602

To shed light on the levels and patterns of genetic diversity of upland cotton (Gossypium hirsutum) germplasm, we surveyed more than 325 cotton lines/cultivars of historical importance with more than 260 evenly spaced RFLP loci. Substantial genomic tracts appear monomorphic, possibly suggesting founder effects in the relatively short history of breeding this self-pollinated crop in USA. Nevertheless, sufficient variability exists in the remaining genomic regions to allow fingerprinting of the germplasm set and to distinguish major public breeding programs. Genetic diversity is not distributed uniformly over the cotton genome or among breeding programs. Dendrograms and Principal Coordinate Analysis indicated that the separation of cultivars based on genetic diversity do not completely reflect the patterns predicted based on the traditional upland cultivar separations of Acala, stripper, Mid South, and Southeast. Detailed analysis of released cultivars/germplasm lines from three public breeding programs indicated that genetic erosion has occurred in two of the three programs. We found evidence of interspecific introgressions that can be tracked within a breeding program. These rare alleles are restricted to a small group of cultivars that according to historical accounts were clearly developed through interspecific hybridization. While the non-random distribution of genetic variation across both the genome and the gene pool offer clues as to the locations of genes that may play key roles in cotton improvement, the general paucity of variation highlights the need to make greater use of secondary and tertiary gene pools.