Ability of SSRs to Detect Differences Among Cotton Cultivars.

A valuable collection of diverse cotton (Gossypium hirsutum) genetic resources is available in the U.S. Cotton Germplasm Collection.  Within the above collection is a group of improved cultivars, collected world-wide, that represent the most accessible and immediately useful germplasm to breeders, but whose diversity has not been adequately characterized.  Molecular tools provide a means to characterize the underlying genetic diversity within these cultivars that is not measurable through classical agronomic descriptors alone.  The overall objective of this research is to determine the genetic diversity and relationships among cultivars available in the U.S. Cotton Germplasm Collection, collected from several cotton-growing regions of the world, including Africa, China, and the U.S.  As a preliminary step, we identified a subset of 24 cultivars and used them to identify informative SSR markers.  Eighteen cultivars from the U.S. Cotton Germplasm Collection (four from northern Africa, four from southern Africa, five from China, and five from the U.S. that are now obsolete) and six commercial cultivars of relatively recent origin were assayed at 76 SSR loci using agarose gel electrophoresis.  Sixty-one of these loci were polymorphic with an average polymorphism information content (PIC) value of 0.41.  The number of alleles identified at each locus ranged from two to eight with an average of 2.9 alleles per locus.  The molecular characterization of germplasm will provide cotton breeders with more information for the selection of unique and desirable parental germplasm to introduce genetic diversity, reduce genetic vulnerability, and provide genetic improvements for yield, agronomic, and fiber quality traits.