Cotton Breeding and Genetic Diversity.

The major cultivated cottons of commerce are AD allotetraploids (2n=52) species.  The dominant species in terms of world production is Gossypium hirsutum L (>90%).  G. barbadense L (long staple) is the other cultivated tetraploid species.   There are two diploid A genome species and four diploid D genome species among the 45 diploid species (A-G and K genomes).  Upland cotton is the term used for G. hirsutum cotton grown in the United States.  At least three major events have affected the genetic diversity of the U.S. upland cotton germplasm.  Only two diploid species are thought to have been involved in the development of allotetraploids, only a small subset of wild tetraploid genotypes were domesticated, and only a small subset of these wild genotypes from Central America formed the germplasm base for upland cotton in the U. S.  Essentially all cotton cultivars in the U. S. are developed by private cottonseed breeding companies.  This results in incomplete public information concerning pedigrees of cultivars and affects coefficient of parentage calculations.    It is generally believed that the major seed breeding companies tend to primarily cross within their own company germplasm base.  This genetic base is less diverse than the base among companies.  However, many successful cultivars are still being developed by reselection within current cultivars or crosses between existing cultivars.  Thus, the current germplasm base does not appear to be limiting short-term breeding progress for improvements in yield and fiber properties.  However, long-term progress should benefit from a broadening of the genetic base.  This manuscript will describe genetic diversity, linkage groups, correlation of traits of economic interest, and public breeding systems being used to add useful diversity to the cotton germplasm base.