THE DISTRIBUTION OF GOSSYPIUM-HIRSUTUM CHROMATIN IN GOSSYPIUM-BARBADENSE GERM PLASM - MOLECULAR ANALYSIS OF INTROGRESSIVE PLANT-BREEDING

Cotton is unusual among major crop plants in that two cross-fertile sp ecies are widely cultivated for a common economic product, fiber. Both historical evidence and classical genetic studies suggest that many i mproved forms of Gossypium barbudense (''Sea Island'', ''Egyptian'', a nd ''Pima'' cottons) may include chromatin derived from G. hirsutum. U sing 106 restriction fragment length polymorphism (RFLP) loci well-dis tributed across the cotton genome, we revealed the amount and genomic distribution of G. hirsutum chromatin in 54 G. barbadense collections from around the world. The average G. barbadense collection was compri sed of 8.9% alleles apparently derived from G. hirsutum. Pima cultivar s (7.3%)had fewer G. hirsutum alleles than Sea Island (9.0%) or Egypti an (9.6%) cultivars. G. hirsutum alleles were not randomly distributed , as 57.5% of the total introgression observed was accounted for by fi ve specific chromosomal regions that span less than 10% of the genome. The average length of an introgressed chromosome segment was greater than or equal to 12.9 cM. Overlap of introgressed chromatin in differe nt breeding programs hints that retention of these G. hirsutum chromos omal segments may impart a selective advantage to G. barbadense genoty pes. Although cluster analysis generally grouped germ plasm from commo n classes and/or breeding programs together, no 2 genotypes were ident ical - thus differences in the length and repertoire of introgressed c hromosome segments also permit DNA fingerprinting of G. bardadense cul tivars.