GENETIC DIVERSITY IN ELITE COTTON GERMPLASM DETERMINED BY MORPHOLOGICAL-CHARACTERISTICS AND RAPDS

Limited interspecific introgression has been achieved in the breeding of the two primary cultivated species of cotton (Gossypium hirsutum L. and G. barbadense L.). Genetic diversity of 16 near-homozygous elite cotton genotypes derived from interspecific hybridization was investig ated at the DNA level with the random amplified polymorphic DNA (RAPD) procedure and at the phenotypic level with stable and highly heritabl e morphological characters. Eighty random decamer primers were used to amplify DNA via the polymerase chain reaction (PCR) and 135 RAPDs wer e generated. Nineteen morphological traits were measured on the genoty pes in field experiments in 1992 and 1993. Morphological characters we re chosen that easily distinguish typical G. hirsutum (upland cotton) from G. barbadense (Pima cotton). Dendrograms were generated for genet ic distance from the RAPDs and average taxonomic distance from the mor phological data. Both procedures produced two clusters with one resemb ling G. hirsutum and one G. barbadense. Classification of all genotype s based on the two methods gave similar results with a correlation of 0.63 between the genetic distance and taxonomic distance. Several geno types were identified that were genetically and phenotypically distant from typical G. hirsutum and G. barbadense. The level of polymorphism exhibited by these genotypes could be exploited in genetic mapping po pulations to tag economically important traits, such as fiber quality. These genotypes also could serve as a germplasm source of unique alle les in G. hirsutum that are derived from G. barbadense. This experimen t demonstrates for the first time that RAPD analysis can reliably dete rmine genetic relationships within a diverse array of Gossypium germpl asm.