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 investigated at the DNA level with the random amplified polymorphic DNA (RAPD) procedure and at the phenotypic level with stable and highly heritable morphological characters. Eighty random decamer primers were used to amplify DNA via the polymerase chain reaction (PCR) and 135 RAPDs were generated. Nineteen morphological traits were measured on the genotypes in field experiments in 1992 and 1993. Morphological characters were chosen that easily distinguish typical G. hirsutum (upland cotton) from G. barbadense (Pima cotton). Dendrograms were generated for genetic distance from the RAPDs and average taxonomic distance from the morphological data. Both procedures produced two clusters with one resembling G. hirsutum and one G. barbadense. Classification of all genotypes based on the two methods gave similar results with a correlation of 0.63 between the genetic distance and taxonomic distance. Several genotypes 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 populations to tag economically important traits, such as fiber quality. These genotypes also could serve as a germplasm source of unique alleles in G. hirsutum that are derived from G. barbadense. This experiment demonstrates for the first time that RAPD analysis can reliably determine genetic relationships within a diverse array of Gossypium germplasm.