Genetic diversity of Upland cotton (Gossypium hirsutum), which is critical to effectiveness of election, is being investigated at the biochemical level. Techniques were developed to assay five isozymes, ACO, SKDH, PGM, MDH, and PGI, from a single horizontal starch gel system. A method was also developed to study PER isozyme profiles on the basis of isoelectric focusing on a miniature gel system.

Monomorphic banding patterns were observed for ACO, MDH, PGI, and PGM within preliminary sets of 63 cultivars and 40 wild race stocks of G. hirsutum. Certain bands of PGM and ACO were absent from some single seed samples of certain cultivars, indicating either the existence of developmental control of gene expression or genetic heterogeneity within certain cultivars. Isozyme banding patterns were more or less uniform and therefore seemed independent on the site of cultivar development. Four of the six isozymes were monomorphic among the cultivars and wild race stocks of G. hirsutum. Three SKDH and five PER banding patterns were observed. Five of the six isozymes were polymorphic among the different species of Gossypium. These results indicating interspecific genetic introgression from other tetraploid species of cotton to G. hirsutum would expand genetic diversity and enhance subsequent breeding efforts to improve cotton.