Isozyme Diversity in North American Cultivated Red Clover

Red clover (Trifolium pratense L.) is a forage legume with considerable economic importance in world agriculture. Knowledge of the amount and distribution of genetic variability within a species is vital to breeders and geneticists when selecting breeding germplasm. The objectives of this study were to assess genetic diversity in 34 North American red clover cultivars by means of isozymes. Isozymes assayed were esterase, β‐glucosidase, phosphoglucomutase, peroxidase, diaphorase, phosphoglucoisomerase, and superoxide dismutase. Eleven of the 13 loci (84.62%) were polymorphic in at least one cultivar. Percentage polymorphic loci within cultivar ranged from 61.54% in cv Morred, Persist, and Redland II to 84.62% in cv Arlington, Ram, and Red Baron, with an overall mean of 73.98%. At the species level, the number of alleles per polymorphic locus was 2.55 and effective number of alleles per locus was 1.64. Within‐cultivar averages were 2.71 and 1.59, respectively. Genetic diversity was 0.292 at the species level and 0.285 for within populations. Most of the genetic diversity (98.4–99.7%) was distributed within the cultivars. Grouping the 34 cultivar on the basis of genetic distance indicated that their isozyme variability could be represented by a few cultivar of each of four groups plus the cv Morred and Redon.