Genetic diversity in the core subset of the U.S. red clover germplasm

Biochemical diversity present in accessions of the red clover (Trifolium pratense L.) U.S. core subset is unknown. Its isozyme characterization would facilitate the study of relationship among accessions and assist in the identification of unique accessions and duplicates and in the detection of genetic differences among accessions. This study was undertaken to assess genetic diversity in the core subset using the isozymes esterase, beta-glucosidase, phosphoglucomutase, peroxidase, diaphorase, phosphoglucoisomerase, and superoxide dismutase. Ten isozyme loci with 30 alleles were detected. All loci were polymorphic in at least one accession. Percentage polymorphic loci within populations ranged from 50 to 100% with an average of 77.5%. At the species level, the number of alleles per polymorphic locus was 3.00, and the effective number of alleles per locus was 1.81. Within accession averages were 2.75 and 1.66, respectively. The core subset had a large amount of genetic diversity. Most accessions were different from each other except PI 207972 and PI 251564, PI 217507, and PI 229799 that were alike. One accession, PI 235867, was not a red clover. Most accessions (56) were in Hardy-Weinberg equilibrium, and thus they are more likely to maintain genotypic and allelic frequencies when increased. Genetic diversity at the species level was high and there was nearly twice as much variability among the wild populations as among the cultivars or landraces included in the core subset.