Cultivar identification by means of isoenzymes 2. Genetic variation at 4 enzyme loci in diploid ryegrass lolium-spp

Fifteen cultivars of perennial ryegrass (L. perenne) and 6 cultivars of Italian ryegrass (L. multiflorum) have been scored for four enzyme loci, Pgi-2, Got-3, Pgm-1 and Pgd-1 [phosphoglucoisomerase, glutamate oxalacetate transaminase, phosphoglucomutase and 6-phosphogluconate isomerase] by starch gel electrophoresis. Cultivars were pairwise compared by means of allelic frequencies assuming Hardy-Weinberg proportions. At first, the comparisons were carried out for each locus separately. The 2 loci Pgi-2 and Got-3 distinguished perennial ryegrass cultivars fairly well, but the discrimination in Italian ryegrass was unsatisfactory at any single locus. By summing the test values for each locus, a combined evaluation of distinctness was obtained. Then cultivars could be pairwise distinguished with 99% confidence in 96% of pairs of perennial ryegrass and in 80% of pairs of Italian ryegrass. Indications of instability were found in some cultivars from a few tests of homogeneity of additional seed lots. General biochemical, genetic and statistical prerequisites for the use of isoenzyme variation in cultivar identification and registration are discussed.