Frequency of the no mark leaflet allele in red clover

Red clover (Trifolium pratense L.) is known for trifoliolate leaves with light marks (i.e., variegation) on the leaflets. However, red clover plants without leaf marks occur in some wild and cultivated populations. The no mark (NM) phenotype is due to a homozygous recessive genotype. This study was conducted to evaluate the core collection of red clover for frequency of the recessive allele that imparts the NM phenotype. Ninety-eight seeds from 82 accessions in the core collection and one selected population (Blankleaf, NSL 303023) were planted in individual containers in the greenhouse. Seedlings were evaluated weekly for leaf markings. If a plant had no mark on any, of its leaves from emergence to flowering, it was classified as a NNI phenotype. We assumed that all evaluated accessions were diploid and in Hardy-Weinberg equilibrium for the leaf mark locus. Estimates of gene frequencies for the NM trait ranged from 0.0 for 21 out of the 82 accessions to 0.67 for PI 419294 from Greece. The grand mean was 0.20. Our data indicated the recessive allele was absent or at least extremely rare in about 25% of the accessions. Assuming the core collection represents the genetic variability in the species, our data provide a basis for designing additional studies to determine if natural and/or artificial selection are responsible for variation among populations for this conspicuous feature of red clover.