Color index for red clover seed

Red clover (Trifolium pratense L.) seed coats range in color from yellow to purple with the majority of populations having seeds with various proportions of both. Our objectives were to determine the extent of variability for seed color in red clover and evaluate the potential of a color classification scheme as a descriptor for red clover populations. Two to four replicates of 100 randomly selected seeds were classified for color for single seed lots of the National Plant Germplasm System (NPGS) red clover core collection and 15 cultivars. In addition, four 100-seed samples of multiple (2-5) seed lots of five cultivars were evaluated. Individual seeds from each sample were placed into I of 5 (1 = >95% yellow to 5 = >95% purple) different color classes. This allowed a color index (CX) to be calculated for each sample by the formula [2(seeds per class X class number)]/ (total number of seeds evaluated). Extensive variability was found among accessions within the core collection for CX, with a range of 4.4 for PI 207972 to 2.4 for PI 120105. A highly significant difference was observed among cultivars for CX; however, most had mean CXs between 3.0 and 3.3. Slight, but significant, differences were found among lots within 'Arlington' (range 3.3-3.5) and 'Altaswede' (range 2.5-2.8) for CX. However, the difference between Arlington and Altaswede mean CXs averaged across seed lots was more than three times larger than the greatest intracultivar seed lot difference. Frequencies of Classes I and 5 were relatively consistent across environments. From analysis of variance of five seed lots from each of Arlington and 'Kenstar', estimates of variance components associated with cultivar, seed lot within cultivar, and 100-seed sample within seed lot indicated 94% of total variance of a randomly selected sample was due to differences between cultivars. Our data indicated CX used in conjunction with class frequencies, if necessary, could be a useful descriptor for red clover populations.