In order to study the genetic variation for seed yield and its components among 29 accessions of cocksfoot (Dactylis glomerata L.), a complete randomised block design was conducted under spaced plant condition over two consecutive years in Karaj, Iran. Analysis of variance showed significant differences among accessions for heading date, plant height, fertile tiller number, seed yield, panicle length, seed yield panicle’, seed number panicle’, thousand grain weight, harvest index and forage dry matter (DM) yield for mean in each year as well as combined over two years. The data were also analyzed as split plot in time over two years. In combined analysis, the effects of genotype, year and intraction between genotype and year were significant for all traits. The varities of EU1053, EU1O1 12, EU197 and Iranian ecotype of SAR11773 were the best ecotypes/varieties for both seed and forage production. Using principal component analysis, the most important variables for seed yield characters were identified. The first three independent components accounted for 72% of total variation. The first principal component indicates that seed yield, harvest Index and seed number panicle’ were important characters for classification. Plant height and DM yield were important characters in the second component. Based on ward cluster analysis, 29 entries were divided into 5 groups. Accessions in clusters 3, and 5 averaged well above the overall mean for seed yield as well as forage DM yield, respectively. Majority of accessions in cluster 1 and 2 were originated from different parts of Iran, whereas, most accessions in other clusters were originated from either USA or European countries. The accessions in clusterl were defined as early maturities, low DM yield and high seed production. Accessions from a defined geographic area tended to cluster, but some accessions from some particular areas tended to spread among several clusters.
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