Genetic diversity and variation in North American orchardgrass (Dactylis glomerata L.) cultivars and breeding lines

Orchardgrass (Dactylis glomerata L.) is a high quality forage grass naturalized to temperate climates. Used extensively in hay and grazing agriculture, hundreds of orchardgrass cultivars have been released over the past 50 years. However, progress in yield and other agronomic characteristics in orchardgrass cultivars has occurred slowly and often inconsistently. One cause of the slow progress could be a lack of genetic diversity among orchardgrass cultivars, or an over-abundance of diversity within cultivars. With an emphasis on North American cultivars, this study assessed the genetic diversity within and among 52 orchardgrass cultivars, breeding lines and accessions. Genetic similarity within cultivars ranged from 52 to 71%, similar to values from wild-land, unselected accessions. Populations from Wisconsin and Missouri breeding efforts that resulted from two cycles of genotypic recurrent selection were included as checks. Neither group of selection populations exhibited more within-population similarity compared to the wild-land accessions (ecotypes) and cultivars. Genetic differentiation was detected only for the selection populations and several cultivars and breeding lines that had a tendency to originate from eastern Asian germplasm and have late flowering times. These results indicated an abundance of genetic variation within the orchardgrass cultivars, but a paucity of genetic differentiation among cultivars.