Genetic diversity and population structure of Eurasian populations of reed canarygrass: cytotypes, cultivars, and interspecific hybrids

Reed canarygrass (Phalaris arundinacea L.) is an important forage crop and potential biofuel feedstock due to its wide environmental adaptation. The P. arundinacea 'species complex' is made up of three cytotypes, 2x, 4x, and 6x, with the 4x cytotype (P. arundinacea L.) most common. Active breeding programs have developed cultivars since the early 20th Century, but little is known about the genetics of the species complex. With the aid of DNA markers, we evaluated the population structure of 83 wild accessions collected throughout Eurasia, 24 cultivars, and the genetic relationship between 4x and 6x cytotypes. Seven subpopulations were present in Europe with a high level of admixture, suggesting that reed canarygrass germplasm has spread throughout Eurasia, either naturally or by humans for use in agriculture. Our results indicate that cultivars have incorporated much of the diversity found in wild populations, although modern low-alkaloid cultivars appear to come from a relatively small gene pool. We also found some evidence that the 6x cytotype is made up of three sub-genomes that are a combination of genomes present in 4x P. arundinacea and 4x P. aquatica, although the 6x cytotype does not appear to be a direct hybrid between the species.