Genome size variation in the Poaceae supertribe Poodae, the major grass lineage of temperate climates (tribes Aveneae, Festuceae and Poeae)

Nuclear DNA amounts were examined by flow cytometry for 70 genera and 214 species and subspecies taxonomically belonging to the supertribe Poodae of the grass subfamily Pooideae. This supertribe contains most of the grasses distributed in the temperate extratropical regions of the world and is important because of its many cultivated species (e.g., grains) and its prominence as a major component of grasslands. The majority of holoploid genome sizes (2C values) ranged from 5 to 10 pg, with the full range of values representing a 30-fold variation. Most monoploid genome sizes (1Cx values) were between 2 and 3 pg, with a total of 12.3-fold variation. The minimum values in Poodae are only about twice those of Brachypodium stacei, which has the smallest genome known for the subfamily Pooideae, and those of rice and some other species of the rice subfamily (Oryzoideae) and a few species of the subfamily Panicoideae with miniature genomes. The maximum values of our study group are among the largest found within the entire family Poaceae, only slightly exceeded by a some in the tribe Triticeae (wheat and related species). The effects of polyploidy and dysploidy, their association with genome “downsizing” as well as with cases of size increase, were analyzed in both autopolyploids and allopolyploids. The origin of the low chromosome number of only x = 2 in some Poodae species and the transition from perennial to annual life form were addressed in the light of genome sizes, which were also discussed in a phylogenetic framework.