Estimation of nuclear DNA content in Sesleria (Poaceae)

Taxonomy of the genus Sesleria Scop. is complicated by the fact that most of the typical characters are of quantitative nature and under strong environmental control. In some cases, unequivocal determination of individual species may be difficult. In this study, we have employed flow cytometry to estimate ploidy levels and to determine nuclear DNA content in populations of five central European Sesleria species [S. albicans Kit. ex Schult., S. caerulea (L.)Ard., S. heufleriana Schur, S. sadleriana Janka, S. tatrae (Deg.)Deyl]. Two DNA ploidy levels were found: tetraploid and octoploid. These ploidy levels (i.e. 2n = 4x = 28 and 2n = 8x = 56) were confirmed by chromosome counting. The 2C DNA content of tetraploid species ranged from 9.097 pg in S. caerulea to 9.585 pg in S. heufleriana. Octoploid taxa had approximately two times higher DNA content, ranging from 17.729 pg in S. sadleriana to 18.278 pg in S, tatrae. During the course of the study, two plants representing a so far unknown octoploid cytotype of S. heufleriana were discovered. Furthermore, it was found that octoploid Sesleria species had lower nuclear DNA content than a theoretical double of mean DNA content of related tetraploid species. In all species, the intraspecific variation of nuclear DNA content was small, not exceeding 3%. The relationship between Sesleria species and their evolution is discussed in the light of data on nuclear DNA content obtained for the first time in this study.