Variance And System Inference Of Leymus Species Based On ITS Sequences

Leymus Hochst. is a perennial gemus of grass in the tribe Triticeae (Poaceae) There are about 32 species and 19 subspecies in Leymus. They are distributed in the temperate regions of Eurasia, North and South America, extending to the subtropic and the tropic alpine regions. All the species are polyploids with the chromosome numbers ranging from 2n=4x=28 to 2n=12x=84. Many species of Leymus are not only main components of grasslands and grass marshlands, but also fine varieties of herbage and forge. Being an important genetic resource, Leymus is significant to the improvement of Triticeae cereal crops. However, the origin and definition of the genus, precise taxonomic ranks and relationships among the species in the genus have been under discussion. In this study, seven Leymus species and their nine related species were reconstructed base on nrDNA ITS. The main results showed as follows:1. In the ITS trees, most of the Leymus species and Psathyrostachys species are in the same clade, which suggested that Leymus species derived their Ns genome from Psathyrostachys species. Different Leymus species clustered with different Psathyrostachys species indicated that Psathyrostachys species served as the donor to different Leymus species.2. Leymus arenarius is closely related to L. racemosus which may adopt different chromosome doubling or hybridization, or origin from common ancestor. Only the clones of L. triticoides and L. duthiei were monophyletic. The possible reason is L. triticoides from North America is far from most other Leymus species distributed in Central Asia or Eurasia, while L. duthiei is growing in the understory, formating a relatively independent status in long-term evolution.3. Phylogenetic tree shows that different clones of the same species are not always together, reflecting a big genetic differentiation of ITS sequences in Leymus species. The widely distribution, large numbers and high ploidy may lead to the big genetic differentiation.4. Leymus arenarius and L. tianschanicus had the close relationship with Agropyron cristatum,Ag. mongolicum (P) and Eremopyrum triticeum (F). F and P genomes might be the donor of Xm genome of Leymus species.5. The estimates of nucleotide diversity for ITS sequences within Leymus species showed a big genetic variation and diversity in ITS sequences.