PHYLOGENETIC-RELATIONSHIPS OF 10 GRASS SPECIES - AN ASSESSMENT OF PHYLOGENETIC UTILITY OF THE INTERNAL TRANSCRIBED SPACER REGION IN NUCLEARRIBOSOMAL DNA IN MONOCOTS

Entire sequences of the internal transcribed spacers (ITSs) and 5.8S s ubunit of nuclear ribosomal DNA (nrDNA) were obtained from nine grass species by direct double-stranded sequencing of polymerase chain react ion (PCR) amplified DNA fragments. These sequences from subfamily Pooi deae (Triticum aestivum, Crithodium monococcum, Sitopsis speltoides, H ordeum vulgare, Secale montanum, Avena longiglumis, Bromus inermis, Br achypodium distachyon) and subfamily Panicoideae (Sorghum bicolor) tog ether with published ITS sequence of rice (Oryza sativa, Bambusoideae) were analyzed using Wagner parsimony (PAUP) and the neighbor-joining distance method to assess the phylogenetic utility of ITS sequences at various taxonomic levels. Among the aligned sequences that ranged fro m 588 to 603 nucleotides in length, 118 of 269 variable sites containe d potential phylogenetic information. A member of Bromus, B. inermis, was the sister taxon to the Triticeae species. Brachypodium was more d istantly related to Triticeae than was Bromus or Avena. These data, wi th Oryza sativa as the outgroup, indicate monophyly of the Pooideae sp ecies and of the members of the tribe Triticeae within Pooideae. Phylo genetic trees of the 10 grass species generated from the ITS sequence data were in general agreement with phylogenies based on molecular dat a from ribosomal RNA (rRNA) and chloroplast DNA (cpDNA) of similar gra ss taxa. This study reaffirms that sequences of the ITS region are use ful for phylogenetic inference among closely related monocot species.