C-banding and localization of 18S-5.8S-26S rDNA in tall oatgrass species

The tall oatgrasses (Arrhenatherum spp., x = 7) are perennial diploid or autotetraploid forages of temperate grasslands. The most economically important species is common tall oatgrass, A. elatius (L.) P. Beauv. ex J. Presl & C. Presl. We were interested in cytogenetically characterizing this species due to its potential as a tertiary germplasm source for improving heat and cold tolerance in common oat (Arena satira L.). We used C-banding and fluorescence in situ hybridization with an 18S-5.8S-26S (45S) ribosomal DNA probe to examine the degree of chromosomal variation among tetraploids of the tall oatgrass genus. C-banding karyotypes were analyzed for three geographically diverse accessions of A. elatius and one accession each of A. album (Vahl) Clayton, A. parlatorei (Woods) Potzt., and A. thorei Durieu [= A. longifolium (Thore) Dulac]. Tall oatgrass chromosomes were predominantly euchromatic an d metacentric to submetacentric, with occasional subteiocentric chromosomes. The A. parlatorei karyotype was the most distinct of the six accessions, having a prominent telomeric C-band. Arrhenatherum album, A. elatius, and A. thorei had a single nucleolus organizer region (NOR) locus as evidenced by the appearance of four in situ hybridization sites on somatic metaphase chromosome preparations using the wheat 45S ribosomal DNA (rDNA) clone pTa71.