High frequency of karyotype variation revealed by sequential FISH and GISH in plateau perennial grass forage Elymus nutans

Elymus nutans L. (StHY, 2n = 6x = 42) is extensively selected from the natural population and domesticated as perennial grass forage in the Qinghai-Tibet plateau in China due to its high tolerance to environmental stresses, such as cold and drought. Karyotyping was conducted in 12 randomly selected plants by sequential fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH). GISH discriminated St, H and Y genomes, indicating that E. nutans has retained its ancestral genome, and large chromosomal rearrangements have not occurred. However, FISH using an AGG satellite and Afa-family repetitive sequences, revealed marked variation in the signalling patterns of most of the chromosomes. Many of the plants carried chromosomes with a specific pattern in the homozygous state, indicating that self-pollination or sib-crossing occurs in small populations during selection for domestication. In addition, several intergenomic translocations appeared, possibly caused by homoeologous chromosome recombination. The nature of the polymorphisms seen in the chromosomes of the domesticated Population of E. nutans is discussed.