Genome size and Giemsa C-banded karyotype of tetraploid Bromus ciliatus L.

Summary Tetraploid Bromus ciliatus L. is a North American bromegrass that has been placed in the Pnigma section of Bromus. The objective of this study was to characterize the genome of tetraploid B. ciliatus by cytogenetic methods and compare it to the genomes of other species included in the section Pnigma. All the plants of the accession (USDA PI 232214) selected for chromosome counting were tetraploids (2n = 28). The mean 2C nuclear DNA content for tetraploid B. ciliatus was 19.13± 0.07 pg as determined by flow cytometry which is significantly greater than the tetraploid DNA content of B. inermis Leyss. (11.74± 0.16 pg). C-banding procedures were used to identify individual mitotic chromosomes and to develop a karyotype for B. ciliatus. The genome of the tetraploid B. ciliatus consisted of 16 median chromosomes, eight submedian chromosomes, and four chromosomes with satellites which included one pair with a large satellite and one pair with a small satellite. The general pattern of the distribution of constitutive heterochromatin in B. ciliatus was quite different than the other bromegrasses that have been analyzed to date. Except for two pairs of chromosomes, all chromosomes in tetraploid B. ciliatus had telomeric bands on one or both arms. Some of the chromosomes with telomeric bands had centromeric bands that were located at one or both sides of the centromere and intercalary bands which were generally absent in the other bromegrass species. It was possible to identify all chromosomes of tetraploid B. ciliatus and to match the pairs of homologous chromosomes by using chromosome lengths, arm length ratios and C-banding patterns. The results of this study indicate that tetraploid B. ciliatus has different genomes than the European species evaluated to date in the section Pnigma.