Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/21/2003
Publication Date: 1/1/2004
Citation: Tuna, M., Vogel, K.P., Gill, K., Arumuganathan, K. 2004. C-banding analyses of bromus inermis genomes. Crop Sci. 44:31-37. Interpretive Summary: Smooth bromegrass is one of the most widely used pasture grasses in the United States. It has been tetraploid (28 chromosomes) and octaploid (56 chromosomes) forms. It has been difficult to characterize the chromosomes of smooth bromegrass because of their similarity. The Geimsa C-banding chromosome staining method and chromosome morphology was used to cytogenetically characterize the tetraploid and octaploid smooth bromegrass. Idiograms or graphic representations of the sets of chromosomes (karyotypes) of each ploidy level of smooth bromegrass were developed from the experimental results. Comparisons of the karyotypes indicates that the octaploid form of smooth bromegrass is not simply a doubled form of the tetraploid. At least one of its genomes or parent set of chromosomes is differentiated from the genomes of the tetraploid form. This information will enable bromegrass breeders to more efficiently structure their breeding programs.
Technical Abstract: Smooth bromegrasses (Bromus intermis Leyss) has both tetraploid and octaploid genotypes or strains that have been difficult to characterize cytogenetically because of uniformity among chromosomes. The objective of this study was to identify individual chromosomes of polyplid B. inermis using the Giemsa C-banding procedure and chromosome size and morphology to develop more detailed karyotypes for genomic comparisons. Root tips from plants from four tetraploid and three octaplid accessions were used to produce chromosome squash preparations that were used in the cytogenetic analysis. The tetraploid B. inermis genome consisted of twelve chromosomes with two telomeric bands and sixteen chromosomes with only one band on the short or long arm. All the chromosomes of the tetraploid form except for four chromosomes which were very similar to each other were identified by using C-banding patterns, chromosome length and arm ratio. The octaploid B. .inermis genome had only four chromosomes with no C-band, approximately fourteen chromosomes with two telomeric bands, and approximately thirty- eight chromosomes with only one band on either the short or long arm. It was not possible to identify all chromosomes and pair homologous chromosomes due to the similar morphology of some chromosomes. Based on this study, tetraploid B. inermis is an allotetraploid since all chromosomes except four could be separated into identifible pairs. The number of chromosomes of octaploid B. inermis with large and small satellites indicates that it is not a doubled form of the tetraploid B. inermis.