Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2005
Publication Date: 3/14/2006
Citation: Tuna, M., Vogel, K.P., Arumuganathan, K. 2006. Cytogenetic and nuclear DNA content characterization of diploid Bromus erectus and Bromus variegatus. Crop Science 46:637-641. Interpretive Summary: Erect brome, Bromus erectus, and Bromus variegatus are bromegrass species that are native to Europe and Asia. Both of these species are diploids which means they each have two sets of 7 chromosomes. They are potential progenitors of smooth bromegrass, Bromus inermis, which is widely grown in North America as a pasture grass. Smooth bromegrass is a polyploid and can have either 4 or 8 sets of chromosomes. The objective of this study was to determine the nuclear DNA content of these species and characterize their chromosomes using cytogenetic analyses and compare them to other diploid and polyploid bromegrass species. The results indicated that these species have a similar amount of DNA as other Eurasian diploid bromegrass species but they have significantly less DNA than North American diploid bromegrasses. The chromosomes of the two species can be distinguished from each other and other diploid bromegrass previously evaluated by their morphology and chromosome staining pattern. The results suggest that if these diploid species were the donor species for polyploid smooth bromegrass and related meadow bromegrass, significant evolutionary changes have occurred since the initial formation of these polyploidy species including chromosome loss and re-arrangement.
Technical Abstract: Bromus erectus Huds. (erect brome) and B. variegatus M. Bieb. are Eurasian Bromus species that have been tentatively identified as potential progenitors of smooth bromegrass (Bromus inermis Leyss) which is the principal cultivated bromegrass in North America. The objective of this study was to characterize the genome of diploid accessions of B. erectus and B. variegatus using nuclear DNA content and cytogenetic analysis using Giesma C-banding. The nuclear DNA content for B. erectus (6.19 ± 0.08 pg 2C-1) was less than that of B. variegatus (6.76 ± 0.05 pg 2C-1). It was not possible to develop complete karyotypes for both species, because within species, multiple chromosomes were similar in size and C-banding. The two species can be distinguished cytogenetically with the karyotypes that were developed. Both species had two pairs of chromosomes with satellites but the size of the satellites and the number and position of C-bands on these chromosomes differed between species. Bromus variegatus had five pairs of chromosomes with telomeric C bands on both arms, while B. erectus had four pairs of chromosomes with a single telomeric band on the long arm and a single pair with telomeric bands on both arms. Comparisons with the previously reported karyotypes and nuclear DNA contents for tetraploid and octaploid B. inermis suggest that if the diploid species B. erectus, and B. variegatus were the donor species for these polyploids, significant evolutionary changes have occurred since the initial formation of these species including chromosome loss and re-arrangement.