Cytogenetic and nuclear DNA content characterization of diploid Bromus erectus and Bromus variegates

Bromus erectus Huds. (erect brome) and B. variegatns M. Bieb. are Eurasian Bromus species that have been tentatively identified as potential progenitors of smooth bromegrass (B. 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 (2n = 2x = 14) and B. variegatus (2n = 2x = 14) using nuclear DNA content and cytogenetic analysis using Giemsa C-banding. The nuclear DNA content for B. erectus (6.19 ± 0.08 pg 2[C.sup.-1]) was less than that or B. variegatus (6.76 ± 0.05 pg 2[C.sup.-1]). These two species can be distinguished cytogenetically with the karyotypes that were developed. Complete karyotypes were not developed for both species because within species, multiple chromosomes were similar in size and C-banding. 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. Comparison 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.
THE GENUS Bromus L. contains more than 100 species of grasses with wide geographic distribution and is divided taxonomically into several sections (Armstrong, 1991). The largest section, Pnigma, consists of [...]