Karyotype and nuclear DNA content of hexa-, octo-, and duodecaploid lines of Bromus subgen. Ceratochloa

Abstract

The subgenus Ceratochloa of the genus Bromus includes a number of closely related allopolyploid forms or species that present a difficult taxonomic problem. The present work combines data concerning chromosome length, heterochromatin distribution and nuclear genome size of different 6x, 8x and 12x accessions in this subgenus. Special attention is paid to the karyotype structure and genomic constitution of duodecaploid plants recently found in South America. Hexaploid lineages possess six almost indistinguishable genomes and a nuclear DNA content between 12.72 pg and 15.10 pg (mean 1Cx value = 2.32 pg), whereas octoploid lineages contain the same six genomes (AABBCC) plus two that are characterized by longer chromosomes and a greater DNA content (1Cx = 4.47 pg). Two duodecaploid accessions found in South America resemble each other and apparently differ from the North American duodecaploid B. arizonicus as regards chromosome size and nuclear DNA content (40.00 and 40.50 pg vs. 27.59 pg). These observations suggest that the South American duodecaploids represent a separate evolutionary lineage of the B. subgenus Ceratochloa, unrecognized heretofore.

Pollen viability and meiotic abnormalities in brome grasses(Bromus L., Section Ceratochloa) from Argentina

“…Hitchcock. More recently, Klos et al (2009) demonstrated that the A 1 , B 1 , and B 2 genomes are almost undistinguishable.…”

Karyotype characterization and comparison of three hexaploid species of Bromus Linnaeus, 1753 (Poaceae)

“…The large differences among nuclear 2C values for the same chromosome number suggests that the three species diverged through chromosomal rearrangements. In a study of hexaploid Bromus species, Klos et al (2009) also reported interspecific variations (2C = 12.72 to 15.10 pg) in relation to the nuclear genome size. According to these authors, chromosomal changes occurred during the evolution of the hexaploid Bromus species, most likely through the gain or loss of highly repeated DNA sequences.…”

“…The basic chromosome number of the genus Bromus is x = 7, and its species possess karyotypes varying from 2n = 2x = 14 (diploid) to 2n = 12x = 84 (duodecaploid) (Fedorov 1969, Armstrong 1984, 1987, Klos et al 2009, Williams et al 2011). Most of the species are diploid (2n = 2x = 14) or tetraploid (2n = 4x = 28) (Martinello and Schifino-Wittmann 2003), but large variation in chromosome number among Bromus species has been found, such as: Bromus cappadocicus Boissier et Balansa, 1857, and B. tomentosus Trinius, 1813, with 2n = 2x = 14; B. erectus Huds., 1762, B. biebersteinii Roemer et Schultes, 1817, and B. stenostachyus Boissier, 1884, with 2n = 4x = 28; B. tomentellus Boissier, 1846, B. variegatus M. Bieberstein, 1819 (Sheidai et al 2008), B. auleticus (Martinello and Schifino-Wittmann 2003), B. bonariensis Parodi et J. H. Camara, 1963, B. brevis Steudel, 1854, B. parodii Covas et Itria, 1968, B. brachyanthera and B. catharticus Vahl, 1791 (Schifino and Winge 1983, Naranjo 1985) with 2n = 6x = 42.…”

“…This way, the distinction between karyotypes of Bromus species with the same chromosome number is generally carried out based on the size of the satellite portions (Armstrong 1983, Joachimiak et al 2001) and heterochromatin distribution (Klos et al 2009). …”

“…The nuclear genome size was measured for Bromus hexaploid (2n = 6x = 42) species. In spite of the same chromosome number, the seven species showed distinct nuclear 2C values, varying from 2C = 12.72 pg in Bromus willdenowii Kunth, 1829, to 2C = 15.10 pg in Bromus lithobius Trin., 1836 (Klos et al 2009). …”