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

Abstract

Chromosome morphometry and nuclear DNA content are useful data for cytotaxonomy and to understand the evolutionary history of different taxa. For the genus Bromus Linnaeus, 1753, distinct ploidy levels have been reported, occurring from diploid to duodecaploid species. The geographic distribution of Bromus species has been correlated with chromosome number and ploidy level. In this study, the aims were to determine the nuclear genome size and characterize the karyotype of the South American Bromus species: Bromus auleticus Trinius ex Nees, 1829, Bromus brachyanthera Döll, 1878 and Bromus catharticus Vahl, 1791. The mean nuclear 2C value ranged from 2C = 12.64 pg for B. catharticus to 2C = 17.92 pg for B. auleticus, meaning a maximum variation of 2C = 5.28 pg, equivalent to 41.70%. Despite this significant difference in 2C value, the three species exhibit the same chromosome number, 2n = 6x = 42, which confirms their hexaploid origin. Corroborating the genome size, the chromosome morphometry (total, short- and long-arm length) and, consequently, the class differed among the karyotypes of the species. Based on the first karyograms for these Bromus species, some morphologically similar and several distinct chromosome pairs were found. Therefore, the karyotype characterization confirmed the hexaploid origin of the studied Bromus species, which differ in relation to the karyogram and the nuclear 2C value. Considering this, cytogenetics and flow cytometry can be used to discriminate Bromus species, contributing to taxonomy and systematic studies and providing information on the evolutionary history of this taxa.

A phylogenetic analysis ofBromus(Poaceae: Pooideae: Bromeae) based on nuclear ribosomal and plastid data, with a focus onBromussect.Bromus

“…The following combination of characters distinguishes Bromus from other grass genera: sheaths connate for most of their length, awns subterminal when present, ovary apices with hairy bilabiate appendages, and simple starch grains ( Smith, 1970 ). The genus has considerable variation in chromosome size, genome size, ploidy type, and ploidy level, which ranges from 2 n = 14 to 2 n = 112, with a base chromosome number of x = 7 ( Stebbins, 1981 ; Armstrong, 1991 ; Tuna, Vogel & Arumuganathan, 2005 , 2006 ; Klos et al, 2009 ; Sadeghian, Jafari & Hatami, 2010 ; Keshavarzi, Direkvandi & Khoshnood, 2016 ; Artico et al, 2017 ). Hybridization has played a role in the genus’s diversification and evolution.…”