FISH Based Karyotypes of Some Diploid and Polyploid Species in the Grass Genus Bromus L.

The genus Bromus contains more than 100 species distributed over all continents. The ploidy level within the genus varies from diploid to decaploid. Studies of the genome structure, evolution and diversity of the grass genus Bromus have been hindered by the morphologically similar chromosomes which make karyotyping difficult using classical cytogenetic methods. The objective of this study was to exploit new molecular cytogenetic approaches (fluorescence in situ hybridization, FISH) using 5S, and 45S rDNA as chromosome markers for identification of Bromus chromosomes to generate more informative karyotypes . Relative distribution patterns of 5S and 45S rDNA sequences were species-specific and fluorescence in situ hybridization of these two types of the tandenly repeated sequences by using as probe made it possible to identify nearly half of the chromosomes in all species tested except tetraploid B. ciliatus. B. ciliatus had signal on only four chromosomes and its karyotype was the most distinct. It appears that diploid species are more distinct than their related polyploids. The results of this study confirm the previous reports suggesting that Eurasian polyploid species of section Pnigma of genus Bromus are closely related and carry different number of copies of the same genomes.