Giemsa C-banded karyotypes of Hordeum taxa from North America

Giemsa C-banding patterns of Hordeum pusillum, H. intercedens, H. brachyantherum (2x, 4x, 6x), H. jubatum, H. arizonicum, and H. depressum (2x and 4x) were rather similar, with mostly small to very small bands with no preferential disposition. The use of C-banding patterns did not improve the level of identification of taxa beyond that reached by the use of chromosome morphology. Widespread banding-pattern polymorphism prevented a reliable identification of homologues among populations based on this character alone. Chromosome length did not differentiate taxa. The ratio longest/shortest chromosome was remarkably constant over taxa, only differentiating the race of H. brachyantherum (4x) from Newfoundland, H. arizonicum, and H. depressum (4x). Marker chromosome morphology suggested the presence of one genomic common to all taxa. A further but different genome was common to the perennial polyploids, indicating an alloploid origin and a close relationship calling into question the biological relevance of some sectional divisions in Hordeum. A number of intraspecific chromosome polymorphisms were observed rendering the number of marker chromosomes, a poor diagnostic marker. A pair of relatively shorter submetacentrics than previously reported in Hordeum distinguished the genomes of H. arizonicum and H. brachyantherum (4x) from Newfoundland. A partial inactivation of the nucleolus organizers of one parental genome in interspecific hybrids is considered more common than generally appreciated.