PHYLOGENETIC RELATIONSHIPS OF AN UNKNOWN TETRAPLOID BROMUS, SECTION BROMOPSIS

A previously unreported member of the section Bromopsis, having taxonomic similarities to B. pumpellianus and B. pacificus, was recently found in westcentral Alaska. Its relationship to these species and to B. inermis and B. ciliatus has been investigated. Both this unreported member (Bromus X) and B. pacificus were shown for the first time to be tetraploids (2n = 28); forms of B. ciliatus originating in Russia and North America were diploids (2n = 14); and a number of Alaskan B. pumpellianus were octoploids (2n = 56). Chromosomes with large satellites were found in Bromus X, B. pumpellianus, and a tetraploid form of B. inermis but not in B. pacificus or B. ciliatus. Seed was produced and hybrids resulted from crosses of Bromus X with B. pumpellianus and tetraploid B. inermis but no seed developed from crosses with B. pacificus and B. ciliatus. A relatively high frequency of stainable pollen among the hybrids suggested that they were partially fertile. It was concluded that Bromus X was a very close relative of B. pumpellianus and B. inermis but was not closely related to B. pacificus or B. ciliatus.