THE GENOME CONSTITUTION AND PHYLOGENY OF ELYMUS AMBIGUUS

Abstract

Two Elymus ambiguus Vasey & Scribn. collections from Utah and Idaho were 2n = 28, and the species behaved meiotically as an allotetraploid. The E. ambiguus plants were highly self‐sterile, and they hybridized readily with Asian E. junceus Fisch. (2n = 14), E. karataviensis Roshev. (2n = 28), E. multicaulis Kar. & Kir. (2n = 28), and North American E. innovatus Beal (2n = 28). Chromosome pairing at metaphase‐I in the E. ambiguus X E. junceus triploid hybrids indicated that one E. ambiguus genome was closely homologous with the E. junceus genome. Chromosome pairing in the tetraploid hybrids indicated that both E. ambiguus genomes were more or less homologous with the genomes of E. karataviensis, E. multicaulis, and E. innovatus. The basic genome formula of E. ambiguus may be written as JJXX, where J is the E. junceus genome and X is a genome of unknown origin. Chromosome pairing in the hybrids indicated that E. ambiguus is more closely related to North American E. innovatus than to the Asian species. The E. ambiguus X E. innovatus hybrids were the only hybrids that set seed. Gene flow between E. ambiguus and E. innovatus is biologically possible, but geographic separation of the species precludes natural introgression.