Cytogenetics of Agropyron ugamicum and Six of Its Interspecific Hybrids

Seven collections of Agropyron ugamicum Drob., introduced into the United States from Central Asia in 1965, proved to be tetraploid, 2n = 28, and self-fertilizing. Hybrids were obtained between A ugamicum and six other Agropyron species with known genome constitutions: North American A. spicatum (Pursh) Scribn. & Smith, 2n = 14, SS; Middle Eastern A. libanoticum Hack., 2n = 14, SS; Eurasian A. caninum (L.) Beauv., 2n = 28, SSHH; Eurasian A. mutabile Drob., 2n = 28, SSHH; North American A. trachycaulum (Link) Malte ex H. F. Lewis, 2n = 28, SSHH; and North American A. pringlei (Scribn. & Smith) Hitchc., 2n = 28, SSHH. Chromosome pairing in triploid hybrids showed that one of the two genomes of tetraploid A. ugamicum was partially homologous with the S genome of diploid A. spicatum and A. libanoticum. Pairing in the tetraploid hybrids showed that A. ugamicum had only the S genome in common with A. caninum, A. mutabile, A. trachycaulum, and A. pringlei. The second genome of A. ugamicum is designated as Y, and the genome formula of A. ugamicum is SSYY. Species with S and Y genomes are East Asian grasses. The diploid source of the Y genome is unknown. If a YY diploid still exists, it probably occurs in Western China or Himalayan countries. All hybrids were totally sterile, which precludes introgression between A. ugamicum and the other six species. Two hybrids, A. libanoticum x A. ugamicum and A. ugamicum x A. trachycaulum, were exceptionally vigorous, and they may have economic potential as forage grasses if fertility can be restored.