Genome Relations of South American Agropyron tilcarense with North American and Asian Agropyron Species

Agropyron tilcarense J. H. Hunziker is a caespitose, self-fertilizing, South American allotetraploid (2n = 28) wheatgrass, which readily hybridized with Asian A. libanoticum Hack. (2n = 14) and North American A. spicatum (Pursh) Scribn. & Smith (2n = 14), A. dasystachyum (Hook.) Scribn. (2n = 28), and A. trachycaulum (Link) Malte ex H. F. Lewis (2n = 28). Chromosome pairing in the hybrids indicated that the genomes of diploids A. libanoticum and A. spicatum were more or less homologous with one of the two A. tilcarense genomes and that both genomes of A. dasystachyum and A. trachycaulum were closely similar to those of A. tilcarense. The genomes of A. tilcarense differed from those of the other species in structural chromosomal rearrangements, primarily interchanges. The basic genome formula of A. tilcarense was designated as SSHH, the same as that of A. dasystachyum and A. trachycaulum. The triploid hybrids with A. libanoticum and A. spicatum were highly sterile; the tetraploid hybrids with A. dasystachyum and A. trachycaulum averaged 59 and 62 seeds per plant, respectively. Some hybrids had excellent vegetative vigor and may have plant-breeding potential via introgression or induced amphiploidy.