SYNTHETIC AGROPYRON‐ELYMUS HYBRIDS: III. ELYMUS CANADENSIS X AGROPYRON CANINUM, A. TRACHYCAULUM, AND A. STRIATUM

Hybrids were produced with relative ease from controlled crosses of Elymus canadensis L. with European Agropyron caninum (L.) Beauv., North American A. trachycaulum (Link) Malte ex H. F. Lewis, and Asian A. striatum Nees ex Steud. All hybrids appeared to be completely sterile and were, for the most part, morphologically intermediate between their parents. The E. canadensis X A. caninum hybrids were exceptionally vigorous and leafy and may have some potential as forage grasses if fertility can be achieved. All parent plants were tetraploid, 2n = 28, and they behaved cytologically as alloploids. Chromosome pairing in the hybrids indicated that both E. canadensis genomes were closely homologous with those of A. trachycaulum and somewhat less homologous with those of A. caninum. Interchanged and inverted chromosome segments apparently constitute the major differences between E. canadensis, A. trachycaulum, and A. caninum genomes; however, cryptic structural differences must also exist. Partial -homologies were detected between one A. striatum and E. canadensis genome, but their other genomes were distinctly different. The genome relations between the parent species were expressed in terms of the following genome formulas: E. canadensis, SISiXiXi; A. trachycaulum, S2S2X2X2; A. caninum, S3S3X3X3; and A. striatum S4S4YY or X4X4YY, where "S" refers to a genome derived from A. spicatum and "X" and "Y" are genomes of unknown origin. ELYMUS CANADENSIS L. is one of the most widely hybridized species in the Triticeae tribe. It can be hybridized with most, if not all, eastern North American Elymus species (Brown and Pratt, 1960; Church, 1967) and with several western North American species, including E. glaucus Buckl. (Dewey, 1965) and E. cinereus Scribn. and M\'Jerr. (Dewey, 1966b). It crosses readily with Sitanion hystrix (Nutt.) J. G. Smith (Dewey, 1967a) and presumably with all other Sitanion species. E. canadensis is known to hybridize with at least 10 Agropyron species including A. spicatum (Pursh) Scribn. and Smith (Stebbins and Snyder, 1956), A. subsecundum (Link) Hitchc. (Dewey, 1966a), and A. dasystachyum (Hook.) Scribn. (Dewey, 1967b). With the exception of diploid A. spicatum and octoploid E. cinereus, all of the aforementioned species are tetraploid, 2n = 28, and each contains a genome partially or fully homologous with the A. spicatum genome (Stebbins and Snyder, 1956). Both E. canadensis genomes are more or less homologous with those of the eastern North American Elymus species (Church, 1967), E. Received for publication 4 March 1968. Cooperative investigations of the Crops Research Division, Agricultural Research Service, USDA, and the Utah Agricultural Experiment Station, Logan, Utah. Approved as Journal paper No. 756, Utah Agr. Exp. Sta. glaucus (Dewey, 1965), Sitanion hystrix (Dewey 1967a), Agropyron subsecundum (Dewey, 1966a) and A. dasystachyum (Dewey, 1967b). This paper extends the known hybridization range of E. canadensis to two more Agropyron species. E. canadensis has been previously crossed with A. caninum (Cugnac and Simonet, 1953); however, E. canadensis var. glaucifolius (Muhl. ex Willd.) Torr. was used in that hybridization. LePage (1965) reported a natural hybrid with A. trachycaulum and E. canadensis as the putative parents, but the parentage of this hybrid has never been verified. The E. canadensis X A. striaturm Nees ex Steud. hybrid is unique in that it is the first recorded hybrid of E. canadensis with an Asian species. The prime objective of this investigation was to determine the genome relations among the parent species through a study of chromosome pairing in the parents and hybrids and thereby contribute to a better understanding of the taxonomic and phylogenetic relations among Agropyron and Elymus species. Morphological, fertility, and cross-compatibility data are included to supplement the cytological data. MATERIALS AND METHODS-All plant materials came from seed initiaLly acquired from the USDA Plant Introduction Station at Pullman, [The JOURNAL for October (55: 1003-1132) was issued 29 October 1968] AMERICAN JOURNAL OF BOTANY, Vol. 55: No. 10, 1968