SYNTHETIC AGROPYRON‐ELYMUS HYBRIDS: II. ELYMUS CANADENSIS X AGROPYRON DASYSTACHYUM

Pollination of 40 emasculated E. canadensis florets with A. dasystachyum pollen gave rise to 12 shriveled seeds, one of which was viable. The hybrid seedling developed into a vigorous plant whose vegetative and spike characteristics were for the most part intermediate between those of the parents. Both parents behaved cytologically as allotetraploids, 2n = 28, and formed 14 bivalents regularly at metaphase I. Chromosome associations in the hybrid, 2n = 28, averaged 0.42 1, 13.70 II, 0.02 III, and 0.03 IV in 142 metaphase-I cells interpreted. The hybrid produced 165 seeds under open-pollination during its second year in the field. E. canadensis and A. dasystachyum apparently contain closely homologous genomes whose major structural differences consist of several inverted segments and possibly a small reciprocal translocation. The close homology between the E. canadensis and A. dasystachyum genomes was unexpected in view of the wide morphological, ecological, and reproductive differences that separate the two species. ELYMUS CANADENSIS L., Canada wild-rye, is an allotetraploid, 2n = 28, self-fertilizing bunchgrass normally found on moist, open sites throughout most of the United States (Hitchcock, 1951). It hybridizes quite readily with several other Elymus species (Brown and Pratt, 1960; Dewey, 1965c), some Agr-opyron species (Stebbins and Snyder, 1956; Dewey, 1966), and a Sitanion species (Dewey, 1967). iNIost of the species with which E. canadensis hybridizes are also selffertilizing, allotetraploid bunchgrasses. These species, including E. canadensis, contain closely related genomes (Dewey, 1966), one of which was apparently derived from A. spicatum (Stebbins and Snyder, 1956). Agropyron dasystachyum (Hook.) Scribn., thickspike wheatgrass, is a tetraploid, 2n = 28, cross-pollinating, rhizomatous species common to moist or arid sandy sites from the Great Lakes westward (Hitchcock, 1951). It has been hybridized experimentally with diploid, 2n = 14, and tetraploid, 2n = 28, forms of A. spicatum (Pursh) Scribn. and Smith. The two species have one closely homologous genome (Dewey, 1965a). A. riparium Scribn. and Smith, the glabrous form of A. dasystachyum, has been hybridized with A. repens (L.) Beauv., 2n = 42 (Dewey, 1965b), and A. caninum (L.) Beauv., 2n = 28, (Allderdice, 1965). Chromosome pairing in these hybrids indicates homologies between one A. riparium and A. repens genome and both A. riparium and A. caninumn genomes. Controlled 1 Received for publication 7 November 1966. Cooperative investigations of the Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, and the Utah Agricultural Experiment Station, Logan. Approved as Journal paper No. 613, Utah Agr. Expt. Sta. intergeneric hybrids involving A. dasystachyum have not been previously reported, although A. dasystachyum has been suggested as a parent of the natural intergeneric hybrid A groelyrnus turneri LePage (Nielsen, 1961). Elymus canadensis and A. dasystachyunm appear to have at least one genome in common, i.e., the A. spicatum genome. The rather wide morphological, ecological, and reproductive differences between these species suggest more or less unrelated second genomes. The prime objective of this investigation was to determine the genome relations between E. canadensis and A. dasystachyum through a cytogenetic studv of these species and their intergeneric hybrid. MIATERIALS AND METHODS Elyrnus canadensis and A. dasystachyum were hybridized in the field in 1963. E. canadensis P.I. 232249, a M\Iontana collection, served as the maternal parent. Forty florets from one spike were hand-emasculated; then the spike was bagged. Two days later pollen-bearing spikes of a Canadian accession of A. dasystachyum P.I. 236663 were introduced into the bag. The A. dasystachyum spikes, which were borne on detached culms sustained in a carton of water in the bag, continued to shed pollen for several days. Pollination appeared to be good. Seed began to form in almost all florets, but most developing seeds aborted within 10 days after pollination. Twelve shriveled seeds were later harvested, but only one germinated. This viable seed subsequently developed into a vigorous plant, which proved to be a hybrid. The hybrid was established in the field in 1964, and spikes were collected from it and the parents for