Artifical and Natural Hybrids in the Gramineae, Tribe Hordeae. VIII. Four Hybrids of Elymus and Agropyron

The following artificial hybrids were studied: Elymus patagonicus x E. glaucus, Agropyron agroelymoides x A. sp. "Calmuco" and its reciprocal, A. agroelymoides x E. glaucus and A. agroelymoides x A. spicatum var. inerme. All of them are intermediate between their parents in most morphological characteristics and are completely sterile except in the case of the hybrids between A. agroelymoides and A. sp. "Calmuco," which have between 0.18 and 2.8 per cent of seed fertility. Meiosis is very irregular, especially in the pentaploid hybrids A. agroelymoides x E. glaucus and E. patagonicus x E. glaucus. If autosyndesis does not occur in the latter hybrid, E. patagonicus would have a genome of seven chromosomes almost completely homologous to the E1possessed by E. glaucus and another genome somewhat related to the A2from E. glaucus. In A. agroelymoides x A. spicatum var. inerme a remarkable autosyndesis of the A. agroelymoides chromosomes was detected, a circumstance which renders genome analysis some-what difficult. Genome homologies, therefore, do not appear completely evident in the hybrids involving A. agroelymoides. However, it is likely that A. agroelymoides and A. sp. "Calmuco" have in common an homologous genome and that there is also some close homology between a genome (A3) of A. agroelymoides and a corresponding genome belonging to E. glaucus (A2). This A3genome would be at least partly homologous to the A1from A. spicatum var. inerme. Multivalents (trivalents to octovalents) were very frequent in the A. agroelymoides hybrids, a circumstance which, together with the potential autosyndesis of A. agroelymoides chromosomes, could be explained assuming the existence of translocated-duplicated segments in the A. agroelymoides haploid chromosome complement. In all the hybrids there is evidence for heterozygosity for inversions; in A. agroelymoides x E. glaucus bridge-fragment configurations were very frequent. Inversion heterozygosity exist also in the parental strain A. sp. "Calmuco." The morphological as well as the cytogenetic evidence indicates that A. agroelymoides and A. sp. "Calmuco" are the most closely related of the five entities studied. Agropyron agroelymoides itself is regarded as a segmental alloploid. The three South American hexaploids A. agroelymoides, A. sp. "Calmuco" and E. patagonicus, which morphologically are not wholly typical of the traditional genera where they have been tentatively placed, might have arisen through hybridization and