Trispecies Hybrids of Agropyron, Elymus, and Sitanion

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Abstract
Open-pollination progeny of diploid A gropyron spicatum x A. dasystachyum, tetraploid A. spicatum x A. dasystachyum, A. dasystachyum x Elymus glaucus, E. canadensis x A. dasystachyum, and E. canadensis x A. subsecundum F1's averaged 3.4%, 1.3%, 4.3%, 9.9%, and 55.6% trispecies hybrids, respectively. Pollen parents of the trispecies hybrids included A. brachyphyllum, A. cristatum, A. desertorum, A. trachycaulum, A. tsukushiense, E. patagonicus, and Sitanion hystrix. Two of these, A. trachycaulum and S. hystrix, are close relatives of the five North American species that entered into the F1 hybrids; but the other four are distantly related species from Asia and South America. Frequency of trispecies hybridization appears to be influenced by (a) the particular F1 hybrid combination, (b) the individual hybrid within that combination, and (c) the pollinating species. The morphology, cytology, and fertility of 14 trispecies hybrid combinations are described. The morphology of the immediate pollen parent was always strongly reflected in the trispecies hybrids, but characteristics of the other two species were generally obscured. Recognition of trispecies hybirds and identification of their parentage are difficult, if not impossible, unless the parentage of the maternal F1 hybrid is known with certainty. Chromosome pairing in the trispecies hybrids was consistent with the hypothesis that both genomes of tetraploid A. dasystachyum, A. subsecundum, A. trachycaulum, E. canadensis, E. giaucus, and S. hystrlx are similar. Hexaploid A. tsukushiense, A. brachyphylluin, and E. patagonicus apparently contain a genome closely or partially homologous with the A. spicatum genome. Three of the 14 trispecies hybrid combinations produced an occasional seed, and the remaining 11 produced none.

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