Probable origin of standard crested wheatgrass, Agropyron desertorum Fisch. ex Link, Schultes

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Abstract
The origin of Standard crested wheatgrass (Agropyron desertorum, Fisch. ex Link, Schultes) has been the subject of considerable speculation, and both amphiploidy and autoploidy have been proposed as evolutionary pathways. Amphiploids, derived from hybrids between Fairway crested wheatgrass (A. cristatum, L., Gaertner) and the narrow-spiked diploid (A. mongolicum Keng) were hybridized with A. desertorum. Objectives were to test the hypothesis that A. desertorum arose from hybrids between A. mongolicum and A. cristatum. Hybrids between A. mongolicum × A. cristatum amphiploids and A. desertorum were reasonably fertile. Meiotic relationships in the amphiploids and hybrids with A. desertorum were more or less typical of that found in autotetraploids. The data support the premise that the genomes of A. desertorum, A. cristatum, and A. mongolicum are basically homologous, although some structural differentiation is evident. Multivariate analyses, based on 31 morphological characters, failed to separate A. desertorum from the amphiploids. Our findings support the hypothesis that the ancestral germplasm of A. desertorum was derived from hybridization between A. mongolicum and A. cristatum followed by chromosome doubling. We further propose that A. fragile is an autotetraploid derivative of A. mongolicum and that variants of A. desertorum could be generated from hybrids between A. fragile and tetraploid A. cristatum.Key words: Cytogenetics, grass breeding, Agropyron mongolicum, Agropyron cristatum, phylogeny, taxonomy

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