Western wheatgrass [Pascopryum smithii (Rydb.) Love (= Agropyon smithii Rydb)] is an allogamous North American range grass cultivated for seed production, hay, low-maintenance turf, and soil stabilization. The USDA maintains western wheatgrass cultivars, synthetic multiple-origin germplasms, and source-identified single-origin accessions in the National Plant Germplasm System. The objective of this study was to test similarity of amplified fragment length polymorphism (AFLP) genotypes among individual plants classified by accession and geographic provenance, and compare rates of DNA variation between single-origin and multiple-origin germplasm. Individual plants from 36 of 39 source-identified single-origin germplasm sources group strictly by accession, on the basis of the average proportion of shared DNA fragments between individual genotypes. Conversely, individual plant genotypes from three of the four synthetic multiple-origin accessions did not cluster by accession and displayed higher rates of DNA variation than did single-origin accessions. Although different accessions of the same cultivar generally group together, off-types were detected in six of the nine cultivar accessions. Pairwise comparisons of interpopulation genetic distances (phi(st)) among 39 single-origin accessions were correlated with geographical distances among the original collecting sites (r = 0.66). Genotypes representing these accessions form three natural groups on the basis of phi(st) that correspond to three geographic regions of the USA: northern Great Plains, northern Rocky Mountains, and southern Rocky Mountains. Therefore, georaphically significant sources of DNA variation were detected and maintained within and among these ex situ germplasm sources. These results document genetic identity and diversity in the USDA western wheatgrass germplasm collection and support the premise that geographic provenance contributes to germplasm integrity.
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