Use of Wheat SSRs to Assess Genetic Diversity in Medusahead (Taeniatherum caput-medusae)

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Medusahead is a close relative of bread wheat that is native to Eurasia but has become a noxious, invasive weed in North America. Intergeneric use of primers for bread wheat simple-sequence repeat (SSR) markers was tested in medusahead in order to expand the pool of available genetic resources for study of this plant. Forty-two primer pairs were screened in medusahead, of which 29 produced visible bands in agarose gels. Amplicons from eight of these markers were sequenced and analyzed for the presence of SSRs and single-nucleotide polymorphisms (SNPs) among medusahead individuals from six populations in the western Great Basin. Of the eight sequenced amplicons, two contained SSRs, both of which were polymorphic and shared by the original bread wheat marker. Six of the eight markers combined to detect 33 SNP loci. BLAST comparisons of the eight amplicons revealed variable numbers of matching sequences from wheat and other grass species ranging from 0 to > 200 matches. Using data from the polymorphic loci, population genetic analysis of the six invasive medusahead populations indicated that they arose from two separate introductions with two additional subclusters possible within the two principal clusters. Extrapolating from these results, it is reasonable to expect that between 170 and 830 of the approximately 1,200 publicly available bread wheat SSRs would produce useful marker loci in medusahead.Nomenclature: Bread wheat, Triticum aestivum L.; medusahead, Taeniatherum caput-medusae (L.) Nevski, ELYCM.

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