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

Management Implications: Medusahead is an invasive annual grass that is unpalatable to livestock and contributes to increased wildfire risk on 250,000 ha of rangelands, mainly in western North America. It is native to Eurasia and has no known natural enemies in North America and is now the target of a classical biological control program. Currently there are few genetic markers available for the study of medusahead. An increase in the number of genetic markers would enable or facilitate many studies with important implications for field practitioners. These include precise genetic fingerprinting for medusahead plants to track the spread of invasive populations and link them to putative source populations in the weed's native range, as well as genetic analyses of medusahead traits associated with invasiveness, which will lead to improved control strategies through better understanding of the invasion process. Making new genetic markers can be expensive and technically challenging but this article shows that markers for medusahead can be adapted from the large pool of existing wheat simple-sequence repeat (SSR) markers using technology available to most minimally equipped genetic labs at a reduced cost compared to conventional SSR marker development. These results suggest that between 170 and 830 wheat SSR primer pairs could be successfully adapted to produce genetic markers in medusahead.