Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2013
Publication Date: 7/1/2013
Citation: Rector, B.G., Ashley, M.C., Gaskin, J.F., Longland, W.S. 2013. Use of wheat SSRs to assess genetic diversity in medusahead (Taenintherum caput-medusae). Invasive Plant Science and Management. 6:352-361.
Interpretive Summary: Medusahead is a noxious weed that is native to the Mediterranean region. There is a need for genetic markers to be developed to study invasive medusahead populations in the western USA. Taking advantage of the close taxonomic relationship between medusahead and cultivated wheat, ARS scientists screened six medusahead populations from California and Nevada with 42 simple-sequence repeat (SSR) markers from the publicly available wheat genetic map. Twenty-nine of them produced a successful result and eight of these were sequenced for more precise evaluation. Six of those eight markers produced a total of 35 useful genetic marker loci that were scored and analyzed for eight medusahead plants in each of the six study populations as a demonstration of the markers’ utility. The results showed that these six populations were likely to be the result of at least two separate introductions from Eurasia. Based on the overall results, it is estimated that if all 1,200 SSRs from the wheat genetic map were screened, at least 170 of them would produce over 1,000 useful genetic marker loci in medusahead, thereby greatly expanding the genetic resources available for study of this important weed while avoiding the normal costs associated with SSR production.
Technical Abstract: Medusahead (Taeniatherum caput-medusae) is a close relative of bread wheat (Triticum aestivum) that is native to Eurasia but has become a noxious, invasive weed in North America. Intergeneric use of primers for bread wheat microsatellite (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, some of which were highly polymorphic among the six tested populations. BLAST comparisons of the eight amplicons revealed variable numbers of matching sequences from other grass species ranging from 0 to >200 matches. Population genetic analysis of the six invasive medusahead populations indicated that they arose from two separate introductions with two additional sub-clusters possible within the two principal clusters. Extrapolating from these results, it is reasonable to expect that >170 of the ~1,200 publicly available bread wheat SSR primer pairs could produce >1,000 codominant, PCR-based marker loci in medusahead.