Bread wheat (Triticum aestivum ssp. aestivum) is, together with rice and maize, one of the main staple food crops of the world; in 2012 some 675 million tones were produced worldwide . The importance of bread wheat has lead to the development of several species-specific genetic marker systems, such as SSRs (simple sequence repeats) , and DaRT markers  in addition to the generalist marker systems, for example AFLPs , previously in use. The development of Single Nucleotide Polymorphism (SNP) panels in wheat was long hampered by the lack of a reference genome sequence. However, the rapid development of sequencing methods recently enabled the completion of the wheat genome sequence , which has led to the development of SNP panels [6, 7]. These genome-wide SNP panels allow not only wheat breeding to be addressed at a whole new level, but analysis of the evolution of domesticated wheat species can now be approached on a genomic scale.
The progenitor species of all domesticated wheat, wild emmer (T. turgidum ssp. dicoccoides), arose as an allotetraploid 300,000–500,000 years ago [8, 9]. Much more recently, around 10,000 years ago, domesticated forms of emmer with a tough rachis emerged . There is evidence that the two main cultivated, free-threshing wheats, tetraploid durum and hexaploid bread wheat, emerged from domesticated emmer wheat , although de novo domestication of durum from wild emmer has not yet been ruled out . Bread wheat is believed to have arisen from a cross between a domesticated tetraploid wheat and the diploid wild grass Aegilops tauschii although it is not clear whether the tetraploid ancestor was the naked durum or the hulled emmer [11, 13, 14].
Durum wheat (T. turgidum ssp. durum), the most widely grown tetraploid wheat, is cultivated to a far lesser extent than hexaploid bread wheat. The cultivation of other domesticated tetraploid wheats, such as emmer (T. turgidum ssp. dicoccum) and rivet (T. turgidum ssp. turgidum), is very limited. These relict crops have little agricultural importance, which has also lead to them being studied to a lesser extent than bread wheat. However, some SSR  and SNP  markers have been specifically developed for durum. The tetraploid wheats are an important genetic resource for breeding novel genetic diversity into bread wheat  and hence their genetic analysis is of importance. In addition, durum, emmer and rivet are an integral part of the evolutionary history of domesticated wheat. Exploring the distribution of genetic diversity in tetraploid wheats is thus valuable, both to document the genetic diversity present and to explore aspects of wheat evolution.
To date, the phylogeography of tetraploid wheat has mainly been explored in the Mediterranean region where its dispersal has been investigated using both AFLP and SSR markers [18, 12]. Using the analysis of SSR markers in Italian emmer wheats, Isaac et al.  suggested a point of origin of emmer cultivation within the country; however, only a subset of the landrace accessions showed geographical structuring of genetic diversity. Oliveira et al. , also using SSR markers, showed that part of the genetic diversity found in durum wheats is geographically structured as an effect of the older evolutionary history of durum, but also that the effects of more recent seed trade could be detected through the wider dispersal of some genotypes.
The number of markers utilized in phylogeographic studies is a major component of the level of resolution that can be obtained . For this reason, the potential number of markers and ease of genotyping make SNP markers an attractive choice for analyses of population structure when aiming to detect higher levels of genetic structuring. The rapid discovery of SNP markers in elite bread cultivars has provided a wealth of markers that also have the potential to be utilized in the genetic analysis of tetraploid wheats. There are, however, potential problems to the transfer of markers between genetically differentiated materials. Ascertainment bias, the selection of loci from a small number of individuals that are not representative of the different allele frequencies present in a population, not only underestimates biodiversity but can also affect analyses of population structure [21, 22], although some authors have found limited effects on the general outcome . However, there are few studies that compare the phylogeographic effects of biased and unbiased markers in the same set of individuals.
Here we revisit the study of tetraploid wheat landraces in the Mediterranean by Oliveira et al. . An overlapping set of tetraploid wheat accessions is analysed using a panel of SNP markers in order to investigate whether a 15-fold increase in number of markers, although markers of a different type, will enable the detection of higher levels of phylogeographic structuring and further insight into the evolutionary history of tetraploid wheats.