Genetic variation is a major component of plant development and adaptation, and recent studies have shown that genetic variation among plant species can have important ecological effects. Oriental beech (Fagus orientalis Lipsky) is a dominant tree species in the Hyrcanian forests, where it occupies approximately 18 % of the forested area. In this study, nine expressed sequence tag simple sequence repeat (EST-SSR) markers were used to determine the genetic diversity and structure of Iranian Oriental beech populations growing at different altitudes. We further compared the genetic structures of the Iranian populations to a F. orientalis and a Fagus sylvatica L. population from the hybrid zone of the two taxa in southeast Europe, and to a F. sylvatica population from central Europe. All populations showed a high genetic diversity, which was similar to other F. orientalis and F. sylvatica populations from Europe. The genetic differentiation among Iranian beech populations was very low. In contrast, distinct genetic differentiation was found between the Iranian populations and the analyzed European populations (F. orientalis and F. sylvatica). One EST-SSR was identified to differentiate (GST: 0.503) between F. orientalis and F. sylvatica with very pronounced allele frequency differences between taxa. Specifically, the Fagus sylvatica characteristic allele 189 was almost absent from all Iranian populations and present in low frequencies in F. orientalis populations from other regions. This study helps to extend the knowledge of genetic diversity and genetic structure of Iranian Oriental beech populations. It further gives insights into the genetic differentiation between F. orientalis populations from the center and the edge of the species’ distribution range as well as between Oriental and European beech.
