Assessment of the genetic diversity and relationships of a collection of Mentha spp. in Tunisia using morphological traits and ISSR markers

The taxonomic identity of Mentha species is difficult as it displays variations at morphochemical characters. The aim of this investigation was to study Mentha spp. diversity in 60 Tunisian accessions using morphological traits and molecular markers. Thirty-three botanical descriptors were analysed. The numerical taxonomic analysis identified 58 accessions and defined seven taxonomic groups including M. aquatica, M. longifolia, M. piperita, M. pulegium, M. rotundifolia, M. spicata and M. spicata var. crispa 'moroccan'. Thereafter, genetic diversity of these accessions was investigated using ISSR markers. Nine highly polymorphic ISSR primers were selected to amplify DNA of each accession. Based on UPGMA method, these accessions could be grouped into two major clusters. M. pulegium group occupied a relatively basal position in the dendrogram and formed a single cluster. The second large cluster contained the accessions of the section Mentha, clustered into five subgroups. Molecular separation of the Mentha suggested that hybridisation among species may result in convergence and/or divergence of different species. Our study has shown (1) a high morphological and molecular diversity in the Tunisian accessions and (2) that combining morphological and molecular data is crucial to a proper identification, allowing the correct use of these accessions in future breeding programmes.