Genetic diversity in wild Tunisian populations of Mentha pulegium L. (Lamiaceae)

The allozyme variation of 15 Tunisian wild populations of Mentha pulegium L. threatened by human activities (clearing, hard-grazing, ploughing, traditional uses) was surveyed by the analysis of 14 isozyme loci using horizontal gel starch electrophoresis. The species exhibited a high level of genetic variation within populations (the mean Ap = 2.20, P = 72%, Ho = 0.349 and He = 0.229), which indicates a predominately outcrossing mating system and the recruitment of new genotypes via dispersal seeds. The genetic structure analysis of the populations using F statistics indicates no inbreeding, and showed an excess of heterozygosity for few loci. The moderate differentiation of populations (F_ST = 0.110) and the low rate of gene flow between them (Nm = 2.02) might been caused by recent isolation of the populations through biotope disturbances. The value of Nei's genetic identity varied from 0.839 to 0.999 reflecting a relatively low genetic divergence between populations. Cluster analysis using UPGMA method and Nei's genetic identity values, showed that populations geographically close didn't always cluster together. However, populations within the same bioclimatic stage generally subclustered together indicating that differentiation between bioclimatic regions occurred.