ALLOZYME AND ESSENTIAL OIL VARIATION WITHIN AND AMONG NATURAL TUNISIAN MENTHA PULEGIUM L. (LAMIACEAE) POPULATIONS

Fourteen Tunisian natural Mentha pulegium L. populations were sampled for allozyme diversity and essential oil variation. Populations belonged to five different bioclimatic zones of the country. According to allozyme data, the species maintains a high variation within populations that could result from the mating system and the high rate of seed migration. Population genetic structure estimated by F-statistics was substantial. However, a high genetic similarity between populations was revealed. The high structure among populations and their low genetic divergence indicated their recent fragmentation under anthropic pressures. The essential oil composition assessed by gas chromatography and gas chromatography coupled to mass spectra revealed a high variation between populations for the majority of identified constituents. On the basis of the proportion of particular constituents per population, three chemotypes have been distinguished. Chemical population structure, estimated by a dendrogram based on Mahalanobis distances, was high. However, the relationship between the differentiation of populations and their bioclimatic zones membership was not evident. The principal component analysis performed both on genetic and essential oil data showed high divergence between populations belonging or not to the same bioclimate. Population structure was similar to that obtained by terpenic data. Conservation strategies should take into account results deriving from the two analysis sets. Populations with high level of genetic diversity and those sharing particular essential oil compositions must first be protected appropriately according to their bioclimate.