Genetic diversity in Eucommia ulmoides (Eucommiaceae), an endangered traditional Chinese medicinal plant

Eucommia ulmoides, the only species of Eucommiaceae, has been used as Chinese medicinal plant for more than 2,000 years, and is endangered as a consequence of long-term overexploitation. In this study, genetic diversity within and among the semi-wild and cultivated populations of E. ulmoides collected from its main production area was investigated using two cpSSR and 227 AFLP loci. A moderate level of within-population diversity was observed (hS = 0.549 for cpSSR and H-eB = 0.183 for AFLPs), which could be explained by the dioecious breeding system, longevity, and human mediated seed exchange. Compared to the semi-wild population, the cultivated population possessed relatively low genetic diversity, which suggests cultivation practice may have reduced the genetic diversity of E. ulmoides. Populations were low to moderately differentiated from one another (G(ST) = 0.281 for cpSSR, and theta(B) = 0.100 for AFLPs), which was also supported by the AMOVA analysis that 62.52 and 83.48 % total variation resided within populations based on cpSSR and AFLP analysis, respectively. An isolation by distance analysis revealed that geographical distances was not significantly correlated with genetic distance. Human activities such as seed selection and seed exchange could account for the genetic structure of cultivated populations. In addition, two genetic clusters were detected by the Structure analysis. For conservation purpose, an ex situ conservation measure for conserving the genetically distant populations to maximize genetic diversity of the species is recommended.