Genetic diversity and structure of endangered native yew Taxus baccata in remnant populations in Belgium

Background: The European yew Taxus baccata L. is a conifer tree species for which the autochthonous populations have become rare and endangered in many European countries after a long history of human overexploitation. The general objective of this study was to perform a population genetic analysis of rediscovered and putative autochthonous relict populations of T. baccata in Belgium.Material and methods: We genotyped 223 individuals from eight relict populations in Wallonia, using seven microsatellite loci. The retrieved genetic data was used to assess the allelic richness without and with correction for the population size (A and AC), the observed and expected heterozygosity (HO and HE), level of inbreeding (FIS), and pairwise genetic differentiation among populations (FST). The spatial genetic structure within populations (SGS) was quantified using kinship coefficients (Fij). Principal coordinates analyses (PCoA) and a Bayesian clustering analysis were performed to assess the relatedness among populations.Results: We found high levels of genetic diversity within the relict populations, but also high levels of inbreeding. Furthermore, the results indicated moderate to high levels of isolation and limited gene flow among populations. The Bayesian clustering analysis indicated the presence of four distinct genetic clusters, showing only a weak relatedness among most of the larger relict populations. These results can be explained by long-term fragmentation and isolation of these likely autochthonous populations, possibly due to historical exploitation and interference. Conclusion: The loss of genetic diversity through inbreeding and limited gene flow among populations may currently compromise the long-term survival of wild European yew in Belgium. The high levels of inbreeding could be addressed, for example, by assisted exchange of germplasm between these populations.