Pollen-mediated gene flow and fine-scale spatial genetic structure in Olea europaea subsp. europaea var. sylvestris.

ABSTRACT Background and Aims Wild olive (Olea europaea subsp. europaea, var. sylvestris) is important from an economical and ecological point of view. The effects of anthropogenic activities may lead to the genetic erosion of its genetic patrimony which has high value for breeding programs. In particular, the consequences of the introgression from cultivated stands are strongly dependent on the extent of gene flow and, therefore, this work aims at quantitatively describing contemporary gene flow patterns in wild olive natural populations. Methods: The studied wild population is located in an undisturbed forest, in Southern Spain, considered one of the few extant hotspots of true oleasters diversity. A total of 225 potential father trees and seeds issued from five mother trees were genotyped by eight SSRs. Levels of contemporary pollen flow, both in terms of pollen immigration rates and within-population dynamics, were measured through paternity analyses. Moreover, the extent of fine-scale spatial genetic structure (SGS) and Bayesian clustering were studied to assess the relative importance of seed and pollen dispersal in shaping the spatial distribution of genetic variation. Key Results: The results of this study showed that the population under study is characterized by a high genetic diversity, a relatively high pollen immigration rate (0.57), an average within-population pollen dispersal of about 107 m and weak but significant SGS up to 40 m. The population is a mosaic of several intermingled genetic clusters that is likely to be generated by spatially restricted seed dispersal. Moreover, wild oleasters were found to be self-incompatible and preferential mating between some genotypes was revealed. Conclusions: The knowledge of the within-population genetic structure and gene flow dynamics will lead to identifying possible strategies aimed at limiting the effect of anthropogenic activities and improving breeding programs for the conservation of olive tree forest genetic resources.