Relationship in the Mediterranean olive tree: evidence of sexual and asexual origin in the varietal diversification.
The relative importance of seeds and pollen genes flow in olive's varieties diversification and the somatic mutations accumulated during the history of the vegetative spread of olive's varieties in the Mediterranean Basin are presented according to a parentage analysis approach. For cultivated olive trees, the new genotypes issued from cross between known varieties are less represented in the analyzed samples. Sexual selection of wild or feral olives and asexual variation are equally represented in the Mediterranean Basin. The process of diversification of the cultivated olive trees combines asexual variations caused by mutation in the vegetative propagation with sexual variations obtained by spontaneous sowing seeds. Pairwise comparisons show that varieties whose differ by less than three loci are important reflecting an asexual variation. Similarly, the number of accessions whose relatives have not been revealed by parentage analysis is large, suggesting a selection of local seeding involving wild or feral olives trees. This study show that farmers combine the advantage offered by sexual reproduction in creating diversity and the benefits of fixing the desired characters offered by vegetative propagation to obtain new varieties with better adaptation to environmental changing conditions. Our results also show that farmers benefit from the immediate advantage offered by asexual mutation variability to maintain their best genotypes from recombination effect while offering their varieties new desired traits to their needs. Furthermore, our results show in the case of Morocco, genomes displacement and asexual variations are important in olive varietal diversification compared to France, Spain, where the seed selection appears more important in varietal diversification.