Genetic diversity and population structure of wild olives from the North Western Mediterranean assesed by SSR markers

Background and Aims Olive cultivars and their wild relatives (oleasters) represent two botanical varieties of Olea
europaea subsp. europaea (respectively europaea and sylvestris). Olive cultivars have undergone human selection
and their area of diffusion overlaps that of oleasters. Populations of genuine wild olives seem restricted to isolated
areas of Mediterranean forests, while most other wild-looking forms of olive may include feral forms that escaped
cultivation.
Methods The genetic structure of wild and cultivated olive tree populations was evaluated by amplified fragment
length polymorphism (AFLP) markers at a microscale level in one continental and two insular Italian regions.
Key Results The observed patterns of genetic variation were able to distinguish wild from cultivated populations
and continental from insular regions. Island oleasters were highly similar to each other and were clearly distinguishable
from those of continental regions. Ancient cultivated material from one island clustered with the wild plants,
while the old plants from the continental region clustered with the cultivated group.
Conclusions On the basis of these results, we can assume that olive trees have undergone a different selection/
domestication process in the insular and mainland regions. The degree of differentiation between oleasters and
cultivated trees on the islands suggests that all cultivars have been introduced into these regions from the outside,
while the Umbrian cultivars have originated either by selection from local oleasters or by direct introduction from
other regions.