Genetic diversity and relationships of wild and cultivated olives at regional level in Spain

Genetic diversity and relationships between local cultivars and wild olive trees from three important Spanish olive-growing regions, Andalusia (South), Catalonia and Valencia (from Eastern Mediterranean Coastal area), were studied by means of eight SSR loci. Distinct allelic composition and heterozygosity levels were found in wild olive populations and cultivars. The observed patterns of genetic variation revealed: a) the independent clustering of Andalusian wild olives in a separate gene pool, b) the belonging of wild populations and most cultivars from Catalonia to another gene pool, c) the joined clustering of Andalusian and a set of Valencian cultivars in a third gene pool, and d) clustering of wild individuals from Valencia to the three different gene pools. These results suggest that wild populations of Andalusia may represent true oleasters, the ones from Catalonia may be feral forms derived from cultivar seed spreading, while the population of Valencia seems to be the most admixed one. The significant differentiation between Andalusian and most Catalonian cultivars is indicating an independent selection of olive cultivars in the two regions. The detection of a certain wild genetic background in some Catalonian and Valencian cultivars and the similarity found between wild and cultivated forms may suggest the use of local wild trees in olive domestication. The proposed scenario for the development of olive cultivars in Andalusia includes an empirical selection of outstanding local wild genotypes followed by various generations of crosses and various replanting campaigns, as well as possible introductions of ancestral cultivars. Therefore, our findings would lead us to support the hypothesis that the current diversity found in Spanish olive cultivars may be regionally differentiated and due to both, autochthonous and allochthonous origin. The information obtained in this work gives insights into the genetic resources of the main olive producing country, demonstrating that wild olive populations and local cultivars both represent potential sources of useful variability for olive breeding programs. (C) 2010 Elsevier B.V. All rights reserved.