Genetic and geographical structure in grapevines from northwestern Spain

The grapevine germplasm bank from Estacion de Viticultura e Enoloxia de Galicia contains 110 accessions collected from more than 100-year-old grapevines from northwestern Spain. We identified 60 different genotypes (among which Pinot Noir and Shyrah were included as references) with 32 polymorphic microsatellites (SSRs), 21 of which were unlinked SSRs and without null alleles, which were used to detect genetic structure. We found four reconstructed populations that were highly differentiated by analysis of molecular variance (18.3%): (i) western Galician group (Caino Bravo); (ii) eastern Galician group (Merenzao); (iii) Castilian group (Garnacha) and (iv) southern Spanish group (Moscatel). The greatest genetic differentiation was found between the western Galician/eastern Galician groups and the southern Spanish/Castilian groups, with Fst?>?0.13. Western and eastern Galician groups contained most of the ancient Galician cultivars (86%) and included ancestors from central Europe, such as Pinot Noir and Shyrah in the western Galician group and the introgressant Merenzao (French Trousseau) in the eastern Galician group; the Castilian and southern Spain groups included traditional cultivars from central and southern Spanish and suggest a further introduction of those cultivars in northwestern plantations. Genetic structure corresponded with East-to-West geographical differentiation in the northern Iberian Peninsula, following the old path to Santiago de Compostela from France, with the southern Spanish and Castilian groups in the East (Castilian plateau and southern Spain), the eastern Galician group and the western Galician group in the West. Five new relationships were discovered: Caino Bravo/Caino Longo2, Albarin Tinto/Torrontes1, Treixadura/Treixadura Francesa, Moscatel/Moscatel de Bago Miudo and Moscatel/Moscatel de Hamburgo, indicating that hybridisation and further selection by growers have been the origin of most of the genetic diversity found in northwestern Spain.