Origin of traditional sweet chestnut (Castanea sativa Mill.) varieties from the Northwest of the Iberian Peninsula

Sweet chestnut is a valuable species, highly managed for centuries for nut and wood production, whose genetic structure was affected by translocations. In this study, we selected a total of 51 genetically different clonal varieties from Galicia (NW of the Iberian Peninsula), Central Iberian Peninsula, France and Italy that were genotyped at 9 microsatellites. Almost all Galician varieties include at least two accessions with the same genotype. Several datasets of reference samples, from 29 natural or naturalized populations, were used to classify them into several groups. Genetic distances among varieties showed its cultivation area. Almost all Galician varieties cultivated in orchards were grouped in a single cluster except to ‘Famosa’, ‘Longal’, ‘Garrida’ and ‘Presa’ that were classified to the Central Iberian group and ‘Luguesa’ and ‘Carrelao’ to the French-Italian varieties. The Bayesian analysis with reference samples identified a group of varieties that could be autochthonous in Galicia because they were assigned to the Atlantic or the Cantabrian cluster. Other varieties from the Galician inner mountains that belong to the Mediterranean cluster could be translocated because this gene pool was found previously in several populations in the Iberian and Italian Peninsulas. Additionally, a large number of hybrid varieties between the Western Mediterranean cluster and the Atlantic or the Cantabrian cluster were found. Further analysis indicated that these Mediterranean varieties could be originated in Mercurín, in Central Iberian or Italian Peninsulas, and that ‘Luguesa’ and ‘Puga de Afora’ could be translocated from France or Italy. The results provided in this work provide a valuable information for a more efficient use of sweet chestnut genetic resources.