Genetic characterization of Italian and Spanish wild and domesticated chestnut trees

•A clear separation emerged between the Spanish and the Italian chestnut trees and among samples belonging to north and south of Spain.•Northern Italy and the Galicia region are the geographic areas where the genetic variability is more homogenous and preserved being derived by chestnut spontaneous establishment.•Wild and domesticated chestnuts trees from Iberian Peninsula and Italy showed no significant structure genetic differences. The only native species of the Castanea genus in Europe is Castanea sativa Mill., a widespread and important multipurpose tree species in the Mediterranean area that provides fruit, wood and shelter for hives. With the aim of expanding the knowledge of the genetic variability of the chestnut species (wild trees and varieties) and promoting the traceability of local products, an analysis based on 16 SSRs was carried out on 630 single trees from Italy and Spain. 319 unique genotypes were identified. A Bayesian approach combined with the Markov Chain Monte Carlo (MCMC) simulation method revealed the existence of two genetically distinct groups of chestnuts: Cluster 1 (Spain) and Cluster 2 (Italy), with a clear separation between the cultivars from (northern and southern) Spain and from Italy. The results also confirmed a common genetic structure between chestnut populations from southern Spain and southern Italy, which is the result of historical events and long-term human impact. The results showed no genetic differentiation between chestnut cultivars (grafted trees) and wild chestnut trees, probably as a consequence of the proximity of orchards and natural populations, which resulted in a gene flow between them.