Castanea Sativa Ancient Trees Across Europe: Source of Genetic Diversity

Large old trees are extraordinary organisms. They not only represent an historical, landscape and environmental heritage of inestimable value, but they are also witness to a long history of environmental changes and human interventions. For all this, they constitute a reserve of genetic variability, which can be considered a great resource for management programmes of forest species.The genetic characterization of these trees can be crucial to improve our knowledge of the molecular basis of local adaptation, identify selective drivers, and contribute to explain the contemporary genetic variation of tree species.In this study, we performed a comprehensive field survey to uncover the occurrence of large old chestnut trees in South-Central Italy, Spain and UK. We selected a total of 182 ancient trees that were genotyped using nuclear (SSRs) and adaptive (EST-SSRs) microsatellite markers with the main goals of: (1) to asses their genetic identity; (2) to derive temporal indications on the application of the grafting practice; (3) to compare their diversity with the present chestnut genetic resources; (4) to provide hypotheses on the origin of this ancient germplasm. Using the softwares GeneALex and HPrare, we evaluated the observed (Ho) and expected (He) heterozygosity, allelic richness (Ar) and private allelic richness (pAr). A Bayesian analysis was performed using the software STRUCTURE to identify the different genepools and genotypes. The obtained genetic data were compared with those of natural populations and cultivars collected in the same geographic areas. Higher values of allelic richness were observed in the ancient chestnut trees, a genetic similarity of these individual trees to the natural populations was highlighted.Our final objective is to contribute towards knowledge and valorisation of these large old trees, and to highlight germplasm sources of potential interest for both genetic improvement and conservation of European chestnut