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Alnus cordata (Loisel.) Duby (Neapolitan alder) is an endemic tree species with a restricted distribution range, limited to Corsica and southern Italy. The economic value of its wood, its rapid growth, the tolerance to drought stress and the nitrogen fixation capacity make A. cordata an excellent candidate for breeding, as well as for conservation and management of genetic resources. In this context, we evaluated the genetic variability of southern Italy populations and verified the hybridization capacity with the simpatric species A. glutinosa (L.) Gaertn. Eight pure A. cordata populations, two pure A. glutinosa populations and six mixed A. cordata/A. glutinosa populations located in southern Italy were analyzed using seven microsatellite markers. A low genetic diversity within and among populations was observed, but no inbreeding effects were evident. A variable frequency of F2 interspecific hybrids was observed in most of the mixed populations and few backcross individuals were scored. These results suggest a limited capacity of hybrid individuals to cross back with the parent species, reducing the risk of genetic pollution of A. cordata. This work provides meaningful knowledge for the conservation and management of the endemic species A. cordata, which represents a valuable source of biodiversity to be conserved.

Large old trees are extraordinary organisms. They not only represent a historical, landscape and environmental heritage of inestimable value, but they also witness a long history of environmental changes and human interventions, and constitute an as yet poorly known reserve of genetic variability which can be considered a great resource for management programs of forest species. This is the first genetic study on Italian, large, old chestnut trees (Castanea sativa Mill.). Ninety-nine trees were surveyed and analysed. For each tree, more than one sample from canopy and root suckers was collected to test for the genetic integrity of the individuals. All samples were genotyped using nine nuclear microsatellite markers (nSSRs) and 106 unique genetic profiles were identified. A Bayesian analysis performed with the software STRUCTURE revealed the occurrence of two main gene pools and unveiled the genetic relationships existing among the genotyped individuals, and with the natural chestnut populations living in proximity. A phylogeographic structure of the plastid diversity was also obtained by the use of DNA sequence variation at two marker regions, revealing different origins and probable connections of the old trees with different glacial refugia. Our results contribute to an improved evaluation of the European chestnut genetic resources and provide useful insights into the species’ history and domestication in Italy. The importance of carefully targeted conservation strategies for these invaluable organisms is reaffirmed.