Molecular characterization of Italian and Spanish chestnut trees

Castanea sativa Mill. is the only species of the genus Castanea native to Europe. It is a widespread multipurpose tree cultivated for its nuts and timber. In order to increase the genetic knowledge of chestnut in the Mediterranean area (Italy and Spain), an analysis was carried out on 630 samples (cultivated and wild) using 16 SSRs. Genetic distances and gene pools were calculated using a Bayesian method. A multivariate principal coordinate analysis (PCoA) was performed to validate the revealed genetic structure. The study revealed the existence of two distinct groups of chestnut populations: Spanish and Italian clusters, with a clear separation of the northern and southern Spanish accessions from the Italian ones. The north of Italy and the north-west of Spain emerged as the geographical areas where the genetic variability was preserved, derived from the spontaneous establishment of chestnut. The genetic variation found at cluster level could reflect a combination of historical processes of migration, selection and factors of adaptation to different environments between the Italian and Spanish regions. Furthermore, gene flow between cultivated and wild chestnuts was observed, mainly due to the proximity of cultivated chestnuts to natural populations. Cultivated and wild chestnuts from the Iberian Peninsula and Italy showed no significant differences in terms of genetic variability.