Landscape genetics structure of European sweet chestnut (Castanea sativa Mill): indications for conservation priorities

Abstract Sweet chestnut is a tree of great economic (fruit and
wood production), ecological, and cultural importance in
Europe. A large-scale landscape genetic analysis of natural
populations of sweet chestnut across Europe is applied to (1)
evaluate the geographic patterns of genetic diversity, (2) identify
spatial coincidences between genetic discontinuities and
geographic barriers, and (3) propose certain chestnut populations
as reservoirs of genetic diversity for conservation and
breeding programs. Six polymorphic microsatellite markers
were used for genotyping 1608 wild trees sampled in 73
European sites. The Geostatistical IDW technique (ArcGIS
9.3) was used to produce maps of genetic diversity parameters
(He, Ar, PAr) and a synthetic map of the population membership
(Q value) to the different gene pools. Genetic barriers
were investigated using BARRIER 2.2 software and their locations
were overlaid on a Digital Elevation Model
(GTOPO30). The DIVA-GIS software was used to propose
priority areas for conservation. High values of genetic diversity
(He) and allelic richness (Ar) were observed in the central
area of C. sativa's European distribution range. The highest
values of private allelic richness (PAr) were found in the eastern
area. Three main gene pools and a significant genetic
barrier separating the eastern from the central and western
populations were identified. Areas with high priority for genetic
conservation were indicated in Georgia, eastern Turkey,
and Italy. Our results increase knowledge of the biogeographic
history of C. sativa in Europe, indicate the geographic location
of different gene pools, and identify potential priority reservoirs
of genetic diversity.