Genetic diversity in old populations of sessile oak from Calabria assessed by nuclear and chloroplast SSR

In the framework of forest resources conservation, this study aims to understand the dynamic and the genetic structure of sessile oak forests in Calabria, Italy. Two old populations of sessile oak (Quercus petraea (Mattuschka) Liebl.) from two areas of Sila and Aspromonte massifs in Calabria were analyzed for genetic diversity and population structure based on 6 nuclear simple sequence repeat (nSSR) and 4 chloroplastic SSR (cpSSR) loci. The populations displayed high amount of genetic diversity, which was toughly structured according to their geographical origins. Number of alleles at SSR loci ranged from 11 to 20 with an average of 13.5 per locus. Gene diversity (expected heterozygosity, H-e) estimates ranged from 0.575 to 0.834 with a mean of 0.749. The observed heterozygosity (H-o) was on average 0.458 ranging from 0.150 to 0.682. Polymorphism information content (PIC) values ranged from 0.625 to 0.865 with an average of 0.787. The analysis of molecular variance (AMOVA) highlighted a significant higher estimated variance within populations compared to among populations. Finally, the analysis of haplotypes by using cpSSR suggested a higher diversification in the population from Sila. Hierarchical clustering analysis grouped the genotypes into two major clusters, which agreed with the geographic origin of populations, and was confirmed by the Discriminant Analysis of Principal Components (DAPC). The first cluster included plants/population from Sila massif, while the second encompassed mostly plants/population sampled in Aspromonte massif. Finally, model-based clustering by STRUCTURE analysis also supported the presence of clear genetic structuring in the collection with two major populations (K=2) supported to PCoA analysis as well. Finally, our data indicated the Aspromonte population as a marginal forest with fragmented distribution suggesting different strategies of preservation than in Sila massif.