Regioni di Provenienza del Larice in Piemonte

Forest trees are exposed to many stress factors, most of which are due to human activities: pollution, climate change, habitat fragmentation. In order to survive these threats, and to persist over time, a high adaptive potential is needed. To this end, knowledge of genetic variation are of the utmost importance. Molecular markers are now available and can provide us with the relevant means to acquire information on the genetic structure of populations and to study the pattern of distribution of within-species variability. The purpose of this study was the evaluation of neutral DNA markers (microsatellites) as a tool to study genetic variability distribution of European larch (Larix decidua Miller) in Italy, and to group populations according to genetic similarity. 24 natural European larch populations were sampled and DNA was extracted from young leaves. 9 microsatellite primer pairs were used to detect genetic variability. Levels of within and among populations variability were estimated and genetic differentiation was calculated. Additionally, the ecological features of the collection sites were analysed and homogeneous regions were defined. Lastly, patterns of genetic and ecological variations were compared, allowing us to identify areas that are both ecologically and genetically homogeneous. Since the research is still in progress, this report will focus only on populations from Piedmont. The analysed markers were highly polymorphic, displaying a high number of alleles (275) and a wide size range of PCR products. It was possible to score 58 private alleles, present only in one population. Populations that showed the highest value of genetic variability were Conca del Prà, Stavello, Bersezio and Plan Fourengh. To the contrary, Campliccioli, Saccarello and Pian della Mussa showed high genetic homogeneity. Observed heterozygosity over all populations was lower than the expected one, raising a significant positive mean inbreeding coefficient. The significant value of the latter was possibly due to the presence of null alleles, so that some heterozygotes are mistaken for homozygotes. However, it is not possible to exclude the occurrence of inbreeding, although the mating system of the specie should account for crossing. Partitioning of total genetic variability revealed that nearly all this variation was within populations rather than among populations. The latter was small but significant (GST = 0.037). The dendrogram confirmed the presence of differentiation between populations as well as a certain degree of structuring. In particular, populations from northern Piedmont (provinces of Verbania and Vercelli) clustered together. On the basis of the results obtained in the study and joining ecological data with genetic ones, it is concluded that it would be possible to consider only one Region of Provenances for European larch in Piedmont. However, for practical reasons, it seems more appropriate to divide the area under study into three Regions: Pennine and Lepontine Alps, outer western Alps (including Marittime Alps and areas northern to Turin), inner western Alps (Cozie and Graie Alps). Within these Regions, the populations more suited for production of high quality seed are, respectively, Alpe Stavello, Pian Fourengh and Saucheres Basses, Bersezio. Particular attention should be addressed to Campliccioli and Mua populations, due to the high number of private alleles, that makes them of interest for genetic resources preservation.