Identificazione di Regioni di Provenienza per il tiglio in Piemonte

The Regions of Provenance are areas with uniform ecological conditions and where grow individuals with similar genetic characteristics. Identification of Regions of Provenance is useful to preserve genetic resources as well as to make available propagative material of high quality. Limes are important trees that can be found in threatened ecosystems. In Piedmont only two species are present: Tilia cordata Mill. and Tilia platyphyllos Scop. The aim of the study was the evaluation, through morphological and genetic analysis, of genetic variation of lime in Piedmont, with the aim to define the genetic differentiation between species and to identify stands for seed production. 23 populations were studied, among which 12 of T. cordata, 7 of T. platyphyllos and 2 mixed, where both species are present. In each population 12 plants were randomly selected and 5 leaves were collected from each plant. Morphological analysis was carried out considering 16 characters of leaves. PCA analysis were performed to analyse relationships between species and studied populations. Genetic analysis was performed studying the variation showed at 9 RAPDs loci. Analytical procedures were adopted on the basis of previous works on the species. Concerning morphological analysis, the two species could clearly be separated. The characters that were most effective in discrimination between species were: colour of lower surface of blade (glaucous in T. cordata and green in T. platyphyllos), colour of hairs (brown in T. cordata and white in T. platyphyllos), and, although to a lesser extent, presence of hairs on blades (usually only in T. platyphyllos). The leaf size can also de used as discriminant factor, however its variation is not always clear and effect of environment can be important. Molecular analysis allowed us to identify 78 DNA bands. Principal Coordinates Analysis permitted clearly to distinguish between species, with the exception of one population of T. cordata (Oulx), that was similar to the T. platyphyllos ones. AMOVA showed that most of the genetic variability is present within populations (83%), while genetic differentiation between species was 12%. and genetic differentiation among populations belonging to the same species was as low as 5%. No correlation was found between geographical distances among populations and genetic diversity. Since populations of the same species were genetically similar, it is suggested to identify only one Region of Provenance for specie. Since molecular analysis showed that gene flow between species is possible following interspecific hybridization, for seed stand identification, it is suggested to consider only pure populations.