The uniqueness of the cpDNA haplotypes, the prevalence of clonality and the restricted number of genets recorded suggest that Sardinian white poplar could be a floristic relict of the native flora of the island, which has spread through available habitats on the island mainly by means of vegetative propagation and human activities.

Morphological traits traditionally adopted to discriminate between Populus alba L. and P. tremula L. have frequently led to misclassification of their spontaneous hybrid P. · canescens Sm. Moreover, they may not be of any help in cases of spontaneous backcross phenomena. These limitations can be overcome by molecular markers, which are not environmentally influenced nor subjectively assessed. In this study, the effectiveness of amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers in species and hybrid discrimination was evaluated by analysing a set of reference samples of P. alba,P. tremula and P. · canescens. Species-specific and speciesindicative AFLPs, as well as diagnostic SSR alleles, were recorded in both P. alba and P. tremula reference samples. The results allowed a clear distinction between the two poplar species and their hybrid. Using these diagnostic markers, a natural population of P. alba trees sampled along the Ticino river basin in northern Italy was analysed, and P. · canescens individuals, intermingled with P. alba trees, were detected.

A collection of 66 poplar commercial clones widely cultivated in Italy, China and in other countries of southern Europe and belonging to various poplar species and hybrids, have been fingerprinted using both amplified fragment length polymorphism (AFLP) and simple sequence repeats (SSR) techniques. Three AFLP primer combinations and six SSRs unambiguously genotyped the analysed poplar collection, with the exception of three groups of six, four and two individuals, which turned out to be indistinguishable even if they met the standards currently applied for distinctness, uniformity and stability (DUS) testing when registered. High levels of variation were detected with both\ud molecular techniques; a total of 201 AFLP bands were\ud amplified of which 96% turned out to be polymorphic and\ud up to 15 SSR alleles were identified at a single locus, with\ud a mean of 9.3 alleles per locus in the case of Populus ×\ud canadensis. The probability of matching fortuitously any\ud two genotypes at all the SSR loci in the case of P. ×\ud canadensis was less then 7.5×10− 9. The AFLP-derived\ud dendrogram and principal coordinate analysis (PCOOR-\ud DA) clustered the clones with respect to their taxonomic\ud classification, and allowed their genetic interrelationships\ud to be established. Correct identification of poplar varieties\ud is essential for ensuring the effective correspondence be-\ud tween the real and the declared identity of a clone, to avoid\ud commercial frauds, and to establish breeding programmes.\ud Molecular markers may play a major role to satisfy all these\ud needs