Low genetic differentiation among Italian populations of Populus tremula L. (Salicaceae) estimated using chloroplast PCR/RFLP and microsatellite markers

Chloroplast (cp) DNA polymorphism was analysed in ten Italian populations of Populus tremula L. byPCR- RFLP and microsatellites (SSR) chloroplast markers. Amplified fragments were digested by restriction endonucleases and the resulting restriction fragments were separated by gel electrophoresis. Three cpDNA amplification products showed polymorphism after digestion. By analysing this polymorphism we identified six haplotypes. Five universal pairs of primers were used for the amplification of specific cpDNA microsatellite regions, which are supposed to contain mononucleotide stretches (A/T). Two microsatellite loci showed polymorphism, resulting in a total of six haplotypes. Both PCR-RFLP and SSR chloroplast markers revealed very low genetic differentiation among populations, with G,, = 0.22 and N,, = 0.24 (PCR-RFLP), and G,, = 0.07 and N,,= 0.07 (SSR), resulting about 4-10 times lower than the mean G,, value estimated in broad-leaved forest species for maternally inherited markers. This could be mainly explained by the high efficiency of P, trernula seed wind dispersal over long distances, determining little geographic structure of the genetic diversity.