DISTRIBUTION OF GENETIC DIVERSITY IN PINUS-PINASTER AIT. AS REVEALED BY CHLOROPLAST MICROSATELLITES

Using nine chloroplast simple sequence repeats (cpSSRs) markers, we ev aluated haplotypic variation within and among natural populations of M aritime pine (Pinus pinaster Ait.) in order to shed light on the histo ry of this species. Seven out of the nine cpSSRs analysed were polymor phic, giving a total of 24 different variants. The 24 variants combine d in 34 different haplotypes. The populations which generally showed t he lowest level of haplotypic diversity are those located in Portugal. The Landes (France) and Pantelleria (Italy) populations represent the two main reservoirs of haplotypic diversity. The proportion of geneti c differentiation among populations, estimated using R-st, which is a measure based upon a strict stepwise mutation model, was 0.235. The hi gh level of differentiation was also confirmed by the AMOVA analysis ( Phi(ST) = 0.254, P < 0.001). Four main groups of populations were iden tified on the basis of Principal Component Analysis, with the differen ces being statistically significant (Phi(CT) = 0.299, P < 0.001). Base d on our results the presence of refugia located in the South of Portu gal, previously proposed for this species, may be excluded? and a diff erent possible recolonization process of Maritime pine in the post-gla cial period has been proposed. Populations from North Africa and Franc e might have represented a starting point of the recolonization proces s of Portugal and of the Italian part of the natural range, respective ly. This hypothesis seems to be confirmed by the analysis of the distr ibution of the pairwise differences among individuals within populatio ns: Landes and Pantelleria populations showed a bimodal distribution, as would be expected for ancient gene pools.