Chloroplast DNA variation of white oaks in Italy

Polymorphism in non-coding regions of the chloroplast genome was studied in four white oak species (Q. robur L., Q. petraea (Matt.) Liebl., Q. pubescens Willd. s.I., and Q. frainetto Ten.) in Italy (mainland and associated islands, including Corsica). A total of 924 trees (194 populations) was analysed. This data set also includes results previously obtained on 20 Italian and Corsican populations [Genetics 146 (1997) 1475]. Most of the sampled individuals were classified as Q. pubescens (73.5%). Thirty-four populations out of 194 (17.5%) were polymorphic. The level of population sub-division was very high, as expressed by the value of the coefficient G(ST) = 0.870 (hs = 0.100, h(T) = 0.776). The highest value of total genetic diversity was calculated in Sardinia and in central Italy; the lowest in southern Italy. The highest values of differentiation among populations occurred in Sardinia (G(ST) = 1), and in Corsica (0.927). We found evidence that the Italian oak populations of today mainly originated from Sicilian and Balkan refugia. Their origin and migration routes are more easily seen by considering data separately for the four sampling regions: the north, the centre, the south, and the three main islands. The C (=blue) lineage was common in the southern part of Italy. This may be a trace of a migration from the Balkans via the Adriatic bridge during quaternary cold periods. The northern pail of the country had a set of haplotypes similar to the other Alpine regions. Most Sicilian populations are fixed for one of the two haplotypes that probably originated in the island: one spread over the whole Italian peninsula, where-as the other one did not reach the Alps. Results showed that the Appennines may have played a role in the distribution of the haplotypes western and eastern of the mountains chain. (C) 2002 Elsevier Science B.V. All rights reserved.