Genetic differentiation of oak populations within the Quercus robur/Quercus petraea complex in Central and Eastern Europe

Genetic structure of 25 indigenous populations of sessile and pedunculate o aks (Quercus petraea and Q. robur), originating from three geographical reg ions: Slovakia, Bulgaria and the Republic Mari-El (Russia), was investigate d using isozyme markers. Mean number of alleles per locus ranged between 1. 8 and 2.6 in Q. robur populations and from 2.0 to 3.0 in Q. petraea populat ions, slightly higher expected heterozygosity values were found in Q. robur compared to Q. petraea. One locus, coding for a substrate-nonspecific dehy drogenase, differentiated the two species. The interspecific component of g ene diversity was 46.7% at this locus, compared to 0.4-7.8% at the remainin g loci.