Isozyme and organellar dna analysis of genetic diversity in natural/naturalised european and asiatic walnut (Juglans regia L.) Populations

European stands of Juglans regia L. were analysed in comparison with Asiatic ones (Caucasus, NW and NE China) by means of nuclear (isozyme) and organellar (PCR-RFLP) genetic markers in order to obtain information on the genetic structure, diversity and differentiation of walnut populations at the level of different genomes. The isozyme genetic analysis showed that the genetic differentiation within European populations was similar to that found in Asiatic populations and close to that found in other broad-leaves cross-pollinated tree species. At the intrapopulation level the artificial propagation of walnut, due to human activities, did not affect the genetic differentiation. On the other hand, the genetic differentiation between stands was lower in the European groups than in the Asiatic one. This figure can probably be interpreted with the strong human impact on this species in the European continent. The analysis of cp- and mt-DNA did not reveal any polymorphism.