The genetic structures of a range of Douglas-fir provenance collections after planting in different European countries, assessed with two biochemicalmarker systems

Genetic diversities of Douglas-fir provenance trials planted on several Eur opean sites were compared using both isozyme and terpene markers. A princip al coordinate analysis based on similarity coefficients calculated from iso zyme data indicated that, with the exception of two populations, difference s between populations were small. There were no consistent trends in the va riation in allele frequencies between populations. Most populations contain ed an excess of homozygotes, perhaps due to high selection pressure. Terpen e composition was analysed in two resin systems, and showed a decreasing le vel of population diversity by planting site in the order: Spain-France-Eng iand-Scotland-Italy. Thus isozymes, which are generally considered to be ne utral markers, indicated a modest degree of genetic drift due to sampling e ffects, while terpenes showed that some reduction in genetic diversity had occurred due to local selective pressures. Crown Copyright (C) 2001 Publish ed by Elsevier Science Ltd. All rights reserved.