1. Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Pretoria, 0028 South Africa
2. Section for Ecology and Evolution, Department of Biology, University of Copenhagen, DK-2100 Copenhagen, Denmark
3. Laboratory of Genetics, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands