1. Department of Plant Biology and Forest Genetics, Box 7080, SLU, SE-750 07 Uppsala, Sweden, and Mikocheni Agriculture Research Institute, P.O. Box 6226, Dar-es-Salaam, Tanzania
2. Agricultural Research Western Australia, Locked Bag No. 4, Bentley Delivery Centre, Perth, WA 6983, and School of Biological Sciences and Biotechnology, Murdoch University, Perth, WA 6150, Australia
3. Department of Plant Biology and Forest Genetics, Box 7080, SLU, SE-750 07 Uppsala, Sweden, and Department of Applied Biology, P.O. Box 27, FIN-00014 University of Helsinki, Finland