1. Umeå Plant Science Centre; Department of Forest Genetics and Plant Physiology; Swedish University of Agricultural Sciences; SE-901 87 Umeå Sweden
2. Institut National de la Recherche Agronomique; UMR 1202 BIOGECO 69 route d'Arcachon F-33612 Cestas Cedex France
3. Umeå Plant Science Centre; Department of Plant Physiology; Umeå University; SE-901 87 Umeå Sweden
4. Institut Jean-Pierre Bourgin; UMR 1318 INRA-AgroParisTech; Institut National de la Recherche Agronomique Centre de Versailles-Grignon; F-78026 Versailles Cedex France