1. Swiss Federal Research Institute WSL, 8903 Birmensdorf, Switzerland
2. Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA
3. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA
4. Section for Genetics and Evolutionary Biology (EVOGENE), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway