1. Department of Plant Ecology and Evolutionary Biology, University of Utrecht, PO Box 80084, 3508 TB Utrecht, Netherlands
2. Willie Commelin Scholten Phytopathological Laboratory at Baarn, in the Netherlands
3. S & G Seeds B.V., Westeinde 62, 1600 AA Enkhuizen, Netherlands
4. Institute of Molecular Plant Science, Clusius Laboratory, University of Leiden, Wassenaarseweg 64, 2333 AL Lieden, Netherlands
5. Department of Molecular Cell Biology, University of Utrecht, Padualaan 8, 3584 CH Utrecht, Netherlands