1. Departments of Molecular Plant Physiology and Molecular Cell Biology, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands (N.G., S.C.H.J.T., P.J.W., S.C.M.S.);
2. Advanta Seeds, P.O. Box 1, 4410 AA Rilland, The Netherlands (K.P.M.v.D.);
3. Agrotechnological Research Institute, P.O. Box 17, 6700 AA Wageningen, The Netherlands (S.H.D.H.); and
4. Laboratory of Plant Breeding, Wageningen Agricultural University, P.O. Box 386, 6700 AJ Wageningen, The Netherlands (R.G.F.V.)