1. Max‐Planck Institut für Züchtungsforschung, Carl‐von‐Linné‐Weg 10, D‐50829 Köln, Germany,
2. Institute of Plant Biology, Biological Reseach Center of Hungarian Academy of Sciences, H‐6701 Szeged, P.O.Box 521, Temesvári krt. 62, Hungary,
3. Department of Botany, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel 69978