1. Institute of Biology/Applied Genetics, Freie Universität Berlin, 14195 Berlin, Germany
2. Institute of Experimental Botany, Academy of Sciences of the Czech Republic, CZ-16502 Prague 6, Czech Republic
3. Institut National de la Recherche Agronomique/Ecole Nationale Supérieure Agronomique, GAP Viticulture, F-34060 Montpellier Cedex 1, France
4. University of Antwerp, B-2610 Antwerp, Belgium