1. Grapevine and Wine Experimental Unit, National Institute for Agricultural Research, Angers Research Centre, 42 rue George Morel, B.P. 60057, 49071 Beaucouzé cedex, France, and Joint Research Unit for Genetics and Horticulture (GenHort), National Institute for Agricultural Research, Angers Research Centre, 42 rue George Morel, B.P. 60057, 49071 Beaucouzé cedex, France