Department of Molecular Genetics, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr, 3, 06466 Gatersleben, Germany. junker@ipk-gatersleben.de|Department of Molecular Genetics, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr, 3, 06466 Gatersleben, Germany. junker@ipk-gatersleben.de|Department of Molecular Genetics, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstr, 3, 06466 Gatersleben, Germany. junker@ipk-gatersleben.de