1. The CGIAR Research Program on Roots, Tubers and Bananas (RTB), International Potato Center Sub‐Saharan African Regional Office P.O. Box 25171‐00603 Nairobi Kenya
2. Dep. of Land Resource Management and Agricultural Technology Univ. of Nairobi P.O. Box 29053‐00625 Nairobi Kenya
3. Dep. of Crop Sciences, Plant Nutrition and Yield Physiology Univ. of Gottingen Carl‐Sprengel‐Weg 1 Göttingen 37075 Germany
4. Univ. of Applied Science Bingen (TH Bingen) Berlinstrasse 109 Bingen 55411 Germany