1. USDA, Agricultural Research Service, Department of Horticulture, University of Wisconsin, 1575 Linden Drive, Madison, Wisconsin 53706‐1590 USA
2. N. I. Vavilov Institute of Plant Industry, St. Petersburg, 42/44 190000 Russia
3. Department of Botany, Natural History Museum, Cromwell Road, London SW7 5BD, UK
4. International Potato Center, Apartado 1558, Lima 12, Peru