1. Fukushima Agricultural Technology Centre, Koriyama 963-0531, Japan
2. Institute of Geography Science and Natural Resources, Chinese Academy of Sciences, Beijing 100101, P. R. China
3. Division of Bioresources and Product Science, Hokkaido University, Sapporo 060-8589, Japan
4. 4Division of Crop Improvement, Central Potato Research Institute, Shimla 171001, India