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