1. Dep. of Sustainable Agriculture; Rakuno Gakuen Univ.; Ebetsu Hokkaido 069-8501 Japan
2. Hokkaido Research Organization Tokachi Agricultural Experiment Station; Shinsei, Memuro-cho, Kasai-gun Hokkaido 082-0081 Japan
3. Western Region Agricultural Research Center; NARO; Senyu Zentsuji Kagawa 765-8508 Japan
4. National Institute of Crop Science; NARO; Kannondai Tsukuba Ibaraki 305-8602 Japan