1. Graduate School of Bioagricultural Sciences; Nagoya University; Furo-cho, Chikusa Nagoya 464-8601 Japan
2. Graduate School of Agriculture; Hokkaido University; Kita 9 Nishi 9, Kita-ku Sapporo Hokkaido 060-8589 Japan
3. Department of Crop Science; Obihiro University of Agriculture and Veterinary Medicine; Nishi 2-11 Inada Obihiro Hokkaido 080-8555 Japan