1. Plant Breeding Laboratory Faculty of Agriculture Kyushu University Fukuoka 812‐8581 Japan
2. Graduate School of Bioagricultural Sciences Nagoya University Nagoya 464‐8601 Japan
3. Laboratory of Biological Systems Division of Biological Science Graduate School of Science Nagoya University Nagoya 464‐8602 Japan
4. Biosciences and Biotechnology Center Nagoya University Nagoya 464‐8601 Japan