1. Department of Rice Research, National Institute of Crop Science, Tsukuba, Ibaraki 305-8518, Japan.
2. Corresponding author. Phone: +81-298388951. Fax: +81-298388951. E-mail: hyano@affrc.go.jp
3. Kyowa Medex Co., Ltd., Nagaizumi, Shizuoka 411-0932, Japan.
4. Research Station, Tokita Seed Co., Ltd., Otone, Saitama 349-1144, Japan.