1. National Agriculture and Food Research Organization; Institute of Crop Science; Tsukuba Ibaraki 305-8518 Japan
2. Graduate School of Life and Environmental Sciences; Univ. of Tsukuba; Tsukuba Ibaraki 305-8518 Japan
3. College of Plant Science; Jilin Univ.; Changchun 130062 Jilin P.R. China
4. Inst. of Botany; Chinese Academy of Sciences; Beijing 100093 P.R. China
5. Dep. of Botany; National Museum of Nature and Science; Tsukuba Ibaraki 305-0005 Japan
6. Laboratory of Plant Genetics and Breeding, Faculty of Agriculture; Saga Univ.; Honjo-machi Saga 840-8502 Japan