1. Center for Bioscience Research and Education Utsunomiya University 350 Mine‐machi Utsunomiya 321‐8505 Japan
2. Graduate School of Agriculture Hokkaido University Sapporo 060‐8589 Japan
3. International Institute of Tropical Agriculture (IITA) PO Box 30772‐00100 Nairobi Kenya
4. Department of Biosciences Faculty of Science and Technology Teikyo University 1‐1 Toyosatodai Utsunomiya 320‐8851 Japan