1. Center for Research on Wild Plants, Utsunomiya University, Utsunomiya 321-8505, Japan
2. Faculty of Agriculture, Utsunomiya University, Utsunomiya 321-8505, Japan
3. Department of Biosciences, Teikyo University, Utsunomiya 320-8511, Japan
4. Faculty of Agriculture, Yamagata University, Tsuruoka 997-8555, Japan