1. National Institute of Crop Science, 2-1-18 Kannondai, Tsukuba, Ibaraki 305-8518, Japan; National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan; and National Agriculture Research Center for Western Region, 1-3-1 Senyucho, Zentsuji, Kagawa 765-8508, Japan