1. USDA‐ARS Plant Science Res. Unit and U.S. Dairy Forage Res. Center ClusterDep. of Agronomy and Plant Geneticsm, 411 Borlaug Hall, 1991 Upper Buford CircleUniv. of Minnesota St. Paul MN 55108
2. Dep. of Plant Sciences, P.O. Box 341Wageningen Univ. Wageningen The Netherlands