1. USDA, Agricultural Research Service, Plant Science Research Unit, University of Minnesota 1991 Upper Buford Circle, St Paul, MN 55108, USA;
2. Departments of Agronomy and Plant Genetics, University of Minnesota 1991 Upper Buford Circle, St Paul, MN 55108, USA,
3. Soil, Water and Climate, University of Minnesota 1991 Upper Buford Circle, St Paul, MN 55108, USA