1. Department of Agronomy and USDA-ARS Field Crops Research, Iowa State University, Ames, Iowa 50011
2. New Zealand Dairy Research Institute, Private Bag 11029, Palmerston North, New Zealand
3. Department of Agronomy, University of Nebraska, Lincoln, Nebraska 68583-0915
4. Department of Agronomy, Iowa State University, Ames, Iowa 50011-1010
5. Department of Plant Pathology, University of Minnesota, St. Paul, Minnesota 55108
6. USDA-ARS, Department of Agronomy, Purdue University, West Lafayette, Indiana 47904
7. Department of Crop and Soil Sciences, University of Georgta, Athens, GA 30602
8. Department of Botany, University of Georgia, Athens, GA 30602