1. Dep. Crop Sci.; North Carolina State Univ.; Raleigh NC 27695-7620 USA
2. USDA-ARS and Dep. Crop Science; North Carolina State Univ.; Raleigh NC 27695-7631 USA
3. Pioneer Hi-Bred Int., Inc.; 7300 NW 62nd Ave., P.O. Box 1004 Johnston IA 50131 USA
4. Dep. of Crop and Soil Sciences, and R.S. Hussey; Dep. of Plant Pathology; Univ. of Georgia; Athens GA 30602-7272 USA
5. Dep. Statistics; North Carolina State Univ.; Raleigh NC 27695-7803 USA