1. Southern Regional Research Center, USDA Agricultural Research Service, 1100 Robert E. Lee Blvd., New Orleans, LA 70124, U.S.A.
2. Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
3. DuPont Central Research and Development Department, Experimental Station, Wilmington, DE 19880, U.S.A.