1. College of Engineering, China Agricultural Univ; No. 17 Tsinghua East Rd. Beijing 100083 China
2. Quality & Safety Assessment Research Unit; Richard B. Russell Research Center; USDA-ARS, 950 College Station Rd. Athens GA 30605 U.S.A
3. Crop Genetics and Breeding Research Unit-USDA-ARS; 2747 Davis Road Tifton GA 31793 U.S.A