1. National Institute of Crop Science, Rural Development Administration, Suwon 441-857, Korea.
2. Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164-6420.
3. Department of Crop Science and Biotechnology, Chonbuk National University, Jeon-ju 561-756, Korea.
4. Corresponding author. Phone: +82-63-270-2533. Fax: +82-63-270-2640. E-mail: pcs89@jbnu.ac.kr