1. National Academy of Agricultural Science, Rural Development Administration, Suwon 441-707, Republic of Korea.
2. Corresponding author. Phone: +82-31-299-1154. Fax: +82-31-299-1122. E-mail: kjkpj@korea.kr
3. College of Agriculture and Life Science, Kangwon National University, Chunchon 200-701, Republic of Korea.