1. Agriculture and Agri-Food Canada, 93 Stone Road West, Guelph N1G5C9, Ontario, Canada.
2. School of Life Sciences and Biotechnology, Korea University, 5-1 Anam-dong, Sungbuk-ku, Seoul 136-701, Korea.
3. Corresponding author. Phone: 82-2-3290-3435. Fax: 82-2-927-5201. E-mail: limst@korea.ac.kr