1. State Key Laboratory for Crop Genetics & Germplasm Enhancement, Nanjing Agricultural University; Research Center of Plant Gene Engineering, Nanjing 210095, China.
2. Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
3. Corresponding author. Phone and Fax: +86-25-84396516. E-mail: wanjm@njau.edu.cn