**9. Acknowledgements**

The authors would like to thank all the researchers in the field of distant-graft mutagenesis for offering us the technological instructions on the methods of research. This work has been funded by the project for scientific and technological achievements transformation of Chinese science and technology department (2010GB24910701), the project for special foundation of technological innovation of Harbin (2008RFQYN127) and the project for forefront innovation of Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences (KZCX3-SW-NA09-6).
