**2. History of distant graft**

There has been a long history of over 1400 years for application of distant-grafting to agricultural production. The earliest records was found in sixth century encyclopedia of Chinese agricultural knowledge-- "Essential skill to benefit the Qi-people", where it was recorded that the graft union with high survival rate between pearl and mulberry tree yielded the poor quality fruits while the graft union with low survival rate between pearl and jujube or pomegranate tree yielded the good quality fruits. After that, the grafts between different trees, flowers, vegetables and crops were recorded in many agriculturerelated books such as "Compendium of Materia Medica" and journals such as "Studies in the History of Natural Sciences" and so forth.

From the purpose of distant graft, it could be found that grafting was originally used to improve plant tolerance to cold, resistance to diseases and enhance quality of fruits in the woody trees cultivation and propagation. Since the discovery of inheritable variation induced by grafting, the distant grafts have been used to innovative plant resources and improve plant varieties. Now, the distant graft technology is not only an effective approach for creating new resources and breeding new varieties, but also an important means in plant physiology, pathology, genetic research.
