**4.3.1 Drilling a hole at the stem of rootstock**

When grafting, the surface soil near to the stem of rootstock is first scraped away a little with the bamboo blade. Second the nearest internode from the topsoil is decided to use as graft site. Then the surgical blade is sterilized with alcohol cotton and cut off the section of the internode vertically. After that, the sterilized bamboo stick with the wedged end is rotatedly inserted into the cut section at an angle of 30-45 degree along the stem. The size and depth of drilled hole is depended on the stem thickness of scion seedling and the length of wedged end of the scion seedling. Generally, the depth of hole is 1.0-1.5 cm and the diameter of the hole is about 0.2-0.3 cm.

Distant-Graft Mutagenesis Technology in Soybean 277

be subject to molecular identification through different molecular maker methods. The detailed methods for identification of soybean mutants refer to the methods of Li *et al*.

**5. Main factors influencing distant-graft mutagenesis technology in soybean**  Soybean distant-graft mutagenesis technology is originated from the graft practices that enhance resistance to stress or diseases of crops and all the operative steps may influence the survival rate and the mutants-induced rate. Hence, we should pay attention to the key

The high or low affinity between rootstock and scion directly affects the survival rate of grafting, so choosing a distant-related plant materials whose affinity with soybean is high

Viability of the rootstock and soybean scion is critical for success of the graft. Generally, we use plant materials with strong resistance and adaptability as rootstocks and choose soybean varieties with better integrated traits as scion, so that soybean scion can gain enough water and nutrition from rootstock during the process of grafting and the survival

There are different survival rates of grafting for different graft methods. Though to some extent, selection of graft methods depends on the type of scion and purposes of research, the bud graft is better than the stem graft and branch graft, and the plug is better than the cleft graft and splice graft. For distant grafting in soybean, the side-plug graft on the base of stem is generally an ideal approach. In addition, the skill level of grafting technology has an important impact on the survival rate of graft. If the wedge-shaped stem end of the soybean scion is subject to damage or doesn't get to the bottom of the hole on the base of stem of rootstock when grafting, the seedling of soybean scion would wither to death for lack of

Management after grafting can not be ignored. Water supply and shading time must be controlled timely and accurately after grafting. Insufficient shading time and water supply all have an obvious impact on the survival rate of graft. Especially, when checking and

The grafting combinations between different rootstock and soybean may induce different types of mutant. In our study, it is found that the grafting of different combinations will produce different types of mutations. For example, grafting between soybean and castor

removing the lateral roots of scion, the operator do not hurt the root of rootstock.

**5.2 Main factors affecting the mutation-induced rate of graft** 

often induces seed coat color and oil content mutants in their offspring.

**5.2.1 Combination of rootstock and soybean scion** 

will provide an effective safeguarding for distant grafting mutagenesis in soybean.

**5.1 Main factors influencing the survival rate of grafting 5.1.1 Affinity between rootstock and soybean scion** 

**5.1.2 Viability of rootstock and soybean scion** 

**5.1.3 Methods of graft and level of technology** 

**5.1.4 The level of management after grafting** 

(2003).

steps when grafting.

rate of grafting is improved.

sufficient water and nutrient.
