Grafting Propagation Technique for Pinus sylvestris var. mongolica Grafted with Korean Pine (Pinus koraiensis)

Pinus sylvestris var. mongolica has strong adaptability, is cold-resistant, drought-tolerant, and tolerant of poor soil. Using Pinus sylvestris var. mongolica as rootstock to graft Korean pine (Pinus koraiensis) brings earlier flowering and fruiting, rapid orchard establishment, and good results.

1 Preparation of scions

1.1 Selection of mother trees

Select superior mother trees as scion sources. Within the chosen area, measure the tree height, diameter at breast height, crown width, fruiting layer thickness, number of young cones, number of cones, and male and female flower quantities of each clone individual. At the same time, conduct individual tree seed collection, and test cone number, cone weight, seed yield, seed extraction rate, kernel rate, empty shell rate, pest damage rate, 1000-seed weight, as well as cone length and width. Select individuals with high yield as mother trees.

1.2 Collection of scions

Scion collection should be carried out in early to mid-March of the grafting year, from 1-year-old branches on the outer periphery of the middle to upper part of the mother tree trunk. Branches from the middle-lower part and the inner crown grow weakly and are not suitable as scions. When collecting branches, care must be taken to protect the growth of superior mother trees from being affected, and too many branches should not be collected at one time. Depending on the size of the mother tree, generally collect 10-50 branches per tree, and each branch should carry 15-20 cm of vegetative shoots. After collection, bundle them into bundles according to the superior tree number.

1.3 Storage of scions

The quality of scion storage will directly affect the survival rate of grafting. If the collection site is far from the storage site and long-distance transport is required, the branches should be placed in plastic bags, with a small amount of sawdust added, and the bags sealed for moisture-retaining transport. Storage of branches in an ice cellar is preferable, and the size of the cellar is determined by the quantity of scions. Before the scions are placed in the cellar, put about 50 cm of snow or ice blocks at the bottom, finally cover all the scions with snow or ice blocks, and then seal the cellar opening tightly.

2 Selection of rootstock

The Pinus sylvestris var. mongolica rootstock used for grafting should preferably be transplanted large seedlings 40-50 cm tall. In the 1-2 years before grafting, select robust 2-3 year old seedlings free of pests and diseases and transplant them in a nursery bed or plant them in the afforestation site. For nursery bed transplanting, 2-year-old bed-grown seedlings can be used after 1 year of transplanting; for planting in the afforestation site, 3-year-old afforestation seedlings can be used.

3 Grafting supplies

3.1 Plastic strips

Select polyvinyl chloride agricultural plastic with strong elasticity, and cut it into strips 35 x 1 cm. Used for tying the graft union.

3.2 Adhesive tape strips

Medical white adhesive tape strips. Used for hanging labels, etc.

3.3 Alcohol, absorbent cotton

Used for wiping blades, etc.

3.4 Blades and blade holders

Double-edged or single-edged surgical blades (No. 22), with single-edged blades being preferable. Used for cutting the graft surfaces.

3.5 Pruning shears

Used for trimming scions and rootstock.

4 Grafting period and method

The grafting period can be divided into spring and summer, and it is best to graft in spring when the sap is flowing (around mid-April).

The grafting positions can be divided into: the top of the central leader shoot, and the upper ends of the 1st to 3rd whorled branches. The bark of the central leader is thick, and poor matching between scion and rootstock results in a low grafting survival rate, so grafting should be carried out at the 1st to 3rd whorled branch positions.

Among grafting methods, the pith-cambium side grafting method has the highest survival rate. The thickness of the scion should preferably be about 2/3 of the thickness of the rootstock at the grafting site. Use the upper 7-8 cm of a 1-year-old branch and cut it into a scion, retaining 8-10 bundles of needles at the top, pull off the remaining needles along the direction of the needles, and cut at about 0.5 cm below the retained needles, with a cut surface length of 6-7 cm and a depth reaching the pith. The 1-year-old main branch of the rootstock is the suitable grafting site. After pulling off the needles at the grafting site, cut a surface equal in length to the scion, with the depth reaching the cambium. After combining the scion with the rootstock, bind tightly with plastic strips. The cut surfaces are required to be smooth, preferably completed with one cut. The cut surface of the scion must not be longer than the cut surface of the rootstock. The grafting operation must be fast to reduce resin flow.

5 Management after grafting

In early May, the terminal buds of the scions gradually begin to sprout. The terminal buds and lateral buds of the grafted rootstock should be cut off, and the wounds then coated with lead paint. From late May to early June, carry out the first loosening of the binding, and completely untie the binding bands on dead plants. In mid-to-late July, carry out the second loosening of the binding, and at the same time cut off the terminal and lateral buds of all whorled branches that exceed the height of the graft. After the current-year branches of Pinus sylvestris var. mongolica are cut, many adventitious buds grow again, forming many small young branches, so the rootstock should be cut once more in autumn, but all vegetative branches must not be cut off at one time, as this would affect the overwintering and survival of the graft.

About 90 days after grafting or before the grafted buds sprout in the following spring, remove the plastic strips used for binding, and cut off the terminal buds of the main branch and part of the lateral branches of the rootstock. After the graft survives, tree vigor management must be carried out continuously for 5-7 years. Because within the several years after the graft survives, the height growth of the scion is less than the growth of the rootstock's lateral branches, and the main branch status of the scion is easily replaced by lateral branches. In order to keep the scion always in the main branch position, pruning should be carried out once every early spring to cut off the tips of lateral branches that affect the growth of the scion. After 8-10 years, pruning to promote fruiting should be carried out.