Detailed Explanation of the Top-Bud Cleft Grafting Technique for Korean Pine
Korean pine (Pinus koraiensis Sieb. et Zucc.) is a tall tree of the genus Pinus in the family Pinaceae, with a full and straight trunk. In natural Korean pine forests, the average tree height can reach 25-30 m, the diameter at breast height can reach 40-80 cm, and the lifespan can reach 300-400 years. In places with suitable growing conditions, the tree height can reach 40 m, the diameter at breast height can reach 200 cm, and the lifespan can reach about 500 years; its timber is excellent, with straight grain, strong compressive strength, rich in resin, strong decay resistance, high craft value, and good painting performance. It dries easily and can be used for construction, aviation, bridges, and vehicle and ship timber; its wood has good planing and turning performance and is easy to process, suitable for making various models, and can also be used for plywood, musical instruments, and sports equipment, etc. It is an important precious timber tree species in our country.
Adult Korean pine has a large seed yield, large seeds, and high oil content, and is a woody oil plant with very high nutritional value; the pine nut kernel has very high nutritional value, rich in vitamin A and E, as well as the fatty acids essential to the human body, oleic acid, linoleic acid, and linolenic acid. It also contains pinolenic acid, which other plants do not have, and is a natural green food with very wide applications; it also has certain medicinal value. Long-term consumption strengthens the body and mind, nourishes the skin, prolongs life, eliminates disease and strengthens the body, and also has anti-cancer and anticancer effects; it is also an excellent tree species for urban and rural landscaping and is deeply loved by the public.
Korean pine is a major component species in the natural forests of Northeast China and is also a major afforestation tree species. The climatic conditions of Northeast China are very suitable for the growth and development of Korean pine, which has laid a good foundation for developing Korean pine resources in Northeast China. Many areas in Northeast China regard the development of Korean pine fruit-and-timber dual-purpose forests as a very important silvicultural model for developing the economy in forest regions. However, seedling-grown Korean pine grows slowly in its juvenile stage, bears fruit late, and has a long growth cycle, making it difficult to see economic benefits in the short term from developing Korean pine fruit-and-timber dual-purpose forests. The traditional grafting method also has shortcomings such as a low survival rate, which has greatly affected forest farmers' enthusiasm for developing Korean pine fruit-and-timber dual-purpose forests.
In forest regions, some forest farmers with a certain knowledge base have accumulated a great deal of experience in Korean pine grafting through many years of grafting experiments. After comparing and summarizing these methods, consulting a large amount of information, and conducting experiments personally, the author believes that using cleft grafting for Korean pine is a very good method to solve the above problems of Korean pine. It not only promotes the development of the rural economy, but also provides forest farmers with a way to become prosperous. The cleft grafting technique for Korean pine is summarized as follows:
1 Rootstock cultivation
There are 2 methods of rootstock cultivation. One is to cultivate the rootstock directly in the afforestation site, that is, planting the rootstock in the afforestation site according to the designed spacing between plants and rows, generally planting 3 plants per hole, and grafting when the planted rootstock has grown to the point where grafting can be carried out (about 5 years old). The other is to cultivate the rootstock in the nursery. Select 2-year-old robust Korean pine seedlings, put them into larger plastic container bags, and the nutrient soil in the bags should contain one third organic fertilizer to meet the needs of seedling growth, and graft when the container seedlings have grown to about 5 years old. In forest regions, it is sometimes necessary to graft Korean pine seedlings planted under the forest, but note that before grafting it is necessary to carry out "uncovering" first, then cultivate for another 1-2 years to restore the robust growth of the Korean pine seedlings, and then carry out grafting.
2 Scion collection
2.1 Selection of scion mother trees
In plantations over 30 years old that have already borne fruit, select superior trees and set up sample plots. In each sample plot, investigate 20 fruit-bearing trees, record the number of fruits and the continuity of fruiting for each tree (by looking at fruit scars), and calculate the average value. Trees in the sample plot that exceed the average value are superior mother trees, and are marked for scion collection.
2.2 Collection of scions
Carry this out before sap flow. From the superior trees selected in advance, take branches from the upper part of the crown as scions. When collecting, bring three whorls of whorled branches to prevent drying out. Note that the top shoot of the mother tree must not be collected, and only 60% of the branches may be taken, so as to prevent affecting the growth of the mother tree. After collection, tie the scions into bundles in certain quantities for frozen storage.
2.3 Storage of scions
Dig a cold storage cellar before the soil freezes in the year before scion collection. The cold storage cellar should be dug in a shady place where water does not accumulate. The cellar should be 2 m deep and 2 m wide, and the length depends on the amount of stored scion wood. Cover it with soil and seal it tightly, leaving a cellar opening. When it freezes, pour water into the cellar every night so that the frozen ice layer at the bottom of the cellar reaches more than 50 cm. In spring, place the collected scion wood bundles upright on the ice layer in the cellar, cover the cellar opening well, and maintain a low temperature in the cellar to prevent the scion branches from sprouting and drying out, until the time of grafting and taking the scion wood. Where conditions permit, an empty vegetable cellar or empty fruit cellar can also be used. During storage, check that the temperature in the cellar is below 8°C to ensure that the scion wood does not sprout, dry out, or become moldy.
3 Grafting
3.1 Grafting period
From late April to early May, the period when sap flow is most vigorous is the best time.
3.2 Cutting the scion
Select a plump, pest-free and disease-free scion bud equal in thickness to the top of the main branch of the rootstock, cut it off 3 cm below the bud, remove all needles, and use a single-edged razor blade to cut downward from 0.5-1 cm at the base of the bud into a double-sided wedge shape, with a cut surface length of 2-2.5 cm.
3.3 Cutting the rootstock
Cut off the top bud of the rootstock evenly, and split vertically downward from the middle pith, with a cut length of 2.5-3 cm, or slightly longer than the length of the scion cut surface, whichever is appropriate.
3.4 Joining
Quickly insert the cut scion into the split opening of the rootstock so that the pith and cambium are aligned, and tie it tightly and securely with plastic strips, without exposing any gaps, but be careful not to tie the grafted bud inside.
3.5 Technical key points
During operation, pay attention to the principles of "flat, accurate, clean, fast, and tight." Flat means the cut should be flat, ensuring that the cambium layers of the rootstock and scion cut surfaces can contact each other to the greatest extent; accurate means the scion should be inserted into the rootstock accurately, as far as possible in one insertion, without moving it again; clean means the cut surface should be clean, without bringing in debris, and the blade should be frequently disinfected with alcohol; fast means cutting should be rapid, shortening the exposure time of the cut in the air, and preventing resin overflow and water loss; tight means the tying cord should be tied tightly, link by link, without shifting or twisting, reducing resin overflow, preventing rain penetration, and reducing external infection and water loss. As long as you master these, the Korean pine seedlings you graft will basically survive.
4 Conclusion
During the experiment, by comparing the traditional conifer grafting method with the cleft grafting method, it was found that the cleft grafting method has the following obvious advantages:
4.1 High survival rate. The survival rate of the cleft grafting method can reach an average of more than 95%, while the survival rate of the traditional pith-cambium splice grafting method is about 85%.
4.2 Easy to operate. The operation process of the cleft grafting method is simple and easy to learn, while the traditional pith-cambium splice grafting method is relatively troublesome and not easy to master.
4.3 Saves scions. The cleft grafting method only uses the top bud, and it only needs to be thick enough, without considering the length of the scion branch, so the number of suitable scions collected is greatly increased. The traditional pith-cambium splice grafting method needs to consider the appropriate length of the scion, greatly reducing the number of scion branches suitable for collection.
4.4 Fast growth after grafting and can quickly form a new tree body. For Korean pine grafted by the cleft grafting method, statistics show that the average growth in the same year can reach more than 10 cm, and the average growth in the second and third years can reach 24 cm and 28 cm respectively. With the traditional pith-cambium splice grafting method, if it does not survive in the same year, side branches can still be grafted the next year without damaging the rootstock.
4.5 The rootstock can be grafted 2-3 years earlier than with the pith-cambium splice grafting method.