Plant Propogation and Nursery Management

Exercise 9 & 10

Exercise 9 & 10: Practicing different types of grafting

Exercise: Practicing different types of grafting
Materials Required: Secateurs, grafting knife, scion wood, rootstock, wrapping material
Procedure: Before practicing any grafting method, the selection of optimum size, thickness of root stock and scion is of prime importance. The sequential steps involved in different methods are described as under:
A. Apical Grafting:

Splice or whip grafting:

• In this method, it is essential that both the stock and scion should be of equal diameter.
• For this , about one year old rootstock is headed back at a height of 20-25 cm from the soil and a splice(diagonal) cut 2.5 to 6 cm long) is made at the distal end of the rootstock with the help of a sharp knife. Procedure depicted in Fig.9.1.




Fig.9.1.Different steps involved in splice grafting

• A similar slanting cut is made on the proximal end of the scion. The cut should be smooth and the cut surface of both the rootstock and scion are bound together and tied firmly with polythene strip.
• After the union has taken place, the rootstock above the union is lopped off gradually.
• Sprouts arising below the grafting union must be removed at regular intervals to divert flow of metabolites for the growth of scion only.
Tongue grafting:
• It is modified form of whip grafting. It differs from whip grafting that a reverse cut is made downward at a point about 1/3rd of the distance from the tip and should be about ½ the length of first cut(Fig.9.2.).
• To obtain a smooth-fitting graft, the cut should not split. The rootstock and scion is then inserted into each other, with the tongues interlocking. It is important that vascular cambium layer match along at least one side, preferably along both sides.

Fig.9.2. Different steps involved in tongue grafting

• The lower tip of scion should not overhang the stock as there is a likely hood of the formation of large callus knots. The use of scions larger than root stock should be avoided.
• After the scion and rootstock are fitted together they are securely held by tying with budding/grafting tape or polythene. This method gives better success because of better cambial contact between stock and scion due to formation of tongue. Regular de-shooting of sprouts on stock is required to obtain better growth of scion.
Cleft-grafting (wedge or split-grafting):

• It is one of the oldest methods of field grafting. It is used to top work trees, either in the trunk of a small tree or in the scaffold branches of a longer tree (Fig.9.3).
• In making the cleft-graft, a heavy knife is used to make a vertical split for a distance of 5 to 8 cm down the center of the stub to be grafted.
• This split is made by pounding the knife in with a hammer. The branch is sawed off in such a way that the end of the stub which is left is smooth and free of knots for at least 15 cm.


Fig.9.3.Various steps involved in cleft grafting

• Two scions are inserted, one at each side of the stock where the vascular cambium layer is located. The scions should be 8 to 10 cm long and 10-15 mm in thickness and should have two or three buds.
• The side of the wedge which is to go to the outer side of the rootstock should be slightly wider than the inside edge. When the knife is removed, a hard wooden wedge is inserted to keep it open for the subsequent insertion of the scion.
• The graft should be thoroughly waxed to prevent wilting of the scion. The scion starts growing after 2 to 3 months of grafting.
• The right time for cleft grafting is the later part of the dormant season or just before the start of active growth. Walnut, hazelnut, pecan nut and grapes are propagated by this method.
Wedge grafting (saw-kerfs grafting):
• It is performed in late winter or early spring before the bark begins to slip (Fig.9.4.).
• A sharp, heavy, short bladed knife is used for making a V-wedge in the side of the stub or stock about 5cm long. Two cuts are made, coming together at bottom and as for apart at the top as the width of the scion.
• These cuts extend about 2 cm deep into the side of the stub. The base of the scion is trimmed to a wedge shape exactly the same size and shape as the opening. With the two vascular cambium layers matching the scion is tapped downward firmly into place and slanting outward slightly at the top so that the vascular cambium layers cross.
• After all scions are firmly tapped into place, all cut surfaces including the tips of the scion, should be waxed thoroughly. It is called raw-kerf because the cuts in the side of the rootstock can be made with a saw rather than the sharp knife.

Fig.9.4. Steps involved in wedge grafting

B. Side Grafting Methods:
Side veneer grafting:

• This method is used for grafting small potted liner plants such as seedling of deciduous trees, shrubs and fruit crops (Fig.9.5).
• A shallow downward and inward cut from 1 to 11/2 inches long is made. At the base of this cut, a second short inward and downward cut is made, inserting the first cut, so as to remove the piece of wood and bark.
• The scion is prepared with a long cut along one side and very short one at the base of the scion on the opposite side.
• These scion cuts should be of the same length and width as those made in the rootstock so that the vascular cambium layers can be matched as closely as possible. After inserting the scion, the graft is tightly wrapped with polythene sheet strips.
• After the union has healed, the rootstock can be cut back above the scion in gradual steps.

Fig.9.5.Steps involved in Veener grafting

Approach grafting Methods:

• The characteristic feature of approach grafting is that two independent, self-sustaining plants are grafted together. After the formation of union, the top of rootstock plant is removed above the graft and the base of the scion plant is removed below the graft.
• Generally, it is performed with one or both of the plants to be grafted growing in a container.
• Rootstock plants in containers may also be placed adjoining an established plant which is to furnish the scion part of the new grafted plant. It must be performed in the season when growth is active and rapid healing of the graft-union will take place. The important methods are:
a.) Spliced Approach Grafting:

• In this method both scion and stock should be of same thickness (Fig.9.6.). A splice of 4-5cm bark and wood is removed both from stock and scion.
• The cut on both the partners should be of same size and should be smooth too. The cut surfaces of stock and scion are bound together with some suitable tying material and waxed properly.
• The stock above the union and scion below the union are cut after sometime, when proper union has taken place. It may be necessary to reduce the leaf area of the scion if it is more than the root system of the rootstock can sustain.



Fig.9.6.Spliced approach grafting

b.) Tongue approach grafting:

• The tongue approach graft is the same as that of the spliced approach grafting-except that after the first cut is made in each stem to be joined, a second cut downward on the stock and upward on the scion is made, by providing a thin tongue on each piece (Fig.9.7).
• By interlocking these tongues tightly, a closely fitted graft union can be obtained.

Fig.9.7 Tongue approach grafting

c.) Inlay approach grafting:

• The inlay approach grafting may be used if the base of the rootstock plant is considerably thicker than that of the scion plant Fig.9.8.).
• A narrow slot, 7.5 to 10 cm long is made in the bark of the rootstock plant by making two parallel knife cuts and removing the strip of bark between. This can be done only when the rootstock plant is actively growing and the bark slipping.
• The slot should be exactly as wide as the scion to be inserted. The stem of the scion plant, at the point of union, should be given a long shallow cut along one side, of the same length as the slot in the rootstock plant and deep enough to go through the bark and slightly into the wood.

Fig.9.8. Inlay approach grafting

• This cut surface of the scion branch should be laid into the slot cut in the rootstock plant and held there by nailing with two or more small, flat headed wire nails.
• The entire union must then be thoroughly covered with grafting wax. After the union has healed, the rootstock can be cut off above the graft and the scion below the graft.
3. Repair Grafting:

Inarching:

• Inarching is similar to approach grafting in that both rootstock and scion plants are on their own roots at the time of grafting (Fig.9.9).
• It differs in that the top of the new rootstock plant usually does not extend above the point of the graft-union as it does in approach grafting. Inarching is used to replace roots damaged by cultivation equipments, rodents or diseases.
• It can be used to very good advantage in saving a valuable trees or improving its root system.

Fig.9.9. Steps involved in Inarching

• Seedlings (or rooted cuttings) planted beside the damaged tree, or suckers arising near its base are grafted into the trunk of the tree to provide a new system to supplement the damaged roots.
• The seedlings to be inarched into the tree should be spaced about 10-15 cm apart around the circumference of the tree if the damage is extensive.
• The seeding of compatible species is planted around the tree during dormant season and graft when active growth commences in early spring. Inarching will enhance growth of uninjured older trees.
• A thin slice of bark (6-10 cm in length) at about 20 cm above the ground level is removed from the stock with a sharp knife. A similar cut is made in the scion. Thus, the cambium layers of both stock and scion are exposed.
• These cut are brought together and tied firmly with the help of polythene strip. After the successful union, stock above and scion below union are lopped off gradually.
• In low rainfall areas, it should be done with the onset of rains, while in regions of heavy rainfall; it should be done soon after the rainy season is over, provided temperature does not fall below 150C.
Bridge Grafting:

• Bridge grafting is basically not a method of propagation but a form of repair grafting only in plants, which have been damaged either by frost, rodents or insects (Fig.9.10).
• It may, however, be kept in mind that bridge grafting is only helpful if the trunk is damaged but the root system of the plant is healthy.

Fig.9.10. Different steps involved in bridge grafting A damaged plant parts B.

 
• In this method first, the damaged portion of the stock is cleaned and the irregular edges of the girdled area are cut evenly.
• The scion of desired variety is inserted in such a way that it is attached at both upper and lower ends into the living bark. Similarly, it is important that scions be inserted right side up to ensure the polarity.
• The exposed injured wood must also be covered otherwise; it may serve as an entry channel for decaying organisms.
Bracing:

• Bracing is a form of natural branch grafting that is used by fruit growers to strengthen scaffolding limbs of a tree in order to support the load of the fruit crop. In this method two strong, young lateral shoots from the limbs are to be braced.
• A rope or electrical cord is used to temporarily brace the larger limbs. The weaved smaller shoots, which will naturally graft, are tied with waxed string or poly tape to keep them together.
Precautions:

• Scion wood should have 3-5 buds.
• Wrapping of grafts should be performed carefully to avoid air entry at the point of grafting
• Grafted stock should be irrigated at regular intervals
• De-shooting of sprouts below graft union should be done as the sprouts appear
• The wrapping material should be removed when it gets tightened.