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A budded plant is produced by combining two separate units: the stock and the scion. The stock is the root system of the new plant, often selected for its vigour and capacity to grow well under difficult soil conditions or resist disease. The scion is the tissue which is taken from the high-yielding parent or mother plant and which is applied to the stem of the stock in such a way that the cambial tissues of both join to form a union which is difficult to break. This can only occur if the stock and scion are not compatible i.e. they are not sufficiently closely related, in terms of their genetic and structural composition, to be able to form tissue which is difficult to distinguish from that of a normal seedling.
A knowledge of the degree to which various stock and scion combinations are possible is therefore essential in selecting suitable material for budding.
The most important aspect of budding is that the scion is only partially influenced by the stock as far as its vigour and rate of growth are concerned, and it will continue to produce new branches and fruits which
are identical with those of the mother plant. A main reason for budding is that cuttings from many high quality fruit trees that cannot produce a vigorous root
system.
The main sequence of operations is as follows.
1) Select only healthy and vigorous growth for the "bud-stick' from which the scions will be cut, the buds should be well developed but not in active growth.
The leaves should be removed, leaving only 1cm of the petiole or leaf stalk attached to the stick which should be kept in wet sacking in the shade until used.
2) Choose only stocks which are free from pests and diseases.
3) Make a test cut in the bark or outer layer of the stem of the stock and ensure that the bark will lift easily when a section of it is cut by the budding knife.
Budding should preferably be carried out either during the early or late wet season or after irrigation, when the sap in the plant is actively flowing.
4) Prepare a T-shaped cut in the stock and lever back gently the two sides of the T with the pointed handle of the budding knife. In wet weather, and in the humid tropics generally, the inverted T system of budding is used so that the two flaps of the stock tissue protect the bud from the entry of water.
5) Make a sloping cut in the wood of the bud-stick, about 1.5 cm below the bud (if the inverted T is used) or 1.5 cm above the bud using the upright T method.
The cut continues for about 2 cm below or above the bud, the main objective is to remove the bud, without damage, attached to a boat-shaped piece of bark. The internal wood remaining attached to the scion may be eased gently away from the bark, but the bud must not be damaged or bruised.
6) The bud shield or scion is then inserted into the T incision, as shown in the diagram and the surplus length of bark neatly trimmed away.
7) The union is then bound with polythene or other suitable tape material, to exclude water and air; the bud should not, however, be completely covered. A leaf may be tied over the bud to protect it from excessive sun or rainfall.
8) After 14-21 days, the tape may be carefully removed and the union inspected, the bud should by this time have shown signs of developing if the operation has been successful.
9) The top portion of the stock may be either removed by cutting with secateurs, or cut half-way through and broken over to lie on the ground attached to the stump of the stock; this is intended to encourage the flow of food materials from the root to the developing bud.
10) When the bud has developed into a shoot, the portion of the stock immediately above the bud is carefully removed and the young scion shoot tied to a stake for support. This method of shield budding can be used for citrus, mangoes and rubber, with slight modifications to suit specific crops. In humid areas, for example, citrus is budded on the stock at a height of 15 cm or more to avoid disease.
Budding can only be carried out efficiently after practical experience has been gained, preferably under skilled supervision.
Patch budding has been proved to be a rather more rapid method than shield budding, though rarely used.
Grafting
The main types of graft union used in West Africa are the side graft, crown graft and saddle graft. The principles involved in selecting compatible material, and the need for sharp tools and skill in performing the operation are similar to those used in budding.
Side grafting The stock and scion are prepared and united as shown in This type of graft is sometimes used with avocado pear.
Crown grafting This may be used where it is required to alter the fruiting characteristics of a tree so that it produces fruit of a different selection or cultivar from that with which it was originally budded or grafted, or may be used on mature stocks which are too old for budding. In this instance, the scion is grafted on to the wood of an existing mature branch.
Saddle Grafting avocado pear but which is not widely used in West Africa. The scion and stock are prepared and united as shown in.
Approach grafting This is rarely used, since it is a time-consuming operation. With some mangoes which it This is a graft which is used on practical experience has been gained, preferably under skilled supervision.
Patch budding has been proved to be a rather more rapid method than shield budding, though rarely used.