Besides natural methods of vegetative propagation, artificial modes of propagation are also being used. Farmers, gardeners and horticulturists have adopted several such methods like grafting, layering, cutting and tissue culture for propagating plants in gardens and nurseries.
In horticultural practices this method is commonly used. In this method the cutting of a plant (scion) is attached to the stem of another rooted plant (stock). After some time the attached cutting becomes an integrated part of the rooted plant. The scion and stock are placed in such a way that no gap remains between them. Finally they become joined in such a way that their vascular systems are united. Usually the scion is of a plant having desirable characters like large sized fruits and the stock has good absorbing capacity. Because of the arrangement of their vascular bundles, grafting experiments are successful only in divots and not in monocots. This method is commonly applied to improve the variety of fruits like mango. Wax is used to cover the place where grafting is being done. This is to avoid infection.
2. Bud grafting:
A bud is taken along with portion of bark from a plant and is used as scion in this process. A T-shaped cut is made and the bud is fixed tightly on the stock with a tape. The bud gets attached to the stock after some time and new branches are formed. Pears, peaches, plum, citrus, roses, etc., are propagated by this method. This method is usually employed during spring.
In rose, sugar-cane, Coleus, Bougainvillea, etc., this method is used to produce new plants. In this process stem cuttings with some nodes and internodes are placed in moist soil which gives rise to adventitious roots and a new plant subsequently. It is a very common method of vegetative propagation. Farmers divide up the rhizomes, tubers or roots stocks at the end of flowering or growing season. Each part grows into a separate plant in the following year. Some plants like dahlia are propagated by root cuttings.
In some plants one or more branches are bent close to the ground and covered with moist soil. After some time, the underground portion of those branches produce new roots and develop into a separate plant as in jasmine, Rhododendron, Magnolia, etc. The stem or branch that develops adventitious roots while still attached to the parent plant is called a layer. In many plants, layering can also be induced artificially.
In mound layering the stem is pruned and the base of the plant is covered with soil. From the base, new shoots develop, which are separated from the parent plant, ad grown into a new plant. Many types of apples and gooseberries are grown using this method.
Air layering is another type of layering in which branches of the plants cannot be bent to the ground. A piece of the branch is scraped (girdled) in this method and polythene or plastic sheet is used as cover to preserve moisture. Roots arise from the scraped part after a few weeks. This branch is then detached from the parent plant which grows into a new plant after plantation.
Layering differs from cutting in that the developments of adventitious buds are induced before the stem is cut to form the new plant.
5. Tissue Culture:
In this technique a small piece of tissue of a desired plant is cut. This is placed with a suitable nutrient medium under proper conditions. The tissue grows into an unorganized mass, known as callus. Small part of this tissue is put in another medium, which induces the formation of plantlets. The plantlets can be transplanted in soil or pots foe developing to maturity. This technique is also called micro propagation. This method is used in propagating plants like Asparagus, orchids, Chrysanthemum. This method allows us to grow whole plant from cells taken from various parts of the plant body.