||This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. (May 2012)|
Artificial reproduction/propagation is the creation of new life by other than the natural means available to an organism. Examples include artificial insemination, in vitro fertilization, cloning and embryonic splitting, or cleavage.
Cutting plants' stems and placing them in compost is also a form of artificial reproduction. We can grow many plants from one plant by using the man-made methods. The process of growing many plants from one plant by man-made methods is called artificial propagation of plants. A number of methods of artificial propagation of plants are used in agriculture (for raising crops), and horticulture (cultivation of vegetables, fruits and flowers). The three common methods for the artificial propagation of plants are:
2. Layering, and
We will now describe all these methods, one by one. Let us start with the cuttings method for the artificial propagation of plants.
1. Cuttings :
A small part of a plant which is removed by making a cut with a sharp knife is called a 'cutting'. A cutting may be a piece of stem, root or even a leaf. While making a cut, care should be taken to see that there are some buds on it.
In this method, a cutting of the parent plant (say, of stem or shoot) having some buds on it is taken and its lower part is buried in the moist soil. After a few days, the cutting develops roots; shoot, and grows into a new plant. Cuttings are a means of asexual reproduction in plants. The new plant formed from a cutting is exactly similar to the parent plant.
The plants like rose, Bougainvillea, Chrysanthemum, grapes, sugarcane, bananas, and cactus, etc., can be grown by means of cuttings. For example, rose plants and chrysanthemums are propagated (or reproduced) by means c cuttings from stems (or shoots) as follows: A piece of stem (or side shoot) having bud is cut from an; existing rose plant with the help of a knife. The lower part of this Gutting is buried in moist soil. After a few days, the end of cutting buried in soil develops roots and later on grows to become a new rose plant. An advantage of cuttings method is that by using this method we can produce many new plants from just one plant quickly, without waiting for flowers and sexual reproduction.
2. Layering :
In this method, a branch of the plant is pulled towards the ground and a part of it is covered with moist soil leaving the tip of the branch exposed above the ground. After some time, new roots develop from the part of the branch buried in the soil. The branch is then cut off from the parent plant. The part of the branch which has developed roots grows to become a new plant (just like the parent plant). Jasmine plant (chameli) is propagated or produced by the layering method.
We can see from that one left side branch and one right side branch of the parent jasmine plant have been buried in moist soil. The parts of branches which are buried in soil grow their own roots. When this happens, the branches of the parent plant connecting the newly formed plants are cut off so that the newly formed plants may grow on their own and develop into mature plants (like the parent plant).
Many plants like strawberry and raspberry are propagated by the natural layering method. The natural layering occurs because these plants form runners (which are soft horizontal stems running above the ground). Wherever the ends of such runners touch the ground, new plants are formed at those places. In this way, many more strawberry or raspberry plants are formed from" the parent plant in a natural way.
The layering method is used for the propagation (or reproduction) of plants like : Jasmine, Strawberry, Raspberry, Lemon, Guava, Hibiscus (China rose), Bougainvillea and many slender ornamental plants.
3. Grafting :
Grafting is a method in which the cut stems of two different plants (one with roots and other without roots) are joined together in such a way that the two stems join and grow as a single plant. This new plant will have the characteristics of both the original plants.
(i) The cut stem of a plant (or tree) having roots (and fixed in soil) is called stock. Stock is the lower part of a plant (or tree) having the roots.
(ii) The cut stem of another plant (without roots) is called scion. Scion is the upper part of a plant which may have leaves on it (but no roots).
In carrying out grafting, two plants (or trees) are chosen which are to be used as scion and stock. First, the stem (or branch) is removed from the plant chosen to be made scion (for its desirable characteristics) by making a slanting cut. This gives us the scion with a slanting cut. The stem of second plant (or tree) to be used in grafting is also cut in a slanting way. The lower part of this plant (or tree) is stock. It has also a slanting cut.
The scion is placed over the stock. The cut surfaces of the scion and stock are fitted together and bound tightly with a piece of cloth and covered properly with polythene sheet (so as to prevent harmful infection by bacteria or fungus, and loss of water and plant sap from the cut and joined ends of stock and scion).
While joining the scion to the stock, care should be taken to make sure that the cambium layer of scion is in contact with the cambium layer of stock (because the cambium layer in the stem is responsible for growth).
The cut soon heals and the stock and scion of two plants grow together and become one plant. The scion continues to produce its original leaves, flowers and fruits but it gets water and minerals for making food from the chosen stock. So, the fruits will have the characteristics of both the plants (from which scion and stock have come).
Grafting is used to breed fruit trees and flowering bushes. Apple, peach, apricot and pear trees are often grafted. We will now describe some of the advantages of the grafting method of artificial propagation.
(i) Grafting enables us to combine the most desirable characteristics of the two plants (scion and stock) in its flowers and fruits.
(ii) By grafting method, a very young scion (shoot part of a plant) .can be made to flower and produce fruits quite fast when it is grafted to the stock (stem having roots) of a mature plant.
(iii) It enables us to obtain flowers and fruits having different desired characteristics by grafting scions from different varieties of plants on the same stock. Many varieties of mango have been produced by grafting method.
(iv) Grafting can be used to produce varieties of seedless fruits.
Artificial vegetative propagation is usually used for the propagation (or reproduction) of those plants which produce either very few seeds or do not produce viable seeds. Some examples of such plants which are reproduced by artificial vegetative propagation methods are: Banana, Pineapple, Orange, Grape, Rose, etc.