New individuals are produced from a single parent without the act of fusion of gametes. The new individuals so formed are generally identical to the parent plant, as only mitotic divisions take place during their development. Regeneration of new plants from portions of vegetative organs is very common and is called vegetative propagation. For this purpose, organs like the root, stem, leaf, flower etc are variously modified.
This type of reproduction is very common in angiosperms and is well exploited by man. Vegetative reproduction results in the multiplication of plants and therefore also called as vegetative multiplication.
The methods of vegetative propagation may be classified into 2 types.
Among seed plants, vegetative propagation by natural methods is very common. A vegetative part reproducing by this method should possessa) Sufficient food for early growth of new plant
b) Growing budThe common structures that take part in natural vegetative propagation are roots, stem, leaves and buds.
Some examples for propagation by stem are fromstolons - Vallisneria, strawberry
offsets - Eichhorniarhizome - banana, ginger
bulbs - Alluim cepa, orioncorns - colacasia
tuber - potato
A-Bulb of onion, B-L. S. of bulb; C-Corm of Crocus
Other examples are Begonia, Kalanchoe Streptocarpus and Saintpaulia.
Horticulture have used the various methods of vegetative propagation adopted by plants in nature. These practices constitute the artificial means of vegetative propagation.These methods are meant for
Some common and important methods of artificial vegetative propagation are
Stem cuttings are most commonly used for this purpose. The factors to be considered for cutting are optimal length with a few nodes and internodes, diameter of the cutting, age of the plant and the season. Application of hormones leads to the quick formation of adventitious roots. For example sugarcane, roses, croton hibiscus, citrus plants, bougainvillea are grown by stem cutting.Root cutting from lemon, tamarind, etc also develop roots and shoots when planted in a moist soil.
In plants where the stem cannot be bent to the ground, the stem is girdled or given an slit at an upward angle. Then, it is covered with moist moss or cotton and wrapped in a polythene sheet to preserve the moisture. After a few weeks, adventitious roots arise from the injured part. The branch along with the roots is then separated from a parent plant and planted to grow into a new plant.
Grafting may be of the following types like approach grafting, bud grafting, tongue grafting, crown grafting and wedge grafting.
In this method, a healthy and woody branch is selected and the bark is sliced in a ring form of about 3-5 cm in length. A thick plaster of grafting clay (plaster formed of clay, cow dung, finely cut hay and water) to wrapped up with rag and tied on to the debarked portion. Care is taken to keep the gootee moist. In about 2-3 months, the roots emerge from the gootee. The gootee is now cut below the plaster for propagation. Lemon, orange, guava and litchi are usually propagated by using this method.
For micro propagation, a small amount of tissue from a suitable part of the parent plant is excised and grown on a nutrient medium under aseptic conditions. The tissue then develop into an undifferentiated mass of cells called callus. A small portion of the callus tissue is transferred to another suitable nutrient medium where they develop and differentiate into small plantlets. These plantlets on being transplanted in pots or soil, develop into mature plants.
a) It makes possible propagation of plants that have lost their capacity to produce seeds. E.g., banana, roseb) Plants like Bermuda grass (Cynodon dactyoln) which produce only a small quantity of seeds are propagated vegetatively.
c) It is a more rapid, easier and cheaper method.d) The plants produced will have the same characters and the hereditary potentials as the parent plant. The beneficial characters will be preserved in the neat generation.
e) Most of the ornamental plants are propagated by vegetative reproduction.f) Grafting enables the physical and physiological joining of 2 separate individuals for the best economic advantage.
g) It is a method to get rid of pathogen from any part of plant.Vegetative propagation is very important for plants with reduced power of sexual reproduction, long dormant period of seed or poor viability. Under these conditions this method is the only way of propagation of the plant.
b) Subsequent generations show a general fall in vigour and vitality.c) Adaptability, to changed environment decreases due to the absence of variations.
d) Overcrowding and severe competition among the daughter plants results in low yield.