What is Vegetative Propagation?
It is the process of multiplication where new plants develop from any portion of the vegetative organs of plants without involving the seeds. It occurs in lower as well as higher plants. Human beings for the process of vegetative propagation variously use stems, roots, and leaves of many plants. These are called vegetative propagules.
Characteristics of Vegetative Propagation:
- A single organism is involved without the production of gametes.
- The individuals formed are genetically identical to the parent.
- The cell divisions are only mitotic in nature.
- It is the simplest and a rapid way of reproduction under favorable conditions.
- Genetic variations may occur as a result of random mutation.
Methods of Vegetative Propagation:
Methods of Vegetative Propagation have been further divided into two types-
- Natural Vegetative Propagation.
- Artificial or Horticultural Vegetative Propagation.
Natural Methods of Vegetative Propagation
In these methods, vegetative propagules (somatic parts) of the plant detach from the body of the mother and develop into new plants under suitable conditions. It is done by the following means-
Vegetative Propagation by Roots:
The intact roots of many woody plants such as Murraya, Albizia lebbeck, Guava, Dalbergia sissoo which are growing just below the ground develop adventitious buds. The buds put out shoots and produce new plants.
The roots of plants like Sweet Potato, Dahila, Asparagus, Tapioca, Dioscorea (yam), etc. are tuberous and store abundant food material. They bear adventitious buds and provide a means of Vegetative Propagation. The buds present on the roots grow into leafy shoots called slips. The young slips are detached from the parent plants and grown separately.
Vegetative Propagation by Underground Stems:
Underground modified stem such as suckers, rhizomes, corms, bulbs and tubers possess buds which grow into new plants and help in vegetative reproduction.
Suckers of Mint and Chrysanthemum arise from the base of the erect shoot, grow horizontally in the soil and then come out to form new aerial shoots. These shoots become independent plants when suckers break away from parent plants.
Rhizomes serve as means of vegetative propagation by perennating under unfavorable conditions and producing new aerial shoots during the favorable season. Example– Typha, Ginger, Canna, Banana, Turmeric, Aspidium, Adiantum, Saccharum, etc.
Corms are specialized underground stems which bear many buds. They perennate in the unfavorable conditions and produce new plants under favorable conditions. Plants of Amorphophallus, Colocasia, Crocus, Freesia, Gladiolus, etc. propagate with the help of corms.
Bulb plants of Onion, Garlic, Narcissus, etc. serve as means of vegetative propagation by producing new plants when sown in the soil.
Tubers are modified underground stem branches having several buds. Each eye of the potato tuber is a bud that grows into a new potato plant when planted with a portion of the swollen tuber. The potato crop is raised by tubers and not by seeds.
Vegetative Propagation by Subaerial or Creeping Stems:
Runners are creeping modified stems that produce adventitious roots at nodes. Each node gives rise to aerial shoot which becomes a new plant. Example– Lawn grass, Oxalis, Centella, etc.
They are special arched above-ground horizontal branches that develop at the base of a crown and help in vegetative propagation. Example– Fragaria (Strawberry), Blackberry, Jasmine, etc.
They are one internode long runners which occur in some aquatic plants. Breaking of offsets help in Vegetative Propagation. Generally found in rosette type of plants. Example– Pistia (Water Lettuce), Eichhornia (Water Hyacinth).
Vegetative Propagation by Aerial Shoots (Aerial Stems):
Fleshy phylloclades occur in Opuntia and some other plants. Each segment of such stems can form a new plant. Sugarcane is propagated by planting segments of stems having at least one node.
Vegetative Propagation by Leaves:
Leaves are not a common means of vegetative propagation in nature. However, Bryophyllum is known for its remarkable ability to reproduce from leaves. In Bryophyllum daigremontianum plantlets develop from the buds present on the marginal notches of the intact leaves. These plantlets become detached and develop into independent plants. In other species of Bryophyllum and Kalanchoe, new plants arise only when the leaf is injured or detached. Some other plants propagated by entire leaf or leaf cuttings are Begonia, Streptocarpus, Adiantum caudatum, and Saintpaulia. Adiantum caudatum is also called Walking Fern because its leaf tips form new plants when they come in contact with soil.
Vegetative Propagation by Bulbils:
These are fleshy buds produced in the axil of foliage leaves in place of axillary buds. They grow to form new plants when shed and fall on the ground. Example– Oxalis, Allium, Pineapple, Dioscorea (Yam), Chlorophytum, Lily, etc. In Century Plant (Agave), the floral buds are modified into bulbils that grow into new plants when shed from the mother plant.
Vegetative Propagation by Turions:
A turion is a swollen bud, which contains much-stored food. It is detached from the parent plant and remains inactive through the winter and gives rise to a new plant in the following spring. Turions are found in a number of water plants. Example– Utricularia, Potamogeton, etc.
Artificial or Horticultural Methods of Vegetative Propagation:
Artificial methods are man-made techniques to propagate desired varieties according to human requirements. Rainy and spring seasons are the best seasons for vegetative propagation. Some of the common modes tried for artificial vegetative propagation are given below-
Vegetative Propagation by Cuttings:
Cuttings are short lengths of the plant which when removed and placed in soil under suitable conditions develop adventitious roots and leaves and grow into independent plants.
In certain plants like tamarind, lemon, and primrose root cuttings when put in the damp soil give rise to roots and shoots and form new plants.
Sometimes a small piece of one-year-old stem with an appropriate length and diameter is cut and dipped into root promoting hormones like Indole Butyric Acid (IBA), Indole Acetic Acid (IAA), and Naphthalene Acetic Acid (NAA) before planting in soil. Example– Grape, Coffee, China rose, Durantia, Sugarcane, Clerodendron, Citrus, etc.
Some plants like mahonia, rubber, Sansevieria, and blackberry can be propagated by leaf cuttings. Here the leaves are cut transversely into two or three parts with each part having at least one bud. These are planted in the soil in vertical positions. With time adventitious roots grow downward and a new plant emerges.
Vegetative Propagation by Layering (Soil Layering):
In this method, roots are artificially induced on the stem branches before they are detached from the parent plant for propagation. There are two common types of layering-
It is the most common method of propagation of herbaceous plants. In this method, the lower branch of the stem is bent down and partially defoliated. An injury is made in the defoliated portion. The injured and defoliated portion is covered with a light layer of moist soil in such a way that the growing tip of the branch remains above the soil surface. After a few days, the pegged portion develops adventitious roots. The rooted branch is then cut, separated from the parent plant, and grown into a new plant. Examples– Jasmine, Currant, Quince, Strawberry, Gooseberry, Cherry, etc.
Gootee or Air Layering:
This method is commonly used in the case of shrubs and trees which do not possess a branch near the ground. In this method, a ring of bark is removed from the base of an aerial branch. The girdled portion is then covered with moist or grafting clay and wrapped with a polythene sheet. The wrapped portion is called gootee. The girdled portion of the branch inside the gootee develops roots. Now the branch is cut and planted in the soil after removing the polythene. This method is used in vegetative propagation of litchi, Pomegranate, Orange, Lemon, Lokat, Bougainvillea, etc.
Vegetative Propagation by Grafting:
Parts of two different plants are joined to form a composite plant. In this case, one plant must have a strong root system whereas another plant has high fruit yield or flower production. A plant with a root system is called stock while with shoot is scion or graft. Cambium bearing shoot (scion) of one plant is joined to cambium bearing root (stock) of a related plant through different types of grafting like–
Tongue or Slice or Whip Grafting:
Oblique sloping cut or notch is given to both stock and scion. The two perfectly fit upon one another. They are tied together. Here stock and scion are of the same diameter.
A V-shaped notch is made on stock and a wedge-shaped cut is made on the scion. Both are also of the same diameter.
Several scions having wedge-shaped cut are grafted on the slit at the top of the stock. Here, the stock has a large diameter than the scion.
A V-shaped notch is given to stock at one side. One end of the scion is sharpened. It is inserted in the stock. Here, the stock also has a larger diameter than the scion.
In grafting, the scion is fixed over the stock in a manner that cambia of the two come in contact. The union is covered with grafting wax. It is then tied with the help of a tape, rubber, or nail. Example– Mango, Pine, Guava, and Apple, etc.
Vegetative Propagation by Plant Tissue Culture (Micropropagation):
It is the technique of raising new plants from small pieces of tissue (taken from shoot tips or other suitable parts of the plant) over a culture medium under aseptic conditions. A small amount of tissue from a suitable part of the parent plant is excised and grown on a culture medium. The tissue develops into an undifferentiated mass of cells called a callus. The callus can be maintained and multiplied indefinitely. When small portions or even single cells of the callus tissue are transferred to another suitable medium containing specific doses of growth hormones, they develop and differentiate into small plantlets. The plantlets are then transplanted in pots or soil to develop into mature plants.
The tissue culture technique has been commercially used for raising rare varieties of ornamental plants like orchids, gladiolus, carnation, roses, etc. It is also useful for producing virus-free healthy plants (especially in potato, tapioca, and sugarcane, etc.) from the tissues in the shoot apical meristem, which are virus free. In addition, this technique enables the production of an unlimited number of plants within a relatively short time.
Significance of Vegetative Propagation:
- It is good for the multiplication of seedless plants. Example– Banana, Sugarcane, Pineapple, and seedless Orange and Grape.
- The important advantage of vegetative propagation is that a plant can be retained and multiplied indefinitely without any change or variation.
- It is the fastest method of reproduction. Example– Potato crop requires more than one year with the help of seeds, however, it takes only 3 to 4 months with the help of tubers. Similarly, Lily takes 4 to 7 years through seeds, however, 1 to 2 years by bulbs.
- By grafting, desirable quality of fruit/ flower/ seed can be obtained.
- Disease-free plants can be cultured by micropropagation and micrografting.
- Since plants produced through tissue culture (micropropagation) are genetically identical, they show genetic uniformity.
- Plants with long seed dormancy or poor seed viability or poor seed can be propagated vegetatively. Example– Cynodon dactylon (Lawn, Dhoob, or Bermuda grass).
- The survival rate of daughter plants is almost 100 percent in vegetative propagation.
- Good quality and better yield varieties can be preserved for a long duration in the offsite collection, herbarium, botanical gardens, etc.
- Diseased parents always give diseased clone.
- Clone undergoes degeneration due to the absence of sexual reproduction.
- Vegetative organs cannot be preserved for long-duration like culms of sugarcane.
- Vegetative propagules get easily decayed and are prone to bacterial, viral, and fungal diseases.
- Do not cause any variation in plantlets, thus decrease in the adaptation power.
- There is an absence of a dispersal mechanism. Vegetative propagation in a particular area causes overcrowding. It results in intraspecific competition.