One of the interesting Biology Topics is the study of animal behavior and how it is influenced by genetics and the environment.
Artificial Vegetative Propagation – Definition, Types, Examples, and Advantages
We can grow many plants from one plant by using man-made methods. The process of growing many plants from one plant by man-made methods is called the 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 Cuttings, Layering, and Grafting. We will now describe all these methods, one by one. Let us start with the cutting method for the artificial propagation of plants. These are man-made techniques developed for the propagation of desired varieties of plants. The various techniques are cutting, layering, grafting, micropropagation, etc.
1. Cuttings Method
A small part of a plant that 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 cutting, care should to taken to see that there are some buds on it. Cuttings are cut pieces of roots, stems, and leaves which when placed in the soil can sprout to form new plants.
The propagation of plants by the ‘cuttings’ method.
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 [see Figure (a)]. After a few days, the cutting develops roots and shoots, and grows into a new plant [see Figures (b) and (c)]. 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, cactus, etc., can be grown by means of cuttings. For example, rose plants are propagated (or reproduced) by means of cuttings from stems (or shoots) as follows: A piece of the stem (or side shoot) having bud is cut from an existing rose plant with the help of a knife. The lower part of this cutting 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 the cutting method is that by using this method we can produce many new plants from just one plant quickly, without waiting for flowers and seeds.
The cutting from a plant is kept in a jar of water. See how new roots have grown.
Rose plants are grown by the cutting method.
Sugar cane plants are grown by the cutting method.
Banana plants are also grown by the cutting method.
Cuttings Basic Characteristics:
- Cutting is the detachment of part of a plant to grow into a new plant.
- Young healthy lateral branches are suitable.
- Some of the leaves may be removed to reduce transpiration and so conserve water.
- The cut end of the stem is placed into well-drained aerated compost.
- A new root system develops at the cut end.
Advantages: fast, easy, cheap, and new plants are genetically identical to the parent plant.
Cutting is of the following kinds:
(a) Root Cuttings: These are long pieces of roots used in the propagation of lemon, apple, blackberry, raspberry, etc. Nowadays root promoting chemicals (IAA, IBA, NAA, etc.) are employed for successful rooting. Root cuttings are usually taken from 2 to 3-year-old plants during their dormant season when they have a large carbohydrate supply. Root cuttings of some species produce new shoots which then form their root systems, while root cuttings of other plants develop root systems before producing new shoots.
(b) Stem Cuttings: It is a common method of plant propagation. Cut pieces should have at least one node and should be one year old. Their lower ends are dipped in root-promoting hormones for several minutes before planting in soil which develops adventitious roots. A few examples are rose, sugarcane, Duranta, Citrus, grape, china rose, etc.
(c) Leaf Cuttings: Leaf cutting are used almost exclusively for a few indoor plants. Leaves of most plants will either produce a few roots but no plant or just decay. Snake plants (Sansevieria) can be propagated by leaf cuttings. Leaves are cut transversely into two or three parts and planted in a vertical position in the soil, e.g., Sansevieria, Begonia, and Bryophyllum.
2. Layering Method
In layering, the development of adventitious roots is induced on the stem before it is separated from the parent plant. It is done in plants like lemon, rose, strawberry, grape-vine, etc. 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 as shown in Figure.
The propagation of jasmine plants (chameli) by the layering method.
We can see from Figure 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 that are buried in soil grow their own roots (see Figure). 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 strawberries and raspberries are propagated by the natural layering method. 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.
Layering Basic Characteristics:
- A young healthy stem is bent into a small hole with the terminal bud above soil level.
- The hole is filled with soil.
- A new root system develops at an underground node.
- The terminal bud forms a new shoot system.
- The new plant can then be separated from the ‘parent stem’.
Layering is of the following kinds:
(a) Mound Layering:
The shoot is pruned and the lower part is covered by soil when a number of new shoots develop. Soil and sawdust are poured over the base to form a mound. Each shoot develops roots. Rooted shoots are separated and planted, e.g., apple, pear, grape-vine, etc.
(b) Gootee or Air Layering:
This technique is adopted in such plants which do not possess branches near the ground, e.g., pomegranate, guava, lemon, orange, litchi, etc. During early monsoon rains, a 3-5 cm long ring of bark is removed from the basal region of a healthy and woody branch. It is covered by a thick plaster of grafting clay. To it, water is added along with a small quantity of root-promoting hormones like IAA, IBA, or NAA. It is then wrapped in polythene to preserve moisture. After a few weeks, adventitious roots arise from the injured part. The rooted branch is then separated and used for planting.
(c) Simple Layering:
In this layering, soft, basal, partly-injured branch is pegged at one place, e.g., cherry, jasmine, grape-vine.
(d) Serpentine Layering:
The branch is pegged at several places so as to form many plants, e.g., Clemans.
(e) Trench Layering:
The branch is pegged in a horizontal position in a trench. It develops a number of vertical shoots, e.g., walnut, and mulberry.
(f) Drop Layering:
A plant capable of forming several branches (e.g., dwarf Rhododendron) is grown in deep soil. Adventitious roots develop at the base of branch shoots. They are separated and planted.
(g) Tip Layering:
A shoot is bent in the soil in such a way, that its basal end is slanting while the upper region is upright. Soil is pressed. It induces root formation and later growth of shoot tip, e.g., blackberry, dewberry, raspberry.
3. Grafting Method
Grafting is a method in which the cut stems of two different plants (one with roots and the 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.
- 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.
- The cut stem of another plant (without roots) is called a scion. The scion is the upper part of a plant that may have leaves on it (but no roots).
It is a process of attaching a cutting from one plant to the rooted stem of another. The rooted stem on which the graft is made is called the stock. The cutting that is attached to the stock is known as a scion. The new composite plant has the root system of the stock and the shoot system, i.e., flowers and fruits of the scion. The success of the grafting mostly depends upon the union of the cambium of scion and stock.
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 [see Figure (a)]. The stem of the 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 [see Figure (a)].
The grafting method for the artificial propagation of plants (or trees).
Grafting was used to grow this apple tree.
The scion is placed over the stock [see Figure (b)], The cut surfaces of the scion and stock are fitted together and bound tightly with a piece of cloth and covered properly with a 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 the 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.
- Grafting enables us to combine the most desirable characteristics of the two plants (scion and stock) in their flowers and fruits.
- By the 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.
- 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 the grafting method.
- Grafting can be used to produce varieties of seedless fruits.
- fast, flowers, and fruit are identical to the scion parent.
Grafting Basic Characteristics:
- Grafting produces new plants by joining a branch of the desired shoot system (scion) of one plant into the vigorous root system (stock) of another.
- Complementary-shaped cuts are made in the stem of the scion and rootstock.
- The scion stem is joined to the rootstock stem.
- The meristematic tissue of the scion and rootstock are in contact and its growth unites them.
Grafting is of the following kinds: Grafting is generally used for fruit trees like apples, mango, citrus, lemon, etc., and roses. The various techniques of grafting are as follows:
(a) Tongue Grafting:
An oblique sloping cut or notch is given to both stock and scion. The two perfectly fit upon one another. They are tied together. Stock and scion are of the same diameter.
(b) Crown Grafting:
In this case, the diameter of the stock is greater than the scion and many scions are used for grafting on a single stock.
(c) Wedge Grafting:
In this case, the diameter of the stock and scion is the same and a V-shaped notch is made in the stock while the scion is cut like a wedge.
(d) Side Grafting:
A V-shaped notch is made on one side of the stock for the insertion of one scion in each lateral cut of stock. The diameter of the stock is larger than the scion.
(e) Approach Grafting:
Two independently growing plants are brought together. The shoots of the two are given cuts at the same level for a distance of 2.5 – 5 cm. The cuts are in the form of removing smooth slices of bark (spliced approach grafting), tongue-shaped cuts for interlocking, and deeper vertical cuts if the stock is thicker than the scion. The union of the stock and scion is tied with the help of a bandage, tape, etc. In approach grafting, the scion is cut below the graft while stock is cut above the graft after the establishment of the union.
(f) Bud Grafting:
A scion is a bud with a small piece of bark and cambium. The bark of the stock is given an incision deep enough to reach the cambium. The sides of the incised bark are lifted and the bud graft is inserted in the slit with the bud being left exposed. The joint is treated with grafting wax and bandaged. Bud develops after 3-5 weeks. The stock is cut above the graft. Bud grafting is practiced in apple, peach, and rose.
Differences between Layering and Grafting:
|1. The development of an adventitious root is induced on the stem before it is separated from the parent plant.||1. It is a process of attaching a cutting from one plant to the rooted stem of another.|
|2. Due to layering only a single plant is involved.||2. Due to grafting two plants are involved.|
|3. There is no involvement of stock or scion. Only or single branch of desired variety is selected.||3. Here, the rooted stem on which the graft is made is called stock, and the cutting that is attached to the stock i.e., scion.|
|4. During layering new plant can be separated from the ‘parent stem’.||4. Fast-producing flowers and fruit which are identical to the scion parent.|
4. Micropropagation Method
The rapid process of vegetative multiplication of plant material in tissue culture and their in vitro propagation technique is called micropropagation.
Micropropagation is the practice of rapidly multiplying stock plant material to produce a large number of progeny plants, using modern plant tissue culture methods. Micropropagation is used to multiply noble plants such as those that have been genetically modified through conventional plant breeding methods.
It is the rapid raising of new plants from small plant tissues with the help of the tissue culture technique. Orchids, Gladiolus, Chrysanthemum, and many other ornamental plants are raised using micropropagation. Micropropagation is also used to provide a sufficient number of plantlets for planting from a stock plant that does not produce seeds or does not respond well to vegetative reproduction.
Basic Characteristics of Micropropagation:
- A very small sample of meristematic tissue is removed from the tip of a branch.
- This tissue sample is likely to be free of virus infection.
- The tissue sample is placed on sterile nutrient agar in a test tube.
- Plant growth regulators can be added to stimulate and control development.
- A plantlet will grow from the tissue sample.
- The plantlet is then transferred to a suitable compost for further growth.
Micropropagation can be achieved by the following methods:
(a) Multiple Shootlet Production: Shoot tips are used for tissue culture for raising mini plants. Shoot tips in culture medium produce multiple buds and each bud grows into a shoot By using rooting hormone, the shoot is induced to produce roots. Micropropagation by this method is successfully employed in potatoes, cardamom, raspberry, peach, almond, orchids, bananas, etc.
(b) Somatic Embryogenesis: The embryos developed from a single somatic cell by tissue culture are known as somatic embryos or embryoids. In carrots and alfalfa, the somatic embryos can be produced in thousands in a small volume of nutrient medium.
(c) Meristem Culture: In meristem culture, the meristem and a few subtending leaf primordials are placed into a suitable growing media. An elongated rooted platelet is produced after some weeks and is transferred to the soil when it has attained a considerable height. A disease-free plant can be produced by this method. Experimental results also suggest that this technique can be successfully utilized for the rapid multiplication of various herbaceous plants.
(d) Callus Culture: A callus is a mass of undifferentiated parenchymatous cells. When living plant tissue is placed in an artificial growing medium with other conditions favorable, a callus is formed. The growth of callus varies with the homogenous levels of auxin and cytokinin and can be manipulated by the endogenous supply of these growth regulators in the culture medium. The callus growth and its organogenesis or embryogenesis can be referred into three different stages.
- Stage I: Rapid production of callus after placing the explants in culture medium.
- Stage II: The callus is transferred to another medium containing growth regulators for the induction of adventitious organs.
- Stage III: The new plantlet is then exposed gradually to the environmental condition.
(e) Suspension Culture: A cell suspension culture refers to cells and or groups of cells dispersed and growing in an aerated liquid culture medium (Street, 1997, Thorpe 1981) is placed in a liquid medium and shaken vigorously, and a balanced dose of hormones. Suezawa et. al., (1988) reported Cytokinin-induced adventitious buds in kiwi fruit in a suspension culture sub-culture for about a week.
(f) Embryo Culture: In embryo culture, the embryo is excised and placed into a culture medium with proper nutrients in an aseptic condition. To obtain quick and optimum growth into plantlets, it is then transferred into the soil. It is particularly important for the production of interspecific and intergeneric hybrids and to overcome embryo abortion.
(g) Protoplast Culture: In protoplast culture, the plant cell can be isolated with the help of wall-degrading enzymes and grown in a suitable culture medium under controlled conditions for the regeneration of plantlets. Under suitable conditions, the protoplast develops a cell wall followed by an increase in cell division and differentiation and grows into a new plant. The protoplast is first cultured in a liquid medium at 25°C to 28°C with a light intensity of 100 to 500 lux or in the dark and after undergoing substantial cell division, they are transferred into solid medium congenial or morphogenesis in many horticultural crops response well to protoplast culture.
Stages of Micropropagation:
Micropropagation usually comprises the following stages (Murashige, 1974). The stages are:
- Initial Stage: This initial stage of micropropagation involves the selection and growth of stock plants for about three months under controlled conditions.
- First Stage: In this stage, the initiation and establishment of culture in a suitable medium is achieved. The selection of appropriate explants is important. The most commonly used explants are organs, shoot tips, and axillary buds. The chosen explant is surface sterilized and washed before use.
- Second Stage: In this stage, the major activity of micropropagation occurs in a defined culture medium. This stage mainly involves the multiplication of shoots or rapid embryo formation from the explant.
- Third Stage: This stage involves the transfer of shoots to a medium for rapid development of shoots. Sometimes, the shoots are directly planted in the soil to develop roots. In vitro, rooting of shoots is preferred while simultaneously handling a large number of species.
- Fourth Stage: This stage involves the establishment of plantlets in soil. This is done by transferring the plant- lets of stage III from the laboratory to the environment of a greenhouse. For some plant species, stage III is skipped, and unrooted stage II shoots are planted in pots or in a suitable compost mixture.
The different stages described above for micropropagation are particularly useful for comparison between two or more plant systems, besides better understanding. It may, however, be noted that not all plant species need to be propagated in vitro through all the stages referred to above.
Advantages of Micropropagation:
The micropropagation technique is preferred over the conventional asexual propagation method because of the following:
- This technique helps in the rapid multiplication of plant material required for agriculture, horticulture, and forestry.
- By this technique, a large number of offspring or plantlets can be obtained every year. Genetic uniformity is easily maintained.
- Cloning can be done throughout the year in a very small space under controlled conditions.
- Resistance to diseases can be developed in many plant species.
- Offsprings can be obtained of sterile plants or of free hybrids of extraordinary characteristics.
- Valuable germplasm can be stored for a long time.
- Only a small amount of tissue is needed for the regeneration of millions of plants.
- It provides a means for the international exchange of plant materials.
- Micropropagation has been successfully done for many trees of high economic value.
- Production of artificial seeds in Eucalyptus has been successfully achieved (Muralidharan and Mascarenhas, 1989).
- Genetic transformation and in vitro regeneration of conifers have been successfully performed (Gupta, 1989).
Disadvantages of Micropropagation:
Micropropagation is not always the perfect means of multiplying plants. Conditions that limit its use include:
- It is very expensive and can have a labour cost of more than 70%.
- A monoculture is produced after micropropagation, leading to a lack of overall disease resilience, as all progeny plants may be vulnerable to the same infections.
- An infected plant sample can produce infected progeny. This is uncommon as the stock plants are carefully screened and vetted to prevent culturing plants infected with viruses or fungi.
- Not all plants can be successfully tissue-cultured, often because the proper medium for growth is not known or the plants produce secondary metabolic chemicals that stunt or kill the explant.
- Sometimes plants or cultivars do not come true to type after being tissue cultured. This is often dependent on the type of explant material utilized during the initiation phase or the result of the age of the cell or propagule line.
- Some plants are very difficult to disinfect fungal organisms.
Differences between Vegetative Propagation and Artificial Propagation:
|Vegetative Propagation||Artificial Propagation|
|1. It is a process by which new plant individuals arise without the production of seeds and spores.||1. It is a common practice among horticulturists by using several techniques like cutting, layering, grafting, and micropropagation.|
|2. By this propagation, a plant that persists in a location over a long period of time, constitutes a clonal colony.||2. It is commonly used to increase the population of endangered species via artificial regeneration.|
Differences between Monocarpic and Polycarpic Plants
|Monocarpic Plants||Polycarpic Plants|
|1. Monocarpic plants flower only once in their lifetime.||1. Polycarpic plants flower repeatedly every year.|
|2. After flowering, the plants may die.||2. These plants do not die after flowering.|
|3. Reproductive phase is not too long and uninterrupted. e.g.: Raddish, Bamboo, Carrot, etc.||3. Reproductive phase is very long and is interrupted by an inter-flowering period, e.g.: Mango, Orange, Jackfruit, etc.|
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, Pineapples, Orange, Grapes, Rose, etc.
Advantages of Artificial Vegetative Propagation
The artificial propagation of farm and garden plants has several advantages. Some of the important advantages of the artificial vegetative propagation of plants are given below:
- The new plants produced by artificial vegetative propagation will be exactly like the parent plants. Any desirable features of the parent plant will be replicated in the new plants.
- The fruit trees grown from seeds may take many years before they start to bear fruit. But the fruit trees that are grown from cuttings or by grafting start to bear fruits much earlier (only after a few growing seasons).
- The plants grown by vegetative propagation usually need less attention in their early years than the plants grown from seeds.
- Many plants can be grown from just one parent plant by artificial propagation.
- We can also get seedless plants by artificial propagation.
Cuttings, layering, and grafting are the traditional methods for the artificial propagation of plants. For commercial purposes, they are being replaced by modern methods of artificial propagation of plants involving tissue culture. In tissue culture, they just put a few plant cells (or plant tissue) in a growth medium with plant hormones in it and it grows into new plants.