Asexual reproduction of plants

Reproduction of plants

Reproduction of plants or the propagation of plants occurs mainly in two ways.

1. Asexual reproduction
2. Sexual reproduction

Asexual reproduction of plants

Vegetative reproduction in plats is an asexual reproduction method. 

The process of generating new plats from underground or aerial parts of a mother plant is referred to as vegetative reproduction. This gives rise to daughter plants that are identical to mother plant. Vegetative reproduction/ Vegetative propagation is two types.

• Natural vegetative propagation
• Artificial vegetative propagation

 Natural vegetative propagation

Generation of new plants naturally from underground or aerial parts of a mother plant is known as natural vegetative propagation. This occurs from various vegetative parts of a plant. Some examples are given below.

Roots

E.g :- Curry leaves, Bread fruit, Guava, Slime wood

Leaves

E.g :- Begonia, Akkapana/ Sathaikkaraichchan, Queen of the night

Suckers

Small plants that rise horizontally from the basal part of stem under the soil are known as suckers.

E.g :- Paddy, Banana, Pine apple, Chrysanthemum, Hulankeeriya, Kaladuru

Runners

Plant stems that run along the surface of soil connecting the stem to soil by adventitious roots the runners.

E.g :- Gotukol/ Vallarai, Sweet potatoes, Maharaavana raevula/ Ravanan meesai

 Bulbils

Special reproductive structure formed by a modification of a vegetative bud or a flower bud is known as a bulbil.

E.g. :- Pine apple, Jute, Hondala

Underground Stems

Stems of plants which grow under the soil are known as underground stems. Vegetative propagation, storage of food and spending dormant period in adverse climatic conditions are some functions of underground stems. Underground stems are categorized into four types according to the external features.

1. Rhizome - E.g. :- Ginger, Turmeric, Cannas, Araththa
2. Corm - E.g. :- Big rooted Taro yam(Habarala/Nersshembu), Cocoyam (Gahala/Shembu),Taro, Elephant foot yam
3. Bulb - E.g. :- Red onion, Big onion, Leeks
4. Stem Tuber - E.g. :- Potato, Coleus potato (Innala)

Artificial vegetative propagation

Production of plants vegetatively by man is known as artificial vegetative propagation. This can be done in several ways.

• Rooting of stem cuttings
• Layering
• Grafting
• Tissue culture

 Rooting of stem cuttings

New plants can be obtained by planting stem cuttings of a mother plant. It is more appropriate to select twigs from a healthy plant that do not bear tender leaves, flowers or fruits at that time. This method is widely used for some plants like Rose, Shoe flowers, Ixora, Bougainvillea and Croton.

Layering

Initiate rooting while it is still attached to the mother plant is known as layering. Layering is of two types.

1. Ground layering
2. Aerial layering

Ground Layering

Rooting is initiated from a branch of the plant closer to the ground level by this method. First a small cut is made on the underside of the selected twig. Then the twig is bent and burried under the soil. After few weeks, the twig will develop roots. Then the twig is separated from the mother plant and is planted.

 E.g. :- Jasmin, Lemon

Aerial Layering

This method is used for the twigs which are high above the ground. A ring of bark of the twig is removed. A mixture of compost and coir dust is placed round that place and tied with a strip of polythene. After few weeks the twig will develop roots. Then the twig is separated from mother plant and is planted.

E.g. :- Pomegranate, Lemon

 

Following are some advantages of layering.

• Plants that do not produce seeds can be propagated successfully.
• Several number of plants can be produced easily.

Grafting

Connecting a twig or a bud of a plant to a plant of same or closely related species is known as grafting. Two parts of the plants grafted are mentioned below.

1. Stock

 The rooted part of the plant is known as stock. Following are the characteristics that should be shown by a stock.

• Bearing a strong root system.
• Having a uniform growth. 
• Withstanding environmental changes and diseases.

2. Scion

The twig or the bud taken from another plant and grafted to a stock is known as scion. Following are the characteristics that should be shown by a scion.

• Should be a variety of good characteristics 
• Should be free from pests and diseases

In the process of grafting, stock and scion are fused together by their cambium. Therefore grafting can be done only on the dicotyledonous plants, which have cambium tissues. Grafting can be done in two ways as follows.

1. Bud grafting 
2. Twig grafting

Bud grafting

Selecting a plant bud as the scion and grafting it to a stock is known as bud grafting It is done as follows.

• Cutting a live bud (which is located above the leaf scar) using a grafting knife.
• Making a cut on the stock and insert the bud into the cut.
• Wrapping the place from bottom to top using polythene strips.
• After few days, when the bud is about to emerge, remove the wrap and re-wrap keeping the bud open.
• Cutting the stem of the stock about 15 cm above, from the bud after about three weeks.

Twig grafting

In this method, a twig of a plant is taken as the scion. Procedure of grafting is given below.

• Selecting a twig of a fruit-bearing plant (It is more suitable to select a twig which has no tender leaves, flowers or fruits).
• Cutting the twig without damaging the cut.
• Fixing the twig to the stock, so that the cambium are contacted.
• Wrapping the place from bottom to top using polythene strips.
•  Removing the wrap when the twig is observed to be growing.

Tissue culture

New offsprings, which are identical to the parental plant, can be produced by cultivating any vegetative tissue of a plant in a culture medium under controlled conditions. Offsprings thus obtained are called a clone. Genetically identical clones can be obtained by tissue culture. Generally, tissues are taken from apical buds, lateral buds or root tips for this purpose. Sucrose, mineral salts, vitamins and plant growth substances are included in the culture medium used for tissue culture. Agar is used to solidify the medium. Sterilized conditions and controlling of temperature and light should be practised for the success of tissue culture.

Following are the principle steps followed in tissue culture

1. Introducing the part of vegetative tissue, obtained from mother plant, into the culture medium. 
2. Allowing new roots and buds to be developed from the tissue called callus, which is grown from the vegetative tissue introduced.
3. Separating the plantlets and placing them in test tubes or flasks to grow further.
4. Gradually let the new plantlets to get adapted to natural conditions to be cultivated in the field.