Vegetative Propagation (Reproduction) of Plants.

Vegetative reproduction is the use of the vegetative part of a parent plant to produce a new plant. It is also referred to as artificial vegetative propagation. These vegetative parts are mainly the stem, the root, and the leaf. Methods of vegetative reproduction

The use of specialized vegetative plant organs.
The use of cuttings
By simple layering
By air layering or marcotting
Grafting
Budding
Micropropagation or tissue culture
Use of aponitic embryo or aponitic seed.

SPECIALISED VEGETATIVE PLANT ORGANS

Examples of specialized vegetative plant organs or parts for vegetative reproduction are:

Bulbs
Corm
Tuber
Rhizome
Sucker
Stolon
Runner
Specialized leaves

Adaptations for vegetative reproduction

The organs appear fleshy and have stored food to support sprouting.
Possess viable vegetative buds on the organs.
They also, possess adventitious roots and lateral roots.
Presence of lenticels as respiratory openings.
Presence of scaly leaves to protect the buds and to conserve moisture in the organs.
Digested food substances and mineral salts in the bulbs grow through cell multiplication and
elongation, and sprout out as new plants.
Adventitious roots develop to hold the new plant to the ground.

Features of specialized vegetative plant organs

Bulb

Bulb is a short flattered underground stem covered in fleshly leaves that store food.
The stem of a bulb is short and conical in shape
The stem does not store food.
The leaves are arranged in concentric circles around the stem.
The internodes are very short.
Terminal buds produce aerial shoots, while axillary buds give rise to daughter bulbs.
Adventitious or, fibrous roots arise directly from the base of the stem.
Scaly leaves protect the fleshy leaves and the buds.
Fleshy leaves store food which is mainly water and sugar (glucose).
Bulb serves as a storage organ for onion.
Other examples of bulbs are harmattan lily, spider lily, garlic, tulip, and shallot.
Method of propagation: using the whole onion bulb.
Method of storage: the onion bulb is dried and stored in well-ventilated containers or baskets.
The bulb is rounded.

Rhizome

It is a horizontal underground stem with buds at the nodes and adventitious roots.
It has terminal buds that form aerial shoots.
It has lateral buds that develop into lateral branches.
There are scaly leaves that surround the thick stem.
The nodes are separated by long internodes.
Adventitious roots grow from the stem and nodes.
Most rhizomes are swollen with stored food which is mainly starch.
Rhizomes are the plant’s storage organs.
New plants grow from the buds
Examples of rhizomes are ginger, canna-lily, bush cane, spear grass, and turmeric.

Corm

A corm is a short, thick, round underground stem that stores food.
The food stored by the stem is mainly water and starch.
The stem is covered by thin-scale leaves.
Buds and adventitious roots are present at the bottom of the dry-scale leaves.
Aerial shoots are produced by the terminal buds.
Daughter corms are produced by the buds which use the stored food to grow before the mother corn dies.
The corm serves as the storage organ for cocoyam.

Economic importance of cocoyam:

cooked for human consumption.
the young and tender leaves are used as vegetables.

Examples of corn are cocoyam and gladiolus.

Root tuber

Root tuber is a swollen food-storing root.
Buds or eyes are present on the stem and adventitious roots are found on the swollen root.
The root tuber serves as the storage organ for cassava.
The main method of propagating cassava is by stem cutting.

Importance of cassava.

For making starch.
For making gari.
For preparing food such as fufu, ampesi, and kokonte for human consumption.
Examples of root tubers are sweet potato, cassava, and carrot.

Stem tuber

The stem tuber is the swollen end of the underground stem which contains a larger amount of stored food.
The buds or eyes on the tubers grow into new plants which produce new tubers.
The stem is enlarged and stores food.
The’ food stored in the stem is mainly starch, water, vitamin C, little protein, and mineral salts.
Yam tuber is not divided into nodes and internodes.
The main method of propagating the yam is seed yam, yam setts, and yam cutting.
Cultural practices usually performed on yam between the time of planting and harvesting are
mulching, fertilizer control, weed control, and pest control.

Yam tuber is stored by the following methods:

Tubers are tied up in well-ventilated barns.
Place yam in shallow trenches and cover with soils or wood shavings.
Place yams on wooden platforms raised above ground to keep them dry.
Place yams in pyramidal shapes and cover them with palm leaves leaving a hole in the middle for circulation of air.
Tubers are peeled off and dried.

Economic importance:

For making flour.
For preparing food for consumption.
Examples of stem tubers are yam and Irish potato.

Runner

A runner is a stem growing horizontally over the surface of the ground.
New plants and roots develop at the nodes along the stem.
They have buds and scale leaves.
Examples of plants with runners are Doop grass, sweet potato, Strawberry, and Desmodium.
The method of propagating the runner is by stem cutting.

Sucker or offshoot

It is a new plant that develops from the stem of the parent plant.
They have scale-leaf and large terminal buds.
Sucker does not store food.
They may either have their roots in the soil or are joined to the stem above the soil.
It is sometimes also called Ratoon, Crown, Division, or Slip.
Examples are Banana, Pineapple, and Guinea corn.

Propagation by cutting.

This is the most popular and extensive method of propagation of plants.
The three methods of cutting are stem cutting, root cutting, and leaf cutting.
The stem cutting is further divided into hardwood cutting and softwood cutting.
Examples are; cassava, cane sugar, crotons, coleus, balsam, yam, and sweet potato can be propagated by cutting.

Propagation by layering

The two types of layering are ordinary layering and marcotting (air layering).
Layering means bending a branch or shooting it down to the ground without breaking it till it develops roots.
A mixture of sand and well-rotted compost placed around the stem will help in root development.
The stem is cut off from the parent plant when roots have been formed and the new plant transplanted.

Ordinary layering as a method of artificial vegetative propagation

A branch of the plant is bent to the ground.
The nodes make contact with the soil.
It is pegged to the ground and then covered with rich soil to enhance root development.
The plant is watered periodically.
When the roots emerge, the branch is cut from the parent plant.
It can then be transplanted.

Example of plants propagated by layering.

Bougainvillea.
Rose plant.
Hibiscus.
Indian rubber plant.
Marcotting (air layering)

This is another method of layering plants.

Instead of bending down the branch, the layering is done on the branch as it still stands.
This process consists of tying a ball of soil around the stem of a plant.
Examples of plants propagated by marcotting are citrus, mangoes, and roses.

Propagating by grafting

Grafting is defined as the union of the cambium layers of two woody stems.
Grafting can also be defined as the act of joining parts of a plant together in such a way that they will unite and continue to grow as one plant.
The part of the graft combination which is to become the upper portion of the plant is called the scion and the lower portion of the graft is called the stock or rootstock.
Only plants, which have a close relationship can be united in this way.

Grafting as a method of artificial vegetative propagation

In the process, the scion is cut at the slanting or V-shape position from the mature tip and shall be about 7.5-10cm in length.
All leaves on the scion should be removed.
The stock should be cut similarly such that the two surfaces will neatly fit together and bound together with tape.
If the union succeeds, the scion will grow after about 2 to 3 weeks.
However, the plants from which the scion and stock are obtained should have approximately the same age and size.
Examples of plants propagated by this method are mango, orange, and cocoa.
Factors to be considered when grafting ornamental plants
Closely related species.
Health condition of species.
Availability of stock and scion.
Prevailing weather conditions.
The plants should be of approximately the same age and size.

Propagation by budding or bud grafting

This is the art of joining a bud with a stock together in such a way that they will unite and continue to grow as one plant.

Budding as a method of artificial propagation of vegetative

Select a plant or stock with a well-established rooting system.
The bark of the stock is carefully opened by a T-shaped cut using a sharp knife.
A dormant bud is carefully removed from a matured seedling which is about two years old.
Carefully scrap off the woody part of the bud to expose the cambium.
Insert the bud into the stock.
The union is then wrapped with tape or washed cloth.
Care is taken to cover all the cuts till the but is exposed.
When the bud breaks dormancy and is well established and growing, the part of the stock plant above the union is removed.

Advantages of budding

Changing of undesirable variety to a desirable variety.
Combination of good qualities of two different plants of the same species into one plant.
Perpetuation of some varieties which cannot be propagated by any means.
Growing of two or more kinds of fruits or flowers on one plant or tree.
Rapid method of developing new varieties of plants or crops.
Hastens seed selection.
Hastening maturity or fruity time.

Leaf-cutting:

In this, method of propagation, the main vein of the leaf is cut in a few places of the secondary veins and then laid flat upon the soil.

This method can be applied to Bryophyllum, Crenatum, and some Begonia.

Difference between root tubers and stem tubers.

Root tubers	Stem tuber
Scale leaves are absent	Scale leaves are present.
Absent of bud or eyes	Presence of buds or eyes.
Adventitious roots do not give rise to new plants.	The adventitious root produces new plants at the base of the aerial shoots.

Note:

The only difference between budding and grafting is that, in grafting, a shoot is used for the scion, whereas in budding, a bud with part of the bark of the plant is used as the scion.
The only advantage budding has over grafting is, that with budding, many buds can be obtained a from single plant, while in grafting shoots have to be taken from several plants if many operations are to be performed.
Whereas ordinary layering occurs on the ground, marcotting occurs in the air.

Difference between bulb and rhizome.

Bulb	Rhizome.
Swollen leaves present	Leaves are not swollen.
Scale leaves are reddish or whitish.	Scaly leaves are brownish.
Stem reduced.	Stem elongated.

Tissue Culture of Plants

Tissue culture is the growth of a tissue in an artificial liquid or solid culture medium.

Somatic embryogenesis, meristem tissue culture, and anther tissue culture are three methods of cloning plants due to the ability of plants to grow from single cells.

Many plant cells are totipotent, which means that each one has the genetic capability of becoming an entire plant.

During somatic embryogenesis, hormones are added to the medium and they cause leaf or other tissue cells to generate small masses of cells, which can be genetically engineered before being allowed to become many new identical plants.

Thousands of little “plantlets” can be produced by using this method of plant tissue culture.

Many important crop plants, such as tomato, rice, celery, and asparagus, as well as ornamental plants such as lilies, begonias, and African violets, have been produced using somatic embryogenesis.

Plants generated from somatic embryos are not always genetically identical clones.

They can vary because of mutations that arise spontaneously during the production process.

These mutations, called somaclonal variations, are another way to produce new plants with desirable traits.

Somatic embryos can be encapsulated in hydrated gel, creating artificial “seeds” that can be shipped anywhere.

Meristem tissue can also be used as a source of plant cells.

In this case, the resulting products are clonal plants that always have the same traits.

Anther tissue culture is a technique in which the haploid cells within pollen grains are cultured in order to produce haploid plantlets.

Conversely, a diploid (2n) plantlet can be produced if chemical agents, to encourage chromosomal doubling, are added to the anther culture.

Anther tissue culture is a direct way to produce plants that are certain to have the same characteristics.

Cell Suspension Culture

A technique called cell suspension culture allows scientists to extract chemicals (i.e., secondary metabolites) from plant cells, which may have been genetically modified, in high concentration and without having to over-collect wild-type plants growing in their natural environments.

These cells produce the same chemicals the entire plant produces.

For example, cell suspension cultures of Cinchona ledgeriana produce quinine, which is used to treat leg cramping, a major symptom of malaria.

And those of several Digitalis species produce digitalis, digitoxin, and digoxin, which are useful in the treatment of heart disease.

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