Vegetative Propagation in Plants (Lecture 4)

Learning objectives

1.Define Asexual/vegetative reproduction (or propagation) in plants

2.List the specialized plant structures which help in vegetative propagation. and describe their general, morphology with examples.

3.Differentiate between natural and artificial ways of vegetative propagation.

4.Differentiate between cuttings, layering, gootee and grafting by giving examples.

5.Define micropropagation and describe methods employ in it.

6.State advantages of micropropagation.

7.Disadvantages of vegetative propagation.

 

Learning Objective 3

Differentiate between natural and artificial ways of vegetative propagation.

Natural And Artificial Means Of Vegetative Propagation

Many small plants, growing vegetatively near the mother plant are propagating naturally.

Man has taken advantage of this natural phenomenon and has artificially propagated plants vegetatively by using the specialized vegetative organs by cuttings, grafting and layering.

When we use the vegetative parts for propagating crops or ornamental plants it is termed artificial vegetative propagation.

Vegetative Reproduction

i.Natural (by specialized special vegetative structures)

ii.Artificial

In fields (by specialized vegetative structures, cuttings, layering, grafting)

In laboratory (micropropagation-tissue culture)

Learning Objective 4

Differentiate between cuttings, layering, gootee and grafting by giving examples.

Artificial/Horticultural Methods Of Vegetative Propagation

 Utilization of specialized vegetative structures :

• Some specialized structures as tuber, corm, bulb, -runner and sucker produce new plants.
• Man has used these structures for artificial’ multiplication of such plants in agriculture and horticulture.

–Quick production of new plants

–Combining good qualities of two different varieties

(a) Cuttings

• Cuttings refer to regeneration of pieces of roots, shoots etc. and formation of a complete plant from them.
• It is very common method employed for artificial vegetative propagation. Sugar cane, Roses, Citrus, Money plant, Grapes, Cocoa, Bougainvillea, carnations and many other plants are largely and rapidly propagated by stem cuttings. A cutting is put into the soil.
• Cuttings of some of the plants can be grown even in water, where they strike roots and develop adventitious buds.
• In some cases, as in lemon even root cuttings can yield a new plant.

Nowadays special growth hormones like

lAA (Indole acetic acid),

IBA (Indole butyric acid),

NAA (Naphthalene acetic acid)

are applied in dilute quantities to the lower end of stem cuttings. Such application of hormones leads to the quick formation of adventitious roots.

Favorable time for planting of cuttings is the spring.

(b) Budding

In budding, a bud with small portion of surrounding bark is taken from the stem of a desired plant.

It is then inserted into the small slit made in the bark of stock.

Both are tied together and not allowed to dry.

Buds of stock are not permitted to sprout.

This method is widely practiced in rose, plums, etc.

(c) Layering 

(c) Layering

• In this method, a lower branch of a plant is bent down and covered with moist soil, leaving the growing tip above the soil.
• A ring of bark is removed from the stem before it is bent down.
• In a few weeks when enough roots have developed on the underground portion above the ringed part, it is clipped off from the parent plant and grown separately as an independent plant.
• This is a common practice with plants like jasmine, straw-berry, grapewine, bougainvillea.

i.An injury is made on it by cutting a shallow ring around (ringing) or

ii.by giving a V-shaped cut at the Lower side of bent portion of layer (notching). or

iii.by giving an oblique upward cut on bent portions of the layer at the node (tonguing).

Injured parts can be treated with auxins (hormones) to stimulate the formation of adventitious roots e.g., jasmine. Strawberry, Clematis.

• Aerial-layering or gootee is a similar practice where bending of branches is not possible because of the height of plant or due to woody nature of stem.
• In this method, a ring of the bark is removed from a selected branch, treated with auxins (hormones) and covered with moist moss and enclosed in a polythene sheet.
• When roots appear, the stem is cut below the roots and planted to form a new plant.

(d) Grafting 

• Grafting is an ancient and valuable horticultural practice that is being used between two closely related varieties.
• This consists of inserting a small branch into a rooted plant.
• The rooted plant taken as a stock, is resistant to diseases and is physically sturdy.
• In this stock, a branch is inserted which is known as the scion or graft. (The scion or graft is the stem cutting from the desired plant) Usually the grafting ends of stock and scion fit well with each-other and are bound firmly with tape or rubber band, until their tissues unite and vascular continuity is established.
• Grafting is widely used in viticulture (grape growing) and the citrus industry.
  Grafting has been found extremely useful in propagating improved/novel varieties of various flowers and fruits like rose, bougainvillea, citrus, mango and apple.
• It is especially important for propagation or seedless Varieties of plants.

Learning Objective 5 & 6

Define micropropagation and describe methods employ in it.

State advantages of micropropagation.

B. Artificial means of Propagation in Laboratory

• Micropropagation is a method of propagating a large number of plants from a single plant in a short time under laboratory conditions .
• This method allows propagation of rare, endangered speciesthat may be difficult to grow under natural conditions, are economically important, or are in demand as disease-free plants.

Micropropagation (Tissue Culture)

• To start propagation of plants through tissue culture, a part of the plant such as a stem, leaf, embryo, anther, or seedcan be used.
  A small piece of tissue, organ or even a single cell is taken from a plant and is transferred to a sterilized container with nutrient medium that contains all the minerals, vitamins, and hormones/growth regulators required by the plant. .
• The tissue grows very-very fast into an unorganized/undifferentiated mass, called callus.
• The callus can be maintained and multiplied for an unlimited period.
• When small portions of the callus are transferred to another specialized medium with hormones, it induces differentiation and plantlets (little plants).
• These plantlets are first grown under greenhouse conditions before they are moved to field conditions.

Advantages of Micropropagation

Entire plant can be grown from a small piece of stem, leaf or root tissue

Recently large-scale planting of cardamom plants by micropropagation is being successfully tried in some part of our country.

In orchids, carnations (clove pink), chrysanthemums, and asparagus micropropagation has been used very successfully.

Used in mass production of house plants and crops such as bananas and strawberries.

Provides a larger number of plants more quickly than cuttings.

Can be used to check cells for a particular feature e.g. resistance to chemicals or a particular disease

Learning Objective 7

Describe the advantages of vegetative propagation.

Advantages of Vegetative propagation

It is the only means of reproduction in specie’s which are seedless or which usually do not produce viable seeds, such as banana, figs, pineapple, and chrysanthemum.

It is rapid, easier and cheaper compared to production of plants by seeds.

Plants raised through vegetative propagation are exactly like the parent plant.

Those form seeds show variations due to the fusion of two gametes (mixing of genetic characters) from different varieties.

Thus, by vegetative propagation selected varieties of various plants can be maintained without losing their desirable characters.

Improved varieties of ornamental plants and fruit trees can be multiplied easily.

Disadvantages Of Asexual Reproduction

Most organisms which only perform the asexual reproduction process have less chance to adapt to the changes of the environment as they need stable environments.

Only one parent plant is required for the asexual reproduction,  the new plants are identical to the parent so that good features will always be passed on, the chromosomes and genes of the parent will be copied, So, there will be genetic defects or the mutation in the offspring with no exception.

The asexual reproduction does not have the genetic diversity, There is less variation produced with the offspring, and the  organism becomes less adapted to certain environmental changes, the entire communities will not adapted to the harsh environment.

The asexual reproduction usually leads to struggle for the existence as well as the overcrowding .