Objectives: By the end of this subtopic learners should be able to:
Define plant propagation.
Define sexual and asexual reproduction in plants.
Explain the advantages of each propagation method.
PLANT PROPAGATION
Plant propagation is the process of creating new plants from a variety of sources such as seeds, cuttings, bulbs and other plant parts.
There are two methods of plant propagation which are:
i) Sexual ii) Asexual
Methods of plant propagation
i. Sexual reproduction in plants
Sexual reproduction in plants is the production of new plants (offspring) by the combining of male and female gametes.
Sexual reproduction involves the production of new plants using seeds.
Pollen is transferred from the anther to the stigma, fertilisation occurs and seeds are produced.
The small plants that are grown from seeds are called seedlings.
Most plants which are planted from a seed may have different characteristics than their parents.
Parts of a flower
Male reproductive organs (stamen)
Anther produces pollen grains.
Filament supports the anther above the female reproductive organ.
Female reproductive organs (pistil)
Stigma it has sticky surface for pollen grains.
Style it is a tube or pathway that leads to ovary.
Ovary it contains ovules that develop into seeds.
Pollination
This is when pollen grains are deposited on the stigma from the anthers.
When they reach the ovary the male gametes unite with the female gametes in ovules.
When female and male gametes meet fertilisation occurs leading to the formation of a zygote.
Cross pollination
Cross pollination is the process when pollen grains are carried by insects or wind from one flower to another on different plant of the same species.
Self-pollination
Self pollination is when both male and female gametes come from the same flower.
Germination
Germination is the process by which a plant begins to grow from seed.
Conditions needed for germination
Suitable temperature: for enzymes to work effectively.
Oxygen: for aerobic respiration to provide energy to the growing embryo.
Water: for chemical reactions to take place in solution, dissolve nutrients for transportation, activate enzyme and soak testa.
ii. Asexual reproduction
Asexual reproduction is the reproduction of new plants without the help of flowers.
The reproduction of a new plant is done without combining male and female gametes but through the use plant parts
The new plants produced will be identical to the parent plant.
Roots, leaves and shoots are used to grow new plants.
Types of asexual reproduction
a. Tubers
These are underground roots which have buds that stores food during winter and provide a new plant with food until it is able produce its own.
For example potatoes or sweet potatoes.
b. Runner plants
These are horizontal slender whip like shoots which are sent out by parent plant to root which is far way to produce another new plant.
For example strawberry and lawn.
c. Rhizomes
Rhizome is a stem of a plant which is grown underground , which produces adventitious roots and stems shoots from the nodes.
If cut into several pieces and planted it can produce another new plant.
They have inter-modal spacing which produces roots from the bottom of the nodes.
d. Bulbs
Bulbs are stems with fresh leaves that function as food storage organs growth, development and physical activity which is stopped.
These bulbs are made up of rings called scales where food is stored.
e. Grafting
This is a technique used to combine two or more plants so that they grow together.
Part of one plant (scion) is removed and attached to a healthy, rooted part of a second plant (stock).
Useful qualities from both plants are combined into one.
Examples of plants that can be grown through grafting are rose flowers and apples.
f. Cuttings
This is a piece of stem 30-40cm long with desirable qualities and the cut ends turn into a new plant when placed in moist soil or dipped in rooting powder or planted in pots, plastic bags.
Most cuttings produce roots and leaves which grow into new plants which are identical with the parent plant, for example mango, litchi, lemon and rose.
Sugarcane is a good example of a cutting which is propagated and planted in furrows and covered up with soil.
Types of cutting
1. Stem cuttings
These are divided into four different groups basing on type of plant and time to maturity.
These are hardwood, semi-hardwood, soft wood and herbaceous.
Lower leaves of cuttings should be removed.
Cuts should be done mostly below a node.
2. Root cuttings
Root cuttings are pieces of roots, that form new shoots.
These are often made in winter or early spring before plants begin growing.
3. Leaf cutting
They are prepared from leaves with or without petioles.
A bud which is located where the leaf stalk combines with stem to give a rise to new roots and leaves.
Leaf cuttings will not be a permanent part of the plant but they gradually die off when a new plant grows.
Advantages of sexual and asexual reproduction:
a. Sexual reproduction:
High genetic variability.
Facilities adaptation.
Speeds up evolution.
b. Asexual reproduction:
Saves energy.
Greatest increase in fitness for each individual.
Disadvantages of sexual and asexual reproduction:
a. Sexual reproduction:
It is costly to buy certified seeds.
Its is time consuming.
Usually sacrifices the fitness of one sex to the other.
