Crop Propagation Methods – SS1 Horticulture and Crop Production Lesson Note (First Term)

Crop propagation is the process of increasing the number of plants of a particular species, either by seeds (sexual) or by parts of the parent plant (asexual).

Behavioural objectives

1. Define crop propagation.
2. Distinguish between sexual and asexual propagation.
3. State the advantages and disadvantages of propagating crops by seed.
4. Describe the common asexual methods: cuttings, grafting and budding, layering, and tubers, corms and bulbs.
5. Choose a suitable propagation method for a given situation.

What is crop propagation?

Propagation is the process of increasing the number of plants of a particular species.

There are two main methods of crop propagation: sexual and asexual.

• Sexual propagation: uses seeds, which come from two parents.
• Asexual (vegetative) propagation: uses parts of the plant such as stems, roots or leaves, taken from one parent.
• Example: a farmer with one very good mango tree who wants ten more must propagate it.
• Simple picture: seeds are like babies from two parents, while asexual plants are clones of one parent.

What is sexual propagation?

Sexual propagation is the growing of new plants from seeds formed when male and female parts of flowers join.

How is a seed formed?

1. Pollen from the male part of a flower reaches the female part (pollination).
2. The male cell from the pollen joins with the egg inside the ovule (fertilisation).
3. The fertilised ovule develops into a seed.
4. The seed is sown and grows into a new plant.

What are the advantages of propagating by seed?

• Easy: seeds are easy to carry, store and sow.
• Cheaper: a packet of seeds usually costs less than 100 seedlings.
• New varieties: a seed may give a plant better than the parent.
• Common method: maize, beans and pawpaw are grown from seed.

What are the disadvantages of propagating by seed?

• Waiting time: some seeds take a long time to grow into a tree that bears fruit.
• Variation: the fruit may not taste like the parent fruit.
• Poorer plants: a seed may also give a plant worse than the parent.

What is asexual propagation?

Asexual (vegetative) propagation is the growing of new plants from a part of one parent plant, without seeds.

• Clone: a new plant that is an exact copy of its single parent.
• Parts used: a stem, branch, bud, root or underground storage part such as a tuber.

What are the advantages of asexual propagation?

• Exact copies: a very sweet parent orange gives new plants that are equally sweet.
• Faster growth: a plant from a cutting often bears fruit sooner than one from seed.
• Seedless plants: crops such as seedless grapes and some pineapples have no seeds, so this method is needed.

What are the disadvantages of asexual propagation?

• No new varieties: all the plants are alike.
• Shared weakness: a disease that affects the parent can affect every clone.
• Skill needed: grafting and budding need practice.

What are the common asexual propagation methods?

There are four common asexual methods used on Nigerian farms: cuttings, grafting and budding, layering, and tubers, corms and bulbs.

1. What are cuttings?

A cutting is a piece of stem, root or leaf cut from the parent and planted to grow roots.

• Examples: cassava and hibiscus are grown from stem cuttings.

1. Choose a healthy, mature stem from the parent plant.
2. Cut it into pieces, each with several buds (nodes).
3. Plant the pieces in moist soil.
4. Water regularly until roots and shoots appear.

2. What are grafting and budding?

Grafting and budding join a part of a good plant onto the root system of another strong plant so that they grow as one.

• Rootstock: the strong plant with roots, which receives the new part.
• Scion: the piece of branch or bud taken from the good parent plant.
• Grafting: a piece of shoot (scion) with several buds is joined to the rootstock. It is common for mango.
• Budding: a single bud is joined to the rootstock. It is common for citrus (orange and lemon) and rubber.

1. Choose a healthy rootstock.
2. Take a scion or bud from the good parent tree.
3. Make a cut in the rootstock and fit the scion or bud into it.
4. Tie the joint firmly and keep it protected.
5. Remove the tie once the two parts have joined and growth starts.

3. What is layering?

Layering is the rooting of a branch while it is still attached to the parent plant.

1. Bend a low branch of the living plant down to the ground.
2. Cover part of the branch with soil, leaving the tip above ground.
3. Keep the soil moist until the buried part grows roots.
4. Cut the rooted branch from the parent and plant it elsewhere.

• Air layering: a branch is wounded and wrapped in moist soil while still on the tree, so it roots in the air.

4. What are tubers, corms and bulbs?

Tubers, corms and bulbs are swollen underground plant parts that store food and can be replanted to give new plants.

What is the difference between sexual and asexual propagation?

Sexual propagation uses seeds from two parents, while asexual propagation uses a part of one parent and gives clones.

Which propagation method should you choose?

Choose seeds to create new varieties and vegetative parts to multiply a good plant exactly.

• New variety wanted: use seeds.
• Very good tree to multiply quickly: use cuttings or budding.
• Plant has no seeds: use a vegetative method.
• Cheap, large planting of grain or vegetables: use seeds, as with maize and beans.

Evaluation

1. What is crop propagation?
2. State two advantages and two disadvantages of propagating crops by seed.
3. Why is a farmer who wants to multiply a very sweet orange tree advised to use budding instead of seeds?
4. Name the four common asexual propagation methods.
5. Name one crop propagated by tubers, one by corms and one by bulbs.

Assignment

1. Draw a table comparing sexual and asexual propagation under these headings: parents, likeness, speed and examples.