CLASS : JSS 2
SUBJECT : AGRICULTURAL SCIENCE
TERM : FIRST TERM E-NOTE
Crop propagation is the process by which plants are multiplied as independent units. Crop propagation simply means the multiplication of crops through reproduction. For instance, 1 seed of maize if it undergoes propagation can multiply and yield up to 100 seeds. There are two types of propagation – sexual and asexual.
In this type of propagation, seeds are used for planting. A seed is a developed ovule which is formed as a result of union of the male and female gametes in a process called fertilization. Seeds maybe planted in THE SOIL (directly into the field) e.g. Okra, Maize, Cowpeas or they may be raised in the nursery before transplanting them into the field e.g tomato, pepper, tobacco, cocoa etc . It is the use of seeds for planting. Crops that can be propagated by seeds include maize, rice ,wheat, sorghum, millet, soyabeans , groundnut, tomatoes, pepper, okra, mango, pear, guava, kola, oil-palm, cotton, cocoa, rubber, apple etc
This is the method of propagation in which plants are multiplied independent of seeds. Gamete cells are not involved in this propagation, only one parent is involved. This method is suitable for propagating plants which do not produce seeds but propagation is difficult with the seeds. e.g. plantain, sugar-cane, cassava and cocoyam. It is the production of new plants from parent plants using vegetative parts ( roots, stem, and leaves). Examples of crops that are propagated asexually includes cassava, yam, cocoyam, sugarcane, plantain, banana, pineapple, ginger, bitter leaves, potato.
Natural Method of Asexual Propagation
The methods include the following
- Corms – An underground stem which stores food in form of starch. It has buds and bears leaves which develop to become erect. e.g cocoyam
- Bulbs – A bulb is an underground stem which does not store its food in the stem but stores food at the bases of old leaves. It has a short stem that bears adventitious roots. The leaves are covered by brownish membraneous scales in between the auxillary buds. e,g, Onion, Lily
- Rhizomes – An underground horizontal stem. It stores food in the stem and it develops thin scales and nodes. each node has bud with some adventitious roots. It has the ability to regenerate and therefore difficult to eradicate e.g. spear grass, ginger
- Suckers – Modified stems which produce lateral branches that end in terminal buds. e.g banana or plantain
- Stem tubers – These are swolllen underground stems which store food in form of starch. Stem tubers have very tiny buds with vestigial scale leaves. e.g Yam. Sweet potato
- Runners – Stems which are too weak to stand erect and therefore grow horizontally on the surface of the ground e.g. carpet grass, sweet potato
Artificial Method of Vegetative Propagation
This involves growing new plants by man from cut portions of the parent plant. It may also involve union of a bud with root stock or shoot with root stock as in budding and grafting. Artificial methods include cutting. budding, grafting, layering and marcotting.
- Cutting – A part of the mature plant is cut and used for propagation. Three common types of cutting are leaf cutting, stem cutting and root cutting.
- Budding – Process of uniting a bud with a stock. Budding is a form of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. The new organism remains attached as it grows, separating from the parent organism only when it is mature, leaving behind scar tissue.
- Grafting – Grafting is a technique used by farmers and scientists to attach the tissue of one plant to the tissue of another. It allows for asexual reproduction of plants, and for making some neat new decorations for your yard
- Layering – Bending a mature branch or shoot down to the soil without breaking it.
Advantages and Disadvantages of Propagation Methods
Advantages of Sexual Propagation
- See is easy to carry, store, procure and plant
- It increases the vigour of the plant
- Very easy to practice
- Well stored seeds remains viable for a long time
- Crop improvement can be practiced with the use of seeds
- Crops are easily multiplied
- Transmission of disease can be avoided.It gives rise to variations and better adaptability
- It reduces the quantity of seeds for consumption
- Some seeds do not germinate due to dormancy
- Pollination will not occur if pollinating agents are unavailable
- Some seeds are eaten up by animals like rats, birds and termites
- Seedless crops can not be propagated by this method
- Some crops that are planted with seeds take long time to mature. E.g. orange
- Individuals with undesirable characteristics maybe produced
Advantages of Asexual Propagation
- Produces individuals which show more resistance to diseases and pests
- It produces individuals that mature early
- New plants can withstand adverse weather and soil condition
- New plants produced resemble their parents
- Plants mature very early
- Plants with uniform growth rate and quality is produced
- Plants produced show more resistance to disease and pests
- The new plants produce resemble their parent plants
- Plant produced can withstand adverse soil and weather conditions
- They are used to bring good qualities of two plants together
- The new offsprings similar to the parents can carry undesirable characteristics
- It gradually reduces the strength and vigour of succeeding generations
- Vegetative organs are not easy to store
- Planting materials are bulky and difficult to transport
- Diseases are easily transferred from parent to offspring
- Vegetative parts of plant cannot be stored for a long time for planting
- Crop improvement cannot be carried with these method
1. Define propagation and name the two types
2. Name 15 crops that can be propagated by seeds.
3. List 10 crops that can be propagated by vegetative methods.
4. Write 5 methods of propagating crops asexually
5. Write 4 advantages of seed propagation and 4 advantages of vegetative propagation.