Walt agriculture: Vegetative propagation

Vegetative propagation

This is the natural regeneration of plants other than seeds to develop new plants. The new plants are sometimes called Clones

Advantages of vegetative propagation

It is possible to maintain desirable characteristics such as disease resistance and physical appearance
It makes it possible to propagate crops that are seedless or have viable seeds
The growth habit of a crop can be regulated to attain a desirable shape and size
It is possible to produce more than one crop variety on the same plant
Vegetative propagation imparts desirable characteristics to crops, such as seedless in citrus fruits
It is completely independent of the processes of pollination and fertilization
It enables cross-bred plants to be maintained in their new condition indefinitely
The new plants are exactly the same as the parent plant when vegetatively propagated
The young plants are hardy and vigorous than seedlings. This is due to a lot of food reserves available to the growing plant
Vegetatively propagated plants grow and mature faster than seed propagated plants

Disadvantages of vegetative propagation

Vegetatively propagated plants are difficult to breed and genetically improve since there is no possibility for cross breeding
If the vegetative materials curry a disease there is the danger of transferring diseases to the new plants or locations
Vegetative materials are bulky , making them difficult to transport and plant out
Due to high moisture content, most vegetative materials cannot be stored for a long time, they lose viability or sprout in store
It is difficult to dress vegetative materials against diseases and pests
Vegetative materials' planting cannot easily be mechanized
Due to the amount of materials required and the transport costs involved. It is expensive to plant a large field with vegetative materials

Methods of vegetative propagation

These involve use of specialized vegetative and perennating organs

Bulbs; a bulb is modified shoot with short stem and storage leaves. Bulbs are used in propagation of onions, garlic, and tulips.

Corms; a corm is a short, swollen, vertical underground stem. Corms are used in propagation of coco yams, taro

Stolons; this is a creeping horizontally growing stem that grows on top of the soil surface. It is used in propagation of blackberry, gooseberry, blackcurrant, and redcurrant

Runners; runners bear axillary buds and the buds give rise to adventitious roots and new plants. They are used in propagation of strawberry and creeping buttercup

Rhizomes; rhizomes bear leaves, buds and adventitious roots. Rhizomes are used in propagation of ginger, cardamom, and turmeric.

Suckers; these shoots which radiate from buds below the ground level. They are used in propagating crops such as banana, pineapples, and sisal

Tubers; tubers have axillary buds that have capacity to sprout in to new independent plant. Tubers are used in propagation of crops like; potatoes and arrow root and yams

Bulbils; these are aerial bulbs or buds produced in leaf axils, which on separation, are capable of growing into a new plant. They are used in propagating sisal.

Turf splits; turf is a clump or bunch of tillers originating from a common base. Turf splits are used in propagation of most pasture grasses

Crowns; these develop from the top of fruits. Mature crowns on fruits are dormant but become active after detachment from the fruit. They are used in propagating pineapples

Slips; these are shoots borne on the peduncle just below or on the base of the fruit. Slips are used in propagation of pineapples.

Vines; these are soft cuttings obtained from mother plants and planted directly into the main field to give rise to new plants. They are used in propagation of sweet potatoes.

Cuttings

These are pieces of plants (stem, roots, or leaves) that are cut and then planted. They have buds which develop into a shoot. Cuttings are used to propagate plants like sugarcane, tea, and cassava.

The ability of the cuttings to root and shoot depends on the following factors;

Plant species; some plant species have natural ability to establish from cuttings. These cuttings easily sprout when provided with suitable growth medium
Age of the plant; cuttings from young plant parts root better and easily than leaf or root cuttings.
Type of rooting medium; the rooting medium must be sterile , porous but capable of providing sufficient oxygen and moisture
Chemical and other treatments given to cuttings such treatment with growth hormones
Weather conditions such as humidity , temperature and sunlight
Watering frequency
The amount of leaves on the cutting

Cuttings to use for plant propagation should have the following qualities

Should have reasonable number of buds and the buds should be viable
Should be free from pest and diseases
Buds should be free from mechanical or pest or diseases damage
Should be of average maturity with enough food reserves
Should be from desired variety
Should be alive or fresh for optimum viability
For some cuttings, should have optimum number of leaves

Layering

Layering is the practice of stimulating a part of a branch to produce roots while still attached to the mother plant. The rooted part is then cut off and planted as a new plant

Procedure of layering

The process of layering starts with selection of a suitable branch on the growing plant, the branch should not be having any form of deformities and should be free from pests or diseases
The selected branch is then wounded mildly. Wounding allows transportation and accumulation of healing and growth hormone around the wound. Accumulation of especially Idole acetic acid (IAA) induces growth of roots around the wound. The process of rooting is also encouraged by presence of suitable rooting medium around the wound
Prepare the rooting medium; the rooting medium can be sandy soil mixed with organic matter or peat soils. The rooting medium should be well sterilized, provide optimum aeration and moisture.
The rooting medium is then placed around the wound and then wrapped with a piece of perforated polythene sheet or cloth
The rooting medium should be watered periodically to prevent drying of the rooting medium
After about 2-4 months depending on the species, when the roots have fully developed, the branch is cut off and then planted out in pot nursery or directly planted in the field

Types of layering

Marcotting or aerial layering; it is used when the branch or the stem cannot bend to touch the ground; instead, the soil is curried up and tied to the branch. This form of layering requires more skills and labour, and success is fairly low.

Tip layering; in this method, the tip of the shoot bearing the terminal bud is wounded and then bent to the ground. It is then held in position using pegs and covered with layer of moist soil. The covered part is induced to produce roots by applying a moist rooting medium

Compound or serpentine layering; in this method, the branch is bent several times and held in the soil with pegs. This produces several new rooted plants from the mother plant. This form of layering is commonly used in runners and stolons

Trench or ground layering; in this method, the branch to be layered is first wounded, then bent to the ground and laid in a trench. It is then held in position using pegs and covered with a layer of moist soil. The covered part is induced to produce roots by applying a moist rooting medium. The branch is then cut off from the mother plant and transplanted

Stool or mound layering; this method is used when the branch or stem cannot bend enough to reach the ground level. In this form the soil the soil is heaped high to form a mound where the branch or stem can be able to reach or the rooting medium is placed in the container and then raised high supported on a stand or stool, and then the branch is slightly bent into the rooting medium in the container.

Benefits of layering

The propagule has high chances of survival than cuttings
A large planting material is obtained in a short period of time
Plants propagated from layered propagules mature faster than plants from cuttings
Seedlings from layering are more adapted to the environmental conditions
Seedlings from layering are more resistant to pests and diseases

Disadvantages of layering

The method requires more skills to curry out
There are high chances of spreading pests and diseases from mother plant to the propagules
Propagules are usually large requiring more labour to handle and plant

Grafting

This is an artificial plant propagation method involving uniting a shoot from one plant to the root stock or another plant so that they grow as one plant. The shoot and the rootstock should be from plants of the same species.

The upper portion of the graft is called the scion whereas the lower portion of the graft is called the stock. Grafting is only done in woody plants and in plants of the same species.

The union of the graft is due to regeneration of cambial tissues; callus cells are responsible for the healing of the union wound.

Advantages / benefits of grafting

Grafting can be used to change the plant from being undesirable to desirable. This is done by replacing the undesired shoot with desired shoot
It enables propagation of crop that would be difficult to propagate by other means
Grafted crops mature faster than seed propagated crops
Grafting can be used to test for disease resistance in some crops. This is done by grafting susceptible scion to a resistant stock and observing the response
It makes the growing of more than one type of plant on one stock possible. This economizes space required to grow the different types of crops in the garden
Root stocks with desirable qualities such as disease and pest resistance, drought resistance and resistance to salinity can be harnessed for production of beneficial but susceptible crops
Grafting may be used to repair damaged plant parts; when the stem or branch is damaged either by pests or browsing animal, it can be cut off and replaced with a better health stem or branch
Provides an opportunity of utilizing good qualities of the rootstock and scion of different plants

Disadvantages of grafting as mean of propagation of crops

The method requires a lot of skills to carry out
It is not reliable as any slight mistake can lead to total failure.
It can only be done in propagation of some few crops
The method requires a lot of time and labour
Grafted crops can easily be damaged by wind
Spread of diseases from the mother plant to the grafted plants may occur
Grafting can only take place in closely related families thus not giving a chance to have different families on the same root stock.

Procedures of grafting

Select a seed from a mother that is vigorous and well adapted to the soil condition to provide the rootstock
Raise the seed in a pot nursery
A seedling is ready for grafting when the stem is pencil thick
Select a dormant shoot from a mother plant with desired qualities and of the same species as the rootstock to provide the scion
Grafting should be done on a cool day or in a cool environment
Use a sterilized razor blade or grating blade to cut the scion and the stock.
Make matching cuts on both the scion and the stock. The cuts can be V-shaped or straight slanting cut on both the scion and stock.
Remove all the leaves from the scion to reduce transpiration
Join the scion to the stock; make sure the cambia of the scion and the stock are in contact
Tie the joint with grafting tape and apply grafting wax to prevent bacterial and fungal infection
Keep the grafted plant in cool humid environment and away from wind until buds starts to grow
Remove the grafting tape after the joint has healed and then transplant to the main field

Conditions that should be fulfilled for grafting to be successful

The scion and the stock must be from woody plants
The scion and the rootstock must be from plants of the same species
The scion and the rootstock must be of the same growth habit
The scion and the rootstock should preferably be of the same diameter
During grafting the cambia of the scion and the rootstock must be in contact
The scion must be dormant at the time of grafting
The scion and the rootstock must be at the proper physiological stage of growth
Post graft care such as keeping the graft union moist and protected from infection until the wound has healed

Factors affecting the success of grafting

Compatibility of the scion and the root; the scion and the rootstock should be from genetically related plants (plants of the same species)
Type of the plant; grafting is only possible in some plants especially those with woody stems
Grafting technique used; the cuts made in the scion and rootstock should be matching for the joint to be firm and to encourage maximum cambial contact
Post grafting care; good care of newly grafted plants is vital to accelerate union and healing of the plants. Plants should be provided with warm temperature and high humidity and the joint protected from infection.
Pest and disease infestation; any pest or disease infestation to the newly grafted plants can lead to failure of the plants. These can be controlled by ensuring high level of hygiene in the nursery.
The quality of the rootstock or the scion; these should be healthy and vigorous. The scion should be dormant and not actively growing at the time of grafting.

Incompatibility in grafting

Graft incompatibility is a situation where the grafted plants fail grow as one plant exhibited by death of the scion

Signs of incompatibility in grafted plants

Browning of the scion
Premature death of the planting Abnormal growth of the scion or rootstock
Poor health of the plant

Causes of graft incompatibility

Physiological and bio chemical differences between the scion and the rootstock
Grafting of plants of different growth habits
Diseases especially viral infections to scion
Incompetent workmanship (lack of grafting skills)
Unfavorable micro-climate provided to the grafted planting
Grafting of actively growing scion

Methods of grafting

Splice grafting; a straight slanting cut is made on both the scion and the stock so that the joining surfaces come together obliquely

Cleft grafting; the top of the stock is cut off and a wedge cut is made in the rootstock where a wedge shaped scion into the stock

Saddle grafting; a V-shaped cut is made on the stock and the scion is cut in wedge shape that fits properly into the stock

Whip or tongue grafting; in this method , a straight slanting cut is made on both the scion and the stock and then after a second cut is made on both scion and stock to produce a notch -like arrangements that accommodates each other and fit slightly together

Side grafting; in this method V-cut is made on the side of the rootstock at an angle of about 30 where a wedge shaped scion is fitted

Budding or bud grafting

This form of grafting which involves uniting a bud from one plant to the rootstock of another plant where it regenerates as new plant. The bud and the scion should be from plants of the same species.

The bud to graft should be in dormant state while the stock should be the one that is highly adapted to soil condition and vigorous.

Methods of budding

T-budding

It is used on young socks with a bark which is able to slip off. In this method a vertical cut is made through the bark of the rootstock and after, a horizontal cut is made at the top of the vertical cut to make a T-shaped cut. The bark is then loosened and the bark flaps lifted. A shield shaped piece of bud is inserted under the bark and the union is wrapped with the grafting tape

Patch budding

This is used on old stocks with hard bark or with a thick bark that cannot peel off or cannot be lifted from the wood. In this method a rectangular piece of bark is removed from the rootstock where a rectangular shaped bud is inserted and then wrapped with grafting tape

Procedure for bud grafting

Select a seed from a mother that is vigorous and well adapted to the soil condition to provide the rootstock
Raise the seed in a pot nursery
A seedling is ready for bud grafting when the stem is pencil thick
Bud grafting should be done on a cool day or in a cool environment
Select a dormant bud from a plant of the same species as the rootstock
Use a sterilized razor blade or grafting blade to cu the bud. Peel off wood from the bark of the bud patch
Make a T-cut in the bark of the rootstock and gently lift up the bark
Gently push the bud under the bark
Wrap the bud with grafting tape and apply grafting wax to prevent water and infection from bacteria and fungi
Cut off the part of the stock above the bud and remove any other bud from the rootstock
Inspect the bud after about 15- 20 days, green color of the bud indicates that the bud is still alive and that the graft is successful. Browning of the bud indicates that the bud is dead
Buds are ready for transplanting after 40- 60 days

Care given to drafts and buds

Wrapping the grafts and buds with grafting tape to make the union firm and to prevent the scion from falling off.
Protection of the union against water that can lead to rotting
Reducing the amount of leaves to reduce transpiration and dehydration of the scion
After the union is firm, the grafting tape should be removed to prevent girdling due to buildup of translocate substance above the union
Once the bud is established the part of the rootstock above the bud should be cut off to encourage the bud to sprout

Advantages of budding

Budding is simple than grafting
Shoots from buds are more strong and resistant to wind damage than shoots from grafts
Budding is more economical since a single shoot can produce several buds
Several buds from different varieties can be grafted on the same stock easily
Unlike in shoot grafting buds do not easily spread pests

Tissue culture

Tissue culture is the growing of living cells from shoot tips in a controlled medium. In tissue culture, living tissues from desired varieties are placed in the growth medium that leads to rapid cell division to take place. The cells are then cloned (sub culture) each cell developing into independent plantlet. The culture medium is made up of nutrients, indoleacetic acid, and cytokinins

Advantages of tissue culture as a method of propagating crops

Tissue culture seedlings are free from diseases
Many seedlings can be obtained in a short period of time
The seedling are not as bulky as cuttings
In crops which are difficult to produce using seeds or vegetative organs, this is the only quick means of multiplying such crops
Crops are identical genetically and all crop are the same in behavior e.g uniform ripening of crops making harvesting easier

Limitations of tissue culture as means of propagating crops

The method is expensive since it requires special lab equipment and chemicals
The method requires special skills to carry outbreak
Cell mutation may take place it the lab resulting into change in crop behaviour
Tissue culture seedling take more time to mature
In some crops such as root and tuber crops the first harvest is always low
The seedlings are highly susceptible to pests and diseases

Walt agriculture

Vegetative propagation

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