PROPAGATION OF HORTICULTURAL CROPS

Getting plants off to a healthy start is critical to successful crop production. Propagation in this
case is a natural process through plants generate new individuals.
Crop propagation is also referred to as reproduction.
Sexual propagation
The intentional reproduction of a new generation of plants by the germination and growth of
seeds that were created in the previous generation through the fertilization of a plant ovary via
the union of male and female sex cells results in a genetically unique plant generation.
Types of plants grown from seed
a. Annuals: Plants that germinate, grow vegetatively, flower, and produce seeds, thus
completing their entire life cycle within a single year. Sexual propagation (propagation
using seeds) is the only practical means of propagation for annuals. These crops include,
vegetables, cereals, legumes, field crops and root crops
b. Biennials: Plants that complete their entire life cycle within two years. Growth is
primarily vegetative in year one. In year two, growth is directed primarily toward
reproduction in response to vernalization: The process wherein plants are exposed to
decreasing day length and temperature followed by increasing day length and
temperature. This process occurs in temperate climates when plants go from one growing
season, through Winter and into the following Spring. Sexual propagation is the only
practical means of reproducing biennial crops.
c. Perennials: Plants that live more than two years. Once beyond their juvenile life phase,
perennials grow vegetatively, flower, and produce seeds every year. The life span of
perennials depends on the genetics of the species and the environmental conditions in
which the plants are growing. By definition, perennials can live three to thousands of
years, but lifespan within a particular species tends to vary. Perennials can be grown from
seed, although many are reproduced asexually/vegetatively to hasten maturity, maintain
genetic uniformity, and therefore retain desired morphological characteristics. Examples
of these are; coffee, fruit trees, bananas.
ASEXUAL PROPAGATION
asexual propagation is the reproduction of plants by means of division, cuttings, tissue culture,
etc. This process occurs in nature, but is a primary method for reproducing many ornamental
cultivars and the vast majority of fruits, berries, and nuts.
Clonal or asexual propagation results in a new generation of plants genetically identical to
the parent or source plant, thus carrying forward all desirable/known characteristics in a
predictable manner.
They include the following:
 Stem tubers: Swollen underground stems that have buds (eyes) that develop into new
plants are used e.g. Irish potatoes, sweet potatoes.
 Suckers: these are plants that develop from the mother plant below the ground level and
can be used for planting. It is common in bananas, sisal, pineapples etc.
 Splits: these are individual shoots that develop especially grasses e.g. guinea grass, in
tillering plants pyrethrum, sorghum.
 Bulbs: these are underground stems with modified leaves to store food. Between the
modified leaves are auxiliary buds which grow into new plants e.g. onions, garlic and
lilies.
 Rhizomes: These are underground stems with nodes and internodes which store food and
are able to germinate into new plants e.g. Couch grass, spear grass etc. These are
horizontal succulent stems growing above the producing
 Runners: ground surface adventitious roots and new plants at their nodes e.g. Wandering
Jew, sweet potatoes, straw berry, pumpkin etc.
 Corms: these are vertical underground stems with short internodes and scaly leaves.
They can be used as planting materials e.g. Cocoyam.
 Slips: these are plants that develop externally from the stem or fruit of an old plant e.g.
pineapples.
 Crowns: these are vegetative structures which are particularly found on top of a
pineapple plant and establishes slower than the suckers when planted.
 Bulbils: tiny plants produced in the inflorescence at the these are end of the plant’s life
cycle e.g. sisal, nut grass,
 Stolons: these are horizontal creeping stems above the ground modified to store food e.g.
star grass.
 Root tubers: These are swollen underground roots that can also be used for planting e.g.
Sweet potatoes
 Cuttings: these are portions or parts of the plant that may be cut and used for multiplying
plants.
There are 3 types of cuttings ice.
 Stem cuttings e.g. sugarcane, and spear grass.
  Root cuttings e.g. guavas, apples, pears etc.
 Leaf cuttings e.g. African violet. cassava,

Factors that affect rooting of cutting

 Oxygen supply: the root forming process requires ample supply of oxygen.
 Light intensity: Soft wood cuttings and herbaceous cuttings use more light for synthesis
of carbohydrates while for hard wood cuttings supply of enough carbohydrates and
darkness encourage rooting.
 Temperature: Cool to warm temperatures around the roots promote rooting because they
reduce transpiration rate.
 Relative humidity: High relative humidity prevents desiccation and encourages rooting.

Leaf area: Some cuttings require leaves to root while others don't.
 Chemical treatment rooting hormones applied at the basal end of the cutting quicken the
rooting process.

Common rooting hormones include;

 IAA (Indole Acetic Acid)
 IBA (Indole Butytric Acid)
 NAA (Naphthalene Acetic Acid).

Layering
This is a method of vegetative production which involves inducing arts of the stem to produce
roots while still on the plant before they are at off to be planted elsewhere. The part of the plant
is wounded to expose the stem cambium to give rise to roots. The wounding or bending of the
stem movements of products of photosynthesis which accumulate at the wounded or bent part to
support rooting
Types / forms of layering
–Tip layering:
The branch tip is bent to the ground and covered with soil to produce roots .It is held in
position by pegging
Simple layering:
This is done when a branch is buried in the soil at only one point reasonably away from
the tip and then held in position by pegging

Compound/serpentine layering:
The branch is bent and buried in the ground at several points and pegged to provide roots.
It is called serpentine because the branch is in a serpent — like shape.
Air layering / marcotting:
This method is mainly used for plants which cannot be bent to the ground. The bark is
removed from a small section of the branch, and moist fertile soil or moist sawdust in a
polythene bag is wrapped around the wounded section.
Grafting
This separate woody plant parts to raise new is the process of uniting two plants.
The two plants are normally of the same species or closely related species.
The lower part (the part of the root system) is called the Root stock, while the upper part that is
grafted onto the root stock is called the Scion. The Scion must have one or more buds to give rise
to a new plant. If a bud is completely used, the method is called budding or bud grafting. For
successful grafting the cambium of the root stock must be in contact with the scion Cambium.
Only dicots are grafted because they undergo secondary thickening unlike monocots.

Methods of grafting
Whip/slice grafting:

In this method, a straight slanting cut is made on both the Scion and root stock. They are then
joined together and wrapped with a grafting tape. It is used for materials of the same diameter

when the stock diameter is bigger than that of the Scion. The root stock is cut to form a V- shape
and the scion to form a wedge shape. The Scion is then inserted into the stock. Wax is put over
the cut surface to prevent drying.
Side Grafting:
This is the grafting of a scion of a small diameter into an already growing tree. A cut is made
into the stock at an angle of 20° —30° and the scion is inserted to ensure firm contact between
the cambium of the stock and the scion. e Saddle Grafting: A Scion with a deep V — cut is fitted
onto the

Procedure of budding
 Considerations
 Budding starts when the stocks are pencil thick
 Select the suitable tree species and get their buds and stocks.
 Make a T- cut on the stock and the bark gently separated from the wood.
 Insert the bud into the T- cut. The bud is bound to the stock with polythene papers or
tape to prevent water entry.
  Apply wax or Vaseline on the outside of the wrapping to reduce bacteria or fungal
entry.
 After 2 weeks remove the wrapping. If the bud is the process is successful and if the
bud is not green , then is brown the process successful.
 When the green bud produces the shoot, the end part of the root stock (Stub) 1s off to
transpiration.
 cut reduce The buds are then transplanted to the field.

Considering for successful grafting

Compatibility. This is the ability of the scion and stock to form a union. The scion and the
stock should be disease free. The two plant parts should belong to the same family or species.
Use suitable equipment or tools when grafting
The scion should have buds. The cambium layer of the scion and stock must touch each
other. Use sharp cutting knives or blades. Both the scion and stock should be woody.
The scion should be from a good quality plant.
 The technique of grafting i.e. the quality of cut, joint made should be standard and
care should be taken to protect the union.
 Availability of grafting tape and wax.
 Graft quickly.
 The stage of growth of scion and stock i.e. They should not be too old.
 The stock should also have desirable qualities.

Aims/reasons for grafting crops

To propagate the clones which cannot be propagated by other means.
To obtain new varieties or produce more than one type of fruits/trees (composite
trees). To repair damaged trees e.g. Bridge grafting. To produce plants that mature
and produce fruits at an early stage Le. shorten maturity age. To test disease
resistance in crops. To facilitate improvement of fruit trees in terms of quality and
quantity.
To impact disease resistance e.g. by grafting the resistant crop with a susceptible one
to improve the susceptible crop
To enhance vigor of defective trees.
To develop branches that are lacking on the tree.
Disadvantages
Certain undesirable characteristics by the stock are transferred to the offspring.
Requires skilled man power to carry out.
Expensive especially in buying some materials that are required e.g the wax and
grafting tape. It is labor intensive i.e. requires a lot of attention.
Only plants of the same family are used.
 There is absence of genetic variation.
It encourages pre- mature aging of the plants.

Process of grafting a crop e.g. Mangoes, Oranges

 Select a suitable scion and stalk.
 Remove the leaves from the scion.
 Make a slanting cut, using a sharp knife.
 Fit the scion and the stock together with the cambium of the stock touching that of the
scion.
 Wrap the joint with a grafting tape. Apply wax on the tape.