Complete Plant Propagation in Horticultural Crops: Sexual and Asexual Propagation Methods Complete

PLANT PROPAGATION IN HORTICULTURAL CROPS

Plant propagation refers to the multiplication of an individual plant or group of plants. Perpetuation of plants is called propagation. New plants or new individuals are required for establishing new plantings / new gardens/ new orchards.

METHODS OF PROPAGATION:-

(A). SEXUAL (SEED) PROPAGATION:- It refers to multiplication of plants by seed. In sexual process male and female gametes are fused to produce seed. In sexual propagation during meiosis segregation, reassortment or rearrangement of characters takes place. So, the plants thus produced may or may not be similar to their parents and the propagated plants may also be different from each other.

It is called as seed propagation, since the propagation is through seed (Seed is the result of fusion of male and female gametes) and also sexual propagation because sexes are involved. Plants that are produced from seeds are called seedlings.

Advantages of Seed propagation:-

Seedling trees generally live longer, bear more heavily and are hardier than vegetatively propagated trees.
Seedlings are comparatively cheap, and can be more easily raised than vegetatively propagated materials.
Plants which are difficult to propagate, e.g., papaya and phalsa by vegetative method can only be propagated by seed.
In breeding for evolution of new varieties, the hybrids are first raised from the seed.
Rootstocks, on which desirable scion variety is budded or grafted, are usually raised from seeds.
Seeds of some fruits like citrus and mango varieties are capable of giving out more than one seedling from one seed.
Since most virus diseases are usually not transmitted through seed propagation. So, it is useful in producing virus free plants.
Seeds also act as a convenient method for storing plants for a long time.

Disadvantages of Seed Propagation:-

Seedling trees are not uniform in their growth, yielding capacity compared with asexually propagated plants. Seedling trees are not usually true to type and show variation.
Seedling trees take more time to come to bearing than grafted plants. Seedling trees are very large, cause problems for efficient management of orchard trees.
Continuous seed propagation leads to inferiority in the progeny.
Hybrid trees can not be multiplied true to type because of segregation of characters.
Some sexually propagated seeds loose viability with in a short period.Eg.Citrus, mango, jack, papaya, jamun etc.

(B). ASEXUAL PROPAGATION:-

It is called with different names -- Asexual propagation, Vegetative propagation, Clonal propagation. Asexual propagation is reproduction by means of vegetative parts of the plant such as roots, shoots, or leaves other than seed. In this propagation sexes are not involved–hence it is called asexual propagation. It involves the use of any part of the plant, other than seed i.e. vegetative parts –hence vegetative propagation.

Advantages:-

There are many horticultural plants that normally produce little or no viable seeds. The edible seedless fruits are certainly very important economic crops.
Fruit trees raised by vegetative means (grafting) bears fruits just like those of the tree from which the scion has been collected. Hence, asexual propagation helps in maintaining the characteristics of each cultivar.
Propagation by vegetative means is some times easier, more rapid and economical than that by seeds.
Budding or grafting may be used to make certain fruits adaptable in unfavorable environmental conditions. Frequently, certain root stocks are better adapted to the environment than the roots of the variety desired or other rootstocks. Rangapur lime is more salt tolerant than other citrus rootstocks.
Vegetatively propagated plants are usually less vigorous than seed propagated ones.
Vegetatively propagated plants are more precocious in bearing (flower earlier than seed propagated plants).
Another use of vegetative propagation is found in fruit plants, which are selfincompatible.
Certain injuries can be repaired by means of bridge grafting.

Dis-advantages:-

New variety can not be evolved by means of the vegetative method of propagation.
Vegetative propagation in many cases is more expensive than seed propagation.
Vegetatively propagated plants are comparatively short lived.
Vegetatively propagated plants are comparatively less hardy.
Transmit viral diseases from plant to plant.

Plants Propagated by Separation:- Separation is a method of propagation in which underground structures of plants are divided not by cutting but by breaking along natural lines between segments.

Two specialized underground structures- Bulbs and Corms

(a). Bulb:- A bulb is a specialized underground organ that consists predominantly of fleshy leaf scales growing on a stem tissue (basal plate).The scales wrap around a growing point or primordium to form a tight ball. Lateral bulblets, or miniature bulbs, originate in the axils of some of these scales and when developed (offsets) may be separated from the mother bulb to be planted independently as new plants. E.g. Onion, daffodil, tulip, Lily etc.

(b). Corm:- Corm is a modified stem. Food is stored in this compact stem, which has nodes and very short internodes and is wrapped up in dry, scaly leaves. Several small corms, or cormels, arise at the base of the new corm. The cormels may be separated from the mother corm at maturity (die back) and used to propagate new plants.Eg. Amorphophallus, Colocasia, Gladiolus etc.

Plant Propagation by Division:- It is a method of propagation of plants using cut section of a particular part like rhizome, tuber and tuberous root etc.

(a). Rhizome:- A rhizome is a specialized stem structure in which the main axis of the plant grows horizontally just below or on the surface of the ground. The stem looks segmented due to composed of nodes and internodes. The rhizome tends to be oriented horizontally with roots arising from the lower side, when transplanting each section should have at least one lateral bud or eye. Eg. Bamboo, Banana, Iris etc.

(b). Stolon:- It is a term used to describe various types of horizontally growing stems that produce adventious roots when come in contact with the soil. The stolon can be treated as a naturally occurring rooted layer and can be cut from the parent plant and planted separately. Eg. Mint, Bermuda grass etc.

(c). Runner:- A runner is a specialized stem that develops from the axil of a leaf at the crown of a plant, grows horizontally along the ground and forms a new plant at one of the nodes. Eg. Straw berry, oxalis, blue berry etc.

(d). Potato Stem Tuber:- A tuber is specialized swollen underground stem which possesses eyes in regular order over the surface. The eyes represent the nodes of the tuber. The tuber is divided into sections so that each section has a good amount of stored food and a bud or eye, which produce a whole plant. Eg.Potato.

(e). Sweet potato Root Tuber:- These are thickened tuberous growth that functions as storage organs. These differ from the true stem tuber, in that they lack nodes and internodes. Buds are present only at the crown or stem end. Eg. Dahlia, Begonia, Sweet potato.

(f). Offset:- It is a short thickened horizontal branch growing out of the crown ending at the apex with a tuft of leaves and a cluster of leaves below. These are special type of branches or lateral shoots which are produced from the base of main stem of parent plant. Eg. Pistia, Agave, Water hyacinth etc.

(g). Suckers:- It is a lateral branch developing from the underground parts of the stem or roots. The suckers arise from below the surface of the soil. There are two types of suckers.

1). Shoot Suckers:- These will arise from the base of the stem. The suckers may grow upwards and directly give raise a leaf shoot. Propagation by shoot suckers can be done by separating the suckers and planting. Eg. Chrysanthemum, Banana, Pineapple.

2). Root Suckers:- The root suckers will arise from the adventitious buds on the roots. Propagation by shoot suckers can be done by separating the suckers and planting. Eg. Guava, Millingtonia etc.

PLANT PROPAGATION BY CUTTINGS

A cutting is a part of a plant that will produce roots when put in soil media and eventually produce a new plant quite true to the parent plant. A cutting may be a piece of stem, a leaf or part of a leaf, a piece of root, or root stock, or even a scale of bulb.

Classification of cuttings:- Cuttings are usually classified in to 3 groups:-

1) Stem cuttings:- Stem cutting: Stem cuttings can be divided in to 4 types:-

Hard wood stem cuttings
Semi hard wood stems cuttings
Soft wood stem cuttings
Herbaceous stem cuttings

2). Root cuttings

3). Leaf cuttings

PLANT PROPAGATION BY LAYERING:-

Layering is the developing of roots on a stem while it is still attached to the parent plant. A layered stem is known as a layer. Layering includes several forms of Ground and Aerial Layering.

When rooting is encouraged on the aerial part of a part of a plant after wounding it is known as Air Layering or Gooty or Marcottage.

When branches running parallel to ground are utilized, it is known as Ground Layering.

Classification of Layering:-

I. Ground Layering

Tip layering
Simple layering
Trench layering
Mound layering or stool layering
Compound or serpentine layering

II. Air Layering. (Gootee or Marcottage)

(1). Tip Layering:- It is generally followed in plants which have trailing type of shoots. It is quite similar to simple layering. E.g. Purple, Black Raspberries and Trailing blackberries etc.

(2). Simple Layering:- In this method, a branch is bent to the ground and some portion of it is covered by soil leaving the terminal end of the branch exposed. Root initiation takes place at the bent and buried portion. After allowing sufficient time for root formation, the rooted stem is separated from the mother plant. Eg. Bougainvillea, Jasmine, Rangoon creeper.

(3). Compound or Serpentine Layering:- Compound layering is essentially the same as the simple layering except that the branch is alternatively covered and exposed along its length. The branch for compound layering must be long and flexible so that it can be layered at different places along its length. Eg. Bougainvillea, Jasmine, Rangoon creeper.

(4). Mound (stool) Layering:- In this method, a plant is cut back to the ground level during the dormant season and soil is heaped around the base of the newly developing shoots. After slowing sufficient time for root initiation, individual rooted layers are separated from the mother plant and panted. Eg. Apple roots tocks, Guava, Litchi, Quince etc.

(5). Trench Layering:- Trench layering consists of growing a plant or a branch of a plant in a horizontal position in the base of a trench and filling in soil a round the new shoots as they develop, so that the shoot bases are etiolated. Roots develop from the base of these new shoots. Etiolated roots develop from the base of these new shoots. Trench layering is used primarily for woody species difficult to propagate by mound layering. Eg. Apple rootstocks, Litchi, Quince.

II. Air Layering:- In air layering roots form on an aerial shoot. The rooting medium is tied to the shoot for getting root initiation. Sphagnum moss is the best rooting medium for air layering as it holds large quantities of water till root initiation and through the root initiation and through the root development. Eg. Crotons, ficus, fig, Guava, Phalsa, Pomegranate.

PLANT PROPAGATION BY GRAFTING

Grafting is an art of joining parts of two independent plants in such a manner that they unite and grow together into single independent plant.The part of graft combination which is to become the upper portion or the shoot system or top of the new plant is termed the scion or cion and the part which is to become the lower portion or the root system is the rootstock or under stock or some time stock.

Methods of Grafting:-

(a). Simple Inarching / Approach Grafting:- This method provides a means of establishing a successful union between certain plants which are difficult to graft by any other method as the two plants will be on their own roots till the formation of successful graft. Eg. Guava, mango, Sapota.

(b). Veneer Grafting:- This is also a kind of side grafting with slight modification .It is used widely for grafting small potted plants and insitu grafting .Eg. Avocado, Mango etc.

(c). Epicotyl (Stone) Grafting:- This method of grafting is done on the epicotyl region of the young seedlings; hence the name epicotyl grafting. Eg. Cashew, mango etc.

(d). Soft Wood Grafting:- It has been developed to graft small and young rootstocks which are grown in situ or in pots. Eg. Cashew, Mango.

PLANT PROPAGATION BY BUDDING

Budding is also a method of grafting wherein only one bud with a piece of bark and with or without wood is used as the scion material. It is also called as bud grafting.

Methods of Budding:-

(a). T-Budding (Shield budding):- This method is known as T-budding as the cuts given on the stock are of the shape of the letter T, and shield budding as the bud piece like a shield. This method is widely used for propagating fruit trees and many ornamental plants. This method is generally limited to the stock that is about 0.75 to 2.50cm in diameter and actively growing so that the bark separate readily from the wood. Eg. Citrus, Rose etc.

(b). Inverted T- Budding:- Inverted T- Budding may give better results as it is more likely to shed excess water. Inverted T budding procedure is same as that of T budding except the horizontal cut on the stock is made at the bottom of the vertical cut rather than at the top.

(c). Patch Budding:- In this method a regular patch of bark is completely removed from the stock plant and is replaced with a patch of bark of the same size containing a bud from the desired mother plant. E.g., Ber, Citrus, Cocoa and rubber.

(d). Ring Budding:- The bud is prepared by taking a ring of a bark, 3cm long with the bud in the centre. In the root stock, two transverse cut 1.5cm apart are made and these are connected with a vertical cut and a ring of bark is removed. The prepared scion bud with the ring of bark is fitted in the exposed portion of the rootstock and tied .E.g, Cinchona.

(e). Top working:- Top-working for changing a variety is generally done on long lived species, growing in a healthy condition. Short lived species, old trees or diseased trees are not suitable for top working; in such cases new planting is considered more economical and useful than top working.