Lesson 38. Macro Propagation Methods

38.1 PROPAGATION

Production of seed individual includes

(i) Sexual or seed propagation

(ii) Asexual or vegetative propagation

38.1.1 Sexual propagation: Reproduction by seed; but seed is under ordinary condition a result of fusion of male and female germ cells or gametes, characters of both parents are inherited by the seed or the new individual and therefore the new individual formed in this way are not true-to-type.

38.1.2 Asexual propagation: Does not involve the gametes from parents. It is simply a vegetative or somatic extension of one parent and there is no chance of inheriting a mixture of characters.

38.2 SEED PROPAGATION

38.2.1 Seed: Anatomically, seed is an embryo plant or fertilized, ripened ovule consisting of a rudimentary stem and root, together with a supply of food sufficient for establishing the plant in a new location and enclosed in a protective coat (seed coat).

38.2.2 Viability: A seed is viable if it is capable of germinating or ability of seed to germinate.

38.2.3 Vitality: The vigour or strength possessed by the seed for growth.

38.2.4 Short viable seeds: cashew, jack fruit, jamun, citrus, mango, neem etc.

38.2.5 Seed with hard seed coat: babul (acasia), gulmohar, chiku, amaltas etc. Such seed should be given some treatment before growing for quick germination.

(1) Mechanical treatment:

(i) Scarifying: Seed is filled in a scarifier which is a drum with inner surface rough, hard and sharp. The hard seed coat is filled and ground out by rotary action.

(ii) Others: Breaking or cracking with hammer, drilling a hole, rubbing against stone, filling.

(2) Chemical treatment:

- Sulphuric acid at conc. of 50 % and 25 %

- Potassium hydroxide and hydrochloric acid

(3) Soaking in water: Seed are soaked in warm water for 24 hours or 4 to 5 days sometime they are soaked in cow dung paste.

(4) Stratification: Keeping seed in alternate layers with sand or soil and kept constantly moist but not waterlogged.

38.3 SEXUAL METHODS

38.3.1 Advantages:

  • Seedling trees (sexual method) are generally long lived; bear more heavily are comparative more hard.
  • Propagation from the seed is the only means of reproduction where the method of vegetative propagation is not possible or economical as in papaya, phalsa, mangosteen etc.
  • Inbreeding for evolution of new varieties, the hybrids are first raised from seed and it is, therefore, essential to employ this method in such cases.
  • Propagation from seed has been responsible for the production of some chance seedlings of highly superior merits, which has been of some chance seedlings of highly superior merits, which has been of great benefit to the fruit industry. It may be mentioned that commercial mango varieties originated from seed and were, later on, perpetuated vegetatively.
  • Seed like those of some citrus species and some mango varieties are capable of giving out more than one seedling from one seed. They can be carefully detected in the nursery stage.
  • The rootstocks upon which the fruit varieties are budded or grafted are really obtained by means of sexual propagation.
  • Seedlings are comparatively cheaper and easy to rise.

38.3.2 Disadvantages:

  • The seedling trees are not uniform in their growth, yielding capacity and fruit quality as compared to grafted trees.
  • They make more time to bear the maiden crop as compared to the grafted plants.
  • The seedling trees become large for economic management i.e. the cost of harvesting, pruning and spraying is more as compared to the grafted trees.
  • It is not possible to perpetuate the exact characters of any superior selection through seed and so to multiply superior hybrids or chance seedlings, vegetative methods have to be employed.
  • In case the seedlings, it is not possible to avail of the modifying influence of rootstocks on the scion as in case of vegetatively propagated fruit trees.

38.4 ASEXUAL OR VEGETATIVE PROPAGATION

It is also known as clonal propagation. Vegetative parts such as leaf, stem or root are used instead of seeds. It is a function of the somatic mechanism of plants. It is therefore essential to have some fundamental knowledge of the basic anatomy of certain parts.

38.4.1 Roots and stem structures

i. Root:- An organ for absorption of water and nutrients and serve as an anchor for the plant. Older portions mainly work of transporting water and nutrients and stored food material where as only younger fibrous roots absorbed the water and nutrients.

ii. Stem:- Supports leaves flowers and fruits  and acts as a link between roots and leaves. It also acts as a temporary storage place for reserved food materials.

iii. Dicotyledonous plants:- The vascular bundles (xylem, phloem and cambium) have a regular systematic arrangements so made that they form a circular ring. Mango, Chiku, Guava.

iv. Monocotyledonous plants:- They do not form a ring but are more or less scattered at random throughout the thickness of the stem. Banana, Date, palm, Coconut.

v. Xylem:- They are well differentiated thick walled fibers, conducting vessels and wood parenchyma on the outer side of wood, ventral cylinder. Main function of xylem is to transport water and nutrient (salt) absorbed by roots to the upper portion of the plants.

vi. Phloem:- They are well differentiated, fibrous and conducting tissues on the inner side of the bark or cortical layer. Main function of phloem is to transport food material (CH2O), hormones and co-factor synthesized by leaves.

vii. Cambium:- Between xylem and phloem there is a thin layer of thin walled, undifferentiated meristematic tissues is known as cambium. They occur in a continuous ring. Their main function is to divide and sub-divide giving rise to new cells that may later on became differentiated in to one another of the various tissues of the wood of bark.

viii. Function of cambium necessary for plant propagation:-

  • Use full in secondary growth of stem and root.
  • Regeneration and over walling over is possible for recovery of injury to the plants.
  • Callus produced by cambium is necessary for budding, grafting and cutting etc.
  • Adventitious roots on stem mostly arise from cambium.

ix. Callus:- It is a mass of undifferentiated (parenchyma cells) tissues produced by cambium which gradually covers the points or areas originally exposed (arising from the living cells of both scion and stock).

x. Regeneration:- Recovering the injured surface all over at the same time.

xi. Over walling:- Recovering the injured surface from the outer margins.

xii. Buds:-  A bud is a rudimentary stem or embryo stem when, a bud develop into a branch is known as vegetative bud. But when it develops into a flower is known as flower bud. It is also called fruit bud.

          Bud is defined as a growing point of undifferentiated tissues surrounded by embryonic leaves or blossoms.

1) Terminal bud: A bud formed at the tip of a branch which has stopped growing for the season.

2) Axillary or lateral bud: This is a regular bud which develops in the leaf axil or the node.

3) Adventitious bud: This is a bud formed on an unusual part like internode, leaf, or root.

4) Dormant bud: When its dormancy period is less than one year(season) is known as dormant bud.

5) Latent bud: If for some reason a dormant bud does not start growing even after a year, it may not grow even for more number of years is known as latent bud.

xiii. Suckers: These are shoots growing from latent adventitious buds on roots.

xiv. Water sprouts: These are shoots growing from latent adventitious buds on stems or branches.

38.4.2 Advantages of vegetative propagation:-  Seed propagation is easier method and very widely used for sowing other agricultural crops, vegetative propagation is the practice adopted mostly by horticulturist. Following are the advantages:

  • True breeding seeds can be ensured on by vegetative method because it is a reproduction of somatic cells. There is no cross pollination and segregation.
  • When seed is not formed, vegetative methods is the only way i.e. Banana and some (seedless) varieties of grape and citrus.
  • Vegetative propagated plant bear earlier but life period is shorter than seed propagated plants e.g. mango and chiku graft bear early fruiting.
  • Some disease or insect resistant scion can be grown on suitable rootstock for the particular soil condition, i.e. Jamburi is resistant to gummosis and we can successfully grafted citrus on jamburi, in Australia, Northern, spy apple is used as root stock for apple, which is resistant to woody aphis, similarly, European varieties of grapes grafted on the root stock of American varieties to avoid the damage of phyloxera insect.
  • Dwarfting trees are practiced by budding or grafting on suitable roots orange on wood apple.
  • Branches of male plant can be grafted on female plants.
  • Reduction in the size and number of thorns i.e. jamburi root stock for citrus.
  • Correction of mistakes by budding or crown grafting or side grafting.
  • In cooler regions trifoliate orange is used as (citrus) rootstock against heavy frost.
  • More than one variety can be grown on one plant e.g. Roses.

38.4.3 Disadvantages:- The following are the disadvantages of Asexual method of propagation in fruit plants.

  • The vegetative propagated plants, particularly the budded and grafted ones are not generally so vigorous and long lived as the seeding trees.
  • No new varieties can be evolved by the vegetative means of propagation.

38.5 FACTORS AFFECTING ROOT FORMATION IN CUTTINGS

i. Medium for rooting of cuttings: The medium in which cuttings, are planted must be loose and easily worked so as to facilitate planting of cuttings as well as their removal without damage to new roots. Ordinary budding sand, if clean and free from any foreign materials and dirt is a very satisfactory medium. Loose sandy loam soil with good drainage is the most suitable alone for planting cuttings directly in the nursery.

Decaying organic matter in the medium is objectionable since it will promote the growth of fungi and bacteria, which in turn might be cause the cutting to die before root formation.

ii. Temperature:- Control of temperature is very important in rooting of cuttings. Very high temperature is not inductive to root formation 65 °Fahrenheit to 70 °Fahrenheit is the best temperature for most plants.

iii. Humidity:- A high degree of humidity is essential otherwise cuttings will be desiccated. The roundabout area, the walls, paths and beds must be frequently sprinkled with water to maintain humidity.

iv. Chemical treatment:- Synthetic hormones like the indole-3-acetic-acid, indole-3-butyric acid and napthaleneacetic acid are very useful in increase root formation.

v. Mechanical treatments:- These include partial removal of leaves, slanting basal cut and some injury near the basal end. It is believed that by injury areas of callus is exposed for rooting.

vi. Stored food:-  Two fundamental requirements are there for successful rooting of cutting (i) The plant must have the capacity to develop roots. (ii) Energy must be supplied for these processes (Rooting).

The available carbohydrates and nitrogen markedly affect the rooting of cuttings. Shoots from which cuttings are to be taken are sometimes girdled to increase the stored food above the girdle. The girdle also prevents auxins from flowing dow.

vii. Age and maturity of the tissues:- Certain kinds of plants can be grown best from semi hard wood cuttings but not so  from terminal or herbaceous cuttings. Some other grows best only from the fully matured basal portions and still others grow best from heel or mallet cuttings, only in which second year wood is also included.

viii. Etiolation:- It is considered to be necessary for better rooting.

38.6 GRAFTAGE

Graftage is the process of joining a part of a plant with another in such a way that both will unite to work as a unit and the unit will continue growth. Two different methods based on the same principles are included under the term graftage viz, grafting and budding.

38.6.1 Special terms in connection with grafting and budding:-

i. Stock:- Stock is that part of a graft which has the root and which supports the growth, made by the other component scion. Root system of the stock and the above ground growth of the scion constitute a graft. A stock is called “seedling root stock” if it is grown from seed and “clonal roots stock” if it is propagated by vegetative methods of propagation e.g. cutting, layering etc.

ii. Scion:- Scion is a portion of the stem or branch of the variety that is desired to propagate. It may be a shoot or a branch a few inches long or one feet long and has many dormant buds on it. It may be taken from current or past season’s growth or even older wood, but in most species growth of current or past season makes better scion than does the older wood. The scion for grafting is a piece of a branch while the scion for budding is only a single bud with a little bark.

iii. Matrix:- Matrix is the place on the root stock that is prepared for joining the scion or the bud.

iv. Compatibility:- The word compatible designates the suitability of the reciprocal influence of stock and scion on each other. If the influences of one on the other are all suitable to each other we say that both are compatible.

38.6.2 Limitations of graftage:-

          For the successful union of the two parts, following three conditions must be fulfilled.

  • Close botanical relationship.
  • Continuous contact of cambium layers and tight fitting(closeness of fit)
  • Compatibility
Last modified: Tuesday, 13 August 2013, 5:01 AM