A well established orchard is a life long endowment. But fruit trees differ in their nature and to retain their desirable characters such as high yielding, better quality of fruit, early maturing, resistance to pests and diseases and early fruiting one has to adopt suitable propagation methods depending upon the type of fruit trees.
Propagation of plant is the multiplication or reproduction of plant by means of seed or any other part of the plant. The basic objectives of plant propagation are :
(a) Increase the number of plants
(b) Preserve the essential characteristics of the plant
Basically there are two methods of propagation :
1. Sexual propagation : In this method plants are raised from seeds
2. Asexual propagation : Parts like branches, stem, roots or leaf are developed into new plants. This is also known as vegetative propagation.
Medium of Propagation
Medium is the substance on which plant parts or seeds are placed during propagation. E.g., soil is a medium on which seedling are raised. This medium provides stability, mechanical support and creates favourable condition for their growth and development. The medium should be sufficiently firm and porous so as to facilitate the holding of seeds or plant parts and fairly moisture retentive. It should also be free from weed seeds and disease organisms. The following are the most commonly used media :
Soil
Soil is the most common medium of propagation but on its own it is an insufficient medium for growing seedlings. It is usually mixed with well rotten farmyard manure in varying proportions.
Sand
Pure sand is used as a rooting medium of soft wood cuttings and is also used for mixing with soil for proper drainage of the excess water.
Leaf mould
Leaf mould is prepared by decomposing leaves. Mixing a small quantity of ammonium sulphate is good for the seedlings.
Saw dust
For propagation of plants as well as for growing plants, saw dust can also be used.
Containers
A well prepared medium is filled into containers before the plants are grown in them. Besides land, several types of containers are used to hold a medium and these are :
Sexual Methods of Propagation
Multiplying plants through seeds is called sexual propagation. Being the easiest and cheapest, this method is generally employed on a commercial scale in fruit crops such as mango, jamun and citrus.
1. Advantages of sexual propagation
* Plants propagated from seeds are hardier and generally long living
* Plants which are difficult to propagate through asexual methods are multiplied by seeds
* New varieties and hybrids can be raised
* The root stock on which fruit varieties are budded or grafted are usually obtained by sexual propagation
* Seedlings are cheaper and easy to raise
2. Seed selection and storage
The following points should be taken into consideration while selecting the seeds from a mother plant :
Freshly harvested seeds should be thoroughly cleaned, dried in the sun by spreading them on mats or on clean dry floor and stored in a dry cool and aerated place. Seeds live longer when dried fully and stored at lower temperatures. A temperature of 5 to 6 degree centigrade is optimum for the storage of many seeds. The seeds have varying storage capacity : some seeds can be stored only for a short period while others can be stored for a longer period.
3. Seed dormancy
Dormacy is the inability of the seed to germinate for a period soon after its maturity. The embryo of the seed remains inactive from the time of its development to the time it germinates. Dormacy can be caused by external and internal factors. Lack of moisture, unfavourble temperatures and lack of oxygen are the common external factors, whereas internal factors are mechanical inhibition of seed coat for water uptake, restricted movement of gases, resistance to embryo expansion, chemical inhibition of germination by certain substance present in the seed or fruit.
A common cause of dormancy is the impermeability of the seat coat to water. Under natural conditions, the seed coat decomposes if the soil contains sufficient moisture and warmth and germination occurs. However, germination can be accelerated by subjecting seeds to the following pre-germination treatment.
The soaking of seeds in water hastens germination by making the seed coat soft. Soaking period depends upon the hardness of the seed coat. Normally seeds are soaked in cold water for 24 hours. But guava seeds have to be soaked for two weeks before sowing.
It is a treatment in which seeds are immersed in hot boiling water and allowed to soak in the gradually cooling water for 12-24 hours. This treatment is also used for seed borne diseases.
This treatment consists of rubbing the seeds in folds of sand paper which enables the seed coat to become permeable to water.
The seed covering can be rendered more permeable to water by treating the seeds with certain chemicals. Sulphuric acid diluted to 25 to 50% an be used for this purpose.
This treatment brings about certain physiological changes within the embryo. The seeds are arranged in alternate layers of moist sand or soil and are stored at zero degree centigrade for 1 to 4 months, e.g. apple, pear and cherry.
4. Sowing of seeds
Seeds are sown in carefully prepared and raised seed beds in earthen pots or wooden boxes. The soil should be well pulverished and mixed with well rotten dry farmyard manure at the rate of 1 kg er square metre. Most of the fruit seeds are sown in lines at 0.5cm to 1.25cm deep and 10cm apart line to line and plant to plant. The seed is covered either with sand or leaf mould.
The young seedlings in seed beds are usually subject to damping off disease. The disease is severe when seedlings are overcrowded or soil is kept continuously wet. Damping off disease can be controlled by the following methods :
Asexual Propagation
A sexual propagation is the reproduction by means of vegetative parts of a plant such as roots, shoots or leaves. It is also known as vegetative propagation.
1. Advantages of Asexual propagation
a. Fruit plant propagated vegetatively are true to its parent plant and as result, there is uniformity in growth, yield and quality of fruits.
b. Some fruit trees can be propagated only through vegetative method, e.g., banana and pineapple.
c. Vegetatively propagated trees start bearing fruits earlier.
d. Some fruit plants those are susceptible to certain diseases, can be grown without pest or disease infection by budding or grafting on to a disease resistant root stock.
e. Resistance to unfavourable climatic conditions like drought or cold can be secured.
f. Trees can be considerably dwarfed by using proper root stocks.
g. Cross-pollination can be effected by grafting shoots of other suitable varieties on the branches of self unfruitful variety.
h. Grafting can be used to encourage healing of tree wounds caused by rodents, rabbits or implements.
i. It is possible to grow 2 or 3 varieties on the same plant, e.g., one can get 3 to 4 varieties of roses on the various branches of the same root stock. Different varieties of mango on a same mango tree can also be grafted.
Methods of Asexual Propagation
Broadly asexual propagation is divided into methods based on plant’s own roots; and methods based on roots of other plants. These two methods are further classified into divisions and subdivision based on various factors such as source of root stock, rooting time, parts of plants and techniques of propagation.
In this method parts of the same plant used for propagation. Based on the time of separation of parts and rooting this method is classified into divisions and subdivisions :
Suckers
These are plants parts those arise from the base of mother plant. In pineapple the suckers emerge from the leaf axil near roots. These are detached neatly with attached roots and planted directly in the field.
Runners are parts of mother plant which are capable of producing roots in contact with the soil while remaining part of the mother plant. They are detached and planted directly in the field, as in the case of strawberry.
Layering is the development of roots on a branch while it is still attached to the parent plant. This rooted system is then detached to become new plant growing on its own roots.
Various stem treatments are done for root formation. These treatments cause an interruption in the downward flow (carbohydrate/starch, auxins and other growth factors) from leaves and growing tips to other parts of plants. These materials accumulate near the points of treatment and rooting occurs in this area.
This type of propagation is divided into two groups : separation and division
In this method plant parts in the form of bulb and crowns are separated and planted.
In this method plants parts are multiplied by division. Rhizomes, tubers and root tubers are the parts usually multiplied by division.
In this method cutting of roots, leaf and stem are detached from mother plant before rooting and placed under suitable conditions. These cuttings develop into full plants. According to the parts used for propagation they are classified as follows :
The method consists of cutting roots into pieces of 10 to 25cm length, which are usually planted in horizontal positions, e.g., Guava and bread fruit.
Many plants with fleshy leaves can be propagated by leaf cutting. The leaf is detached from the mother plant and planted with half of leaf stalk covered with soil. Many ornamental plants are propagated by this method.
This method involves the union of two plant parts ; root stock and scion.
Root stock is the part of the graft which provides the root system to the grafted plant. The plant selected for root stock should be healthy, vigorous, one year old and adaptable to climate and soil. It should also match with the scion variety in growth habits. Root stock can be raised from seeds and cuttings. They can be planted in pots, alkathene bags, nursery beds or directly in the orchard.
It is the shoot system of the grafted plant which is taken from the selected or desired commercial variety to be multiplied. The selected scion wood should have healthy swollen buds ready to grow but not actually growing. This is generally on the topmost portion of an actively growing branch.
When the root stock and scion plants are brought together, union between the two takes place. The union is called graft and the operation is called grafting.
In grafting freshly cut scion and stock are brought together in such a manner that the cambium region (cellular layer between the wood of a tree and its inner bark) of both the scion and stock come into an intimate contact. The outer exposed layer of cells in the cambium region of both scion and stock produce a particular type of cells which soon intermingle and interlock. These cells are called callus cells. Certain cells of this newly formed callus tissue which are in line with the cambium layer of the scion and stock form into new cambium cells. These new cambium cells produce new vascular tissue (tube like cells through which food material pass) which establishes vascular (tubular) connection between the scion and stock, a requisite for successful graft union.
d. Limitation of grafting
Grafting is limited only to dicotyledonous plants (Plants which have two cotyledons or seed leaves) where stem have a cambium layer. In monocotyledonous plants (Plants which have a single cotyledon or embryo lobe) which do not have such a cambium layer grafting is not possible, e.g., Cereal grains and grasses.
Generally the greater botanical relationship of the plants grafted better the chance of graft union becoming successful. Grafting with a variety and between varieties is generally successful.
The root stock influences scion or the resulting tree and its fruits in many aspects. The most noteworthy reaction between stock and scion are intimately related to growth rate and usually can be plainly seen by an examination of the trunk at the point of the union. A smooth bud union indicates a balanced physiological functioning between the stock and the scion. The shape and form of trees are also sometimes affected by the stock. On certain stocks the trees become dwarf.
In some cases root stock also influences the yield of the scion variety grafted on them. Generally the stocks which have dwarfing effect on scion tend to stimulate early fruiting. Similarly slow growing stock with dwarfing tendency tend to hasten fruit ripening. The grade, size and quality of the fruits such as acid and sugar content are also influenced by the root stock.
Depending on the types of plants, their age and growth habits different methods o grafting are practiced. The following are the important grafting techniques :
Inarch method consists of uniting the stems of two separate plants which are propagated with considerable difficulty by other methods. The root stocks raised in pots are placed close to a selected scion on the tree in such a way (using a platform) that they can be grafted.
In this method, grafting is done using tongue like structure made on scion and root stock. The scion remains attached to the mother tree and root stock in a pot.
In this method the scion is fixed on root stock like a saddle. The union is established while the scion remains separated from the stock.
This method of grafting is used to join together plant parts which are under one inch in thickness. This is also called splice grafting and is commonly used for apple.
In this method a tender veneer (scion shoot shaped into a long slender piece) is grafted to the side of the root stalk. The stock may be reared in pots or on the nursery bed.
This is also known as bark grafting. This method is mainly exercised for renovating old trees by grafting tender shoots. In this method also the scion remain separated from the mother plant during the grafting period.
In this method a wedge shaped scion is grafted into notch made on the side of the root stock.
This is the opposite of saddle grafting. In this method the scion is made into a wedge and the root stock made into a cleft.
It is not a propagation in the true sense of the word. It is generally used to join living tissues of trees which are damaged partially or completely around a tree trunk by rodents, animals, cold or racking. The bridging of the damaged or injured portion of the tree is done to save it by establishing the flow on both sides of the injury.
Budding is a form of grafting in which scion, in the form of only one mature bud portion along with a bark, taken from the desired plant is inserted in the root stock between nodes in such a way as to cause an intimate contact with cambium tissues. The root stock may be grown on beds or in pots. Both the scion and stock should be of pencil thickness for successful budding.
If the scion buds are to be obtained from a far away place, the branch with the buds should be transported. Under such conditions in order to reduce the loss of moisture through transpiration and other physiological activities, the terminal bud and leaves should be removed leaving the leaf stalk intact to protect the lateral buds. The cut portion of the branch on top (while removing the terminal bud) and at the base should be scaled with wax to prevent moisture loss. The branch should be packed in a polythene bag with sufficient air space within it.
After budding the joint is tied and made water and air tight. When the joint is established the shoot portion above the budding should be removed to facilitate the growth of the bud. Extreme care should be taken to ensure that the germinating bud is protected and congenial condition for its proper growth.
The followings are some of the important types of budding :
This technique is commonly practiced in oranges and roses all over the world. Shield budding consists of inserting a shield like bark with a bud on the root stock.
It is done by fixing a bud with a patch of bark 0.5 to 1 cm wide and 2.5 to 3 cm long ver a thick stock which is more than a year old.
In forkert budding the bud is inserted under a flap on root stock.
Relatively thick barked trees thinner than one inch and in the active stage of growth are commonly budded by this method. In this method a bud with a piece bark covering three-fourth of the circumference of the stem is used. Such a piece of bark is referred as flute.
This method is useful only to small stock of not more than 3 / 4 “ to 1” in daimater. This is more or less an extension of the flute method.