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TRAINING
Before actually discussing the subject of training, it is necessary to understand the various terms used to make the subject more intelligible.
Trunk: The main stem of the plant.
Head: The point on the trunk from which first branches arise.
Scaffold branches: The main branches arising from the head are known as scaffold branches. Trees in which scaffold branches arise with in 60-70cm height from the ground level are called low head trees and those in which they come out from the trunk above 120cm are called high head trees.
Crotch: The angle made by the scaffold limb to the trunk or the secondary branch to the scaffold limb is called crotch.
Leader: The main stem growing from ground level up to the tip dominating all other branches is called leader.
Water shoot: A vigorous growing unbranched shoot arising on any branch or leader is called water shoot. Water sucker: The growth appearing on rootstock portion is called water sucker.
The reasons for training fruit trees, ornamental trees, shrubs etc. are:
1) There are no. of plants, which grow wild and don‘t bear if they are left to themselves and will not have any symmetry in their growth.
2) Most of the time, the unpruned trees put forth vegetative growth only. Hence, bearing will be delayed.
3) When plants are grown in rows at close spacing, they grow tall and occupy interspaces, making intercultural operations difficult to practice.
4) For want of sunlight, the lower branches wither and die. The shaded fruits (apple, citrus etc.) fail to develop colour.
5) Untrained trees will generally be less productive because of excessive vegetative growth for most of the time.
6) The framework being weak in untrained trees, it breaks easily due to strong winds as well as heavy loads of crop.
All the above problems can be overcome by training the trees. Man can train the plant to suit his desire. By training the plants, ideal conditions a can be provided for better production.
The fruit trees are trained to a particular system depending upon their habit of growth and the flowering and ornamental shrubs etc.can be trained to a particular shape like animals, birds etc.
It is necessary to pay attention to the training of a plant during the first few years when it is young. In this period, its permanent framework is built up as decided upon by the grower. The main objectives to be kept in view in training the fruit trees are:
To facilitate orchard cultural operations.
To provide an attractive appearance.
To admit more light and air to the centre of the tree and to expose maximum leaf surface to the sun
for increasing production
for complete colour development
To protect the tree trunk from sunburn injury.
To secure a balanced distribution of fruit bearing parts on the main limbs of the plant.
Most deciduous and evergreen woody trees are best trained to a single stem with a low head. In case of pomegranate, custard apple and fig it would be better to train two or three stem plant and remove the other stems that may grow later. 61 In the tropical climate, the high-headed trees are unsuitable as their exposed trunks are subject to sunscald in summer. Low headed trees are common all over the world. In such trees the heads or crown is kept so low on the trunk that there is only a distance of 60-- 90cm (2—3 ft.) between the ground and the lowest branch. Such low headed trees come in to bearing comparatively much earlier, are able to resist stormy winds more effectively and their spraying and harvesting also become easy.
The formation of the main frame work of the tree is the most important part of the training.
1) Usually, two to four main branches are encouraged. These should be allowed to arise from different directions and also at some distance from one another, so as to form a well-balanced head.
2) The frame work is greatly strengthened, if the branches are spaced at about 15cm distance with medium crotches (40—500 )
3) If two or more branches of equal size are allowed to arise from one place, they form a bad crotch and often split from their common joint.
The most important systems of training followed in most of the fruit crops are:
Central Leader system:
In this system, a tree is trained to form a trunk, which extends from the surface of the soil to the top of the tree.
In many kinds of trees, the central axis or the main branch naturally grows vertically upwards and smaller side branches grow from it in various directions.
If the central leader is allowed to grow indefinitely, it will grow more rapidly and vigorously than side branches resulting in a robust close centre and tall tree. In such a tree the bearing is confined in top portion of the trees.
Merits and demerits:
1) The main advantage of this system is the development of strong crotches.
2) Its main disadvantage is shading of the interior of the trees.This weakens the central leader and thus shortens the life of the tree
3) Since trees are very tall, harvesting and spraying become difficult and costly.
4) The lower branches, which remain more or less shaded, become ultimately less vigorous and less fruitful.
5) Owing to the shading of the inferior, the bearing surface moves to the periphery (outer shoots) of the tree.Thus fruiting surface is reduced and eventually yields are reduced.
6) The very high shape of the plants makes them prone to wind damage.
7) This method of training is not suitable for high altitude and hot arid places where wind velocity is high.
This system is also called as close centre, since the centre of the plant is closed and also as pyramidal system, since the plant trained looks like a pyramid.
This system of training is practiced in case of certain apple varieties and pears.
Open Centre system: In this system of training, the main stem of the plant is allowed to grow only up to a certain height by beheading it in the young stage ie.within an year of planting and inducing all the subsequent vegetative growth by lateral branches
This results in the low head in which the bulk of the crop is borne closer to the ground than in case of central leader tree.
Merits and demerits:
1) It allows more light to reach all parts of the tree which is helpful
(a) for better colour development of the fruit
(b) fruiting area is spread all over the area of the trees.
2) Trees become low headed. So, pruning, spraying, harvesting etc., are facilitated.
3) The branches form weak and narrow crotches, which may frequently break under severe stress and strain such as bearing of heavy crop and strong winds.
4) Sun scalding of central leader is also possible.
5) The branches form very close to each other all most from the same spot.
6) In this system the plants take a ‘bowl or vase' shape, which provides a good base for setting of frost. So this system is not suitable for high altitude areas where frost observance is common.
Since the main axis is removed, it leaves the centre open and hence open centre and the tree looks like a vase (bowl), hence it is other wise called as vase system.
This system of training is practiced in plums and peaches.
Modified Leader system:
This is intermediate between the above two systems and has the advantages of the both. This system is developed by first training the tree to the leader type allowing the leader to grow unhampered for the first four or five years.
The main branches are allowed to arise on the main stem at reasonable intervals.
After the required number of branches has arisen, the main stem is headed back and lateral branches are allowed to grow as in the open centre system.
Merits and demerits:
1) This results in a low-headed tree with well-spaced limbs, well distributed fruiting wood and low height to carryout orchard operations conveniently. This system of training is practiced in fruit plants like citrus, pear, apple and walnut etc.
Which system of training is the best?
Among the above three systems of training, the modified leader system is the best and most desirable because:
Narrow to medium crotches and there by breakages are eliminated
The indeterminate growth of the central axis is also prevented keeping the tree height under control, so as to make orchard operations easy and cheap.
No danger of sun scorching and fruit quality is good.
Principles of training:
Irrespective of the system of training practiced, the following general principles are to be observed:
1) The branches should arise on the main trunk alternatively at intervals of at least 15cm and not all at one place.
2) They should be equally distributed around the stem.
3) Up right branches should not be encouraged. Branches should have medium crotches.