Growth and Development of Horticultural Crops (1+1)

Canopy management

• Canopy in a fruit tree refers to its physical composition comprising of stem, branches, shoots and leaves. The canopy density is determined by the number and size of the leaves, architecture of stem, branches and shoots. Canopy management of the fruit tree deals with the development and maintenance of their structure in relation to the size and shape for the maximum productivity and quality. The basic concept in canopy management of a perennial tree is to make the best use of the land, the climatic factors for an increased productivity in a three dimensional approach. Tree vigour, light, temperature and humidity play a vital role in the production and quality of the fruits.
• The major objective is to achieve maximum productivity in a shortest period with out adversely affecting tree health and bearing of the orchard. The natural tree canopy of the fruit tree varies greatly from species to species and cultivar to cultivar. The size, shape and volume of canopy are affected by climate, planting density, rootstock, method of propagation, training, pruning, regularity of bearing, soil type, nutrition, irrigation, intercrop, growth regulators used, diseases, pests, environmental pollution etc.,
• The crux of the canopy management lies in the fact, as to how best we manipulate the tree vigour and use the available sunlight and temperature to increase the productivity and quantity and minimize the adverse effects of weather parameters.
• Some of the basic principles in canopy management are as follows.
1. Maximum utilization of the light
2. Avoidance of the build up of micro-climate congenial for the diseases and pests
3. Convenience in varying out the cultural operations, maximizing the productivity and quality
4. Economy in obtaining the required canopy architecture.
• Light is an important factor in production of fruit. It has a role in flower induction as well as in fruit development through carbohydrate synthesis. While increased assimilates in the shoots is a pre-requisite for flowering in mango and other fruits generally, high yield of quality fruits are attributed to high light interception and distribution in the tree canopy. The fruit yield is related to light interception, whereas fruit quality is a function of light distribution. Light interception is influenced by plant density, canopy shape, canopy leaf area index and can be raised by increasing the density of foliage in the canopy, the height of the tree and number of tress per hectare. Light intensity decreases, within the tree canopy as the outer portion shades the inner canopy. Light exposure influences flower bud differentiation, fruit set, fruit colour and quality. In the canopy management, major emphasis is usually required to reduce the excessive canopy shading and increase the air circulation in the fruiting region.
• The practices used to accomplish these objectives are:
a) Control of tree vigour
b) Reduction of canopy shading
c) Training and pruning system to increase light interception and distribution.

• Light was found to perform a triggering action in the process of fruit bud differentiation in grapes. Failure of the flowering in mango trees with dense canopies (Buronkar and Gunjate, 1991) and opening of the canopies through pruning (Madhavarao and Shanmugavelu, 1976), (Rameswar, 1989) support indirectly the role of light in fruits bud formation in mango. However, the light dependence for the flower bud formation is not the same in different varieties. While, White Riesling variety of the grape requires less light intensity, Thompson Seedless requires less light for the fruit bud formation. Hogher light intensities of more than 3,600 ft candles and temperature above 35oC are favourable for the bud fruitfulness in Thompson Seedless grape.
• The light utilized by the plants for the photosynthesis corresponds to 400 to 700 mm of the electro-magnetic radiation from the sun. Kriedmann and Smart 1971 reported that the photosynthesis in grapes rapidly increases upto the light intensity of 5,000 ft (200 watts/m2). The light compensation point, at which the rate of photosynthesis, is just the equal to the rate of respiration in Thompson Seedless grape is 125 ft candles (5 watts/m2). Leaves at the light regimes of lower than the compensation point are the liabilities to the plant. A leaf absorbs more than 90 per cent of the solar radiation depending upon its thickness. Even if the full sunlight in a given locality is 12,000 ft candles, the third layer of leaves in a tree canopy would receive the light at a lesser intensity than the compensation point. Therefore, the tree canopy architecture has to be so managed that every leaf gets light at the intensities, which are more than the compensation point.
• Close planting of the trees and the development of dense canopies may alter the micro-climate around the tree canopy. Temperature and light regimes decrease, while humidity increases. The incidence of powdery mildew will be more under the low temperature and in shaded conditions. Bortrytis rot of the bunches was observed to be less in the vines with exposed canopy. Low temperature and the high humidity caused by dense canopies in grape was found to favour the incidence and spread of the downy mildew. The efficacy of plant protection measures will be reduced, when the canopy is dense and the trees are tall. Canopy size and shape should be such, so that the cultural operations could be carried out in an orchard with ease and mechanization of some operations is possible. They primary aim of the canopy management is to increase the productivity per unit area, quality of the fruit and to reduce the cost of production. The canopy architecture should be easy and less expensive.
Ideal canopy architecture

• Ideal canopy architecture should fulfill as many as possible principles involved in canopy management. i.e., the canopy size should be dwarf, spreading and open in mango and guava. In order to obtain more yields per unit area of the land, it is desirable to have the required surface area per canopy volume by increasing the canopy height. But due to inconvenience in carrying out the cultural operations including harvest, the canopy height should be at manageable level.
• Based on the correlation of tree morphological characters with the fruit yield and quantity, dwarf and spreading trees with larger trunks are the ideotypes in guava (Shikhamany et al., 1977). The standards for an ideal canopy for grapes cv. Thompson Seedless are as follows (Shikhamany, 1983):


Stem height - 135cm Diameter - 7.5	Cane number - 5 per m2 Cane thickness-8 to 10 mm
Cordon length - 90cm	Leaf number per bearing shoot - 12 to 15
Shoot orientation during the growth season-35 to 45 with the ground surfaces	Shooting orientation during the fruiting season- 35-40oC with the ground surface upto a length of 90cm and parallel to the ground surface beyoung 90 cm