|Author: ||J.V. Possingham|
The grapevine is probably the most widely grown temperate fruit crop in the tropics and subtropics with a total world production of over 3 million tonnes.
Currently India with a production of over one million tonnes is the major world producer followed by Brazil producing somewhat less than one million tonnes in the tropics.
Other tropical producers include Yemen 163,000, Peru 136,000, Thailand 40,000, Colombia 19,000, Tanzania 14,000, and Venezuela 11,500 tonnes.
Some are also produced in the tropical parts of both Mexico and Saudi Arabia.
Many tropical countries produce small amounts of table grapes for local consumption.
In the tropics and subtropics there is massive environmental diversity caused by variations in rainfall, temperature and altitude.
There are grape growing areas (usually elevated) with the characteristics of temperate regions with a marked climate initiated dormancy.
In the wet humid tropics grapevines are evergreen, grow continuously and with controlled pruning it is possible to have one cropping cycle per year.
In the dry tropics and subtropical regions grapevines usually have two cycles per year or 3 cycles per 2 years determined by temperature and rainfall.
In the wet lowland tropics where day-length and temperature variation is small the growth cycle of grapevines can be manipulated and cropping induced largely by pruning combined with chemical treatments.
Vegetative growth and photosynthesis is maintained during periods of heavy (monsoon) rain by repeatedly applying fungicide sprays to prevent the infection of mature leaves.
At the same time, young shoots, immature leaves and bunches are removed to reduce the number of sites prone to fungal infection.
Following a period of lower rainfall a form of dormancy and some leaf-fall can be induced by water stress.
The short dormancy period is broken using hydrogen cyanamide or thio-urea combined with irrigation to bring about shoot growth.
Bud development and bunch formation is stimulated on the green shoots by slowing growth, using retardants (cyclocel) and shoot tip removal.
With seedless varieties berry size is increased with dips and sprays of gibberellic acid (GA). Dependent on the climate it takes about 120 days for bunches to form and grapes to reach maturity after breaking the rest period.
Cropping is timed to ripen the grapes during periods of cool and dry weather.
In both drier areas and when growing disease resistant varieties, the bunches that form after the first pruning are retained and two crops per year are taken.
The high relative humidity and temperature of the wet tropics promotes leaf and bunch fungal infections and these must be controlled to maintain leaf function and bunch integrity.
It is somewhat of a paradox that only limited areas of hybrid, disease resistant table grapes are grown in the tropics. Vitis vinifera bunch grapes are preferred because of their superior flavour and texture.
Those that are grown in the tropics all tend to have loose clusters and thick skins that confer a degree of resistance to berry rots.
The seedless varieties such as Thompson and Flame Seedless grown in the tropics tend to have loose open clusters following GA treatment.
The growth of grapevines in the tropics is both rapid and continuous and to sustain high growth rates they require high levels of both organic and inorganic fertilizers.
High populations of plant parasitic nematodes are a feature many tropical soils and tolerant rootstocks of high vigour are required by grapevines for these areas.
Cropping levels tend to be very high (over 50 tonnes/ha) and the vines often become unproductive and die between 6 and 10 years of age.
In most tropical areas the overhead arbour (syn. bower, pandal, pergola) is the main trellising system used because it allows the bunches to hang below the foliage.
This increases airflow around the berries and allows good access to fungicide sprays.
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