CONDITIONS OF GROWTH, DORMANCY AND REST TO PRODUCE TEMPERATE ZONE FRUITS UNDER TROPICAL CONDITIONS.

ISHS Acta Horticulturae 199: II International Workshop on Temperate Zone Fruits in the Tropics and Subtropics

CONDITIONS OF GROWTH, DORMANCY AND REST TO PRODUCE TEMPERATE ZONE FRUITS UNDER TROPICAL CONDITIONS.

Author:

G.R. Edwards

Abstract:
Temperate zone fruit are traditionally grown in regions with hot dry summers and cold wet winters. In such conditions they show pronounced growth periodicity - active growth in spring, growth cessation/flower initiation in summer, leaf fall and cold-requiring rest in winter. In sub-tropical regions there is less seasonal fluctuation in temperature but similar growth periodicity. Inadequate winter chilling to break rest is the factor limiting production. Availability of low-chill cultivars and rest-breaking chemicals have permitted increased production in these areas.

Tropical regions are characterised by relatively uniform temperatures year-round. Growth is favoured at any time of year and there is no distinct cold period to meet the chilling requirement. High elevations have been utilized to provide chilling with little commercial success.

There are two examples of successful commercial culture of temperate fruits under tropical conditions:- Apples in the Batu region of Indonesia, latitude 8°S, altitude 800–1200m. and peaches in the Colonia Tovar region of Venezuela, latitude 10°N, altitude 1200–1750m. In both areas the temperature regime is moderate and uniform; there is insufficient cold to meet the chilling requirement of the cultivars grown, but 1½ to 3 crops have been produced annually for many years. The crucial cultural operation common to both areas is artificial defoliation soon after harvest. Leaf removal, after dormancy and flower initiation, but before the rest period, induces a new growth cycle. These two successes demonstrate that the cold requirement of temperate fruit species can be avoided and very high altitudes with attendant lack of heat units, are not prerequisite for production. This idea was tested in the Philippines in 1984 and 1985 at 1 highland and 5 lowland sites. The cultural treatments were:-

close spacing at planting to encourage competition
tipping and bending of long shoots to promote lateral bud growth
restriction of water supply to reduce vegetative growth
chemical growth retardants - daminozide for apples, PP333 for peaches
defoliation - by hand or chemicals to induce bud break and avoid rest
irrigation to improve bud burst
rest-breaking chemicals where defoliation did not cause bud burst
"ratooning" to re-establish trees.

For apples:- Some fruit was harvested from the third growth cycle, 13 months from planting. There was little difference between sites. For peaches:- At the highland site growth cessation/flower bud formation was normal, rest-breaking chemicals induced bud burst, fruit matured within 12 months of planting. At lowland sites growth was vigorous, flower bud formation delayed, defoliation induced bud burst, but no fruit set. Temperatures at anthesis were too high.