Double-cropping of apples and peaches in the tropics

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DOUBLE CROPPING OF TEMPERATE FRUITS IN THE TROPICS Apples and peaches are also grown in several locations in the tropics where no chilling is received. The culture depends on defoliation to induce the next growth cycle after flower initiation has occurred but before cold-requiring dormancy arises. Extensive commercial apple production occurs in East Java, Indonesia, 8°S latitude and bi-annual cropping of peaches occurs in Venezuela, 10°N. No winter chilling occurs under those conditions. Two crops are harvested each year and cropping is staggered so that fruit may be harvested every day of the year. Success is dependent on relatively uniform temperatures, favourable for tree growth and
fruit development all year round. Successive growth cycles are induced by artificial defoliation after flower initiation occurs but before cold-requiring dormancy develops. There are some important requirements for successful apple culture in the tropics (Notodimedjo et al., 1981). These include: (1) a moderate temperature regime conducive to episodic growth; (2) many growing points on each tree; (3) cessation of shoot growth by terminal bud formation; (4) adequate time for flower initiation to occur; and (5) synchronous bud burst after flower initiation. In Java, the basic system to produce double cropping of apple involves leaf stripping to stimu- late flowering (Janick, 1974). There are regularly two crops per year, typically one in April and the second in October. Notodimedjo et al. (1981) demonstrated that bud burst and flower emergence could be induced at any time of the year by hand defoliation. At the time of defoliation there are high levels of gibberellins and cytokinins in the apices and ABA and other inhibitors in the subtending leaves. Cessation of shoot growth by terminal bud formation depends on competition between a large number of growing points. Flower initiation follows terminal bud for- mation but subsequent flower development is slow until after harvest and defoliation. Physiological dormancy of terminal buds is avoided by defoliation within a month of harvest. No chilling requirement is apparent and no chilling temperatures
occur. Dormancy of most lateral buds is not broken by defoliation. Burst of lateral buds is increased dramatically by bud slicing, partially by branch bending and, under some conditions, by ethephon treatment. There is no evidence for growth control mechanisms that differ from those known in the temperate zone. The requirements for flowering are not met naturally in the tropics but are achieved by manipu- lative treatments notably branch bending and hand defoliation. Although the growth cycle of apples in the tropics is visually quite different from that in the temperate zone, the endogenous mechanisms of growth regulation do not differ appreciably. This has consequences for research. Whereas in the temperate zone each stage of growth occurs only once a year, in the tropics growth control mechanisms may be studied throughout the year as each stage of growth may be found at any time on different trees and bi-annually on any one tree.