GROWTH PERIODICITY IN APPLES UNDER TROPICAL CONDITIONS

The familiar annual growth cycle of apple in the temperate zone is modified quite remarkably in the tropics. In the lowland tropics apples tend to grow continuously from very few growing points. Conventional pruning and training aggravates this. At high altitudes with cold night temperatures little growth occurs. At intermediate altitudes with moderate night temperatures a tendency for episodic growth is more apparent. If many growing points can then be induced to grow simultaneously, moderate elongation growth occurs and terminal buds form in a distinct episodic growth cycle similar to that in the temperate zone. One method of inducing many shoots to grow is to bend branches horizontally. Provided regrowth does not occur from terminal buds, flowers are initiated in most instances. More-or-less synchronous bud burst and flower emergence is then induced by hand defoliation. Prevailing temperatures are favourable for growth throughout the year so that bud burst occurs within 3–4 weeks of defoliation at any time of the year. Some problems are experienced with fruit set if flowering coincides with the wet season. Fruit matures in 4-5 months. If the trees are defoliated again 3–4 weeks after harvest, another growth cycle commences. In this way each tree produces two crops per annum. Furthermore, the time of defoliation can be staggered throughout the year, resulting in correspondingly staggered harvest dates, i.e. year-round production.

This trial-and-error discovery allows the successful cultivation of more than two million apple trees in the vicinity of Batu, near Malang in East Java, and a few smaller areas elsewhere in Indonesia. The altitude is between 600 and 1200 m, the latitude is 7°S, the minimum temperature is around 12°C. Tip-bearing cultivars such as Rome Beauty are mainly used. This culture is described in the references cited. Quantitative observations are presented by Notodimedjo et al. (1981), see p . The annual growth cycle of apple in the temperatu zones and equatorial tropics is compared schematically.