Malus domestica (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Malus domestica Borkh.

Protologue: Theor. prakt. Handb. Forstbot. 2: 1272 (1803).

Family: Rosaceae

Chromosome number: 2n= 34 (diploid cvs); 2n= 51 (triploid cvs)

Synonyms

• Malus pumila auct. non Miller,
• Pyrus malus L. (in part) (1753),
• Malus communis Poir. ex Lamk (in part) (1804).

Vernacular names

• Apple (En)
• Pommier (Fr)
• Indonesia: apel
• Malaysia: apel
• Philippines: mansanas
• Thailand: appoen
• Vietnam: pom.

Origin and geographic distribution

The cultivated apple of today is believed to have been derived from south-western Asia. At present apples are cultivated all over the world. Main areas of cultivation are: Western Europe, the Soviet Union, China, the United States, Turkey, Iran, Japan and Argentina.

Uses

In South-East Asia the fresh fruit is eaten. Some immature fruit is used in preparing fruit salad and a little apple juice is produced from the ripe fruit (Indonesia).

World-wide fresh consumption of the fruit also is by far the most important use, but large quantities are processed into juice and apple sauce. Fruit slices may be preserved by drying in the sun or in heated dryers. Fermentation of fruit of certain cultivars yields cider and distillation gives high-proof alcohol products such as calvados (France). The use of whole or sliced cooked fruit in pastries is also common.

Production and international trade

With a world production of 40 million t in 1988 apple closely follows the banana (excluding plantain) and the orange in volume and ranks second after the grape in importance as a fruit of the higher latitudes. There is a lively international trade and exports from the southern to the northern hemisphere are still growing.

In South-East Asia commercial apple production started in Timor, in the 1960s surpassed by East Java when regulation of the growth rhythm made commercial production possible at intermediate elevations. The success story of apple-growing in East Java is highlighted by statistical data indicating that production increased from 15 000 t/year from about 2 million trees around 1980 to 50 000 t from 7.6 million bearing trees in 1988. Apple-growing is also on the increase in northern Thailand and gaining ground in the Philippines (Luzon); as in East Java the crop in the Philippines is grown on a cycle which is much shorter than one year.

Properties

Apples have a crisp texture, unlike most tropical fruit, and a sub-acid taste depending on the balance between malic acid and sugars. Per 100 g edible portion the fruit contains approximately: water 85 g, carbohydrates (mainly fructose) 10-13.5 g, calcium 10 mg, phosphorus 10 mg, iron 0.2 mg, potassium 150 mg, a trace of vitamin A, small amounts of vitamin B1, B2 and B6 and vitamin C 10 mg. Protein and fat content are very low and the energy value is 165-235 kJ/100 g.

Description

• Small to medium-sized tree, 5-10 m tall, freely branching with long shoots and various types of short shoots (spurs) with a single trunk; when growing unattended in the tropics reverting to a stiff upright bush, 2-4 m tall, through reiteration of axes near the ground. Young stem and twigs tomentose.
• Leaves elliptic-ovate, 4-13 cm × 3-7 cm, rounded at base, margins irregularly saw-toothed, usually densely tomentose beneath.
• Flowers largely terminal on spurs, in several-flowered fascicles; pedicel and calyx usually woolly, calyx persistent in fruit; petals 5, white to pinkish, falling off after anthesis; stamens 15-20; styles 5; ovary 4-5-celled.
• Fruit a pome, globose, ellipsoid to obovoid, usually more than 5 cm in diameter, varying in colour, sweet or acid, much longer than pedicel; endocarp coriaceous; fruit pulp without stone cells.
• Seeds brown, mostly 2 in each cell.

Growth and development

At high latitudes apple trees flush and flower in spring; around the longest day there is a second, minor flush. The flushes are terminated by the formation of buds. During summer flowers differentiate in some of these buds which will bloom next spring; also the buds enter dormancy which deepens with time. Fruit ripens in the autumn after which the leaves are shed. Low winter temperatures are instrumental in breaking bud dormancy in time for the spring flush.

In the tropics growth is very different: shoots all grow more or less vertically, leaves are retained much longer so that the plant becomes evergreen, there is little shoot growth, scattered over the entire year and largely limited to shoot extension, few laterals being formed. Flowering and fruiting are sporadic throughout the year. In cultivation this undesirable trait is suppressed by bending shoots horizontal to build a wide tree frame and by enforcing a synchronous growth cycle, either an annual cycle - through appropriate dormancy-breaking treatments - or a much shorter cycle, based on triggering a flush with bloom before bud dormancy has become too deep to be broken by defoliation. In the latter system trees may produce two crops per year as in East Java. The fruit ripens 3.5-5 months after flowering, depending on the cultivar. At high latitudes much attention has to be paid to cross-pollination by compatible cultivars. Under the favourable conditions for flowering in the tropics, however, the importance of self- and cross-incompatibility is much reduced; even parthenocarpic fruit set is fairly common.

Other botanical information

The apple is of hybrid origin and has probably been derived from M. sylvestris Miller, M. dasyphylla Borkh., M. pumila Miller and some Asiatic species. More than 1000 cultivars are grown all over the world, mainly in non-tropical climates. Due to hybridization, the real identity of most cultivars is not known.

In Indonesia more than 80% of the trees are cv. Rome Beauty; in addition, the cvs Manalagi and Princess Noble are grown. Characteristics:

• "Rome Beauty": leaves elliptical to wide-elliptical, 9.9 cm × 6.4 cm, petiole ca. 3 cm long. Inflorescences in 6-flowered corymbs; sepals 6 mm × 3 mm, petals 2.2 cm × 1.7 cm, stamens about 1 cm long. Fruits flattened globose, about 6.5 cm long and 8(-12) cm in diameter, greenish-yellow with a bright red blush, with an average weight of about 200 g; the flesh is whitish-creamy, with a coarse texture, juicy and slightly aromatic.

• "Manalagi" (a local name, presumably an old Dutch cultivar): fruit globular, small, yellow-green; flesh sweet with a full flavour; commands the highest price.

• "Princess Noble": fruit oblongoid, small, green; flesh white, juicy, acid.

Ecology

At high latitudes apple requires a mild growing season (no extremes of sunshine, temperature or humidity), a sufficiently cold winter to break dormancy and excellent soil conditions to limit stress, as this would affect fruit quality and - if more severe - fruit size and floral development for the next crop. Windbreaks are needed for exposed sites.

In the tropics a short growth cycle requires favourable (mild) growing conditions throughout the year, as may be found close to the equator: altitude 800-1200 m (temperature 16-27°C), sunshine more than 50% of potential sunshine duration, rainfall 1600-3200 mm, relative humidity 75-85%, good soils with irrigation facilities.

For an annual growth cycle in the tropics there should be a prominent change of seasons, the growing season meeting the above requirements, whereas the off-season should preferably be overcast as well as cool, since low light levels as well as low temperature appear to have a dormancy-breaking effect. Such conditions are usually found further from the equator at elevations of 1200-1800 m.

Propagation and planting

Apples are always cloned and since most cultivars can hardly be propagated on their own roots, budding - generally T-budding - is the standard propagation method. In the tropics seedling rootstocks are often imported; in several countries clonal rootstocks of the MM-series (Malling-Merton hybrids, originally bred in England to impart resistance against overwintering woolly aphids) are used with limited success. In Indonesia a rootstock, named "wild apple" or sometimes "Chinese crab apple", is used exclusively; it is multiplied either by collecting root suckers in the orchards or by air layering.

In the nursery as well as in the orchard it is vitally important to work with young shoots, to avoid the problems of deepening dormancy of the buds. Thus rootstocks are budded young with young budwood and the trees are sold with young scion wood, the more so since transplanting sets back tree vigour. Budded trees are defoliated and pruned as soon as extension growth stops, in order to shape the tree frame but also to induce another flush of young shoots. The emphasis on young material implies that everything should be done to maintain high growth rates, so that this young material is sufficiently sturdy to work with.

Potted trees can be sold in leaf, but bare-rooted trees should be defoliated. The trees are planted at 3 m × 2.5 m or in double rows, spacing (3.5 + 1.5) m × 2 m, giving densities of 1333 to 2000 trees per ha. It is quite common, at least in Java, not to plant pollinator trees.

Husbandry

Apples in the tropics tend to be rather fruitful, since the dormancy of flower buds is more easily broken than that of leaf buds. Hence husbandry aims at promoting shoot growth and leaf area duration to sustain the heavy crop. This means that the trees are pampered: clean-weeding around the base or along the tree rows, generous use of manure, fertilizers and mulch, ample watering and intensive crop protection. If this is not enough, fruit thinning and spur pruning can bring the fruit load down to balance the leaf area.

A rapid succession of flushes helps to quickly increase tree volume after planting. The grower stimulates this by defoliating the trees (usually by hand, but chemicals such as urea may also be used) soon after each flush, bending the leading shoots horizontal and tipping these shoots. The combination of bending, tip pruning and leaf stripping triggers a maximum number of lateral shoots to clad the tree frame. Flowers are removed to promote growth, until tree size and the number of inflorescences promise a substantial crop, about 2 years after planting.

Bearing trees are defoliated and pruned within a few weeks after harvest. The emphasis shifts from bending and leader-tipping to removal of superfluous shoots, spur thinning and replacement of wood which has aged (loss of vigour, small fruit size) after having borne several crops; the replacement shoot may still need to be bent horizontally.

Bearing orchards are fertilized at the end of harvest with 60-120 kg N, 40-60 kg P₂O₅ and 60-80 kg K₂O per ha. The lower figures apply to the light crop produced by bloom during the rainy season, which generally sets fruit poorly. Flowering during the dry season results in a very high fruit set, although many fruits are seedless, probably partly because under these favourable conditions the flowers get pollinated before they open. Differences in pollination, fruit set and seed numbers per fruit between dry- and wet-season bloom require further study at the cultivar level.

Diseases and pests

Important diseases of apple in Indonesia are necrotic leaf spot (Marssonina coronaria), powdery mildew (Podosphaera leucotricha) and pink disease (Corticium salmonicolor). Necrotic leaf spot flares up during the rainy season and spreads rapidly. The leaves turn black before they have time to fall, giving the orchard a blighted look. Fungicides are effective, but too little is known of the life cycle of the fungus to time the applications properly. Powdery mildew and pink disease are also controlled with fungicides, but improved orchard hygiene should be the basis for control. Defoliation restricts powdery mildew to the buds; when the trees leaf out infected shoots can be easily recognized; they should be removed to reduce the chances of healthy leaves being infected. Pink disease is a canker which thrives under wet conditions, infecting pruning wounds and in particular growth fissures in narrow branch crotches. To control the disease, all cankers should be completely cut out at the end of the dry season and the wounds dressed with a fungicide, so that the orchard enters the rainy season with a minimal infection pressure.

Numerous pests attack the apple, including a host of sucking insects and mites. As most insecticides are expensive and toxic, there is increasing interest in integrated pest control; the experience gained in citrus orchards may serve as an example.

Harvesting

There are two main seasons in East Java, April and October. However, the harvest period can be controlled by the timing of leaf stripping so that there is a year-round supply of fresh fruit. Generally the fruit is picked rather immature, as the growers dread the risk of leaving the fruit on the tree several weeks longer. Ideally there should be about 3 pickings with an interval of 7-10 days.

Yield

"Rome Beauty" is the most productive cultivar in Indonesia and good growers attain yields of about 25 t/ha for the main crop and 5 t/ha for the crop which flowered in the rainy season.

Handling after harvest

If handled with the necessary care, apples can reach distant markets and still have an adequate shelf life, even in the tropics. The fruit is picked with the stalk; it is graded according to size and quality and packed in rigid boxes or cartons. Apples readily absorb odours from other products and hence should not be transported or stored with commodities such as onions or potatoes.

Genetic resources

Among the wealth of apple cultivars those from continental regions (e.g. "Rome Beauty", "Winterbanana", "Glockenapfel") show more promise than the ones grown in maritime regions (e.g. "Cox's Orange Pippin"). Tip-bearing cultivars, which easily form flower buds terminally (also on the longer shoots), are most suitable, and of course low chilling requirements to break bud dormancy are a great advantage in the tropics. In Batu, East Java, 65 cultivars are being tested.

The Indonesian rootstock appears to be an important genetic resource: it shows no signs of bud dormancy and grows throughout, so that it can be quickly multiplied. It has also done well in other tropical countries; virus-free material should become available around 1992.

Breeding

For the tropics the breeding programmes for low-chilling cultivars in Israel, Australia, Brazil and the United States (Florida), are most relevant. "Anna" is a well-known low-chilling cultivar from Israel, found in most tropical growing areas in combination with "Dorsett Golden", a suitable pollinator.

Prospects

The apple is a high-value cash crop for smallholders who can administer the necessary intensive crop care. For the time being the market within South-East Asia offers unlimited scope for expansion. It is expected that apple growing will spread to all parts of the region which have sufficiently dry highland climates.

Literature

• Dennis Jr., F.G. (Editor), 1987. Temperate zone fruits in the tropics and subtropics. Acta Horticulturae 199. 191 pp.
• Janick, J., 1974. The apple in Java. Horticultural Science 9: 13-15.
• Kusumo, S., 1984. Apel (Malus sylvestris Mill.) [The apple]. CV Yasaguna, Jakarta. 131 pp.
• Saure, M., 1989. Obstarten der gemäszigten Breiten [Fruit species of the high latitudes]. In: Rehm, S. (Editor): Handbuch der Landwirtschafft und Ernährung in den Entwicklungsländern. 2nd edition. Band 4. Spezieller Pflanzenbau in den Tropen und Subtropen. Eugen Ulmer Verlag, Stuttgart. pp. 400-414.
• Soewarno Notodimedjo, Setyono Sastrosumarto, Harjono Danoesastro & Edwards, G.R., 1981. Shoot growth, flower initiation and dormancy of apple in the tropics. Acta Horticulturae 120: 179-186.
• Verheij, E.W.M., 1985. Apple growing in East Java: the scope for improvements. Acta Horticulturae 158: 47-51.

Authors

Surachmat Kusumo & E.W.M. Verheij