1513

2: Edible fruits and nuts

Lansium domesticum Correa

Ann. Mus. Hist. Nat. Paris 10: 157, t. 10 f. 1 (1807).

MELIACEAE

2n = 144 (octoploid, x = 18)

Aglaia dookoo Griffith (1854), Aglaia domestica (Correa) Pellegrin (1911), Aglaia aquea (Jack) Kosterm. (1966).

Langsat (En); this name is used not only for the species, but also to denote one of several types; where in this paper langsat refers to a type, this is clear from the context which includes references to other types such as duku. Indonesia: langsat, duku, kokosan. Malaysia: langsat, duku, duku-langsat. Philippines: lansones (Tagalog), boboa (Bisaya), buahan (Manobo). Thailand: langsat, duku, longkong. Vietnam: bònbon.

Langsat originates in western South-East Asia, from Peninsular Thailand in the west to Borneo in the east; it still occurs wild or naturalized in this area and is one of the major cultivated fruits. On a small scale, langsat is also cultivated in Vietnam, Burma, India, Sri Lanka, Hawaii, Australia, Surinam and Puerto Rico.

The fruit is practically always eaten fresh out of hand, but seedless fruit may be bottled in syrup. The light-brown wood is tough and durable and used for house posts, tool handles, etc. The dried fruit peels are burnt in the Philippines to drive mosquitos away. The peel is also used against diarrhoea because it contains oleoresin. Other parts of the plant used medicinally include crushed seeds (used by the indigenous people of Malaysia to cure fevers) and the astringent bark which is applied against dysentery and malaria; powdered bark is used in poultices against scorpion stings.

Langsat is an important fruit tree in the region. Statistics for 1987 give a production of 26 700 t and an area of 10 500 ha in the Philippines, 71 000 t and 7600 ha in Peninsular Malaysia, and 57 000 t langsat and 39 000 t duku in Thailand from areas of 16 000 and 7000 ha respectively. Production in Indonesia was 76 000 t in 1986. In all of these countries, langsat ranks among the top ten fruit tree crops.
In the late 1980s all four countries were exporting small quantities of langsat, mainly to Singapore and Hong Kong. The fruit is not yet traded in markets in Europe and North America.

The edible portion is 68% of fruit weight. Per 100 g it contains: water 84 g, a little protein and fat, carbohydrates 14.2 g, mainly reducing sugars, predominantly glucose, fibre 0.8 g, ash 0.6 g, Ca 19 mg, K 275 mg, some vitamin B1 and B2 but little vitamin C. The energy value is 238 kJ/100 g.

Tree, up to 30 m tall and trunk 75 cm in diameter, in cultivation usually only 5—10 m tall; bole up to 25 m, irregularly fluted, with steep buttresses; bark mottled grey and orange, furrowed, containing milky, sticky resinous sap; twigs glabrous to pilose. Leaves alternate, odd-pinnate, 30—50 cm long, glabrous to densely pilose, petiole up to 7 cm long; leaflets alternate, 6—9, elliptical to oblong, 9—21 cm x 5—10 cm, glossy, chartaceous-coriaceous, base somewhat asymmetric, apex short acuminate, lateral veins 10—14 pairs, petiolules 5—12 mm long, thickened at base. Inflorescences many flowered, solitary or in fascicles of 2—10 on the trunk or largest branches; racemes simple or branched at the base, 10—30 cm long; flowers bisexual, sessile to pedicelled, solitary, small; calyx fleshy, cup-shaped, 5-lobed, greenish-yellow; petals fleshy, erect, ovate, 2—3 mm x 4—5 mm, white to pale yellow; staminal tube subglobose, up to 2 mm high, anthers in one whorl; ovary globose, appressed pilose, 4—5-celled; style short, thick, stigma broad. Fruit an ellipsoid or globose berry, up to 2—4(—7) cm x 1.5—5 cm, yellowish pubescent, calyx persistent with reflexed lobes; fruit-wall thin (1—1.5 mm) or thick (up to 6 mm). Seeds 1—3, enveloped by a closely adhering, thick, fleshy, translucent white aril; cells without developed seed are also filled with aril tissue.

Langsat seed retains its viability for about 5 weeks if kept moist. In a test in Malaysia germination started after 10 days and within one month exceeded 90%, contrasting with duku seeds, only 25% of which had germinated after 3 months. Multiple seedlings, resulting from polyembryony, are fairly common in both langsat and duku.
The trees grow slowly, preferably under shade which can be reduced after 2—3 years. The trees are shallow-rooted and depend on a layer of litter to protect the numerous surface-feeding roots. Trees come into production late, normally 10—15 years from seed; however, with proper care, seedlings may bear within 7—8 years and grafted trees within 5—6 years (longkong in Thailand). The inflorescences emerge as small buds, usually early in the dry season. Further development may be delayed for several months, but when growth is resumed, full bloom is reached in about 7 weeks. The fruit ripens 14—17 weeks later. A large majority of the flowers set fruit, but yield is often severely limited by early fruit drop, as shown by studies in the Philippines and Malaysia. Phenological observations in West Java revealed that flowering was poor on vigorously growing trees and on branches exposed to the sun. These vigorous trees produced three times as many leaves as the other group, which lost its advantage in flowering through a very poor fruit retention.

Lansium domesticum is a complex and variable species with wild and cultivated forms in which parthenocarpy is the rule and apomixis quite common. The variability is all the more baffling since, according to the few studies conducted, the flowers do not form pollen due to degeneration of the androecium. Some taxonomists have classified the different forms as separate species, others as varieties within Lansium domesticum, but no convincing classification exists. Direct comparison is difficult because different forms are infrequently found growing together; moreover, the vernacular names appear to be used rather inconsistently, the same name being applied to different forms in different regions.
There is a fairly clear contrast between two major groups, the langsat and the duku, both in tree habit and fruiting characteristics. Langsat is the name generally used for slender trees with upright branches and a scraggy habit with sparse, dark green foliage. The spikes are long, carrying 15—25 ovoid, thin-skinned fruits which exude latex until fully ripe. The taste is generally (sub)acid and refreshing. Langsat is adapted to more seasonal climates further from the equator than the duku. Examples are 'Uttaradit', named after a province in northern Thailand and 'Paete', highly esteemed in Luzon Island, the Philippines.
Dukus are spreading trees, often with a dense dome-shaped canopy of bright-green leaves, bearing shorter spikes, usually with few fruits. The fruits are normally larger and more rounded than the langsat fruit, with a thick skin (up to 6 mm) and relatively free from latex. Duku forms are generally sweet and aromatic; the trees appear to be more suited to the humid tropics. 'Du 1' was the first selected duku clone released by the Ministry of Agriculture in Malaysia.
Other types fall into an intermediate group called duku-langsat in Malaysia. Only the kokosan of Indonesia does not fit into either of these 3 groups. The latter's leaves are hairy, the fruit bunches are very compact with dark-yellow, usually quite sour fruit containing large seeds. The kokosan, as the name implies, is eaten by sucking the arils out after biting the fruit. All the other forms are eaten by squeezing the fruit until the skin splits, after which the arils can easily be freed from their segments.
It is not easy to delimit the duku-langsats. The 'Longkong' of southern Thailand, for instance, is a nearly seedless type with a brittle skin and soft aril which is rapidly gaining importance. Some horticulturists group it with the dukus, others group it with the duku-langsats. Likewise 'Mindanao' of the Philippines resembles duku but the fruit is quite sour. More confusing, the 'Duku' of the Philippines and several types named duku in Indonesia in fact appear to belong to the duku-langsats. Similarly the langsep or pisitan of Java, which is usually equated with langsat, has in fact the thick skin of the duku. Fruiting charts for Malaysia show that langsat and duku generally produce only one crop per year, but in large parts of Peninsular Malaysia the duku-langsats tend to be in season twice a year.

Lansium domesticum is grown mainly in mixed stands with companion trees which provide shade. The species is more demanding than the companion crops and only thrives in sheltered, humid environments up to 800 m elevation, but preferably near sea-level. In other words, it requires a warm, moist, almost stress-free tropical environment. Well distributed rainfall (or access to ground water, or irrigation), shade and mulch all help to limit stress. Of the different groups, langsat is grown furthest from the equator (there is an area of 4000 ha near Uttaradit, at 17° latitude in Thailand) and copes with a dry season, if shade and moisture supply are adequate.
The tree has a clear preference for the better soils, in particular those with good drainage and water retention, e.g. river banks in Malaysia. It dislikes sandy coastal soils and alkaline soils. Medium-textured soils rich in organic matter and slightly acid are preferred.

Langsat is still commonly propagated from seed or from spontaneous seedlings found under the trees and raised in pots until they are nearly 1 m tall and can be planted out. Germination and seedling vigour improve with seed size and only large seeds should be used in nursery work. Early seedling growth is very slow. Under intensive care it takes 10—18 months to get a pencil-thick stem suited for grafting or planting out, but plants take twice as long in most nurseries. Propagation from cuttings is possible using green wood, but requires much care. Sometimes large branches are air layered because trees propagated in this way come into bearing within a few years, but the losses after separation of the layers tend to be high.
Propagation by grafting is preferred, the methods ranging from patch budding and side veneer grafting to cleft grafting and suckle grafting, a form of inarching. For cleft grafting, non-petioled 6—10 cm long sticks are used, taken from mature terminal twigs 1 cm thick. The best time for grafting is towards the end of the rainy season. The twigs are tipped and defoliated 2 weeks before use to activate the axillary buds. Seedling langsat is used as the rootstock; out of 20 related species tested in the Philippines, only Dysoxylum altissimum Merr., Dysoxylum floribundum Merr. and Dysoxylum cumingianum C. DC. were found to be compatible. One-year-old rootstocks can be used for inarching.
The trees are commonly planted in home gardens in certain districts, but often also as intercrop under coconut (the Philippines) or mixed with durian, mangosteen or other trees (Thailand, Indonesia). Spacing recommendations vary widely, from 8 m x 8 m (about 150 trees/ha, the Philippines) to 12 m x 12 m for the spreading longkong types in southern Thailand (50—60 trees/ha). These spacings assume the presence of companion trees.

Young trees are carefully shaded and watered during the first few years. The leader of the upright langsat types may be cut back and the emerging laterals tied horizontally to obtain a more spreading habit. In older trees, only watersprouts and diseased branches may need to be pruned.
Generous mulching is recommended. Nutrient requirements are probably low because of slow growth and low yields, but light dressings early in the rainy season and after harvest may be beneficial, especially when substantial crops are produced. Irrigation can be used to advance flowering by one or two months, provided the floral initials have emerged during the preceding dry period. The inflorescences start to grow out 7—10 days after watering. A dry spell while the fruit is on the tree entails the danger of serious crop losses due to fruit cracking when the water status is suddenly improved.

Root rot and anthracnose are serious diseases affecting the tree and the fruit respectively. It is not clear which pathogen causes root rot; there is no evidence that Phytophthora spp. are involved. Anthracnose (Colletotrichum gloeosporioides) is seen as small to large brownish spots on the fruit bunch; it can lead to premature fruit drop and post-harvest losses.
Bark borers are very common pests, particularly in the upright langsat types, which often owe their scraggy appearance to branches killed by caterpillars of the carpenter moth (Cossus sp.) and the green moth (Prasinoxema sp.). The caterpillars pupate in the tunnels. These pests are active during the wet season; part of the damage is destruction of flower buds. Growers scrape the loose bark off infested branches, kill the exposed borers and paint an insecticide on the cleaned branch. Other borers affect the trunk, twigs and fruit. In Malaysia a fruit-boring caterpillar can cause considerable fruit drop; such fruit should be collected and buried to break the life cycle. In Indonesia the larvae of a weevil are found in the fruit. Scales and mites can also do considerable damage. Bats, birds and rodents are keen on the fruit; effective controls include flash-lighting at night and covering the bunches with nylon bags.
The leaves are damaged by leaf miners, leaf rollers, beetles and bugs. Leaf-eating caterpillars and green scales on the fruit are the main problems in Queensland.

The fruit is harvested by a person climbing the tree and cutting the mature bunches with a knife or pruning shears. Care must be taken not to injure the point at which the bunch is attached to the tree, because future inflorescences may be borne there. In fact, rather than climbing the tree, it might be better to use ladders because this can minimize damage to dormant flower buds. Four to five harvest rounds are made to clean a tree of its crop. Picking only ripe fruit, as judged by the colour change, greatly improves fruit quality. Generally the fruits in a bunch ripen nearly at the same time, but where ripening is uneven, this greatly complicates the harvest. The fruit should be harvested dry; wet fruit goes mouldy when packed.
The harvest season is short; the langsat types ripen somewhat earlier than the others, in certain areas the duku-langsats produce two crops per year (although it is not clear whether individual trees produce more than one crop per year) and the timing varies in different regions, so that in major markets the fruit is available from four months (Thailand, the Philippines: July—October) to eight months (Peninsular Malaysia: June—February).

Yield is rather variable; a tendency to biennial bearing is reported from the Philippines. Ten-year-old longkong trees should produce 40—50 kg fruit, increasing to 80—150 kg at 30 years; 300 kg per tree is said to be the top yield. The figures on area and production mentioned above work out to a mean yield of 2.5 t/ha in the Philippines compared with 3.6 t/ha for the langsat and 5.6 t/ha for the duku type in Thailand.

Langsat is a very perishable fruit, the skin turning brown within 4 or 5 days after harvest. Fruit can be left on the tree for a few days waiting for the rest of the bunch to ripen, but even while on the tree it turns brown and becomes unmarketable fairly soon. Cold storage at 15°C with 85—90% relative humidity is possible for 2 weeks if the fruit is dipped in a benomyl solution (4 g/l). The fruit is marketed in bamboo baskets lined with newspaper or banana leaves. Often the fruit is graded before marketing.

In all the countries of South-East Asia there is increasing interest in selected cultivars and clonal propagation. Germplasm collections are very modest; material introduced in Australia is being assessed in Cairns (Queensland). No breeding has been attempted; in fact, breeding will not be possible until trees are found which produce viable pollen, or flowers can be manipulated to do so.

The langsat is a very popular fruit in South-East Asia; the different types of fruit within the species can meet every taste. It would appear that the markets in the region are still undersupplied. However, to assess the prospects properly, a better insight into yield potential and yield-limiting factors is needed. The economics of langsat-growing are particularly influenced by the need to raise the trees under a companion crop, and the long period until fruiting.

Blackler, M.H., 1976. Lansium domesticum: langsat. In: Garner, R.J. & Chaudhri, S.A. (Editors): The propagation of tropical fruit trees. Horticultural Review No 4. C.A.B., Kent, England. pp. 376—385.
Coronel, R.E., 1986. Promising fruits of the Philippines. UPLB College of Agriculture, the Philippines. pp. 275—303.
Lim, M., Hamapat, T., Wanachit, W. & Suwankiri, 1986. Collection of Lansium and Garcinia in southern Thailand. Newsletter IBPGR-Regional Committee for S.E. Asia 10(2): 10—12.
Kostermans, A.J.G.H., 1966. A monograph of Aglaia, sect. Lansium Kosterm. (Meliaceae). Reinwardtia 7(3): 221—282.
Mabberley, D.J., 1985. Florae Malesianae Praecursores 67. Meliaceae (divers genera). Blumea 31: 129—152.
Marsusi, 1979. Fenologi duku (Lansium domesticum Corr.) [Phenology of Lansium domesticum Corr.] In: Anonymous: Peningkatan penelitian dan pengembangan prasarana penelitian biologi [Improvement of biological research and development facilities]. National Institute of Biology, Bogor. pp. 109—116.
Noparat Bamroongrugsa, 1986. Langsat, duku and longkong. Rusamilae Magazin. Prince Songkla University, Pattani, Thailand 10(1): 24—29.
Prakash, N., Lim, A.L. & Manurung, R., 1977. Embryology of duku and langsat varieties of Lansium domesticum. Phytomorphology 27(1): 50—59.
Sunarti, S., 1987. Leaf anatomy and taxonomy of duku. Floribunda 1(4): 13—15 (in Indonesian, summary in English).

Othman Yaacob & Noparat Bamroongrugsa

Othman Yaacob & Noparat Bamroongrugsa, 1991. Lansium domesticum Correa. In: Verheij, E.W.M. and Coronel, R.E. (Editors): Plant Resources of South-East Asia No 2: Edible fruits and nuts. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea