The langsat and duku (Lansium domesticum) are very popular fruits in tropical Asia and particularly so in Thailand, Malaysia, Indonesia and the Philippines. They are similar in size and appearance to the loquat except that the white translucent flesh separates into 5 segments of different sizes. The fruit has a sub-acid flavour with none of the extreme sweetness characteristic of many tropical fruits. It has an appeal to European tastes. Neither the langsat nor duku have been grown to fruiting in Australia, and clonal importations have only commenced since the mid 1970s. However, the tree will grow satisfactorily in north Queensland.
The tree is more tolerant of lower mean temperatures, humidity and rainfall then the rambutan and pulasan, and cultural requirements are not exacting.
II. BOTANY AND FRUIT USE
The genus Lansium, which belongs in the family Meliaceae, contains 6 or 7 species found native to India, Malaysia, Indonesia and the Philippines. Langsat and duku are classified as a single species, but there are differences in tree form and fruit arrangement on the raceme. However unless there are points of difference which require explanation, langsat and duku are combined under langsat in descriptions in this text.
Langsat is a slender tree, 10 to 20 metres high with a straight trunk, slender upright branches, and an irregular or rounded crown. Duku tends to be less tall and has a wider crown than langsat. Leaves are large and divided into 5 to 7 alternately placed leaflets and one terminal leaflet. Leaflets are dark green and shiny above, light green and dull beneath and measure 150 to 200 mm long by 60 to 100 mm wide. The leaves are faintly hairy underneath (langsat) or hairless (duku).
The many-flowered inflorescences (racemes) are borne either singly or in groups of 2 to 5 on the trunk and large branches and are thus essentially cauliflorous. The racemes, erect at first but later drooping as the flowers and fruits mature, are 100 to 300 mm long, being smallest in duku. Flowers are about 12 mm wide and number about 20 to 30 arranged on a spike. Although unbranched, there are usually several spikes emanating from the branch or trunk in one spot. Flowers are perfect and sub sessile. There are 5 sepals and 5 petals which are rounded and imbricate. The stamens are united in a tube with 10 anthers on each flower. The style on top of the tiny ovary is very short and is capped with a 5-lobed stigma. Flowers have a sweet smell.
Fruits are slightly longer than wide in langsat and about 30 or 40 mm long. In duku they are round and 40 to 50 mm in diameter. There are commonly 15 to 25 fruits per spike in langsat and 4 to12 in duku. Another variant or sub species of the langsat grown in Indonesia called the kokosan (very acid to taste) has up to 50 very small fruit on each spike (Anon, 1975). Fruits of both langsat and duku have very short stalks, less than 4 mm long. The skin ripens to a greyish buff or pale muddy yellow colour with brown blemishes. The blemishes appear as the fruit ripens, and extend to cover the fruit when it is past maturity. In some forms of duku the fruits are pink. The skin may be very thin in langsat, or just less than 7 mm thick in duku, and is dull and covered with minute, short pale hairs. In langsat, (but not in duku) there is a milky sticky latex in the skin. The skin peels easily and cleanly from the flesh. The flesh of both is white, translucent and juicy. In langsat, flavour varies from sweet to sour, but in duku it is very delicate and sweet. The flesh separates easily into 5 different-sized segments.
In duku most fruits have no seeds, but when present are up to 25 mm long by 12 to 18 mm wide. In langsat there may be 1 to 5 seeds in each fruit, each up to 18 mm length. Seeds have a thin green coating, are extremely bitter, and are firmly attached to the flesh. Fruits are very refreshing and large quantities can be eaten at one time without feeling particularly full - a fact confirmed by the writer whilst working in Borneo.(N.B. Botanical notes as supplied are from Allen (1965); Bernardo, Jesena and Ramirez (1961) and Coronel (1976)). Figures 1 and 2 (after Molesworth-Allen, 1965) show the characteristics of langsat and duku fruit.
Fruits are most commonly eaten fresh. In Malaysia the seedless or less seedy duku are skinned and bottled in syrup. The product is said to be delicious. In the Philippines, seedless segments can be frozen. The segments are placed in 70% syrup, frozen at minus 40° C and stored at minus 8° C. Frozen fruit remain white with no surface discolouration and the texture is very good. Whole fruits when frozen alone or in syrup are very palatable, but the skin quickly turns brown and the texture of the flesh soft during thawing (Coronel 1977).
III. DISTRIBUTION AND CLIMATIC REQUIREMENTS
Lansium domesticum is native to Malaysia and Indonesia, where it is widely distributed. However it is not generally cultivated outside this area although it is established in southern India, Sri Lanka, and some central American countries. It is not climatically suited for cultivation in California and Florida (Popenoe, 1920). However, the variety Uttaradit from northern Thailand has fruited in southern Florida in more recent times and several other varieties are growing, although apparently no one is contemplating commercial production.
|Fig. 1 LANGSAT|
A divided leaf with a terminal leaflet; a bunch or string of fruits with two removed; A, fruit; arrows point to the sepals at the stalk end, and the lobes capping the apex; B, fruit cut lengthwise through the middle showing one seed and a cavity; C, fruit cut across through the middle showing 5 segments and 3 seeds.
|Fig. 2. DUKU|
Bunch or string of fruits; A, fruit cut across the middle showing 5 segments, one seed, and 4 cavities; B, fruit cut lengthwise through the middle; C, a seed.
Main Production Areas
In Malaysia, duku is more common in southern Malaya, whilst langsat is grown mostly in the north and in the Borneo states of Sarawak and Sabah.
The Philippines has a total estimated area of 7,300 hectares planted to 1,179,500 langsat trees, 819,700 trees of which are of bearing age (Baccon, 1975). Langsat is extensively cultivated in southern Tagalog province (Luzon) (4,520 ha.) and southern Mindanao (1,070 ha). In the southern Tagalog region, langsat is found mainly as backyard trees or as an intercrop with coconut. It is also grown to a limited extent in central and western Visayas and in northern and western Mindanao (Coronel, 1977).
Langsat is cultivated throughout Indonesia, but predominantly in Java. The crop is also very popular in Thailand and is grown quite well on the seasonally dry northern plains which do not accommodate a great number of other fruit tree species.
Langsat grows comparatively well in latitudes and at altitudes not suited to rambutan and pulasan. Langsat is recognised to be more cold tolerant than duku. In Luzon in the Philippines, langsat grows best in areas below an altitude of 400 metres and in Mindanao a similar limit of elevation is placed on duku (Coronel, 1977). In Java, both langsat and duku are cultivated to altitude of 650 metres (Soeseno, 1968; Anon.,1975). Terra, (1952) describes several centres in east and west Java at up to 650 m altitude as having substantial areas of langsat/duku. The special centre for the crop is Singosari in east Java at an altitude of 250 metres. At 600 metres in Java, and 300 metres in southern Luzon, mean minimum yearly temperature is approximately 19°C, and mean maximum approximately 28°C, with a yearly normal of 22°C. This in broad terms corresponds to a latitude of 16 to 20°S in coastal Queensland. However individual months in coastal Queensland are colder than at the altitudes nominated in Indonesia and the Philippines. The broad implication of this comparison is that langsat/duku should grow and fruit satisfactorily in coastal Queensland, at least south to a latitude of 20°S, providing temperatures do not fall to near frost level at any time. Langsat and duku are suspected not to tolerate temperatures below 6°C. However, high temperatures up to 40°C are not detrimental to trees.
Young trees grow best under partial shade at least for the first six years. In the Philippines trees are normally established under coconuts or Leucaena leucocephala, and additional temporary shade is provided at planting. Shade trees are normally pruned at the start of each wet season.
In Indonesia, langsat and duku are more widely distributed into drier areas than the majority of other fruit trees with the exception of sapodilla and mango. Quite a number of areas where the crop is planted have a dry season of 4 to 5 months (Terra, 1952). A similar situation exists in central to northern Thailand. Surprisingly, the langsat is comparatively shallow-rooted.
The crop in southern and central Luzon in the Philippines is subject to a pronounced dry season from December to April. Flower initiation and development normally commences in April in Luzon, and if rain does not fall in this period, then development ceases. However, as soon as rainfall or irrigation is supplied, flower development proceeds. Once started however, watering (in the absence of adequate rainfall) must be sustained otherwise flowers and fruit become atrophied. Early crops in Luzon are induced by irrigating 1 to 2 months in advance of normal flowering (Coronel, 1977). Occasionally in Malaya long dry spells prevent flowering of the main crop (Molesworth Allen, 1965).
IV. VARIETIES AND FRUIT CHARACTERISTICS
Whilst varieties or forms of langsat and duku are defined in each country of production there has been no collective assessment of these. Because of apomictic seed development and the frequent exchange of seed between Asian countries over several centuries, undoubtedly similar forms have different names in different countries.
In the Philippines there are 3 cultivars, Paete, Mindanao and Duku. The origin of Paete is lost in obscurity, but it falls in the langsat group. It is moderately sweet. The variety Mindanao is grown in the southern Philippines and is regarded as the most acid or sour variety. It is a langsat type. Duku was introduced into the Philippines in 1915 and is the sweetest of the three cultivars. However, it has smaller fruit than the Malaysian duku (Coronal, 1977).
|Langsat and Duku cultivars|
Malaysian cultivars are not very well described, and few nurseries distinguish differences other than either langsat or duku. Duku is often referred to as duku-langsat, but the latter name also refers to a form intermediate between langsat and duku. Two selections of duku in Malaysia are Malayan No. 1 and Henting. Thailand has both langsat and duku, but principally the former. One selected variety is Uttaradit (Vangnai, pers. comm.). Singapore has mainly duku, and the best variety is Jurong (Yong, pers. comm.).
Indonesia has a diversity of langsat and duku forms, but varietal names are not well known - if they exist at all. Duku is separated into two groups, one with large seeds, and one with small seeds. Duku is mainly cultivated in the Djakarta, Depok and Yogyakarta districts in Java, and in the Lampung district in Sumatra (Anon.,1975). Langsat is also called Pitjetan in Indonesia and there does not appear to be a breakdown to varieties. Kokosan is a third major group type, with very small acid fruits and large seeds (Anon., 1975). However, Ochse (1931), suggests that langsat is called 'kokosan' in western Java.
V. FLOWERING AND FRUITING BEHAVIOUR
The majority of existing langsat and duku plantings in Asia are of seedling origin, although grafted varieties have become much more popular in recent years. Although there are differences in precocity between langsat and duku forms and between rootstocks, trees are generally slow to bearing. In the Philippines seedling trees start to flower at 12 to 15 years of age. Grafted trees take 7 to 9 years but air or ground-layered plants (if originating from substantial branches) take only 2 to 4 years (Coronel, 1977).
In Malaysia, seedlings take about 15 years to produce first fruit but good culture can reduce this period by at least four years (Molesworth Allen, 1965). In Indonesia, seedling langsat and duku fruit in 8 to 10 years, but this refers mainly to semi-cultivated trees.
Bernado, Jesena and Ramirez (1961) have described flower development in the Paete and Mindanao langsat varieties in the Philippines:
"Flowers between the basal and mid portion of the spike (raceme) start to open first, followed by the basal flowers, then those at the middle portion of the raceme, and finally those at the tip. The corolla dehisces about 24 hours after floral opening but some remain persistent for as long as three weeks or more. The petals remain intact".
In Bernado's observations, emasculating and bagging flowers did not significantly reduce fruit set which suggests autonomic parthenocarpy. However, the presence of red and black ants (Decophyla smaradina and Dolichoderus bituberculatus respectively) may have stimulated increased fruit set. Ants are very common on langsat trees in the Philippines and some other countries at flowering time.
Little information on this subject is available. However, the period from flower set to fruit maturity is normally 3 to 4 months.
Flowering Times and Patterns
Langsat and duku in the more northern latitudes of the tropics - India, Burma, Thailand and Luzon in the Philippines, normally have one crop each year. The first three countries have summer monsoonal rain and mature langsat crops from April to September. Luzon has a late autumn and winter monsoon season and matures the crop from August to October. Thus a dry period at differentiation followed by rain during development and harvest appears to be the norm. In Malaysia there are two crops each year but sometimes only one when a dry period continues past the normal period of flowering for the main crop. The main crop harvests in June to August.
VII. HARVEST AND POST HARVEST HANDLING
Fruit are normally harvested when all the fruits on each bunch have turned full yellow in colour. Experience in the Philippines proves that market demand is greater for fully tree-ripened fruits than for those just maturing. Whole bunches are cut off with a sharp knife or secateurs. Fresh fruit are sold both on the bunch, and as single fruit.
Under ambient temperatures in the tropics ripe fruit do not remain marketable for more than 4 days. This is mainly because of browning of the pericarp.
However, when fruit are treated with a benomyl dip and stored at 15° C in an atmosphere of 5% oxygen and absence of CO2., they remain in good condition for more than 2 weeks (Pantastico, Mendoza and Abilay, 1969).
VIII. SOIL AND WATER REQUIREMENTS
Langsat and duku can grow successfully on many soil types but for the best performance a well-drained sandy or clay loam rich in organic matter is preferred (Coronel, 1977).
The greatest concentration of feeder roots in langsat and duku trees is found in the top 300 mm of the soil profile. However the tree must have some mechanism for drought resistance since it can be grown in areas with pronounced dry seasons (Terra, 1952). But, as shown in Malaya (Molesworth-Allen, 1965) flowering may be held in abeyance or fail entirely for one season if soil moisture is very low during normal flowering periods.
In an average year in north Queensland there is no doubt trees would benefit from irrigation in the months June to December, inclusive.
IX. CULTURAL REQUIREMENTS
Ploughing and harrowing, of land prior to planting is recommended in the Philippines. For compacted soils, and particularly in old coconut plantations, deep ripping ensures destruction of pans and obstructions to good drainage as well as allowing good root development.
Planting sites are prepared by digging a hole slightly deeper and wider than the soil ball on the potted plant. The best planting time is at the start of the wet season. Trees are watered in after planting and temporary shade of coconut leaves constructed over the plants. Permanent shade is usually Madre de Cacao and Leucaena leucocephala (Coronel, 1977). In Indonesia, economic plants such as breadfruit, and avocado are planted for permanent shade (Orgas, 1.937).
In the Philippines, trees are set out at spacings of 5 to 6 metres (280 to 400 trees/ha on a square planting). Indonesian recommendations are for 7.5 to 10 metre spacings (100 to 180 trees/ha).
All researchers propound the benefits of organic mulches, particularly in the first four years after field planting.
Particularly when grown from seed the langsat is a very erect straggly tree. To induce a spreading growth habit, the tip of the stem should be cut off when the young tree is about 1 metre tall. Three well-spaced lateral branches are then allowed to develop and any surplus removed. Once the desired form is achieved subsequent pruning is limited to the removal of water sprouts and dead branches.
Langsat and duku are slow growing trees. Adequate fertilizer and water ensures maximum growth to give the minimum period to first harvest. In the Philippines, two applications each of 100 g ammonium sulphate or 50 g urea are applied in the first year. One application is made after planting, and the other after the wet season. These quantities are increased each year until first fruiting, when a complete mixed fertilizer is supplied. Up to 2 kg of mixed fertilisers are applied per year in equal split applications at the beginning and end of the wet season.
DATE: May 1982
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