Dimocarpus longan (PROSEA)
Dimocarpus longan Lour.
- Protologue: Fl. Cochinch.: 233 (1790).
- Family: Sapindaceae
- Chromosome number: 2n= 30
- ssp. longan var. longan : Dimocarpus longan Lour. (1790), Euphoria longana Lamk (1792) nom. illeg., Nephelium longana Cambess. (1829).
- ssp. longan var. longepetiolulatus Leenh.: Euphoria morigera Gagnep. (1950) nom. inval.
- ssp. longan var. obtusus (Pierre) Leenh.: Euphoria scandens Winit & Kerr.
- ssp. malesianus Leenh. var. malesianus : Nephelium malaiense Griff. (1854), Euphoria cinerea Radlk. (1878) nom. illeg., Euphoria malaiensis Radlk. (1879) nom. illeg., Euphoria gracilis Radlk. (1913) nom. illeg.
- ssp. malesianus Leenh. var. echinatus Leenh.: Euphoria nephelioides Radlk. (1914) nom. illeg.
ssp. longan var. longan :
- longan (En)
- Longanier, oeil de dragon (Fr)
- Indonesia, Malaysia: lengkeng
- Burma: kyet mouk
- Cambodia: mien
- Laos: lam nhai, nam nhai
- Thailand: lamyai pa
- Vietnam: nhan.
ssp. longan var. obtusus :
- Thailand: lamyai khruer, lamyai tao.
ssp. malesianus var. malesianus :
- Malaysia: mata kucing (Peninsular Malaysia and Sabah), isau, sau, kakus (Sarawak)
- Indonesia: buku, ihau (Kalimantan), medaru (Sumatra).
Origin and geographic distribution
Ssp. longan var. longan : Whereas some authors limit the area of origin to the mountain chain from Burma through southern China, others extend it to south-west India and Sri Lanka, including the lowlands. The crop is mainly grown in south China, Taiwan and north Thailand with small acreages elsewhere in Indo-China as well as Queensland (Australia) and Florida (United States) and scattered trees at higher elevations in South-East Asia.
Ssp. longan var. longepetiolulatus : southern Vietnam.
Ssp. longan var. obtusus : Indo-China, cultivated in Thailand.
Ssp. malesianus var. malesianus : all over Indo-China and Malesia, greatest variation found in Borneo.
Ssp. malesianus var. echinatus : Borneo and the Philippines.
Longans as well as the minor fruits of the species are mainly eaten fresh. There are substantial canning industries for longan in Thailand, China and Taiwan. Large fruits are used, preferably those with small seeds. Fruit can be canned in its own juice with little or no sugar, due to the high level of soluble solids. Canned longans retain their individual flavour better than do rambutan or lychee. Longans can be preserved dry, either intact or after removal of the pericarp. The dried flesh is black, leathery and smoky in flavour and is used mainly to prepare a refreshing drink. A liqueur is made by macerating the longan flesh in alcohol.
The seeds are used as a shampoo, like soapberries ( Sapindus saponaria L.), because of their saponin content.
Both the seed and the fruit flesh of longan have several medicinal uses. The leaves, which contain quercetin and quercitrin, and flowers are sold in Chinese herb markets.
The red, hard longan timber and the fairly hard, light brown to yellow "mata kucing" timber are useful, but rarely available.
In eastern Thailand ssp. longan var. obtusus is grown as an ornamental climber.
Production and international trade
Longan production in Thailand was 20 100 t in 1986/1987 and 58 660 t the following year - showing the prominent tendency to biennial bearing - from an area estimated to be 23 500 ha. The exports of fresh, canned and dried fruit, mainly to Singapore, Hong Kong and the EC, were 10 600, 2950 and 0.4 t respectively in 1986. Elsewhere in South-East Asia only East Java produces an appreciable quantity of longan.
The other fruits, such as "mata kucing", are found in their season in some local markets only.
The edible portion of export quality fruit of 3 cultivars ranges from 67 to 78% of the whole fruit. Composition of longan per 100 g edible portion is: water 72.4 g, protein 1.0 g, fat 0.5 g, carbohydrates 25.2 g, fibre 0.4 g, ash 0.5 g, Ca 2 mg, P 6 mg, Fe 0.3 mg, vitamin A 28 IU, vitamin B1 0.04 mg, vitamin B2 0.07 mg, niacin 0.6 mg and vitamin C 8 mg. The energy value averages 458 kJ/100 g. The sugar content is very high. The composition of "mata kucing" fruit is not very different, but carbohydrates - and energy values - are much lower, whereas much higher figures are given for mineral content.
- Tree, up to 40 m tall and 1 m trunk diameter, sometimes buttressed, exceptionally a scandent shrub; branches terete with 5 faint grooves, sometimes warty lenticellate, rather densely ferruginous tomentose.
- Leaves 2-4(-6)-jugate, axial parts mostly densely hairy; petiole 1-20 cm, petiolules 0.5-35 mm long; leaflets elliptical, 3-45 cm × 1.5-20 cm, 1-5 times longer than wide, chartaceous to coriaceous, above often tomentose in basal part of midrib, beneath thinly tufted-tomentose mainly on midrib and nerves.
- Inflorescences usually terminal, 8-40 cm long, densely tufted-tomentose; cymules (1-)3-5-flowered; pedicels 1-4 mm; bracts patent, 1.5-5 mm long; flowers yellow-brown; calyx lobes 2-5 mm × 1-3 mm; petals 5, 1.5-6 mm × 0.6-2 mm, densely woolly to glabrous; stamens (6-)8(-10), filament 1-6 mm.
- Fruit drupaceous, 1-3 cm in diameter, lobe(s) broad-ellipsoid to globular, smooth to warty or sometimes up to 1 cm aculeate, sometimes granular, glabrescent, yellow-brown.
- Seed globular with shining blackish-brown testa; seed enveloped by a thin fleshy, translucent white arilloid.
Growth and development
Longan seeds are short-lived and best sown fresh. Germination takes 7-10 days. Seedling growth is slow and the juvenile phase lasts about 7 years. These characteristics also apply to "mata kucing".
Longan trees grown from air layers come into bearing during the third or fourth year and yields tend to increase with tree size over a very long trajectory. Flowering within a panicle is a sequence of opening of staminate (pistil non-functional), pistillate (stamens non-functional), hermaphrodite and finally staminate flowers again. Male and female phases of flowering overlap 4-6 weeks depending on cultivars. Pollination, by insects, is most effective between 8.00 a.m. and 2.00 p.m. In one study fruit set per panicle improved greatly with bloom rating for the tree, leading to a sharp progression in yield per tree (and an obvious risk of biennial bearing). The period from bloom to harvest is 5-7 months, depending on cultivar and climate. Longan in Thailand flowers just before or after the temperature rise at the end of the cold, dry season. Most fruit is harvested in August and September.
In the panicles of "mata kucing" male and hermaphrodite flowers occur. Flowering lasts only 1-2 weeks, the period varying from late June to mid-October in Sarawak. Pollination is mainly by insects such as ants, flies and honey bees (Apis cerana , A. florea and also A. dorsata). Flowering is often prolific but fruit set is quite low and 2 weeks after flowering, when fruitlets measure 1 cm, many are shed. The fruit ripens about 4 months after bloom.
Other botanical information
The two subspecies and five varieties of D. longan, listed above, are distinguished mainly by differences in the leaflets.
Within ssp. malesianus, var. malesianus shows the greatest variation in Borneo. The fruits are globular to slightly oblong and smooth to warty. In Peninsular Malaysia, the most common form of this taxon is the one with globose smooth fruits which turn brown when ripe. This is the true "mata kucing" and has usually been identified as Euphoria malaiensis. It has a very thin arilloid and is hardly worth eating. This form also exists in Borneo and Sumatra. The more superior forms are found in Sarawak, all with densely thick warty fruits and thicker arilloids. These forms can be roughly grouped into three types based on the fruit characteristics: the "isau" with fruits which are globular and remain green when ripe, the "sau" with fruits which are slightly oblong and also remain green when ripe, and the "kakus" with globular fruits which turn brown when ripe. The leaves, flowers and tree forms also differ. The "kakus" is more widespread in Sarawak, while the "isau" and "sau" are mainly confined to the river banks of the Rajang river and to the Bareo valley.
Var. echinatus differs from var. malesianus in that the fruits have rather long spines resembling the rambutan (Nephelium lappaceum L.). This variety is found in Sabah where the "kakus" also exists.
Three edible longan types are distinguished in Thailand, which presumably all belong to ssp. longan . The first one is a large forest tree with small fruits and a very thin aril, possibly of interest for breeding purposes. The second one is the common longan ("lamyai kraduk"), growing in the northern part of the country as an erect tree, producing small fruits with large seeds and is recommended as a rootstock for commercial cultivars. The third type is formed by the commercial cultivars ("lamyai kraloke") which produce large fruits and small seeds.
Important longan cultivars in Thailand are: "Daw", "Chompoo", "Haew", "Biew Kiew", "Dang", "Baidum", "Luang" and "Talub Nak". In China "Fu Yan", "Wu Long Ling" (both in Fujian), "Wu Yuan" and "Shi Xia" (both in Guangdong Province) are leading cultivars, in Taiwan "Yong Tao Ye" and "Chiau On Diao".
Longan is a subtropical tree that grows well in the tropics but requires a prominent change of seasons for satisfactory flowering. A short (2-3 months) but cool (mean temperature 15-22°C) winter season brings out a prolific bloom; in this respect longan is less demanding and more predictable than lychee. From fruit set onwards high temperatures do not hamper development, but nights should not be warmer than 20-25°C. Ample soil moisture is needed from fruit set until maturity; suitable annual precipitation is about 1500-2000 mm.
Longan thrives on rich sandy loams, it does well on oolitic limestone; moderately acid sandy soils are more marginal and on organic muck soils flowering is deficient, probably because shoot growth continues for too long. In northern Thailand longan orchards are often situated on the lighter soils along former river courses, a ribbon of trees winding between the sawahs. The roots grow down 2-4 m to the water table.
The "mata kucing" thrives in the humid tropical lowlands near sea level, within about 10° from the equator. The trees occur mainly in the substage or understorey in primary or sometimes secondary forests. Rainfall ranges from 2500 mm to more than 4000 mm per year associated with a mean air temperature of 25-30°C and a relative humidity of 65-95%. In Sarawak, the trees grow on alluvial soil, often on river banks. In other areas the trees grow on a wider range of soil types. A pH range of 4.5-6.5 is common in this region.
Propagation and planting
In Thailand longans are propagated through air layering, in China through approach grafting using seedlings of the same cultivar as rootstocks. In the rainy season air layers root in 2-2.5 months; they are nursed in the shade for 6-12 months after separation. Trees obtained by air layering are more susceptible to wind than grafted trees; therefore either they are supported by permanent bamboo props, by soil mounded around the trunk, or rooted seedlings are planted close to the young tree and inarched to improve stability. Cuttings and budlings are rarely used. Tree spacing ranges from 6 m × 6 m to 12 m × 12 m; the latter spacing may also be the end result of thinning of the stand. There is a trend towards closer spacing; regular bearing would help to limit tree size to fit spacings of 6 m × 8 m to 7 m × 10 m.
"Mata kucing" and the other minor crops are commonly raised from seed, though clonal propagation through air layering is not difficult. Seed viability can be prolonged for some time by treatment with a fungicide and keeping the moisture level of the seed above 30%; desiccation is fatal. Rootstocks can be budded using the modified Forkert method, but slow and uneven budbreak remains a problem. For orchards the trees may be spaced 10 m × 10 m, in a square or hexagonal pattern.
Young longan trees are pruned to limit the number of main branches. In bearing trees harvesting is a form of pruning, since the entire panicle is cut. Soon after harvest this should be followed by cutting out some of the subtending twigs. Cutting out these twigs completely simplifies the canopy structure and admits more light to the interior of the tree; it also removes twigs that are least likely to fruit next year, since they have fruited this year. If this is not done side shoots emerge below the cuts of the harvested panicles. These shoots make the canopy more dense and come too late to initiate inflorescences for the next crop.
According to an old report growers in Fukien Province in China practise flower thinning in "on" years. Since prolific bloom in longan appears to be associated with heavy fruit set, the risk of over-thinning is small and as many as 50% of the panicles may be removed. Side shoots emerge below the cuts sufficiently early in the season to mature in time to initiate flowers for the next crop. Thus alternate bearing is suppressed by thinning.
Current pruning practice is mainly to remove suckers in the interior of the tree as well as branches that have lost vitality and panicles that remain after harvest; the skirt is maintained at a height of at least 1 m. These pruning practices do not restrict tree size.
Longans are rather exacting in their water requirements. Ample moisture is needed from flowering until shortly before harvest. Mulching is recommended and supplementary irrigation may be needed during this period. Once the trees become quiescent at the end of the growing season, rainfall may trigger a new flush of shoot growth, upsetting floral differentiation and resulting in failure of flowering.
There is no specific information on fertilizer requirements. Chinese work indicates that high yields are correlated with leaf nutrient levels as follows: N higher than 1.70%, P 0.12-0.20%, Mg 0.20-0.30%. Levels of 0.60-0.80% and 1.50-2.50% are recommended for K and Ca, respectively, but no relation to yield has been found.
For "mata kucing" and related types husbandry is largely limited to harvesting and cutting back of the fruiting twigs.
Diseases and pests
The only disease of importance in longan in Thailand is rosette shoot or witches' broom, caused by a mycoplasm. Affected trees show abnormal growth and poor flowering. No cure is known and affected trees should be grubbed out and burned. Powdery mildew infects inflorescences and young fruit of "mata kucing", causing the same kind of damage as in rambutan. Thread blight occurs on branches and leaves of "mata kucing".
Numerous pests are found on longan. Of particular importance is the longan stink bug ( Tessaratoma javanica ) which can ruin bloom in a year with light flowering. There is also a flower-eating caterpillar. Chemical control interferes with pollination and the interests of bee keepers; the stink bug can be controlled by a hymenopterous parasitoid reared on silk-worm eggs. The fruit is attacked by piercing moths, borer caterpillars and fruit flies. Thai growers sometimes bag the panicles to protect them. The fruit - and that of "mata kucing" c.s. - is also eaten by bats; a draconian control method is electrocution by a high screen of thin, parallel electric wires in the orchard.
Longan fruits, including the fruits of ssp. malesianus , are non-climacteric and have to be harvested when ripe. Maturity is determined by fruit shape, skin colour and taste. Immature fruits are tasteless. The mature longan fruit has a dark, smooth skin, the inside of which is netted and tastes sweet. Longan trees should be picked twice at an interval of 7-10 days; "mata kucing" fruit can all be picked in a single harvest. The whole panicle is cut with a knife or scissors. Panicles should not be dropped. They are sorted and bunched.
In Thailand the average longan yield ranged from 0.99-1.65 t/ha in 1981 to 1987. These average yields are extremely low when compared with well-kept orchards, which should produce up to 12 t/ha per year. For 10-15-year-old trees yields ranging from 60-190 kg/tree have been obtained. In East Java the very best trees produce 150-300 kg in a good year. Crops in Florida from trees 6 m tall and broad, have varied from light (22.5-45 kg) to medium (68-113 kg) and heavy (135-225 kg). The variation is largely due to alternate bearing.
Handling after harvest
Thai growers traditionally pack longan fruits with stalk intact in 35 cm × 50 cm round woven bamboo baskets containing 21-22 kg and lined with longan leaves. Fruit for export, often detached from the panicles, may be packed in corrugated boxes or plastic baskets. Since longan fruit have a high sugar content, they have a shelf life of a few days only at ambient temperature (25-31°C). Longan fruit subjected to hydrocooling or forced air cooling can be stored at 5°C for 40-45 days and at 10°C for 20 days with a relative humidity of 85-90%. For long-term storage fruit can be fumigated with SO2.
Seeds are too short-lived for germplasm collection. Thailand has large tree collections of longan in Chiang Mai and Lamphun. The Thai cultivars differ in shoot, flower and fruit characters from the Chinese cultivars, but on the whole, genetic diversity appears to be narrow. There are several cultivar collections in Australia, the largest being in Kamerunga Horticultural Research Station near Cairns, Queensland.
The University of Agriculture Malaysia with its branch campus at Bintulu, Sarawak, is now the largest collector of germplasm of D. longan ssp. malesianus. The great diversity in Sarawak offers a great opportunity to select superior material. Explorations in remote areas have been regularly made to identify trees with good quality fruit - thick flesh, fruit in consolidated panicles - and to collect budwood.
Seedling progeny are extremely variable and small fruit size appears to be a dominant characteristic. Therefore through the centuries improved cultivars have resulted merely from selection, in particular on large fruit size, high edible portion, crisp flesh, good flavour, and high sugar content. In so doing heavy and regular yields appear to have been sacrificed in comparison with the common longan in Thailand. Now marketing characteristics, such as early or late harvest, a long shelf life and a pure white aril for the canned product, must also receive more attention.
Small fruit size and biennial bearing is the main constraint for expansion of the crop. The suggestions made above to ensure more regular bearing are based on piecemeal evidence, but they are simple to test. It is probably easier to attain good and stable yields of longan than of lychee; since these fruits substitute for one another this considerably enhances the prospects for longan.
If trees bore regularly, growth would be moderated and it would be easier to prune to keep trees a manageable size. Small trees, coupled with closer spacing and regular yields would allow production to be intensified.
The superior races of the spp. malesianus, in particular the var. malesianus in Sarawak and other parts of Borneo, may offer an attractive alternative to longan for the humid tropical lowlands.
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Wong Kai Choo & Saichol Ketsa