9/26/2007

Rambutan Fruits





rambutan

[ram-BOOT-n] Indigenous to the Malay Archipelago, this remarkable looking fruit has a rind that's covered in dark, soft, flexible "bristles." The rambutan is small (1 to 2 inches in diameter) and, depending on the variety, the rind color can be crimson, orange, yellow or green. Inside, a single seed is surrounded by a translucent, grapelike flesh that has a sweet, delicate flavor, which is much like but slightly more acidic than that of the litchi (to which it's related). The rind is easy to peel off; after which the whole rambutan should be popped into the mouth, the flesh eaten and the seed discarded.

Description

It is an evergreen tree growing to a height of 10-20 m tall.

The leaves are alternate, 10-30 cm long, pinnate, with 3-11 leaflets, each leaflet 5-15 cm long and 3-10 cm broad, with an entire margin.

The flowers are small, 2.5-5 mm, apetalous, discoidal, and borne in erect terminal panicles 15-30 cm long.

Rambutan trees are either male (producing only staminate flowers and, hence, produce no fruit), female (producing flowers that are only functionally female), or hermaphroditic (producing flowers that are female with a small percentage of male flowers).

The fruit is a round to oval drupe 3-6 cm (rarely to 8 cm) long and 3-4 cm broad, borne in a loose pendant cluster of 10-20 together. The leathery skin is reddish (rarely orange or yellow), and covered with fleshy pliable spines, hence the name rambutan, derived from the Malay word rambut which means hairs. The fruit flesh is translucent, whitish or very pale pink, with a sweet, mildly acidic flavour.

The single seed is glossy brown, 2-3 cm long, with a white basal scar; it is poisonous and should not be eaten with the fruit flesh.

Production

Rambutan cut open.
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Rambutan cut open.
Rambutan fruit cluster.
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Rambutan fruit cluster.
Image:Rambutan stall.JPG‎
Rambutan for sale in Bangkok.

It is a popular garden fruit tree and propagated commercially in small orchards. It is one of the best known fruits of southeast Asia and is also widely cultivated elsewhere the tropics including Africa, Cambodia, the Caribbean islands, Central America, India, Indonesia, Malaysia, the Philippines, and Sri Lanka. Thailand is the largest producer. Rambutan production is increasing in Australia and, in 1997, was one of the top three tropical fruits produced in Hawaii. It is also produced in Ecuador where it is known as "achotillo".

The fruit are usually sold fresh, used in making jams and jellies, or canned. Evergreen Rambutan trees with their abundant coloured fruit make beautiful landscape specimens.

Cultivation and uses

Rambutan is adapted to warm tropical climates and is sensitive to temperatures below 10 °C, and is grown commercially within 15° of the equator. The trees do best on deep soils that are high in organic matter and thrive on hilly terrain as they require good drainage. Rambutan is propagated by grafting, air-layering, and budding; the latter is most common as trees grown from seed often produce sour fruit. Budded trees may fruit after 2-3 years with optimum production occurring after 8-10 years. Trees grown from seed bear after 5-6 years.

The aril is attached to the seed in some commercial cultivars, but "freestone" cultivars are available and in high demand. There is usually a single light brown seed which is high in certain fats and oils (primarily oleic acid and eicosanoic acid) valuable to industry, and used in cooking and the manufacture of soap. Rambutan roots, bark, and leaves have various uses in medicine and in the production of dyes.

Rambutan trees bear twice annually, once in late fall and early winter with a shorter season in late spring and early summer. The fragile nutritious fruit must ripen on the tree, then they are harvested over a four to seven week period. The fresh fruit are easily bruised and have a limited shelf life. An average tree may produce 5,000-6,000 or more fruit (60-70 kg or 130-155 lb per tree). Yields begin at 1.2 tonnes per hectare (0.5 tons/acre) in young orchards and may reach 20 tonnes per hectare (8 tons per acre) on mature trees. In Hawaii, 24 of 38 cultivated hectares (60 of 95 acres) were harvested producing 120 tonnes of fruit in 1997. It has been suggested that yields could be increased via improved orchard management, including pollination, and by planting high yielding compact cultivars.

Most commercial cultivars are hermaphroditic (producing flowers that are female with a small percentage of male flowers); cultivars that produce only functionally female flowers require the presence of male trees. Male trees are seldom found as vegetative selection has favored hermaphroditic clones that produce a high proportion of functionally female flowers and a much lower number of flowers that produce pollen. There are over 3000 greenish-white flowers in male panicles, each with 5-7 anthers and a non-functional ovary. Male flowers have yellow nectaries and 5-7 stamens. There are about 500 greenish-yellow flowers in each hermaphroditic panicle. Each flower has six anthers, usually a bi-lobed stigma, and one ovule in each of its two sections (locules). The flowers are receptive for about one day but may persist if pollinators are excluded.

In Malaysia, rambutan flowers from March to July and again between July and November, usually in response to rain following a dry period. Flowering periods differ for other localities. Most, but not all, flowers open early in the day. Up to 100 flowers in each female panicle may be open each day during peak bloom. Initial fruit set may approach 25% but a high level of abortion contributes to a much lower level of production at harvest (1 to 3%). The fruit matures 15-18 weeks after flowering.

Both male and female flowers are faintly sweet scented and have functional nectaries at the ovary base. Female flowers produce 2-3 times more nectar than male flowers. Nectar sugar concentration ranges between 18-47% and is similar between the flower types. Rambutan is an important nectar source for bees in Malaysia.

Cross-pollination is a necessity because pollen is absent in most functionally female flowers. Although apomixis may occur in some cultivars, research has shown that rambutan, like lychee, is dependent upon insects for pollination. In Malaysia, where only about one percent of the female flowers set fruit, research revealed that no fruit is set on bagged flowers while hand pollination resulted in 13 percent fruit set. These studies further suggest that pollinators may maintain a fidelity to either male or hermaphroditic flowers (trees), thus limiting pollination and fruit set under natural conditions where crossing between male and female flowers is required.

Cultivars

There are well over 200 cultivars developed from selected clones available throughout tropical Asia. Most of the cultivars are also selected for compact growth reaching a height of only 3-5 m for easier harvesting.

Some seedling trees in Nicaragua are nearly 50% hermaphrodite. The seeds were given by representatives from a World Relief / European Union joint team in 2001 to organizations such as APAC (Ascociación Pueblos en Acción Comunitaria) to distribute the seeds to more than 100 farmers throughout Nicaragua. Some of Nicaragua's farmers in 2005-2006 saw the first production of Rambutan from their trees. Commercial production of the fruit for domestic use is sought in the country, as it is finding favor among Nicaraguans, but it will be several years before growing practices and distribution of the fruits are perfected. Other than seedling trees, the only known commercial cultivars in Nicaragua are R134, R162 and a Yellow Rambutan that lost its name when it was smuggled from Honduras in 2004-2005 (Frankie, J. A., Winrock International).

Pollination

Aromatic rambutan flowers are highly attractive to many insects, especially bees. Those commonly found visiting rambutan flowers include bees (Apis spp. and Trigona spp.), butterflies, and flies (Eristalis sp. and Lucilia sp.). Apis cerana colonies foraging on rambutan flowers produce large quantities of honey. Bees foraging for nectar routinely contact the stigmata of female flowers and gather significant quantities of the sticky pollen from male blossoms. Little pollen has been seen on bees foraging female flowers. Although male flowers open at 6 am, foraging by A. cerana is most intense between 8 am and 11 am, tapering off rather abruptly thereafter. In Thailand, A. cerana is the preferred species for small scale pollination of rambutan.







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