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Zee, F.T. 1993. Rambutan and pili nuts: Potential crops for Hawaii. p. 461-465. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Rambutan and Pili Nuts: Potential Crops for Hawaii

Francis T. Zee

  1. RAMBUTAN
    1. Origin
    2. Morphology
    3. Culture
    4. Postharvest Diseases
    5. Insects
    6. Wild Nephelium species
    7. Future Prospects
  2. PILI NUTS
    1. Origin
    2. Morphology
    3. Culture
    4. Future Prospects
  3. REFERENCES
Rambutan and pili nuts are important crops of commerce in Southeast Asia but are relatively unknown in the United States. The lack of a postharvest quarantine treatment for fruit fly infestation in rambutan, and the inconsistent production and lack of quality control in pili nuts are some of the causes hindering the expansion of these crops. With the decline of the sugar industry and the diversification of its agricultural industries, Hawaii could become a potential production and launching site for these crops into the mainland United States.

RAMBUTAN

Rambutan fruits are consumed fresh, canned, or preserved. The colorful fruits of rambutan are frequently used in displays with flower and fruit arrangements.

Origin

Nephelium lappaceum Linn., Sapindaceae, is native to Malaysia and Indonesia. Rambutan, a tropical relative of the lychee (Litchi chinensis Sonn.), is grown in Southeast Asia, Australia, South America, and Africa, but only exported from Malaysia and Thailand (Laksmi et al. 1987).

Morphology

The word rambutan is derived from the Malay word "hair," which describes the numerous, characterizing, long, soft, red or red and green colored spine-like protuberances (spinterns) on the surface of the fruit. The pericarp of this attractive oval-shaped fruit can be red, orange, pink, or yellow in color and is removable by a twist of the hands. The edible, pearlish white, juicy, crispy, sweet and subacid flavored flesh (sarcotesta) conceals a single seed with a thin, fibrous seed coat (testa).

Rambutan is an evergreen tree about 10 to 12 m tall, has pinnately compound leaves without the presence of an end-leaflet. On the lower surface of each leaflet are the domatia, small crater-like hills located in the axils between the mid and secondary veins. The function of the domatia is unknown (Van Welzen et al. 1988).

Rambutan has perfect flowers, however, they are functionally pistillate or staminate. Most commercial cultivars behave hermaphroditically and are self fertile, with 0.05 to 0.9% of the functional females possessing functional stamens. Insect pollination is needed. Flowers are produced on matured terminal or sub-branches in panicles; they are small, greenish white in color and in large numbers (1,200 to 1,700 flowers per panicle). Depending on the cultivar, flowering may spread over a period of 23 to 38 days, with an average of 3.4% setting fruit. Fruits may be produced in large bunches, with 40 to 60 fruits per panicle, but most often only 12 to 13 per panicle are retained to maturity. Final fruit set is usually between 0.7 to 1.45%. Time required from fruit set to harvest is about 107 to 111 days (Van Welzen et al. 1988).

Fruit size ranges from 27 to 80 g. Edible flesh weight, depending on season and cultivar, may range from 28 to 54% of the fruit weight. Total soluble solids can reach 24% (Lye et al. 1987). Economic life of a tree is about 15 to 20 years and may be up to 30 years. Depending on the location, rambutan can produce up to two crops a year (Laksmi et al. 1987).

Culture

Rambutan trees prefer deep, loamy, well drained soil with a high organic content. Optimum temperature range is above 22°C. An absolute temperature of 5° to 6°C will cause defoliation and poor cropping. Trees need to have well distributed rainfall and wind protection.

At the National Clonal Germplasm Repository, USDA/ARS, in Hilo, Hawaii, rambutan seedlings grew best in full sun, protected from wind, in a 1:1:1 medium of soil, macadamia compost, and volcanic cinder, and fertilized with a high potassium (10-2-33 NPK) fertilizer. Young seedlings given a lower potash formulation (16-7-13 NPK) produced severe marginal necrosis of leaves, stunted growth, and die-back of apical growth.

Well grown rootstocks are bud grafted at 8 to 12 months. Dormant buds with well-healed petiole scars from one to two year old branches averaged 80% success between May and October. Rootstocks should be cut back 25 cm above the bud union and all foliage removed at two weeks after budding. This cutback and defoliation promoted bud break of the new graft 14 to 17 days later (Zee and Kaneshiro unpub.).

Rambutan trees exhibit strong apical dominance and have a tendency to produce long, upright growth if not properly managed. Early pruning and training in the field is needed to develop proper branch scaffolds.

Over 187 clones of rambutan are registered in Malaysia and over 25 additional cultivars are known in Indonesia, the Philippines, Thailand, and Singapore (Lye et al. 1987). Some of the most popular and recommended rambutan cultivars are 'Lebakbulus', 'Benjai' and 'Rapiah' (Indonesia); 'Seematjan', 'Seejonja', and 'Maharlika' (Philippines); 'Deli Cheng' and 'Jitlee' (Singapore); 'Gula Batu' (R3), 'Muar Gading' (R156), 'Khaw Tow Bak' (R160), 'Lee Long' (R161), 'Dann Hijau' (R162), R134, and R167 (Malaysia); 'Rongrien', 'Seechompoo', 'Seetong', and 'Namtangruad' (Thailand).

Postharvest Diseases

Most postharvest problems are related to latent infection, injuries incurred during harvesting, and high humidity and temperature during packaging and transport. The major postharvest diseases are caused by Botryodiplodia theobromae, Gliocephalotrichum bulbilium, and Colletotrichum spp. A survey conducted in Bangkok markets identified about 30% of the postharvest diseases caused by Colletotrichum spp., 10% by Gliocephalotrichum bulbilium, and 5% by Botryodiplodia theobromae. Postharvest storage of fruit in the dark, with low temperatures, may discourage fruit rot (Visarathanonth and Ilag 1987).

Insects

Rambutan is host to 118 different species of insects, but only 17 were identified as attacking rambutan fruits. The following pests are listed in the order of importance: Acrocercops cramerella Snell., Phenacaspis sp., Planacoccus citri Risso., Dichocrocis punctiferalis Guen., Dacus dorsalis Hend., Carpophilus dimidatus L., Carpophilus marginelius Mot. (Osman and Chettanachitara 1987). Rambutan infested with Acrocercops cramerella, cacao pod moth, showed no external symptoms, with up to 40% infestation observed in some cultivars and damage generally between 10 to 15%.

Wild Nephelium species

Some native Nephelium species in Malaysia and Indonesia are N. aculeatum, N. maingayi, N. reticulatum, N. compressum Radlk., N. uncinatum Leenh., N. muduseum Leenh., N. laurinum Blume., N. daedaleum Radlk., N. juglandifolium Blume, N. hypoleucum Kurz. (also in Thailand), N. cuspidatum var. eriopetalum, N. cuspidatum var. robustum, N. lappaceum var. lappaceum, N. lappaceum var. pallen, N. lappaceum var. xanthioides, and N. ramboutan ake (Van Welzen et al. 198?). Species in other Southeast Asian countries include N. obovatum L. (Thailand); N. bassacense Pierre (Malaysia and Vietnam); N. chryseum Blume, N. philippinense, and N. xerospermoides R.D.K. (Philippines) (Martin et al. 1987).

Future Prospects

Thailand is the leading producer of rambutan in the Asian region with about 60,000 ha and 430,000 t (1983/84). Production is concentrated in the provinces of Chanthaburi, Rayong, Trad, and Prajineburi in the east and Surattani, Choomporn, Naratiwart, and Nakornsritummarart in the south. Peak harvest season is between May and August (Laksmi et al. 1987). In recent years, many rambutan plantings in the Chanthaburi area have been replaced by durian, Durio zibethinus L., due to overproduction, high postharvest costs (Hiranpradit pers. commun. 1991) and low return--U.S. $0.10/kg for rambutan vs. U.S. $2.00/kg for durian.

In the northern territory of Australia, rambutan plantings have increased to about 20,000 trees. Production is geared for November and December, when the value of the fruit is the highest at between $7 to $16/kg (Lim 1991).

In Hawaii, small plantings of rambutan are coming into production on the islands of Kauai and Hawaii. Average price is between $9 to $13/kg. The current nursery price for a grafted plant is about $45.

Rambutan can become a potential industry in Hawaii. The population of 1.1 million residents and approximately the same number of visitors each year are potential customers of this exotic fruit. Moreover, the west coast of the United States is only six hours away by air for a potentially feasible export market.

A market analysis conducted by the University of Hawaii for exotic tropical fruit in 1990 identified the lack of a postharvest fruit fly disinfestation treatment and the lack of a cultivar testing program as the major obstacles to rambutan production (unpublished); additionally, the high cost of production and the presence of large competitors in Southeast Asia contributes to the risk. To avoid direct competition with large producers in Southeast Asia and poor market price, the production of rambutan in Hawaii should be geared towards the winter months of November to January, which can be achieved through the use of selected cultivars and better understanding of the environmental, cultural, and cultivar interactions.

PILI NUTS

Origin

Canarium ovatum Engl., one of 600 species in the Burseraceae (Neal 1965), is native to the Philippines and is abundant and wild in the southern Luzon part of Visayas and Mindanao. The Philippines is the only country that produces and processes pili nuts commercially. Production centers are located in the Bicol region, provinces of Sorsogon, Albay, and Camarines Sur, southern Tagalog, and eastern Visaya. There is no commercial planting of this crop, fruits are collected from natural stands in the mountains near these provinces. In 1977, the Philippines exported approximately 3.8 t of pili preparation to Guam and Australia (Coronel et al. 1983).

Morphology

Trees of Canarium ovatum are attractive symmetrically shaped evergreens, averaging 20 m tall with resinous wood and resistance to strong wind. C. ovatum is dioecious, with flowers borne on cymose inflorescence at the leaf axils of young shoots. As in papaya and rambutan, functional hermaphrodites exist in pili. Pollination is by insects. Flowering of pili is frequent and fruits ripen through a prolonged period of time. The ovary contains three locules, each with two ovules, most of the time only one ovule develops (Chandler 1958).

Pili fruit is a drupe, 4 to 7 cm long, 2.3 to 3.8 cm in diameter, and weighs 15.7 to 45.7 g. The skin (exocarp) is smooth, thin, shiny, and turns purplish black when the fruit ripens; the pulp (mesocarp) is fibrous, fleshy, and greenish yellow in color, and the hard shell (endocarp) within protects a normally dicotyledonous embryo. The basal end of the shell (endocarp) is pointed and the apical end is more or less blunt; between the seed and the hard shell (endocarp) is a thin, brownish, fibrous seed coat developed from the inner layer of the endocarp. This thin coat usually adheres tightly to the shell and/or the seed. Much of the kernel weight is made up of the cotyledons, which are about 4.1 to 16.6% of the whole fruit; it is composed of approximately 8% carbohydrate, 11.5 to 13.9% protein, and 70% fat (Coronel and Zuno 1980a,b). Kernels from some trees may be bitter, fibrous or have a turpentine odor.

Culture

Pili is a tropical tree preferring deep, fertile, well drained soil, warm temperatures, and well distributed rainfall. It can not tolerate the slightest frost or low temperature (Chandler 1958). Refrigeration of seeds at 4° to 13°C resulted in loss of viability after 5 days. Seed germination is highly recalcitrant, reduced from 98 to 19% after 12 weeks of storage at room temperature; seeds stored for more than 137 days did not germinate (Coronel et al. 1983).

Asexual propagations using marcotting, budding, and grafting were too inconsistent to be used in commercial production. Young shoots of pili were believed to have functional internal phloems, which rendered bark ringing ineffective as a way of building up carbohydrate levels in the wood. Success in marcottage may be cultivar dependent. Production standards for a mature pili tree is between 100 to 150 kg of in-shell nut with the harvest season from May to October and peaking between June and August. There are high variations in kernel qualities and production between seedling trees.

Most pili kernels tend to stick to the shell when fresh, but come off easily after being dried to 3 to 5% moisture (30°C for 27 to 28 h). Shell nuts, with a moisture content of 2.5 to 4.6%, can be stored in the shade for one year without deterioration of quality (Coronel et al. 1983).

The most important product from pili is the kernel. When raw, it resembles the flavor of roasted pumpkin seed, and when roasted, its mild, nutty flavor and tender-crispy texture is superior to that of the almond. Pili kernel is also used in chocolate, ice cream, and baked goods (Rosengarten 1984). The largest buyers of pili nuts are in Hong Kong and Taiwan, the kernel is one of the major ingredients in one type of the famous Chinese festive desserts known as the "moon cake."

Nutritionally, the kernel is high in calcium, phosphorous, and potassium, and rich in fats and protein. It yields a light yellowish oil, mainly of glycerides of oleic (44.4 to 59.6%) and palmitic acids (32.6 to 38.2%) (Mohr and Wichmann 1987; Coronel et al. 1983).

The young shoots and the fruit pulp are edible. The shoots are used in salads, and the pulp is eaten after it is boiled and seasoned. Boiled pili pulp resembles the sweet potato in texture, it is oily (about 12%) and is considered to have food value similar to the avocado. Pulp oil can be extracted and used for cooking or as a substitute for cotton seed oil in the manufacture of soap and edible products. The stony shells are excellent as fuel or as porous, inert growth medium for orchids and antherium.

Future Prospects

According to Richard A. Hamilton, University of Hawaii at Manoa (macadamia breeder), the current status of the pili is equivalent to that of the macadamia some 30 years ago. It has great potential to develop into a major industry. The immediate concern in pili production is the difficulty of propagation. The lack of an effective clonal propagation method not only hampers the collection of superior germplasm but also makes it almost impossible to conduct feasibility trials of this crop. Few elite pili trees, such as 'Red', 'Albay', and 'Katutubo' were selected in the Philippines (Coronel et al. 1983). The National Clonal Germplasm Repository at Hilo, USDA/ARS, has initiated studies in in vitro and vegetative propagation for the multiplication and long-term preservation of pili.

A recently released pili cultivar in Hawaii may further stimulate the interest in this crop. This new selection, known as 'Poamoho', was released by R.A. Hamilton. Besides the desirable production and quality attributes, its kernels separate easily from the hard shell without the need of prior drying (30deg.C for 27 to 28 h). This is an important cost saving feature for processing.

REFERENCES

Rambutan

Pili

Last update April 24, 1997 aw