Salacca zalacca (PROSEA)
Salacca zalacca (Gaertner) Voss
- Protologue: Vilmorin's Blumengärtnerei ed. 3, 1: 1152 (1895).
- Family: Palmae
- Chromosome number: 2n= 28
- Salacca edulis Reinw. (1825).
- Salak (palm), snake fruit (En).
- Indonesia and Malaysia: salak
- Burma: yingan
- Thailand: sala.
Origin and geographic distribution
Salak grows wild in south-western Java and southern Sumatra, but its precise place of origin is not known. It is cultivated in Thailand, throughout Malaysia and Indonesia as far as the Moluccas, and has been introduced into New Guinea, the Philippines, Queensland (Australia), Ponape Island (Caroline Archipelago) and reportedly occurs on the Fiji Islands.
Salak palm is cultivated for its fruits, the bulk of which are consumed fresh when fully ripe. In Indonesia the fruits are also candied ("manisan salak"), pickled ("asinan salak") and fresh unripe ones may be used in "rujak", a spicy salad of unripe fruit. Mature fruits may be canned. The seed kernels of the young fruits of the Javanese "Pondoh" form are edible. A closely-planted row of palms forms an impregnable hedge and the very spiny leaves are also cut to construct fences; the leaflets are used for thatching. The bark of the petioles may be used for matting.
Production and international trade
Data on production and cultivated area are scarce and variable. Production figures for Java range from 7000-50 000 t in the 1980s, about half the crop being produced in western Java. In Indonesia, where salak is exclusively a smallholder crop, only a tiny fraction of total production is exported, fresh, canned or candied, mainly to or through Singapore.
The flesh is exceptionally firm and crisp for a tropical fruit. It is quite sweet when fully ripe, but unripe fruit is sour and astringent due to the presence of a little tannic acid. When the fruit is ripe, a layer of granular-looking flesh adheres to the kernel, a state known as "masir" in Indonesia; whereas each kernel of an immature fruit lies free in a cavity in the flesh. The unique taste is somewhat comparable to a combination of apple, pineapple and banana.
- A relatively small, usually dioecious, very spiny, creeping and tillering palm, growing in compact clumps formed by successive branching at the base. Roots not extending to great depth. Stem a mostly subterranean stolon with only its terminal leafbearing part more upright, reaching a length of several metres and 10-15 cm in diameter, often branching; new roots growing out of the stem immediately under the crown of leaves; internodes very congested, leaf traces inserted almost horizontally.
- Leaves pinnate, 3-7 m long; leaf-sheaths, petioles and leaflets armed with numerous, long, thin, grey to blackish spines; leaflets 20-70 cm × 2-7.5 cm.
- Inflorescence an axillary compound spadix, stalked, at first enclosed by spathes; male inflorescence 50-100 cm long, consisting of 4-12 spadices, each 7-15 cm × 0.7-2 cm, female one 20-30 cm long, composed of 1-3 spadices, 7-10 cm long.
- Flowers in pairs in axils of scales; staminate flowers with reddish, tubular corolla and 6 stamens borne on the corolla throat and a minute pistillode; pistillate ones with tubular corolla, yellow-green outside and dark red inside, a trilocular ovary with short trifid, red style and 6 staminodes borne on the corolla throat.
- Fruit a globose to ellipsoid drupe, 15-40 per spadix, ca. 5-7 cm × 5 cm, tapering towards base and rounded at top; epicarp (skin) comprised of numerous yellow to brown, united, imbricate scales, each scale ending in a fragile prickle.
- Seeds usually 3 per fruit, with 2-8 mm thick, fleshy, cream-coloured sarcotesta and a smooth, stony inner part, 23-29 mm × 15-27 mm, which is blackish-brown and trigonous with 2 flat surfaces and a curved one; endosperm homogeneous and white.
Growth and development
Seed kernels taken directly from the fresh fruit germinate readily in less than a week under moist, shady conditions, even on top of the soil. After removal from the fruit the kernels quickly lose viability in storage, probably because the embryo dries out irreversibly: 55% germination was found after 1 week, 0% after 2 weeks. Germination becomes visible when the cylindrical embryo-containing plug is extruded through the germpore at the kernel's apex. A radicle soon emerges from the tip of the plug and the shoot, a main root and several secondary roots emerge from the sides of this plug. About 60-90 days after sowing the first complete leaf, bifid and some 20-30 cm long, is fully expanded, the seedling still being firmly attached to the kernel. The palm starts flowering three to four years after sowing. Pollination is probably by insects, notably a weevil, tentatively identified as Nodocnemis sp. In Queensland, Australia, pollen is carried from palm to palm by curculionid beetles, large numbers of which visit the flowers. The fruits are mature five to seven months after pollination. In principle, the palm flowers and fruits continuously, but most reports indicate harvest peaks around May and - a major one - around December in Indonesia. This implies a top fruit set in June-July, i.e. the first half of the dry season, following the small harvest peak. The palm can be productive for 50 years or more.
Other botanical information
The salak palm grown in northern Sumatra is ascribed to a distinct species, S. sumatrana Becc. The species S. zalacca, which is cultivated elsewhere in Indonesia, is subdivided into two botanic varieties, var. zalacca from Java and var. amboinensis (Becc.) Mogea from Bali and Ambon. In Indonesia at least 20 intraspecific taxa are distinguished according to place of origin and cultivation, e.g. "Condet", "Pondoh", "Bali", "Suwaru"; these may obtain cultivar status as vegetative propagation gains importance. "Bali" is monoecious; the inflorescences bear both hermaphrodite and staminate flowers; the latter produce functional pollen.
Salak thrives under humid tropical lowland conditions. In the main production centres, average annual rainfall is between 1700 and 3100 mm. Because of its superficial root system, the palm requires a high water table, rain or irrigation during most of the year, but it does not stand flooding. Fruit yield and quality in Java diminish above 500 m altitude. Salak is usually grown under shade. Soil types in production centres include podzolic soils and regosol.
Propagation and planting
Seeds are sown directly in the field (2-5 seeds together in 5 cm deep holes) or in nursery beds. The seedlings are planted out in the field during the rainy season when they are a few months old. Vegetative propagation is less common. It involves removing rooted lateral offshoots from older plants, or, with higher rates of success, layering or air layering 3-6-month-old shoots. Young palms require heavy shade which may be reduced after about one year. Salak palm, especially when young, is intercropped in mixed gardens with banana, mango and Artocarpus spp. Male trees are maintained at a rate of 2-20%, evenly dispersed among the female trees or as guard rows around them. Plant distances encountered vary from less than 2 m to 6 m.
Weeding is necessary before the leaf canopy is closed. Basal suckers are usually cut out in order not to lower the fruit yield of the mother palm. Lateral shoots may be spared to grow into fruiting stems or to be used for vegetative propagation. If the erect portion of the stem grows too tall, the palm loses vitality, probably because the young roots formed immediately under the crown cannot reach the soil. To rejuvenate the palm, farmers usually push the stem back into the ground and earth it up. Ageing plant parts are cut off and either buried between the palms or burned, the ash being used as fertilizer. Adequate use of fertilizers may make shading in salak cultivation less necessary than is generally assumed. Farmyard manure as well as urea, triple superphosphate and potassium muriate are reported to have been tried by farmers. Fruit taste may be negatively or positively influenced by fertilizing. Exclusive use of urea is said to produce large but perishable fruits, and also to cause strong vegetative growth which increases the risk of the palms toppling over. Irrigation is necessary during the dry season if the superficial root system of the palm cannot reach the water table.
In many places hand pollination is practised by tapping a flowering male spike held above a female inflorescence. Fruit bunches are usually thinned to provide space for the remaining fruits to grow larger. The supporting leaf of a bunch is sometimes pruned to ensure undisturbed development of the bunch. In some places the bunch is tied up because it is believed that if it develops hanging down, the taste is less good.
Diseases and pests
In Java a fungus disease provisionally identified as Mycena sp. sometimes occurs, especially during the wet season; white mycelium overgrows the bunch and fruits finally rot. The fungus Pestalotia sp. causes black spots on the leaves; growers attempt to check the disease by cutting and burning affected leaves. Pink disease (Corticium salmonicolor) can cause serious loss of fruit and plants. Control depends largely on reducing the infection pressure by early removal of diseased parts; proper ventilation to lower the humidity in the crop is also important.
Larvae of the weevils Omotemnus miniatocrinitus and O. serrirostris which tunnel into the top of the palm, and of the weevil Nodocnemis sp. which bore into the young fruit bunches, are occasionally harmful. On the other hand, the latter insect is a pollinator. Growers control weevils by poking a piece of wire into the holes. There are reports of an unidentified grub feeding on the roots and devastating entire stands of salak orchards in central Java. Pests reported to feed on salak palm without indication of harmfulness include the monophagous beetle Calispa elegans , the polyphagous caterpillar Ploneta diducta , a leaf roller (Hidari sp.), the scale insect Ischnaspis longirostris and a bug (Tolumnia sp.), as well as several rodents such as rat and luwak (Paradoxurus hermaphroditus).
Harvesting takes place at a fruit age of 5-7 months, or somewhat earlier if rains cause fruits approaching maturity to swell too quickly and burst. Fruits are harvested by cutting the bunches with a reaping hook. The seasonality generally observed in fruiting (for example, in Java) is probably caused by the negative influence of excessive drought or excessive rain on flowering and/or pollination. Where palms have access to water throughout the year (through a high water table or irrigation), fruiting is indeed more evenly spread over the year.
The scarce data available suggest that annual yields vary from 5-15 t/ha.
Handling after harvest
Fruits picked when not too ripe will stand 2 or 3 days of transportation, for example in bamboo baskets. In a hot and humid climate, fresh fruit will not last much longer than a week after picking. The slightest injury accelerates spoiling. There is a need to establish maturity indices for harvesting and techniques to control fruit rot in order to extend shelf life. Farmers or retailers often sort salaks into size classes before selling them.
Cultivars varying in fruit size and colour have been selected from the wild forms. Seedless and monoecious forms occur, especially in Bali. The Salacca Breeding Laboratory, a private institute in Bogor, has collected virtually all salak cultivars and species in the genus. They include rare species and potentially ornamental ones, namely S. dransfieldiana J.P. Mogea, S. magnifica J.P. Mogea, S. minuta J.P. Mogea, S. multiflora J.P. Mogea and S. ramosiana J.P. Mogea.
Both intraspecific and interspecific breeding has been taken up by the Bogor laboratory. In Chanthaburi, Thailand, the Department of Agriculture started a breeding programme in 1985 to improve S. wallichiana Mart., including crosses with S. zalacca.
Salak cultivation is very likely to expand in Java, especially around the big cities where salak is constantly in demand and fetches high prices. Once the first unproductive years are overcome, a salak garden may be quite profitable because relatively few inputs are needed to keep it in production. Prospects for exports are limited because of the perishability of the fresh fruits, and trade in general would benefit greatly if shelf life could be extended. There seems to be great scope for an increase in productivity. Improvement of vegetative propagation techniques would facilitate the dispersal of selected high quality cultivars.
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- Miller, R.H., 1977. Fruit, germination and developmental morphology of Salacca edulis palm seedling. Phytomorphology (India) 27(3): 282-296.
- Mogea, J.P., 1982. Salacca zalacca, the correct name for the salak palm. Principes 26(2): 70-72.
- Moncur, M.W., 1988. Floral development of tropical and subtropical fruit and nut species. CSIRO, National Resources Series No 8, Melbourne. pp. 127-130.
- Tjahjadi, N., 1989. Bertanam salak [Salak growing]. Kanisius, Yogyakarta, Indonesia. 39 pp.
- Yoe Edy, 1986. Melacak jenis-jenis salak yang paling enak + Bertanam salak [Overview of the best salak types + Salak growing]. Trubus (Indonesia) 17 (197): 7-12.
D.L. Schuiling & J.P. Mogea