Salacca wallichiana (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Salacca wallichiana C. Martius

Protologue: Historia naturalis palmarum 3: 201, t. 118, 119 (1838).

Family: Palmae

Chromosome number: 2n= unknown

Synonyms

• Zalacca rumphii Wallich ex Blume (1843).

Vernacular names

• Rakum palm, sala (En)
• Malaysia: kumbar, salak kumbar, salak rengam
• Burma: yengam
• Thailand: rakum (for the wild forms), sala (for the cultivated forms).

Origin and geographic distribution

The origin of the rakum palm is not clear, but it is found in the lowlands of southern Burma, south of 19°N latitude, in the coastal provinces from Bangkok eastwards in Thailand and in Peninsular Malaysia. Both wild (in the forest) and cultivated the palm is most abundantly found in the hot and humid areas of Thailand which lie between 10-13°N latitudes. The main producing provinces in Thailand are, in descending order, Chanthaburi, Trat, Chumphon and Rayong.

Uses

The rakum palm is grown for the edible sarcotesta of the fruit. The sour unripe fruit can be a substitute for lime in cooking, whereas the ripe fruit is sweet and consumed raw. The wild form is grown as a fruit-bearing fence. Wild clumps in the forest not only produce food, but are also a major source of cork, thatch and other construction materials in rural areas.

Production and international trade

S. wallichiana is popular only in Thailand. The country's production was estimated at 500-1000 t in 1988, the bulk being the inferior type of fruit gathered from the forest. The fruit is sold and consumed locally, mainly fresh. The area planted with the inferior rakum forms has never been recorded. There were estimated to be 6000-10 000 palms of the sala type in the country in 1989. The superior quality fruit of the sala type could fetch in 1989 a farmgate price as high as US$ 5 per kg. This means that good growers could obtain US$ 100-130 per palm per year.

Properties

The palms differ greatly in fruit characters, such as the colour of the pulp (which ranges from pale yellow via pink to dark brown) and texture and thickness of the edible portion. Flesh to seed ratios vary from 10:1 to 2:1 by weight.

Description

• A dioecious, creeping and tillering palm, growing in clumps with very spiny leaves. In palms over 100 years old, the creeping stem can reach 3-4 m, with an erect terminal leaf-bearing part 1 m tall and with many adventitious roots, most abundant towards the tip. Roots can reach a length of 2 m but do not extend to a great depth.
• Leaves 3-7 m long, pinnate; spines flat, linear-triangular, almost perpendicular to the leaf-sheaths, some pointing downwards; leaflets 60-75 cm × 6-8 cm.
• Male inflorescences about 1 m long, branching into many reddish spadices; flowers with 3 sepals, 3 petals and 5 stamens; anthers with functional yellowish pollen; female inflorescences 1-2 m long, with 3-8 reddish spadices, each with staminate and hermaphrodite flowers in 1:1 ratio, both without functional pollen.
• Staminate flowers with a reddish, tubular corolla and 5 staminodes borne on the corolla throat; hermaphrodite flowers with 3 pink sepals, fused at the base, ovary trilocular, hairy, with a short, trifid dark red stigma, staminodes 5-6, borne on the corolla throat.
• Fruit a drupe, occurring in dense heads, obovoid, 2.5 cm long, the skin (epicarp) consisting of orange-brown scales with reflexed brittle points; endocarp not differentiated.
• Seeds 1-3, covered with a fleshy sarcotesta.

Growth and development

Fresh seeds have a high germination rate (90%) and emerge in less than 10 days, but the rate decreases after storage. After about 5-6 years the palm starts flowering. Pollination is mainly by insects. The fruit ripens 7-9 months after bloom. Inflorescences emerge throughout the year but nearly all fruit is harvested between June and August in Thailand. This indicates a heavy fruit set in November and December, i.e. early in the dry season. The skin of 10-16-week-old fruitlets is brown, turning darker to almost black at 17-23 weeks, gradually changing to orange when the fruit ripens. The flesh of 10-19-week-old fruits is off-white and turns to light yellow when the fruits are 20-22 weeks old; as the fruit grows it gradually assumes a more yellow-orange colour. The stones in 10-19-week-old fruits are white and contain a jelly-like substance. The colour changes to yellow at 20-23 weeks of age and to brown thereafter while the contents harden.

Other botanical information

Selection in the rakum palms has given rise to the sala group of cultivars of superior quality. Among them are "Sala Mor", "Sala Sane", "Sala Noenwong" and the spineless "Sakum". "Sala Mor" and "Sala Sane" originated from rakum grown near Bangkok. The rapid expansion of the city in the late 1970s threatened these cultivars with extinction. Some 2000 palms were moved to Phetchabun province, 300 km north of Bangkok. "Sala Noenwong" originated in Chanthaburi province from a seedling of "Sala Mor" about 120 years ago. "Sakum" has its origin somewhere in Chanthaburi or Trat provinces.

The sala cultivars do not grow as large as the rakum types, e.g. leaves of "Sala Noenwong" reach only 3 m. This cultivar is further characterized by abundant suckering, long terminal leaflets and the light-brown colour of the fruit, which has an obtuse tip. "Sala Mor" has leaves of about 4 m length with short terminal leaflets and has greyish-orange fruit with a beaked tip. The spineless "Sakum" has leaves nearly as long (5 m) as the rakum types and the fruit quality is not much better: there is only a little flesh covering the large stones. Both "Sakum" and rakum fruits are greyish-orange with a short, pointed tip.

Ecology

S. wallichiana is at home in the hot lowlands. In the main rakum production centre, the annual rainfall is 2500-3000 mm with 5-6 dry months. Dry weather is needed for good fruit set; spadices emerging in the rainy season tend to rot and the viability of the pollen is poor. The temperature range required is 22-32°C; lower temperatures reduce flowering.

The palm thrives in soils ranging from sandy loam to heavy clay. On low-lying wetlands it grows better than most fruit trees. It can stand drought very well, but in the dry season irrigation is needed for a good yield. In its natural habitat and in mixed orchards rakum is commonly found under shade. In commercial orchards the palms can be grown successfully without shade, provided they are irrigated.

Propagation and planting

Fresh seed germinates readily and propagation from seed is easy. However, vegetative propagation is recommended. Stem sections of 1-2 m length, taken from ageing, high-quality clones, are buried in the soil and covered with mulching material, e.g. rice straw. The soil is kept moist to force viable buds on the cuttings to sprout. The plantlets are separated from the stem and nursed in polythene bags for a year before planting out in the field at the beginning of the rainy season. Vegetative propagation by separating rooted suckers from the mother palms is less common. At Chanthaburi Horticulture Research Centre work is in progress to propagate the palm through tissue culture.

The number of palms per ha varies from 200 to 400, depending on the cultivar. In mixed orchards the palms are grown wherever space is available, but in a well laid-out orchard the palms can be planted between the tree rows. Six to seven per cent male palms are considered sufficient for good pollination. Xenia effects are quite noticeable in S. wallichiana, so it is important to choose a compatible male strain.

Husbandry

In a pure stand weeding is one of the main tasks during the first 1-3 years. A rotary grass cutter or herbicides (Glyphosate) are commonly used to control weeds. In mixed smallholder orchards and home gardens, shading reduces weed problems and hand weeding is practised. In young non-bearing orchards, removing suckers is the most unpleasant chore, but a must. One or two stems per clump are sufficient for good yield. Dense clumps yield poorly and are difficult to harvest. Leaf pruning is not advisable, but may be necessary to facilitate orchard operations. Irrigation in the dry season, together with application of manure and 3-4 kg per clump of a complete fertilizer with a low N-content improves yield and fruit quality considerably. Hand pollination can also raise yields substantially.

Diseases and pests

Some diseases and pests have been observed, but as the crop is relatively new and minor, the study of the causal organisms and their control has not yet received much attention. Fruit rot sometimes occurs, especially during the rainy season. In rare instances weevils attack the growing point of the palm. A fruit-eating worm is also found. Rodents cause serious loss of fruit. Farmers control the damage by covering the large infructescence with chicken wire.

Harvesting

In Thailand June and July are the peak harvest months for rakum; the harvest tails off towards November. For sweet fruit taste rakum should be harvested 28 weeks after anthesis (hand pollination). At this age the sugar content is 13-14°Brix. Fruits over 30 weeks old develop an unpleasant flavour. Fruits which are used for cooking can be harvested after 25 weeks. For the superior sala cultivars harvesting time is 36 weeks and not later than 38 weeks after pollination. At harvest each fruit cluster or the entire infructescence is cut with a hooked knife or pruning shears on long handles.

Yield

The average yield of S. wallichiana varies from 6 to 12 t/ha per year depending on cultivars.

Handling after harvest

The infructescence stalk with several clusters of fruits may be stored and sold, or the clusters are separated and handled as such. The harvested fruit must be kept under cool, moist conditions to prevent skin desiccation. The post-harvest technology has not yet been developed. Loose packing would be the best way to handle the fruit. There is no commercial processing of rakum so far.

Genetic resources

A germplasm collection is being assembled at the Chanthaburi Horticulture Research Centre. It is expected that by the end of 1991 more than 10 accessions of S. wallichiana will be growing at the centre.

Breeding

Breeding work began in 1985. The objectives are to produce palms with the following characteristics: spineless, sparse suckering, thick fruit flesh, sweet and aromatic taste, and high yield.

The following crosses were made in 1985: salak × "Sakum", sala × "Sakum", sala × rakum, "Sakum" × sala and sala selfed. The hybrid seedlings show variable characteristics. Suckering and shoot emergence varied considerably. The cross of sala × "Sakum" yielded almost 50% spineless seedlings. Fruits of salak × "Sakum" were 100% seedless but very astringent. The other seedlings are expected to bear fruit in 1991.

Prospects

Growing sala cultivars is so profitable that a rapid expansion of production is to be expected. Although this will bring the price down, there is still much room for agronomic improvement which will raise yield levels and/or reduce the cost price. However, a concerted research effort is required to make the dense, spiny palms more manageable and to develop post-harvest techniques which will extend the market for this special fruit. There may also be prospects for the crop elsewhere in South-East Asia under similar ecological conditions.

Literature

• Mogea, J.P., 1981. Notes on Salacca wallichiana. Principes 25(3): 120-123.
• Moncur, M.W., 1988. Floral development of tropical and subtropical fruit and nut species. CSIRO, Melbourne. pp. 127-130.
• Salakpet, S. & Polprasid, P., 1990. The flower of the Salacca wallichiana palm. Kasikorn 63: 1 (in Thai).

Authors

Pairoj Polprasid