1468

2: Edible fruits and nuts

Anacardium occidentale L.

Sp. Pl. 1: 383 (1753).

ANACARDIACEAE

2n = 42

Cashew (En). Cajou, anacardier (Fr). Indonesia: jambu monyet, jambu mede (Java). Malaysia: gajus, jambu monyet. Philippines: kasoy, balubad (Tagalog), balogo (Ilokano). Burma: thiho thayet si. Cambodia: svaay chantii. Thailand: mamuang himmaphan (central), yaruang (Pattani), mamuang letlor (Ranong). Vietnam: dào lôn hôt (north), cây diêù (south).

From its origin in north-eastern Brazil cashew spread into South and Central America. The Portuguese introduced it to India and East Africa. It spread to Sri Lanka, Malaysia and Indonesia. The Spaniards took it to the Philippines in the 17th Century. At present cashew is cultivated in many tropical countries; the main producers are Brazil, India, Mozambique and Tanzania.

Cashew is cultivated for the nuts. Botanically the nut is the fruit; the cashew apple is the swollen, fleshy fruit stalk. The seed kernels are extracted by shelling the roasted nuts. In production areas cashew serves as food. Elsewhere it forms a delicacy. The nut contains a high quality oil; the cake remaining after extraction serves as animal feed.
In Brazil, Mozambique and Indonesia the cashew apple is also important; it is eaten fresh or mixed in fruit salads, and a drink is prepared from the juice. Cashew wine (slightly fermented juice) is enjoyed at harvest time and can be distilled to produce strong alcoholic drinks.
By-products are seed-coats and shells. Seed-coats are used as poultry feed. An oil, cashew nut shell liquid (CNSL), is produced in large cells of the pericarp; it has industrial applications and is used as a preservative to treat, for instance, wooden structures and fishing nets. The residue of the shell is often used as fuel in the CNSL extraction plants.
Cashew wood is used as fuel or as a low-quality timber. The bark contains tannins. Wounded trees exude a gum which is used as an adhesive (woodwork panels, plywood, bookbinding), partly because it has insecticidal properties. Young leaves and shoots are eaten raw or cooked. All parts of the tree are also used in traditional medicine, mainly to treat ailments of the skin, as mouth washes and as purgatives.

Early in the 19th Century cashew became a commercial commodity, mainly channelled through India, where most East African nuts were processed. Indian export of cashew kernels rose to 20 000 t in 1940, equivalent to 100 000 t of raw nuts, of which around a third was imported from East Africa. From 1960 onwards, processing plants were set up in East Africa, following expansion of cashew growing. World production of raw nuts rose from 125 000 t in 1955 to 365 000 t in 1986, major contributions being made by East Africa (25%), Brazil (33%) and India (38%).
Cashew is a well-known backyard tree in South-East Asia. Only recently has it received attention as a crop. In 1981 Indonesia had 138 463 ha cashew (increasing to 207 300 ha in 1985), and the Philippines 3790 ha. For 1988 Thailand reported an area of 56 400 ha, half of which was in production, Malaysia 2780 ha, largely along the east coast of the Peninsula. Indonesia, by far the largest producer in the region, grows a sizeable proportion of the crop in plantations. In Burma, nucleus plantations covering 2800 ha are planned in the south, a large expansion in relation to the national acreage of 1040 ha (producing 500 t) in 1985.

The raw cashew nut contains the seed and a papery seed- coat; these account for respectively 20—30% and 2—3% of the raw nut weight; the remaining 70—75% is the nutshell. Raw nuts weigh 4—8 g but may reach 15 g. The seed contains 21% protein and 35—45% oil. The oil contains 60—74% oleic acid and 20—8% linoleic acid.
CNSL contains 90% anacardic acid and 10% cardol. Some persons are allergic to cardol; CNSL should not contaminate the kernels during processing! The juice of the cashew apple is rich in riboflavin (vitamin B2), ascorbic acid (vitamin C) and calcium.

Evergreen tree, up to 12 m tall, with a wide dome-shaped crown. The foliage forms a thin peripheral canopy, studded with the protruding inflorescences. Taproot up to 3 m deep, persistent; lateral roots spreading beyond the crown projection, with sinker roots to a depth of 6 m. Stem branching, main trunk 0.5—1.5 m long. Leaves alternate, obovate to obovate-oblong, up to 20 cm x 15 cm, leathery, red-brown when young, later shining dark green, glabrous, with prominent midrib and veins; petiole 1—2 cm long, swollen at base, flattened on upper surface. Inflorescence a lax terminal, drooping, many-flowered panicle, up to 25 cm long with fragrant male and hermaphrodite flowers; sepals 5, lanceolate to oblong-ovate, 4—15 mm x 1—2 mm, pubescent; petals 5, linear-lanceolate, 7—13 mm x 1—1.5 mm, reflexed, whitish at anthesis, later turning pinkish-red; stamens 10; male flowers with 7—9 stamens of 4 mm and 1—3 stamens of 6—10 mm length; hermaphrodite flowers usually with 9 short and 1 long stamen; long stamens produce viable pollen; style simple, 12 mm long, exserted from corolla to same length as long stamens. Fruit a kidney-shaped nut, about 3 cm x 1.2 cm, with grey-brown, resinous hard pericarp; pedicel much enlarged and swollen, forming the fruit-like cashew apple, pear-shaped, 10—20 cm x 4—8 cm, shiny, red to yellow, soft and juicy. Seed kidney-shaped with reddish-brown testa, two large white cotyledons and a small embryo. The kernel remaining after removal of the testa is the cashew nut of commerce.

The seedling emerges three weeks after sowing. The radicle ruptures the pericarp at its stalk end and as the radicle grows downwards the hypocotyl and the cotyledons emerge. The root grows fast, maintaining a depth of 1.5 times the height of the shoot. The seedling stem soon branches and pruning may be needed to attain a trunk height of 0.5—1.5 m. The juvenile phase lasts only 3 or 4 years.
The lower limbs reach a length of 6 m or more and may be torn off during storms. The shoots grow in flushes. A major flush follows the onset of the rainy season and on many shoots an inflorescence appears within 3—4 months. Anthesis of the first flower occurs about 5 weeks later. Further flowers (up to 1100!) open over the next 5—6 weeks. The flowers are pollinated by insects (honey bees, flies, possibly also ants). The stigma is receptive for one day, starting a few hours before anther dehiscence. Both cross- and self-pollination occur, but there is evidence of some self-incompatibility. The percentage of hermaphrodite flowers may reach 12—16%. The fruit takes 2 months to develop. Later in the wet season flushing becomes less regular, usually from lateral buds of the earlier flush. When two distinct dry seasons occur the trees may go through two flowering periods. Out-of-season flowering is fairly common.

Individual trees may consistently produce up to four times the average yield per tree. Such outstanding trees have been selected for vegetative propagation, but as yet there is little information on the clones. Distinct cultivars are beginning to emerge. In Kenya budded material from selection 'A 81' maintained its superior yielding ability. Of 16 clones selected in Malaysia 'C 11' yields 30% more than 'C 21' and is 2—6 times better than the other clones. In Thailand selections 'SK 60-1', 'SK 60-2', 'SK-A' and 'Sirichai 25' are recommended.

Cashew requires high temperatures; frost is deleterious. Of importance is the distribution of rainfall; the quantity is less important. Cashew fruits well if rains are not abundant during flowering and if nuts mature in a dry period; the latter ensures a good keeping quality. The tree can adapt to very dry conditions as long as its extensive root system has access to soil moisture. In drier areas (annual rainfall 800—1000 mm), a deep and well drained soil without impervious layers is essential. A simple water budget with the aid of pan evaporation figures will show the required soil depth.

Fully mature nuts serve as planting material. Nuts with a low moisture content will remain viable for a year. Seed is taken from the best trees. However, seed from open- pollinated trees is not true to type. Clonal propagation is feasible, the outlook being best for layering, including air layering. Some success is being obtained with budding (about 30% take) and with top grafting. Cuttings have been rooted, but results could not be duplicated on a field scale. Recently the first successes with propagation through tissue culture have been obtained at Gembloux, Belgium.
Germination and early growth require a friable soil. On heavy or compact soils 50 cm deep planting holes are dug and refilled, mixing in some farmyard manure. Three seeds are planted 5 cm deep; the best seedling is retained. Clonal plant material should be planted with much care, as establishment is slow. Cashew trees are commonly spaced 12—15 m apart (44—69 trees/ha). Spacing experiments have shown that at ten years of age productivity in plots with 44, 69, 111, 135 and 278 trees per ha was about 450 kg/ha. Larger tree size compensated for smaller numbers of trees. It is the canopy surface area of the orchard that is of overriding importance in determining productivity, for that is where flowers and fruits are formed. Hedged rows of trees planted at 2—3 m within the row and 12—15 m between the rows, almost doubled the canopy surface area per ha, resulting in a corresponding increase in yield over the first ten years. The optimum width of the interrows depends on climatic conditions and on planting material.

Careful weeding — cleaning the area within 1 m of the trunk and slashing the remainder — is essential until the trees shade out most of the weeds. Fertilizers promote growth of the seedlings and advance the onset of flowering in young trees. With a production of some 420 kg of raw nuts per ha, 13 kg of nitrogen, 4 kg of P₂O₅ and 3 kg of K₂O are removed. These low figures suggest that fertilizing is unlikely to be required where only the nuts are harvested. When higher yields are realized, nutrients may become limiting. Little pruning is practised in cashew. From the sixth year onwards the lower limbs may be removed to allow access for tractor-drawn implements, etc. The removal of such limbs, lifting the canopy skirt to a height of 2 m, entails yield losses of 10%.
The economic life of cashew orchards is 25 years. Replanting is costly and leads to loss of income for at least five years. An alternative is to raise cashew in hedged rows. This increases the canopy surface area per ha. The resulting high productivity can be maintained by coppicing alternate rows at 50—75 cm when adjacent hedges come within 1 m distance of each other. The stumped trees will resume production in the second year. Tree rows may also be grubbed out and replaced with superior selections. The replanted rows come into production after 5 years. However, during that time the remaining hedges can expand fully and reach top yields. When the gap between hedges again becomes less than 1 m the rows of unchecked trees should be cut back, giving ample room for expansion of the rejuvenated/replanted rows. This system allows continuous cropping at higher than normal productivity and gradually improving yield levels. In Australia maintenance of hedgerows with tractor-mounted pruning equipment is being tested.

Under hot and humid conditions anthracnose (Colletotrichum gloeosporioides) attacks young shoots and flowers, which dry up and are shed. Infections of the fruits cause necrosis and shedding. This disease is often associated with insects and/or other fungi. Control is by removing and burning of infected parts; the use of fungicides is generally uneconomic. Selection of resistant material is probably a better measure. Powdery mildew is prevalent in cashew-growing areas. Affected plant parts become covered with white fungal growth. Leaves may shrivel, dry up and be shed. Similarly, loss of flowers may occur. The fungus needs a humid environment and densely planted trees may suffer more seriously than widely spaced trees. Sulphur controls the disease, but even this cheap fungicide is too costly.
The damage caused by Helopeltis bugs is of particular importance in the African and Indian cashew production areas. These insects suck the leaves, but do most damage on inflorescences and young fruits, leading to drying up of the inflorescences and shedding of fruits. Control by treatment with contact insecticides is possible, but prohibitively expensive.
Many other fungi (damping-off, wilts) have been recorded. Similarly other pests may be locally destructive, e g. wood borers, stem girdlers or sucking pests such as thrips. Nevertheless, such diseases and pests are seldom of economic importance.

Harvest is seasonal and lasts 2—3 months, since flowering per inflorescence and per tree is protracted and trees do not reach full bloom at the same time. Best quality is attained where freshly fallen nuts are dried and stored immediately. Nuts should be gathered at least weekly. The area under the tree should be weed-free and swept clean to facilitate nut collection.
After removal of the cashew apple the nuts are sun-dried to reduce moisture from 25% to below 9%. With proper drying, the kernel retains its quality, in particular the flavour. The nuts should not absorb moisture during storage; equilibrium moisture content is about 9% at 27°C and a relative humidity of 70%. The cashew apples ripen before the raw nuts are mature. Ripe apples for fresh use should be picked almost daily.

Yields of seedling trees are low in South-East Asia, as elsewhere, usually in the range of 400—600 kg/ha per year. Disregarding juvenile or otherwise unproductive trees, average yields in Indonesia from 1981 to 1985 ranged between 328 and 420 kg of raw nuts/ha. At 70 trees/ha this works out at 5.3 kg/tree. Farmers in southern Burma reported a similar productivity at 6.1 kg/tree. For the Philippines an annual yield of 1000 kg/ha has been reported.
Although trees come into bloom soon after planting (92% of the trees flowering in their third year at Tavoy, Burma), they are still so small that production is negligible. Average yields per tree increase from 3 kg at ages 3—5, to 4 kg at ages 6—10, 4.7 kg at ages 11—15 and 5.3 kg from the 16th—20th year. From then on yields decline, particularly through breakage of limbs.
World market prices have long been in the order of US$ 7—8 per kg of processed nuts. Internal markets (e.g. Burma at US$ 18) tend to be more lucrative. The current expansion of the crop in South-East Asia is likely to cover local needs soon. This may bring the price down considerably as has happened elsewhere.

Processing was originally done by hand. After roasting in oil (200°C) the nut was cracked with a wooden mallet. Raw nuts are sometimes slit open with a knife, almost inevitably contaminating the extracted kernels with CNSL. In the 1960s factory- processing methods were introduced. The small-scale production in South-East Asia is suited to manual processing, often followed by sorting and packaging procedures in central plants. Occasionally, mechanical processing methods are applied, as in Surabaya, Indonesia. Modern automatic processing plants roast, shell, peel and grade mechanically. To cover the high investments, adequate supplies of nuts should be guaranteed.
Roasting of the nut ruptures the large cells in the shell containing CNSL. Processing without removal of CNSL automatically leads to rejection of the produce for export. After roasting the shells are cracked and the kernels freed; the seed-coat is removed (peeled). The kernels are graded and unscorched, clean kernels are carefully dried to a moisture content of around 5%. The export trade requires packaging into 18 litre metal containers with carbon dioxide.
Grading standards developed in India refer to whole (undamaged) white kernels and indicate the number of kernels per pound of weight. The largest kernels come in grade W210 (440—460 kernels per kg), and the smallest of the 7 grades is W500 (1000—1100 kernels per kg). Further classifications refer to broken kernels, butts, splits, pieces, small pieces and whether nuts are white or scorched.

Many selections of high-yielding trees have been made. Assessments of seedling and clonal offspring are in progress and cultivars are being named. Data collected from individual — often solitary — trees can be very misleading and tests have to be done in orchards. Resistance to major pests and diseases is an important selection criterion. During ten years of testing clonal and seedling progeny, populations can be reduced by culling unpromising material. Seedling progeny from the remaining interpollinating trees are the basic material for a second selection cycle, where possible complemented by other source material. In this way a recurrent selection scheme, with a cycle of 10 years, can be established with continually improved breeding populations. Nuts that are not needed for quality assessments can be distributed to growers as planting material.

The cashew nut is favoured even in non-producing countries and demand seems to be growing. The current low yield levels, however, often make alternative crops more attractive. This relegates cashew to areas with poor soil types and low rainfall. Cashew does well under these conditions, provided the roots can grow unrestricted and fruit matures in dry weather. However, when yield levels are raised by the use of selected material and intensive husbandry, the crop may become competitive with other (cash) crops under more favourable growing conditions.
Priorities for research work are tree spacing in relation to soil moisture regime and rejuvenation pruning. There is an urgent need for a reliable method of clonal propagation. Tree phenology must be studied to clarify how growth, flowering and fruiting determine yield in different environments, and to properly time the cultural operations. In Kenya the combination of clonal material with planting in hedged rows has boosted yields to 3000—4000 kg/ha of raw nuts, 8 times the normal yield level.

Achmad Abdullah, 1987. Studi Kasus, Tanaman Jambu Mente (Anacardium occidentale L.). [Case study, the cashew plant]. Makalah Tanaman Buah-buahan Tropis. Kursus Singkat 5—19 November 1987. Universitas Brawijaya, Malang. 49 pp.
Agnoloni, M. & Giuliano, F., 1977. Cashew Cultivation. Instituto Agronomico per l'Oltramare, Florence. 168 pp.
Lefebvre, A., 1970. Indications préliminaires sur la fertilization de l'anacardier. Fruits 25(9): 621—628.
Lievens, C., Pylyzer, M. & Boxus, Ph., 1989. First results about micropropagation of Anacardium occidentale by tissue culture. Fruits 44: 553—557.
Northwood, P.J., 1966. Some observations on flowering and fruit setting in the cashew, Anacardium occidentale L. Tropical Agriculture Trinidad 43(1): 35—42.
Ohler, J.G., 1979. Cashew. Koninklijk Instituut voor de Tropen, Amsterdam. 260 pp.
Tsakiris, A. & Northwood, P.J., 1967. Cashew nut production in southern Tanzania IV, the root system of the cashew nut tree. East African Agricultural & Forestry Journal 33: 83—87.
van Eijnatten, C.L.M., 1984. Gross margins of cashew cultivation. Indian Cashew Journal 15(3): 7—11.
van Eijnatten, C.L.M. & Abubakar, A.S., 1983. New cultivation techniques for cashew. Netherlands Journal for Agricultural Science 31: 13—25.

C.L.M. van Eijnatten

van Eijnatten, C.L.M., 1991. Anacardium occidentale L.. In: Verheij, E.W.M. and Coronel, R.E. (Editors): Plant Resources of South-East Asia No 2: Edible fruits and nuts. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea