From Plant
Resources of South-East Asia (PROSEA)
by C. L. M. van Eijnatten
Taxon
Anacardium occidentale L.
Protologue
Sp. Pl. 1: 383 (1753).
Family
ANACARDIACEAE
Chromosome
Numbers
2n = 42
Vernacular
Names
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).
Origin and
Geographic Distribution
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.
Uses
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.
Production
and International Trade
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.
Properties
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.
Description
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.
Growth and
Development
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..
Other
Botanical Information
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.
Ecology
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.
Propagation
and planting
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.
Husbandry
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.
Diseases and
Pests
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.
Harvesting
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.
Yield
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.
Handling
After Harvest
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.
Breeding
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.
Prospects
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.
Literature
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.
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