Ricinus communis (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Ricinus communis L.

Protologue: Sp. pl.: 1007 (1753), Gen pl. ed. 5: 437 (1754).

Family: Euphorbiaceae

Chromosome number: 2n= 20

Vernacular names

• Castor (En).
• Ricin (Fr)
• Indonesia: jarak (general), kaliki (Sundanese), balacai (Moluccas)
• Malaysia: jarak
• Papua New Guinea: kaswel
• Philippines: sina, lingang-sina (Pilipino, Tagalog) tangan-tangan, tang-tangan (Bilokano), taua-taua (Ilokano), tangan-tangan, lansinan (Tagalog), tangan-tangan-hawa (Sulu)
• Cambodia: lohông khvâ:ng, lohông pré:ng
• Laos: hungx saa, hungx hna:n
• Thailand: lahung (general), hin (northern), lahung daeng (central)
• Vietnam: thầu dầu.

Origin and geographic distribution

Castor is indigenous to East Africa and probably originated in Ethiopia. It was already grown for its oil in Egypt some 6000 years ago and spread through the Mediterranean, the Middle East and India at an early date. In Chinese and European literature, it is not mentioned until the 9th and 15th Centuries AD, respectively. Castor is now grown in most drier areas of the tropics and subtropics and in many temperate areas with a hot summer. It naturalizes easily and grows in many areas as a ruderal plant.

Uses

The main product of castor is the oil extracted from the seed. The oil which consists mainly of triglycerides of ricinoleic acid is non-drying and non-edible. Traditionally, it is used for illumination and in medicine. As a lamp oil, it is now only used in rural areas and even then often mixed with kerosene. Currently, castor oil is primarily used as a high-quality lubricant and a versatile raw material in the chemical industry. As a lubricant it is characterized by its high lubricity, high viscosity remaining constant over a wide range of temperatures and its insolubility in aliphatic petrochemical fuels and solvents, making it suitable for equipment operating under extreme conditions such as in arctic zones and in aviation. Another specialized use of castor oil is in crumb rubber manufacturing, where it prevents rubber crumbs from coagulating. Highly purified, food-grade castor oil is used as an antistick agent for candy-moulds and as a lubricant for machinery in industrial food processing. Castor oil is further employed as a plasticizer in the coating industry, as a disperser for dyes and as a filler in cosmetics such as lipsticks, nail varnishes and shampoos. Saponification of castor oil yields a clear, transparent soap.

Partial oxidation of castor oil in air at about 100°C yields "blown oil", which remains fluid at low temperatures and is a major component of hydraulic and brake fluids and is used as a plasticizer for inks, lacquers and leather. Dehydration of castor oil turns it into a very pale, odourless, quick-drying oil used in manufacturing alkyd resins, epoxy resins and acryl resins used in heavy-duty paints and varnishes e.g. for refrigerators and other kitchen equipment. Hydrogenated castor oil yields a hard and brittle, odourless wax, mainly applied to modify the qualities of other waxes. Its main component hydroxystearic acid, is used in lubricants, insulators and surfactants and in the production of non-drip paints. Treating castor oil with sulphuric acid yields "Turkeyred oil", a wetting agent used in dyeing cotton and linen fabrics and in leather and fur manufacturing.

Cracking of ricinoleic acid yields a number of compounds, particularly suitable for the manufacture of high quality lubricants and synthetic polymers such as the polyamides nylon 11, nylon 6.10 and more recently developed polyurethanes. Other components derived from cracked ricinoleic acid include aroma chemicals, sebacic acid used in manufacturing jet-engine lubricants, synthetic detergents and additives for insecticides. Castor oil is so important in chemistry and also in military applications that the United States has declared castor oil a "strategic material" of which adequate stocks have to be maintained at all time.

In medicine, castor oil is used primarily as a purgative. It stimulates peristalsis by irritating the intestinal mucosa but causes little griping. The oil is also applied as an emollient in the treatment of sores and as a solvent for antibiotic eyedrops. Neutral sulphated castor oil can replace soap in certain cases of contact dermatitis. Castor oil has been used as an abortifacient and in preparations inducing labour in pregnant women. Ricinoleic acid prepared from the oil is a component of contraceptive creams and jellies.

The presscake of castor beans is poisonous and allergenic and is mainly used as fertilizer or as fuel. Methods to detoxify the presscake to make it suitable as an animal feed have been developed but some toxicity may remain even after treatment, to which horses are particularly sensitive. Another product extracted from the presscake is a lipase used in the industrial processing of fats.

In China, South and South-East Asia, the leaves of castor are used to treat skin diseases. They are also fed to the eri silkworm (Philosamia ricini, syn. Samia cynthia-ricini). Although they are somewhat toxic, mature leaves are occasionally used as a fodder, but care must be taken to avoid the more toxic young leaves. In Korea, mature leaves are dried and stored until winter when they are eaten as a vegetable; in Bengal (India) the young fruits are eaten. Castor is also an ornamental.

Production and international trade

Between 1985 and 1998 the annual world production of castor bean averaged 1.2 million t, while the harvested area declined gradually from 1.6 million ha to 1.2 million ha. India and China are by far the most important producers, accounting together for almost 80% of the production. Brazil has long been the second largest producer, but a dramatic decline in production has occurred since 1985. In South-East Asia, Thailand and the Philippines have a notable annual production of 5000-25 000 t and 500-7000 t, respectively. Production is tending to decline in the Philippines and to a lesser extent also in Thailand. Most castor beans are now processed to castor bean oil in the countries of production. India dominates the export market of castor bean oil (199 000 t of total world exports of 236 000 t in 1997). Production in China seems to be mostly used locally. Major importers of castor seed or oil are France (about 60 000 t oil), the United States (40 000 t oil), Germany (25 000 t oil + 22 000 t beans) and Japan (25 000 t oil). In South-East Asia, Thailand is an important importer. Programmes are in place to promote local production of castor in both the United States and the European Union.

Data on cultivated acreage and yield per ha do not present a fair indication of the actual production in a country since much castor is collected from the wild and because sole cropping of castor by peasant farmers is the exception.

Properties

Per 100 g, castor seeds contain approximately: water 5 g, protein 15-30 g, oil 43-53 g, carbohydrates 7-10 g, crude fibre 15-25 g, ash 2-3.8 g. The seed, and to a minor extent other plant parts as well, contain extremely toxic proteins, the toxic alkaloid ricinine, and allergens.

The oil is non-drying, viscous, nearly colourless, transparent and with a characteristic odour and taste. It has the highest viscosity of all vegetable oils; ricinoleic acid (about 90%) renders the special properties to the oil. Other fatty acids include: palmitic acid (2%), stearic acid (1%), oleic acid (about 7%), linoleic acid (3%).

Ricinoleic acid (12-hydroxy-9-octadecenoic acid) has a single double bond and is further characterized by a hydroxyl group. Dehydration of castor oil in which part of the ricinoleic acid is converted to a polyunsaturated acid yields a quick-drying oil with properties that compare favourably with those of tung oil and linseed oil. It is used in paints, varnishes, waxes and epoxy resins. Hydrogenation of castor oil in which the ricinoleic acid is partly or completely converted to 12-hydroxystearic acid yields a hard and brittle wax. Blown oil, i.e. oil that is oxidized and partially polymerized by bubbling finely dispersed air through it at 80-130°C, is a major component of hydraulic fluids. In inks, it is used to reduce water pick-up and improve drying characteristics.

When the oil is pressed or extracted from the seed, the poisonous proteins remain in the presscake. The main toxic proteins are "ricin" a potent cytotoxin and "RCA" (Ricinus communis agglutinin), a powerful haemagglutinin. Poisoning by ingestion of castor seed is due to ricin, as RCA does not penetrate the walls of the intestines. Ricin is extremely poisonous when injected into the bloodstream; as little as 1 mg can kill an adult. It irreversably inhibits ribosome activity; a single molecule that has entered a cell can inactivate over 1500 ribosomes per minute. It was probably used in the infamous "umbrella" murder of a Bulgarian journalist in London in 1978. Because of its extreme toxicity, ricin is included in Schedule 1 of the Convention on Chemical Weapons (1994) imposing the most stringent restrictions and control on its production, transportation and use. The ricin molecule consists of 2 parts, one responsible for its transport through the cell wall, the other the toxin proper. Pharmacological research is going on to combine the toxic part of ricin with monoclonal and polyclonal antibodies in the development of immunotoxins for the treatment of cancer and Aids.

The alkaloid ricinine (C₈H₈N₂O₂) is a convulsant agent; it causes respiratory depression. Castor seeds are allergenic. They may cause asthmatic reactions in sensitive persons, but others may work in castor processing facilities for years without developing any sensitivity.

As a flavouring, castor oil has been accorded the generally recognized as safe (GRAS) status in the United Sates. The weight of 1000 seeds is between 100-1000 g.

Description

• An evergreen, glabrous, soft-woody shrub or small tree, often grown as annual, 1-5 m tall. Taproot strong and with prominent lateral roots. Stem and branches with conspicuous nodes and ringlike scars of the bracts; shoots usually glaucous, variously green or red; glands often present at nodes, petioles and main axes of inflorescences.
• Leaves arranged spirally, dark green when old; stipules 1-3 cm long, united to a sheathing bud, deciduous; petiole round, 3.5-50 cm long; blade peltate, 10-70 cm across, membranous, palmately lobed with 5-11 acuminate, serrate lobes.
• Inflorescence an erect terminal panicle, later somewhat lateral by overtopping, up to 40 cm long, usually glaucous, with cymes of unisexual flowers, male flowers towards the base, female ones towards the top.
• Flower with short pedicel, 1-1.5 cm in diameter, with 3-5 acute calyx lobes; corolla absent; male flowers with many stamens in branched bundles; female flowers with early caducous sepals, ovary superior with three 1-ovule cells, usually soft spiny, styles 3, red or green, 2-cleft.
• Fruit an ellipsoid to subglobose capsule, 15-25 mm long, brown, spiny or smooth.
• Seed ellipsoid, 9-17 mm long, compressed, with a brittle, mottled, shining seedcoat and with a caruncle at the base; endosperm copious, white; cotyledons thin.
• Seedling with epigeal germination; cotyledons petioled, broadly oblong, up to 7 cm long, flat, with entire margin; first leaves opposite.

Growth and development

Seedlings of castor emerge 10-20 days after sowing. Later development of the plant is in accordance with Leeuwenberg's growth model and with sympodial branching. The successive formation of branches and inflorescences continues throughout the plant's life. The node at which the first inflorescence originates is a cultivar characteristic. In annual cultivars, the first inflorescence is the largest one and may account for up to 80% of the seed yield. In perennial forms flowering is more diffuse. Flowering starts early in the life of castor and continues for a long time. The first flowers may open 40-70 days after sowing. Pollen is mainly shed in the morning and pollination is by wind. As growth is indeterminate, one plant may bear infructescences in different stages of development. Ripening of fruits within an infructescence is uneven, the lower fruits maturing before the upper ones. In wild types, the period of maturation between the first and the last fruits within a given infructescence may be several weeks. In cultivars grown as annuals, the period from emergence to maturation varies from 140-170 days; however, perennial forms are common in peasant agriculture.

Under favourable conditions, castor has a high rate of photosynthesis which has been attributed to a high chlorophyll content in the leaves.

Other botanical information

Ricinus L. comprises only one species (R. communis). Previously described species have been transferred to other genera or grouped within R. communis. Some castors are large perennials, others behave as short-lived dwarf annuals and every gradation between them can be found. Colour differences in leaves, stems and inflorescences have resulted in selection of these variants as horticultural plants. However, attempts to classify such selections as subspecies or varieties are botanically inaccurate; a classification into cultivar groups would be more appropriate. In most countries red and white types (cv. groups) are distinguished based on the colour of young shoots. Within these groups, cultivars are recognized based on seed characteristics. Numerous cultivars exist; "Hale" and "Lynn" are dwarf cultivars in the United States, now mainly used as pollen parents in the production of hybrids. Other well-known cultivars include: "Conner" and "Kansas" in the United States, "Rica" and "Venda" in France and "T-3", "GCH-3", "DCS-9" and "SKI-7" in India.

Castor is used extensively in physiological studies to elucidate mechanisms involved in phloem transport.

Ecology

Castor is a long-day plant but is adaptable to a fairly wide photoperiodic range. At a daylength of 9 hours, growth and development are reduced, but at 12-18 hours, development is normal. Castor grows throughout the warm-temperate and tropical regions. It has been commercially cultivated from 40°S to 52°N, from sea level to 2000 m altitude at the equator, with an optimum between 300-1500 m, the limiting factor being frost. Suitable soil temperatures for germination are between 10-18°C. Castor requires average day temperatures of 20-26°C with a minimum of 15°C and a maximum of 38°C. It prefers clear, sunny days, with low humidity. Temperatures of 40°C or higher at flowering are detrimental.

In regions with an average annual rainfall of 750 mm or less, sowing should be carried out on such a date that 400-500 mm rainfall up to the time of main flowering is assured for the crop. Castor can tolerate water stress because of its deep root system, but is sensitive to excess of water and humidity.

Castor will grow on almost any soil type as long as it is well-drained and reasonably fertile. It prefers deep, sandy loams with pH 5-6.5. Plants with the best tolerance to salinity or alkalinity tend to be large bushy ones with little commercial value.

Propagation and planting

Castor is propagated by seed. Per hole, 2-3 seeds are planted at a depth of 3-8 cm; alternatively it is sown in rows. Crop management varies widely when castor is grown as a cash crop. For mechanized cropping under rainfed conditions, field preparation starts by ploughing deep enough to break up any compact layers. Castor requires a moist topsoil for germination and early growth for a longer period than maize or cotton. In dry regions where total rainfall is low, ridging is a suitable method. Smallholders usually intercrop castor with annual crops or plant it along the edges of fields. Short-cycle cultivars may be grown in sole cropping as a second crop. In intercropping, plant distances may be as much as 4-5 m and castor will receive the treatment of the main crop. With dwarf cultivars in sole cropping, planting may be at 1 m row distance. Closer spacing can result in considerable damage to branches and to shallow lateral roots during weeding. Recommendations for in-row spacing range from 25-30 cm for dwarf to 30-40 cm for larger cultivars, or about 25 000-30 000 plants/ha for crops grown in locations with 750-900 mm rainfall. Under irrigation, row width may be determined by the system of water delivery, and where water is not limiting, 30 000-40 000 plants/ha is feasible, depending on cultivar.

Husbandry

Castor seedlings are poor competitors and weed control is essential. Two weeding rounds are normally sufficient. Where practical, application of a pre-emergence herbicide followed by handweeding is probably most effective. The first weeding is about 6 weeks after sowing. It is often combined with thinning, earthing up and topping. Since the young crop is very susceptible to mechanical damage, weeding should be carried out carefully. Effective weed control often results in a relatively bare soil surface thus offering little protection against erosion. This, combined with the low soil-binding ability of castor, often makes it necessary to include conservation measures in the cropping system and to exercise care in selecting sites for large plantings of castor.

Peasant farmers do not usually irrigate or manure castor, although both are often beneficial for yield. It has been calculated that 3.3 t fruit (2 t seed and 1.3 t hulls) remove 80 kg N, 8 kg P, 26.5 kg K, 8.5 kg Ca and 6 kg Mg.

Diseases and pests

Few diseases are of economic importance. Normally, serious attacks only occur in badly-growing crops and under humid conditions. The most damaging diseases that attack seedlings are various rots ("damping-off" caused by Fusarium , Phytophthora, Rhizoctonia , Sclerotium spp.). The most common foliar disease is rust caused by Melampsora ricini which is now probably of worldwide occurrence; symptoms are the presence of uredopustules on the lower surface of the leaves. In severe cases leaves may be covered completely and dry up. A high degree of resistance is found in e.g. the Indian cultivars "Raichur Dwarf", "VH-701/5" and "837/1". Cercospora ricinella , causing a leaf-spot disease, can become locally damaging in Indonesia. Among the capsule diseases, those caused by Alternaria and Botrytis are the most serious ones. Alternaria ricini causes damage worldwide. Symptoms are the appearance of brown lesions on the leaves surrounded by a yellow halo. Affected capsules may suddenly wilt and turn dark brown or purple; also sunken areas may develop which gradually enlarge to cover the whole capsule. Under very humid conditions inflorescences may become covered by black sooty spore deposits. Seed treatment with a fungicide may control the disease. In later stages foliar application of carbamates or copper-based fungicides may be effective.

Probably the most damaging pests are those attacking the inflorescence, such as mirids (Helopeltis spp.). Peach moth or castor shoot and capsule borer (Dichocrocis punctiferalis) is a most important pest in India and throughout South-East Asia. Young caterpillars feed on the green capsules and bore their way inside at the apical or basal end. At the point of entry a silken gallery is formed. As a single caterpillar may affect several fruits, they may become webbed together by these galleries. As the caterpillars feed inside the fruits, control is difficult. Many other pests have been observed but damage is mostly minor and localized. Tall, perennial forms can often outgrow the effects of insect attack. However, because of their tall stature and long duration, they are more susceptible to damage caused by stem borers than short-term ones.

Harvesting

Castor is harvested in the dry season. The whole infructescence is reaped when about half of its fruits are mature. Harvesting is done every 2 weeks. Simple tools in the form of a tin with a notch for manual harvesting have been developed. Where castor seeds are merely collected from wild or volunteer plants, their harvesting sometimes involves no more than collecting the scattered seeds. Under intensive cropping, harvesting and hulling are the most time-consuming operations. However, suitable machines and cultivars which are adapted to large-scale cultivation have been developed. Mechanical harvesting consists basically of removing fruits from standing plants. Commercial plantings of dwarf cultivars are usually fully mechanized. Important problems still to be solved are the uneven ripening and the varying thickness of the fruit wall, both producing a large proportion of unhulled or broken seeds.

Yield

Average seed yield of castor is about 1000 kg/ha, with a maximum of about 3000 kg/ha. In China and India, average seed yields are about 1000 kg/ha while those in the Philippines fluctuate from 800-1000 kg/ha. Thailand’s seed yields declined from 800 kg/ha in 1985 to 500 kg/ha at present. Statistics on yield are very difficult to compile as castor is often intercropped or grown along field borders.

Handling after harvest

The fruits of traditional cultivars are mostly semi-shattering. After harvesting, the panicles are dried and spread on a floor. They lose most of their seeds in 4-6 days. Unopened fruits are threshed. After separation of the healthy seeds from the trash, the product is ready for storage or for sale. Fruits of modern cultivars are often non-shattering. Such cultivars should only be grown if mechanical dehullers are available, because traditional threshing results in a large proportion of damaged seeds. Castor seed can only be stored in the open for short periods, as both heat and sunlight reduce its oil content and quality. Seed should be handled with care since the thin and often brittle testa is easily damaged.

Genetic resources

Local populations are commonly the best resources for breeding. Large collections are maintained in the Russian Federation (N.I. Vavilov Institute of Plant Industry, St. Petersburg) and in China (Institute of Crop Germplasm Resources, Beijing and Institute of Oil Crops Research, Wuhan), while smaller collections are kept in e.g. the United States, Ukraine, Brazil and India. In Ethiopia (Biodiversity Conservation and Research Institute, Addis Ababa), a collection of local castor is available.

Breeding

All natural forms of castor are diploid; they cross freely and are fully fertile. The frequency of natural out-crossing is commonly between 5-50%, but in some dwarf cultivars it may be as high as 90-100%. Male-sterile and female-sterile lines have been identified and are of great value in breeding. Selection has mostly focused on problems associated with mechanical production such as annual life cycle, dwarf plant architecture, and indehiscent, thin-hulled and sparsely spiny fruits, maturing synchronously. The main aims of modern castor breeding are high seed yield, high oil and ricinoleic acid contents, easy harvesting and resistance to diseases and pests.

Prospects

As a raw material for industry, castor oil has to compete with alternative raw materials. Demand depends on the price of the oil in relation to that of alternatives and the reliability of supply. Both supply and price have fluctuated considerably in the past. Currently, competition is strongest for dehydrated castor oil, as cheap alternatives prepared from soya bean oil are available. With increasing research efforts aiming at the development of new products based on the unique properties of ricinoleic acid, however, the demand for castor oil may increase in the future.

Literature

• Bonjean, A., 1991. Castor cultivation for chemical applications. Galileo/ONIDOL, s.l., France. 101 pp.
• Brigham, R.D., 1993. Castor: return of an old crop. In: Janick, J. & Simon, J.E. (Editors): New crops. Wiley, New York, United States. pp. 380-383.
• Dai, Z.Y., Edwards, G.E. & Ku, M.S.B., 1991. Control of photosynthesis and stomatal conductance in Ricinus communis L. (castor bean) by leaf to air vapor pressure deficit. Plant Physiology 99: 1426-1434.
• Kolte, S.J., 1995. Castor: diseases and crop improvement. Shipra Publications, New Delhi, India. 119 pp.
• Moshkin, V.A., 1986. Castor. Russian Translation Series. Vol. 43. Balkema, Rotterdam, the Netherlands. 329 pp.
• Seegeler, C.J.P., 1983. Oil plants in Ethiopia, their taxonomy and agricultural significance. Agricultural Research Reports 921. Pudoc, Wageningen, the Netherlands. pp. 204-238.
• Soerjono, Sahid, M. & Rachman, S. A., 1978. Beberapa varietas harapan tanaman jarak [Some promising varieties of castor]. Pemberitaan Lembaga Penelitian Tanaman Industri (Bogor) 28: 15-21.
• van Welzen, P.C., 1998. Revisions and phylogenics of Malesian Euphorbiaceae. Ricinus. Blumea 43: 151-154.
• Weiss, E.A., 2000. Oilseed crops. 2nd Edition. Blackwell Science, London, United Kingdom. 364 pp.
• Willey, R.G. & Oeltmann, T.N., 1991. Ricin and related plant toxins: mechanisms of action and neurobiological applications. In: Keeler, R.F. & Tu, A.T. (Editors): Handbook of natural toxins. Vol. 6. Toxicology of plant and fungal compounds. Marcel Dekker, New York, United States. pp. 243-268.

Authors

C.J.P. Seegeler & L.P.A. Oyen