Vernicia (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Vernicia Lour.

Protologue: Fl. cochinch.: 586 (1790).

Family: Euphorbiaceae

Chromosome number: x= 11; V. fordii, V. montana: 2n= 22

Major species and synonyms

• Vernicia fordii (Hemsl.) Airy Shaw, Kew Bull. 20: 394 (1967), synonym: Aleurites fordii Hemsl. (1906).

• Vernicia montana Lour., Fl. cochinch.: 587 (1790), synonyms: Dryandra vernicia Corr. Méllo (1806), Aleurites montana (Lour.) E.H. Wilson (1913).

Vernacular names

General:

• tung (En),
• aleurite (Fr).

V. fordii :

• tung-oil tree (En).
• Arbre à l'huile de tung (Fr)
• Malaysia: tung-yu
• Thailand: ma-yao
• Vietnam: cây tung.

V. montana :

• wood-oil tree, mu-tree, abrasin-oil tree (En).
• Arbre à l'huile de bois, abrasin (Fr)
• Indonesia: kemiri cina, muncang cina (Sundanese)
• Malaysia: mu-yu
• Thailand: ma yao
• Vietnam: cây trẩu.

Origin and geographic distribution

Vernicia occurs naturally in Japan, China and in continental South-East Asia from Burma (Myanmar) to Vietnam. V. fordii is native to Burma (Myanmar), northern Vietnam and China. It is now grown in China, the southern United States and South America and is naturalized in Queensland. V. montana is native to Burma (Myanmar), Thailand, Indo-China and southern China. It has been introduced into most tropical areas and cultivated in Indo-china, Indonesia, Madagascar and Malawi.

Uses

Tung oil, extracted from the seed of V. fordii and the very similar wood oil from the seed of V. montana are quick-drying oils with excellent properties. Because of their similarity, they are often treated together as tung oil. In China, the oil is used traditionally in the manufacture of paints and Chinese black ink, for waterproofing cloth and paper, caulking and painting ships and as a lamp oil. It was also formerly used for insulating electric wires. Currently, its main use is in the production of paints and inks, while low-quality oil is applied in the manufacture of soap and linoleum. Teak oil which is sold for maintaining fine furniture is usually refined tung oil. Developments in environmental and health regulations have led to an increasing use of tung oil to line containers for food, beverages and medicines with an insulating coating. The press cake, after extraction of the oil, is a good fertilizer, but it is poisonous and cannot be used as animal feed.

In medicine, tung oil is used to treat parasitic and other skin diseases and is a strong purgative. It is a component of nearly all Chinese plasters.

The timber is only suitable for simple construction and firewood, where better wood is not available. The timber is white, soft and perishable. Both V. fordii and V. montana are sometimes planted as shade trees.

Production and international trade

The oils from V. fordii and V. montana are rarely distinguished in trade and are both referred to as tung oil, although a distinction between them has been proposed in the United States. Annual world production of tung fruits in the late 1990s was about 500 000 t from 170 000 ha, yielding 90 000 t oil. China produced 85% of the world production: 450 000 t fruit yielding 80 000 t oil. It exported 25% of its production. China was followed by Paraguay with 43 000 t seed and Argentina with 30 000 t seed, while Madagascar, Malawi and Brazil produced small quantities. No production data are available for tung oil or mu oil from South-East Asia. Production, exports and oil quality from China fluctuate yearly resulting also in price fluctuations. Prices fluctuated from over US$ 3000 per t at the end of 1993 to US$ 1200 two years later, while in 1996 prices ranged from US$ 1250 to US$ 2000. Exports from South America are declining. Tung oil was once an important crop in the United States, where the belt from Florida to eastern Texas produced about 50 000 t oil in the 1950s. Subsequent crop losses caused by frost, hurricanes and commercial difficulties led to a complete abandonment of nearly all plantations. However, following the introduction of laws to reduce the use of solvents in paints, plans are being made to establish 2000 ha of V. fordii plantations in Mississippi. Efforts were made in the 1930s to establish a tung oil industry in Indonesia, but little progress was made after World War II.

Properties

The fruit of V. fordii or V. montana contains per 100 g 14-20 g drying oil. The oil is mainly contained in the seed which makes up about 33% of the fruit. The main fatty acid of the oil is α-eleostearic acid or cis-trans-trans 9,11,13-octadecenoic acid. It is a trienoic fatty acid, isomeric with linolenic acid. In eleostearic acid, the 3 double bonds are conjugated making them highly reactive. Under the influence of light or catalysts such as sulphur and iodine, α-eleostearic acid converts to β-eleostearic acid, which is even more reactive and spontaneously polymerizes into a solid mass. The eleostearic acid makes tung oil a virulent purgative when taken internally. The α-eleostearic acid content is 75-80%; other fatty acids include: palmitic acid 4%, stearic acid about 1% and oleic acid 15%. In the triglycerides, most eleostearic acid is bound in the 1 and 3 positions.

Other components of the fruits of both species include tannins, phytosterols and a poisonous saponin. Animals, including cattle, horses and chicken that have eaten the leaves or seed cake show haemorrhagic diarrhoea accompanied by anorexia. In severe cases, they become emaciated and may die in 1-3 weeks. The fruits of Vernicia are attractive in appearance and taste, but ingestion by humans of even a single seed causes severe abdominal cramps, vomiting, diarrhoea and general exhaustion after 3-5 hours.

Description

• Shrubs or trees, monoecious or sometimes dioecious, deciduous or evergreen. Indumentum of simple or bifurcate hairs, at least present on young shoots, leaves and petioles.
• Leaves alternate; stipules triangular-lanceolate, early caducous, leaving fairly prominent scars; petiole terete, striate, with two glands at junction with blade; blade simple, ovate to broadly ovate or 3-5-palmately lobed.
• Inflorescence a terminal, solitary, corymbiform thyrse, branching from the base, unisexual or bisexual and protogynous with a solitary terminal pistillate flower and several staminate flowers per cymule.
• Flowers unisexual, showy, slightly zygomorphic; calyx closed in bud, later valvately rupturing into 2(-3), often unequal lobes; petals 5(-6), free, imbricate, contorted, obovate, clawed; disk of 5-6(-7) erect glands; male flowers with pedicel usually longer than in the female flowers; stamens (7-)8-12(-14), in 2 whorls, united into a column, pistillode absent; female flowers with ovary superior, 3(-5)-locular, with 1 ovule per locule, pubescent or densely sericeous; styles nearly free to united at the base, bifid.
• Fruit large, capsular, ovoid to subglobose, tardily dehiscent, glabrous to pubescent.
• Seed without caruncle, obovoid to subglobose, dorsiventrally compressed, pointed, brown with longitudinally oriented beige variegations, smooth or warty and ridged; hilum large; embryo straight, embedded in copious endosperm; cotyledons broad, flat.

V. fordii.

• Monoecious, flat-topped, much branched, deciduous, shrub or tree, up to 20 m tall. Indumentum fulvous to mostly ferruginous.
• Leaves crowded at the apex of the shoots; stipules 4-12 mm long; petiole up to 26 cm long, glands sessile, about 0.5 mm long; blade 5-25 cm × 4-22 cm, ratio length/width 1:1.2(-1.4), sometimes 3-lobed, 5-veined from the base.
• Inflorescence usually bisexual, appearing before the leaves, 3-16 cm long, few-flowered, with one central female flower and 4-7 lateral male cymules, 3-7-flowered; bracts linear-lanceolate, 2-10 mm long, densely hairy.
• Flowers reddish-white to purple, suffused and veined with pink, yellow in the centre, diameter 25-35 mm; calyx lobes 8-10 mm × 5-8 mm, pubescent at the apex; petals orbicular-ovate to broadly obovate-spatulate, 20-35 mm × 8-20 mm; claw 3-6 mm long; male flower with pedicel 8-18 mm long, stamens (7-)8(-14), the (4-)5(-8) outer filaments 7-10 mm long, the 3(-6) inner ones up to 15 mm; female flower with pedicel slender, 5-14 mm long, ovary ovoid to subglobose, 4-5-locular, gradually narrowing into the styles, styles united at the base, 4-5 mm long, shortly bifid.
• Fruit spherical to subglobose or slightly compressed, 4-6 cm in diameter, apically sharply pointed, basally stiped, smooth, dull brown, sparingly sericeous.
• Seed sub-obovoid, 2-3 cm long, conspicuously warty and ridged dorsally and ventrally.

V. montana.

• In general similar to V. fordii but with following major differences:
• evergreen shrub or tree, 10-15 m tall; stipules 3-5 mm long; glands at the apex of petiole stalked.
• Inflorescence usually unisexual and male ones much larger than the female ones.
• Ovary 3(-5)-locular, gradually narrowing into the styles.
• Fruit surface wrinkled with 3(-5) distinct longitudinal grooves and ridges and few transverse ribs.

Growth and development

Two branching and flowering patterns in V. montana are recognized in Indonesia: the Indo-China type and the China type. Similar types are also recognized in Malawi.

• Indo-China type. This is a fast-growing tree with a tall, straight trunk forming tiers of 5 spreading branches at regular wide intervals. At their distal end, these branches form 5 secondary branches. While the lower 1-2 buds of the secondary branches grow out into new branches repeating the branching structure, the upper buds and the terminal bud of the primary branch develop into short flowering branches. Trees of the Indo-China type are never completely leafless in equatorial areas. They flower throughout the year with peaks around May and October in Indonesia. The distinction between male and female trees is less sharp and even in very productive trees with the highest ratio of female inflorescences, the number of male inflorescences is higher than that of female and mixed inflorescences together. It takes 3-5 years for trees to come into bearing. At higher latitudes where trees lose their leaves during winter, flowering is concentrated in a short period of only 2 weeks in spring. Here, trees are either male or female with only occasional bisexual trees.

• China type. The tree is a more slow-growing, compact and small tree or shrub which starts bearing in the third year after planting and gives high yields in the first 6 years. In Indonesia, the growth rate of its main stem is less than that of the branches. The China type of V. montana behaves similarly in equatorial areas. In Indonesia, trees are leafless during a short rest period in the dry season, and they are either male or female. The flowering period is extended and may vary per tree, but there is a flowering peak around October and sometimes a minor peak of mainly male flowering in May.

Flowers open in the morning. In female flowers, the stigma is already receptive 1 day earlier, while in male flowers, pollen is released at anthesis. Pollen is sticky and pollination is performed by insects such as butterflies and bees. Some honey-bee species, however, are common visitors of male flowers, but are rarely seen on female flowers and contribute little to pollination. In clonal plantations of selected female trees in Indonesia, the number of male flowers may not be sufficient for good pollination. Planting about 5% male trees is enough to correct the problem. The number of fruits set is high and about 80% of the fruit set may abort during development. In the United States, fruit development in V. fordii takes about 18 weeks and mature fruits drop after 20 weeks. Fruit development in V. montana follows a similar pattern.

Bud-grafted tung-oil trees come into production 2-4 years after planting; trees grown from seed a few years later. Maximum production is reached when trees are 10-12 years old. Plantations remain productive for a long time. Although plantations older than 100 years exist in China, production starts to decline when trees are 20 years old and becomes uneconomical when they reach 30 years. A slight biennial or triennial bearing pattern is a common feature in Vernicia plantations.

Other botanical information

The genera Aleurites J.R. Forst. & G. Forst., Reutealis Airy Shaw and Vernicia are closely related and have long been combined in Aleurites. Vernicia comprises only the two closely related species treated here and a third species V. cordata (Thunb.) Airy Shaw which occurs in Japan. Where V. fordii and V. montana grow together and flower simultaneously, hybridization is common, but the hybrids have no agronomic advantages. In China, many V. fordii cultivars exist, including "Luxi Pupu Tong" and "Zhetung 7". In the United States also, some cultivars of V. fordii have been released, e.g. "Folsom", a low-growing, high-yielding, late-maturing cultivar with large, purplish fruits that contain 21% oil. "Lampton" is a very low-growing, early maturing and probably the most productive cultivar with a high tolerance to low temperatures during the cool season. Its fruits are small and contain about 22% oil.

Ecology

V. fordii is mainly grown in the subtropics and temperate regions of Asia and North America. It needs (650-)1000-1700 mm annual rainfall and an average annual temperature of 19-26°C. During winter, it requires a period of 300-400 hours below 7.5°C for flower initiation. During active growth, however, frost may cause serious damage and is one of the reasons why tung cultivation was abandoned in the United States. Planting on hilltops or slopes helps reduce the risk. Yields are best where the difference between day and night temperatures is small. Many tung stands in China are on poor soils, but well-drained, slightly acid soils (pH 6-6.5) with a good moisture-holding capacity are required for high production. In the United States, dolomite has been used to correct soil acidity. Fertilizer requirements vary with soil type. Application of micronutrients is recommended unless soil content is adequate.

V. montana is most widely distributed in the tropics and subtropics of Asia, America and Africa. It is planted in areas with annual rainfall of 850-2000 mm and average annual temperatures ranging from 15-27°C in tropical areas at altitudes of 800-2000 m. It does not require low temperatures for flower initiation and is sensitive to frost. V. montana is often grown on slopes but grows well on flat land provided the area is well-drained. It prefers slightly acid soils and is very susceptible to accumulation of ash and occurs on soils of pH 5.5-8.0. Adequate soil fertility is needed for good production.

Propagation and planting

Commercial plantings of Vernicia consist mostly of selected clones budded on to seedling rootstocks. In Malawi, budding is done in the nursery, but in Indonesia it is done in the field after transplanting. The simple shield method at a height of 5-7.5 cm above the ground is commonly applied. Propagation by seed results in variable stands with 50% male trees. Fresh seed germinates quickly, but germination of older seed may take 2-3 months unless seed is scarified. Seedlings are transplanted into the field when they are 1 year old. In China, planting density is about 600 trees/ha, whereas in Paraguay, the most common density is 330-700 trees/ha. In Florida (United States), tung trees are planted either at a wide spacing with 185 trees/ha or at a narrow spacing with over 250 trees/ha. Plantations with a close planting system reach maximum production at an earlier age but the maximum yields are the same as those from trees that are more widely spaced. Hedgerow systems have also been developed. In this case, pruning and training are recommended to obtain a frame of a few main branches and open crown. Fertilizer should be applied to seedlings in the nursery. In the United States, an application of 600 kg/ha of a NPK 5-10-5 compound fertilizer at planting is recommended.

Husbandry

Young trees of Vernicia are often intercropped with food crops such as maize, groundnut or soya bean in China. In Malawi and Indonesia, intercropping with annuals or planting of cover crops is common. Prolonged intercropping with annual crops may cause damage to the root system, but in China even mature trees are sometimes intercropped with winter crops. Regular weeding around the plants is needed also for ease of harvesting.

Diseases and pests

In China, anthracnose caused by Colletotrichum gloeosporioides (syn. Glomerella cingulata) sometimes causes severe losses. Other important diseases include: root rot caused by Fusarium solani and brown leaf spot caused by Cercospora aleuritides (syn. Mycosphaerella aleuritides). In Malawi, the main diseases of V. montana are die-back caused by Botryosphaeria ribis and the Armillaria root rot. In Indonesia, Rhizoctonia solani causes damage in the nursery but can be controlled by fungicidal treatment. Root rot caused by Botryodiplodia theobromae, Phytophthora palmivora, Pythium sp. and Sphaerostilbe repens has been recorded. Selection of adapted plant material is the best way to avoid these diseases.

Insect pests are rarely a problem as the leaves and seeds are toxic to most animal life. The thrips Selenothrips rubrocinctus causes damage in V. fordii in China, but V. montana is highly resistant.

Harvesting

Harvesting by manual picking of fallen fruits is most common, but in China, green fruits are also picked from the trees. In subtropical areas where harvesting is done during winter months, fruits can be left on the ground for a few weeks to dry. In Java, fruits mature year-round in seedling plantations, but clonal material ripens in a short period. Careful selection of clones can extend the harvesting season. During the rainy season, fruits should be collected every 10 days, and during the dry season about once a month.

Yield

In Florida (United States), fruit yields of 5 t/ha can be obtained from well-managed mature plantations, but worldwide yields are lower. Average yields are 3.5 t/ha in China and 1.8 t/ha in Malawi.

Handling after harvest

In China, the fruit is traditionally collected when still green, placed in heaps and covered with straw or grass. Fermentation takes place in the heaps and the fleshy parts of the fruits rot until the seeds can be easily removed. These seeds are then crushed in a mill consisting of a circular stone trough and a heavy stone roller. After being roasted for a short time in shallow iron pans, the crushed mass is placed in wooden vats with open-worked bottoms over cauldrons of boiling water and thoroughly steamed. Subsequently, fluid is pressed out of the cake yielding commercial tung oil or wood oil. In modern processing, hulling of fruits is done by hand or mechanically. The seeds are then dried and shelled mechanically, after which the kernels are ground with some shell added to facilitate oil extraction. Cold-expression is done in screw presses yielding a clear, light-coloured oil. The cake may subsequently be warm-pressed or solvent-extracted to increase the yield, but the product is of lower quality.

Genetic resources and breeding

Both V. fordii and V. montana are very variable and there are only few true breeding lines. No germplasm collections are known to exist. In the United States, the National Plant Germplasm System no longer maintains its former collection of Vernicia. However, important breeding and selection programmes have been implemented in China and Taiwan.

Prospects

The excellent quality of tung oil may make it worthwhile to consider the possibilities of commercially producing Vernicia in South-East Asia. Extensive testing of new clones and production techniques should precede the establishment of new plantations in this region.

Literature

• Airy Shaw, H.K., 1967. Generic segregation in the affinity of Aleurites J.R. & G. Forster. Kew Bulletin 26: 393-395.
• Chen-Fei, 1998. Study on the selection of 69 asexual tung tree families by canonical correlation analysis. Forest Research 11: 518-522.
• Radunz, A., He, P. & Schmid, G.H., 1998. Analysis of the seed lipids of Aleurites montana. Zeitschrift fuer Naturforschung 53: 305-310.
• Phiri, I.M.G., 1985. Effects of nitrogen and hedge row systems on the yield and quality of tung nuts. Acta Horticulturae 158: 265-271.
• Purseglove, J.W., 1968. Tropical crops - dicotyledons 1. Longmans, London, United Kingdom. 332 pp.
• Sengers, H.H.W.J.M. & Koster, A.C., 1998. Tungolie [Tung oil]. Landbouw Economisch Instituut (LEI/DLO), the Hague, the Netherlands. 115 pp.
• Stuppy, W., van Welzen, P.C., Klinratana, P. & Posa, M.C.T., 1999. Revision of the genera Aleurites, Reutealis and Vernicia (Euphorbiaceae). Blumea 44: 73-98.
• Webster, C.C., Wiehe, P.O. & Smee, C., 1950. The cultivation of the tung-oil tree (Aleurites montana) in Nyasaland (A practical guide for growers). The Government Printer, Zomba, Malawi. 48 pp.
• Wit, F., 1950. Chinese houtolie [Chinese wood oil]. In: van Hall, C.J.J. & van den Koppel, C. (Editors): De landbouw in de Indische Archipel [Agriculture in the Indonesian Archipelago]. Vol. 3. van Hoeve, the Hague, the Netherlands. pp. 621-653.

Authors

N.O. Aguilar & H.C. Ong

3 Minor vegetable oils and fats