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Aleurites fordii Hemsl.

Euphorbiaceae
Tung-Oil Tree

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.

  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Description
  5. Germplasm
  6. Distribution
  7. Ecology
  8. Cultivation
  9. Harvesting
  10. Yields and Economics
  11. Energy
  12. Biotic Factors
  13. References

Uses

Tung trees are cultivated for their seeds, the endosperm of which supplies a superior quick-drying oil, utilized in the manufacture of lacquers, varnishes, paints, linoleum, oilcloth, resins, artificial leather, felt-base floor coverings, and greases, brake-linings and in clearing and polishing compounds. Tung oil products are used to coat containers for food, beverages, and medicines; for insulating wires and other metallic surfaces, as in radios, radar, telephone and telegraph instruments.

Folk Medicine

No data available.

Chemistry

The fruit contains 14–20%; the kernel, 53–60%; and the nut, 30–40% oil. It contains 75–80% a-elaeo stearic, 15% oleic-, ca 4% palmitic-, and ca 1% stearic-acids. Tannins, phytosterols, and a poisonous saponin are also reported (List and Horhammer, 1969–1979).

Description

Trees up to 12 m tall and wide, bark smooth, wood soft; leaves dark green, up to 15 cm wide, heart-shaped, sometimes lobed, appearing usually just after, but sometimes just before flowering; flowers in clusters, whitish, rosethroated, produced in early spring from terminal buds of shoots of the previous season; monoecious, male and female flowers in same inflorescence, usually with the pistillate flowers surrounded by several staminate flowers; fruits spherical, pear-shaped or top shaped, green to purple at maturity, with 4–5 carpets each with one seed; seeds usually 4–5, but may vary from 1 to 15, 2–3.2 cm long, 1.3– 2.5 cm wide, consisting of a hard outer shell and a kernel from which the oil is obtained. Fl. Feb.–Mar.; fr. late Sept. to early Nov.

Germplasm

High-yielding cultivars continue to be developed. Some of the best varieties released by the USDA for growing in southern, United States are the following:

'Folsom': low-heading, high productivity; fruits large, late maturing, turning purplish when mature, containing 21% oil; highest resistance to low temperature in fall.

'Cahl': low-heading, productive; fruits large, 20% oil content; matures early, somewhat resistant to cold in fall.

'Isabel': low-heading, high productive; fruits large, maturing early, 22% oil content.

'La Crosser: High-heading, exceptional productivity; fruits small, late maturing, tending to break segments if not harvested promptly, 21–14% oil content; a very popular variety.

'Lampton': outyields all other varieties; very low-heading; fruits large, early maturing; 22% oil content.

Several other species of Aleurites are used to produce tung-oil, usually of low quality. Aleurites cordata, Japanese wood-oil tree; A. moluccana, Candlenut or lumbang tree; A. trisperma, Soft Lumbang tree; none of which can be grown commercially in the United States. Aleurites montana, Mu-tree, is the prevailing commercial species in South China and could be grown in Florida. (2n = 22)

Distribution

Native to central and western China, where seedlings have been planted for thousands of years; planted in southern United States from Florida to eastern Texas.

Ecology

Ranging from Subtropical Dry to Moist through Tropical Very Dry to Dry Forest Life Zones, this species is reported to tolerate annual precipitation of 6.4–17.3 (mean of 8 cases = 12.,3), temperature of 18.7–26.2°C (mean of 8 cases 22.5), pH of 5.4–7.1 (mean of 4 cases = 6.4) (Duke, 1978, 1979). Tung trees are very exacting in climatic and soil requirements. They require long, hot summers with abundant moisture, with usually at least 112 cm of rainfall rather evenly distributed through the year. Trees require 350–400 hours in winter with temperatures 7.2°C or lower; without this cold requirement, trees tend to produce suckers from the main branches. Vigorous but not succulent growth is most cold resistant; trees are susceptible to cold injury when in active growth. Production of tung is best where day and night temperatures are uniformly warm. Much variation reduces tree growth and fruit size. Trees grow best if planted on hilltops or slopes, as good air-drainage reduces losses from spring frosts. Contour-planting on high rolling land escapes frost damage. Tung makes its best growth on virgin land. Soils must be well-drained, deep aerated, and have a high moisture-holding capacity to be easily penetrated by the roots. Green manure crops and fertilizers may be needed. Dolomitic lime may be used to correct excessive acidity; pH 6.0–6.5 is best; liming is beneficial to most soils in the Tung Belt, the more acid soils requiring greater amounts of lime.

Cultivation

Tung trees may be propagated by seed or by budding. Seedlings generally vary considerably from parent plants in growth and fruiting characters. Seedlings which have been self-pollinated for several generations give rather uniform plants. Only 1 out of 100 selected 'mother' tung trees will produce seedlings sufficiently uniform for commercial planting. However, a `mother' tree proven worthy by progeny testing may be propagated by budding. The budded trees, which are genetically identical with the original tree, will provide an adequate supply of seed satisfactory for planting. Seedlings are used for the root system for budded trees. Buds from 'mother' trees are inserted in stems of 1-year old seedlings, 5–7.5 cm above surface of the soil. Later, original seedling top is cut off and a new top grown for p the transplanted bud, making the tops of budded trees parts of the parent tree. Usually seedling trees outgrow budded trees, but budded trees produce larger crops and are more uniform in production, oil content and date of fruit maturity. Tung seed are normally short-lived and must be planted during the season following harvest. Seeds are best hulled before planting, as hulls retard germination. Hulled seed may be planted dry, but soaking in water for 5–7 days hastens germination. Stratification, cold treatment or chemical treatment of seeds brings about more rapid and uniform germination. Dry-stored seed should be planted no later than February; stratified seed by mid-March; coldtreated and chemical treated seed by early April. Seed may be planted either by hand or with a modified corn-planter, the seed spaced 15–20 cm apart, about 5 cm, in rows 1.6 m apart, depending on the equipment to be used for cultivation and for digging the trees. Seeds germinate in 60 days or more, hence weed and grass control may be a serious problem. As soon as seedlings emerge, a side-dressing of fertilizer (5–10–5) with commercial zinc sulfate should be applied. Fertilizer is applied at rate of 600 kg/ha, in bands along each side of row, 20 cm from seedlings and 5–7.5 cm deep. Other fertilizers may be needed depending on the soil. Most successful budding is done in late August, by the simple shield method, requiring piece of budstock bark, including a bud, that will fit into a cut in the rootstock bar, a T-shaped cut is made in bark of rootstock at point 5–7.5 cm above ground level, the flaps of bark loosened, shield-bud slipped inside flaps and the flaps tied tightly over the transplanted bud with rubber budding stripe, 12 cm long, 0.6 cm wide, 0.002 thick. After about 7 days, rubber stripe is cut to prevent binding. As newly set buds are susceptible to cold injury, soil is mounded over them for winter. When growth starts in spring, soil is pulled back and each stock cut back to within 3.5 cm of the dormant bud. Later, care consists of keeping all suckers removed and the trees well-cultivated. Trees are transplanted to the orchard late the following winter. Spring budding is done only as a last resort if necessary trees are not propagated the previous fall. Trees may be planted 125–750 ha. When trees are small, close planting in rows greatly increases the bearing surface, but at maturity the bearing surface of a crowded row is about the same as that of a row with trees farther apart. However, it is well to leave enough space between row for orchard operations. In contourplanting, distances between rows and total number of trees per hectare vary; rows 10–12 m apart, trees spaced 3.3–4 m apart in rows, 250–350 trees/ha. Tops of nursery trees must be pruned back to 20–25 cm at planting. As growth starts, all buds are rubbed off except the one strongest growing and best placed on the tree. A bud 5 cm or more below top of stump is preferred over one closer to top.

Harvesting

Tung trees usually begin bearing fruit the third year after planting, and are usually in commercial production by the fourth or fifth year, attaining maximum production in 10–12 years. Average life of trees in United States is 30 years. Fruits mature and drop to ground in late September to early November. At this time they contain about 60% moisture. Fruits must be dried to 15% moisture before processing. Fruits should be left on ground 3–4 weeks until hulls are dead and dry, and the moisture content has dropped below 30%. Fruits are gathered by hand into baskets or sacks. Fruits do not deteriorate on ground until they germinate in spring.

Yields and Economics

Trees yield 4.5–5 MT/ha fruits. An average picker can gather 60–80 bushels of fruits per day, depending on conditions of the orchard. Fruits may be gathered all through the winter season when other crops do not need care. Because all fruits do not fall at the same time, 2 or more harvestings may be desirable to get the maximum yield. Fruits are usually sacked, placed in crotch of tree and allowed to dry 2–3 weeks before delivery to the mill. Additional drying may be done at the mill, but wet fruits contain less oil percentage-wise and prices will be lower. Prices for tung oil depend on price supports, domestic production, imports and industrial demands. World production in 1969 was 107,000 MT of tung nuts; in 1970, 143,000; and projected for 1980, 199,000. Wholesale prices are about $0.276/kg; European import prices, $0.335/kg. Growers receive about $51.10/ton of fruit of 18.5% oil content to about $63.10/ton for fruits of 22% oil content. Major producing countries are mainland China and South America (Argentina and Paraguay); United States and Africa much less than the others. U.S. Bureau of Census figures 1,587,000 pounds of tung oil were consumed during February of 1982, representing a 1,307,000 pound drop from January. The largest application for the oil is paint and varnish, which accounted for 566,000 pounds of total consumption in February (CMR, April 26, 1982).

Energy

During World War II, the Chinese used tung oil for motor fuel. It tended to gum up the engines, so they processed it to make it compatible with gasoline. The mixture worked fine (Page, 1981).

Biotic Factors

Bees are needed to transfer pollen from anthers to pistil. When staminate and pistillate flowers are on separate trees, one staminate tree for 20 pistillate trees should be planted in the orchard. Pollination can occur over several days. Tung trees are relatively free of insects and diseases, only a few causing losses serious enough to justify control measures: as Botroyosphaeria ribis, Clitocybe tabescens, Mycosphaerella aleuritidis, Pellicularia koleroga, Physalospora rhodina and the bacterium, Pseudomonas aleuritidis. Other bacteria and fungi reported on tung trees are: Armillaria mellea, Botryodiplodia theobromae, Cephaleures virescens, Cercospora aleuritidis, Colletotrichum gloeosporioides, Corticium koleroga, Fomes lamaoensis, F. lignosus, Fusarium heterosporum forma aleuritidis, F. oxysporum, F. scirpi, F. solani, Ganoderma pseudoferreum, Cloeosporium aleuriticum, Glomerella clngulata, Pestalotia dichaeta, Phyllosticta microspore, Phytomonas syringas, Phytophthora omnivora, Ph. cinnamomi, Poria hypolateritia, Pythium aphanidermatum, Rhizoctonia solani, Septobasidium aleuritidis, S. pseudopedicellatum, Sphaerostilbe repens, Uncinula miyabei, var. aleuritis, Ustilina maxima, U. zonata. Insect pests are not a serious problem, since fruit and leaves of tung trees are toxic to most animal life. Nematodes Meloidogyne spp. have been reported (Golden, p.c. , 1984).

References

Complete list of references for Duke, Handbook of Energy Crops
Last update December 19, 1997