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Page 307 Tamarillo (TreeTomato) The tamarillo or tree tomato 1 (Cyphomandra betacea) is native to the Andes, and has been cultivated on mountainsides since long before Europeans arrived. Today, it is grown in gardens from Chile to Venezuela, and its fruits are among the most popular of the region. On the Colombian and Ecuadorian uplands, for instance, it is found in every city, including Bogotá and Quito. Although distributed throughout much of the world's subtropics, this little tree is usually produced only on a small scale in home gardens. Few people have ever considered it for large-scale orchard production, and it has hardly been developed commercially as yet. However, development of this crop is under way in one country, New Zealand, where tamarillos have been popular for more than 50 years. They got a particular boost during World War II, when bananas and oranges could not be imported. During the last half-century, New Zealand horticulturists have made selections, developed improved fruit types, and created a commercial industry. Indeed, the fruits have become widely popular—children take them to school in their lunch boxes, and until the kiwifruit “boom” of the 1960s, more New Zealand acreage was devoted to tamarillos than to kiwifruit. New Zealand is already demonstrating this fruit's international potential. It is airfreighting tamarillos to North America, Japan, and Europe, and the trade is said to be expanding. Tamarillos are egg shaped, and have attractive, glossy, purplish-red or golden skins. Inside, they look somewhat like a tomato, but their succulent flesh has a piquancy quite unlike that of its more famous cousin. This fruit seems to have a bright future; it is flavorful, pretty, and has flexible uses and a long production season. Moreover, its “tropical” tang could be an asset in the increasing international markets for exotic 1 In English, the plant is traditionally called “tree tomato.” The name “tamarillo” was devised in New Zealand in 1967. it is becoming the standard designation for the fruit in international commerce, and is even becoming common in the Andes, where the name “tomate de árbol” (tree tomato) has been traditional.

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Page 308 ~ enlarge ~ The tamarillo looks much like an oval-shaped tomato, but it grows on a small tree and has a sharp, tangy, unique flavor. (N. Vietmeyer) fruit juices as well as for processed products such as jams, chutneys, sauces, and flavorings for ice creams. For warm-temperate areas, an additional advantage is that tamarillos fetch premium prices because they ripen late in the growing season when few other fresh fruits are available. All in all, this unusual fruit should not be unusual much longer. At present, through lack of horticultural and scientific attention, its true potential has scarcely been touched. PROSPECTS The Andes. The tamarillo, already well known in the Andes, is little promoted, and its potential is far greater than is recognized at present. The trees, by and large, receive little management, and by export standards, the fruits in Andean markets are far from premium quality. Selection and propagation of elite cultivars, 2 better management of the plants, and better handling of the fruits would enhance this crop's prospects. 2 The red-fleshed strain is already being widely cultivated in Colombia because farmers receive premium prices for it. Information from L.E. Lopez J.

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Page 309 With sufficient effort, Andean countries could be at the forefront of an expanding international commercial industry. Colombia has already begun exporting a juice concentrate as well as fresh fruits. If the plant is given research and promotion, this could spark a new Andean industry. Cooperatives of small growers may be particularly adapted to providing the fruits. Other Developing Areas. The tamarillo has much promise for frost-free, subtropical, and warm-temperate areas. A few plants in the home garden can add good nutrition and a novel taste to the family diet. It is particularly good for home use because it is easily propagated, and when grown in warm regions it provides fruits year-round. Also, the trees are very high yielding. Undoubtedly, it has an important future in cool highlands of Third World countries, but true frost-free lands that are not too hot for this plant are uncommon. Industrialized Regions. New Zealand's selection of attractive cultivars and the development of shipping and storage techniques has resulted in a relatively obscure fruit entering international trade within the past decade. This experience is demonstrating that there is a real future for the tamarillo. Research is needed, however, to improve production, particularly in such matters as fruit type and palatability, virus control in the orchards, and yield variability (there is a specific need to create uniform fruit set). The rather acid taste of the fruits arriving in international markets is hindering greater acceptance of the tamarillo as a fruit to be eaten raw. Most likely, sweeter fruit will soon become available from selected cultivars or from improved handling, and this will certainly increase its popularity. As they enter the markets and are promoted, tamarillos could become a common commodity in the produce markets of North America, Europe, Japan, and other regions. The richly colored juice of tamarillos (especially of the deep red types) seems to have much potential for blending with grapefruit and other juices whose consumer appeal may be increased by the added color. USES Ripe tamarillos have fine eating qualities and can be used in many ways. They are usually cut in half, and the flesh scooped out. As with common tomatoes, the seeds are soft and edible. The skin is easily removed—it peels off when dipped briefly in hot water. The fruits are especially good on desserts such as cakes and ice cream, in fruit salads, or (like tomatoes) in sandwiches and green salads. The whole

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Page 310 fruit (including skin) can be liquidized and drunk. In South America, such juices are frequently blended with milk, ice, and sugar to make tasty drinks. 3 Tamarillos are also cooked and eaten in stews, soups, baked goods, relishes, and sweet and savory sauces. In New Zealand, diced tamarillos, with onion, breadcrumbs, butter, and appropriate seasonings, are becoming popular as a stuffing for roast lamb—the national dish. Being high in pectin, tamarillos make good jellies, jams, preserves, or chutneys, but they oxidize and discolor unless treated. The fruit freeze well, either whole (peeled) or pureed, and can be stored this way almost indefinitely. NUTRITION Tamarillos are excellent sources of provitamin A (carotene–150 International Units per 100 g), vitamin B6, vitamin C (25 mg per 100 g), vitamin E, and iron. They are low in carbohydrates; an average fruit contains less than 40 calories. AGRONOMY The plant is usually grown from seed. Seedlings develop a straight, erect trunk about 1.5 m tall before branching. New Zealand practice is to prune seedlings early to encourage multiple stems, which makes the fruit easier to reach and reduces chances of heavily laden trees toppling over. Normally, the trees begin bearing within 18 months of planting out. Peak production is reached usually in 3–4 years. The plant is self-compatible; it can set fruit without cross-pollination. However, the fragrant flowers attract many bees, the trees produce flowers abundantly, and pollination seems to improve fruit set. Because of a shallow, spreading root system, deep cultivation is not possible close to the trees. Also, perhaps as a result of the shallow roots, the plant cannot tolerate prolonged drought. Mulches help conserve moisture and suppress weeds, but during dry periods, ample water must be available. Although adaptable and easy to grow, the tree seems to be short-lived; the life of a commercial plantation is usually no more than eight years. Pruning can be used to make the harvest coincide with periods of peak demand, such as in the off-season. 3 For example, a thick, rich drink made of the fruit and served with chopped fruit on top is popular in Cali, Colombia, and sells under the New Zealand name “tamarillo.”

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Page 311 ~ enlarge ~ Bay of Plenty, New Zealand. Tamarillo harvest. (P. Sale) HARVESTING AND HANDLING Fruits occur in clusters. They can be formed year-round, but in seasonal countries (such as New Zealand) there is a distinct harvesting season. Because the fruits do not mature simultaneously (unless the tree has been pruned), several pickings are usually necessary. The fruits pull off readily, carrying a short stem still attached. The trees bear prolifically and yield generous harvests. A single tree may produce 20 kg of fruit or more each year; commercial yields from mature orchards in New Zealand can reach 15–17 tons per hectare. In handling tamarillos, the most serious problem is fungal rot (glomorella) on the stem, which can quickly extend into the fruit. Copper sulfate (bordeaux mixture) controls this adequately. The New Zealand Department of Scientific and Industrial Research has developed a cold-water dipping process that is also effective. Storage of 6–10 weeks is then possible. LIMITATIONS To develop tamarillo into a practical, widespread crop will not be quick or easy. Even selected New Zealand cultivars usually produce

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Page 312 a variable product, insufficiently reliable to assure importers that shape, color, or sugar:acid ratio will remain consistent lot by lot and year by year. Nor are future yield levels predictable. Large leaves and brittle wood make the trees prone to wind damage. Even light winds easily break off fruit-laden branches. In most locations, permanent windbreaks should be established at least two years before the plants are set out. Even then, staking may be needed to keep branches from breaking under the weight of fruit. Small, hard, irregular, “stones,” containing large amounts of sodium and calcium, occasionally appear in the fruits. They usually occur in the outmost layers of the fruit and do not present much of a problem in fresh fruits because those layers are not eaten. In canning, however, they are a concern because the whole fruit is used. Probably the best solution is a breeding program to select for types without these concretions. The tree is generally regarded as fairly pest resistant. However, some pests of concern are given below. Viruses In most places, viruses are the most significant diseases. They reduce the plant's vigor and can leave unattractive splotches on the fruit. Newly emerged seedlings are, as a rule, virus free, but unless precautions are taken they soon become infected. (The vectors are mainly aphids.) 4 Nematodes Root-knot nematodes damage plants, particularly in sandy soils. Insects The trees are attacked by aphids and fruit flies, and whitefly is sometimes a serious pest. 5 In the Andes, the tree-tomato worm (which also infests the tomato and the eggplant) feeds on the fruits, sometimes causing heavy losses. Fungi The principal fungal disease is powdery mildew, which can cause serious defoliation. Dieback A dieback of unknown origin is at times lethal to the flowers, fruits, twigs, and new shoots. RESEARCH NEEDS Germplasm Collection More types need to be collected and information on their economic traits developed. Identifying and selecting 4 Paradoxically, tree tomatoes are notable for their apparent resistance to tobacco mosaic—a virus that affects tobacco, potatoes, tomatoes, and other solanaceous crops. The plant is perhaps a source of virus-resistant genes for those crops. 5 In warmer areas, biological control with the wasplike insects Encarsia formosa and E. pergandiella appears promising. Information from P. Sale.

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Page 313 superior germplasm—especially that found in the Andes—could assist breeding programs and speed the tamarillo industry toward success. Breeding To support the orderly genetic development of this crop, more information is needed on the plant's reproduction habits and genetics. Long-term breeding aims should include virus-resistant trees, low-growing trees, and deeper-rooted trees. To increase yields, improved fruit set is needed. This is probably not genetic, but the reason for flower and fruit abortion is not established. Other breeding goals should be: The development of pure seed lines to enable the growing of desirable types from seed; Raising sugar:acid ratios; Developing fast-maturing and cold-hardy types to increase the area of potential use in temperate climates; and Creating dwarf cultivars. Plantation Management Improvements are needed in orchard practice and management. Among specific research needs are the following: Controlling viruses; Increasing fruit set; Developing fertilizer requirements; Learning the ideal pH level; Applying trickle and overhead irrigation; Developing growing systems; Understanding the plant's nutrition; and Breaking seed dormancy. 6 Biological control of the tree-tomato worm should be sought for use in the Andes. (Perhaps Bacillus thuringensis would be useful.) Sweetness There seems to be a good possibility that the sweetness of the deep-red fruits can be raised. Already, sweet types are known; however, these are mostly smaller or less eye-catching. Nevertheless, low-acid red specimens have been reported. 7 These deserve greater attention because the combination of the spectacular red color with a sweet taste would cause this appealing fruit to take off. Stones The cause of the “stones” should be determined, and methods developed to eliminate or circumvent this nuisance. 6 Information in this list is mostly from J. Laurenson and represents current goals of New Zealand tamarillo research. 7 Information from S. Spangler. One New Zealand variety, Oratia Red, is sweeter than normal, but even sweeter types seem possible.

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Page 314 Postharvest Handling Work should continue on storage and handling to increase shelf life and to enable tamarillos to be shipped by sea—a development expected to greatly improve the export situation for most countries. Important advances have already been made. Hybrids Several closely related species (see below) produce good fruit, and there is the potential of developing hybrid tamarillos, perhaps with seedless fruits and different flavors. There seem to be substantial genetic barriers to interspecific hybrids, however. 8 Nonetheless, cell fusion and gene splicing, which seem particularly easy in Solanaceae, might prove practical. Tissue Culture Tissue-culture techniques have been developed for the tamarillo. Although their main use will be in multiplying improved material for planting, they are possibly useful in genetic selection and in propagating of difficult hybrid crosses and haploids. Colchicine treatment to produce fertile plants from haploids should be attempted. Work is currently under way to select a virus-resistant strain with the aid of tissue culture. In the meantime, however, virus resistance should be sought in wild species. SPECIES INFORMATION Botanical Name Cyphomandra betacea (Cavanilles) Sendtner Family Solanaceae (nightshade family) Common Names Spanish: tomate de árbol, tomate extranjero, lima tomate, tomate de palo, tomate francés Portuguese: tomate de érvore, tomate francês English: tree tomato, tamarillo Dutch: struiktomaat, térong blanda German: Baumtomate Italian: pomodoro arboreo Origin. The tamarillo is unknown in the wild state, and the area of its origin is at present unknown. It is perhaps native to southern Bolivia (for example, the Department of Tarija) and northwestern Argentina (the provinces of Jujuy and Tucumán). Description. The plant is a fast-growing herbaceous shrub that reaches a height of 1–5 m (rarely 7.5 m). It generally forms a single upright trunk with spreading lateral branches. The leaves are large, shiny, hairy, prominently veined, and pungent smelling. 8 Information from L. Bohs.

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Page 315 Flowers and fruits hang from the lateral branches. The pinkish flowers are normally self-pollinating, but can require an insect pollinator; unpollinated flowers drop prematurely. The fruits are egg shaped, pointed at both ends, 4–10 cm long and 3–5 cm wide, smooth, thin-skinned, and long-stalked. The skin color may be yellow or orange to deep red or almost purple, sometimes with dark, longitudinal stripes. The flesh inside is yellowish, orange, deep red, or purple. It has a firm texture and numerous flat seeds. The most flavorful and juicy flesh lies toward the center of the fruit, becoming more bland toward the skin. Horticultural Varieties. Although there is much variety in the fruits and many local preferences based on color, there are apparently at present few named cultivars. Growers normally select their own trees for seed selection. In New Zealand, where the most extensive selection has taken place, two strains are cultivated: red and yellow. Oratia Red (or Oratia Round) was the first recognized cultivar. The red strain has a stronger, more acid flavor and is more widely grown. Yellow fruits have a milder flavor and are preferred for canning. A dark-red strain (called “black”) was selected in New Zealand in about 1920 as a variation from the yellow and red types. It was propagated and reselected thereafter. Environmental Requirements Daylength. Unknown; probably daylength-insensitive. Rainfall. Cannot tolerate prolonged drought, nor waterlogged soils or standing water. Altitude. Unrestricted. Grows at 1,100–2,300 m at the equator in the Andes; near sea level in New Zealand and other countries. Low Temperature. This species is injured by frost. Short periods below −2°C kill all but the largest stems and branches. High Temperature. In tropical lowlands, tamarillos grow poorly and seldom set fruit. (Fruit set seems to be affected strongly by night temperature.) The plant seems to do best in climates where daytime temperatures range between 16 and 22°C during the growing season. Soil Type. Fertile, light, well-drained soil seems best. Related Species. The genus Cyphomandra, native to South and Central America and the West Indies, contains about 40 species. Many

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Page 316 that are grown for their fruits remain to be investigated. Several are said to produce fruits as good as those of the cultivated tamarillo. These may hold potential as economic crops in their own right, or as germplasm sources for improving the tamarillo. Fruit-bearing species deserving special studies include the following: Cyphomandra casana (C. cajanumensis) Found growing wild on the edge of rain forests in the highlands of Ecuador, especially in the Loja Province. Like the tamarillo, the casana grows rapidly to a small tree, 2 m tall. Its large, furry, deep-green leaves make it an interesting ornamental, but it also produces heavy crops of mild-flavored fruits in about 18 months. The fruits are spindle shaped and golden yellow when ripe. They are sweet, juicy, and said to be rather like a blending of peach and tomato in flavor. The casana seems to need cool growing conditions. Unlike the tamarillo, the casana fruit is a poor shipper. A breeding program for selection of firmer, larger, and better colored fruit could yield a fruit of commercial value. It deserves special attention from horticulturists and scientists as a source of genetic material for such qualities as nematode resistance, root rot resistance, fragrance, flavor, color, and yield. Cyphomandra fragrans Compared with the tamarillo, this tree has greater tolerance to powdery mildew, a smaller and more robust stature, basal fruit abscission (the fruits break away clean without the stalk as found on tamarillos), and a greater degree of cold hardiness. Its fruits resemble small tamarillos, but have a thick and leathery orange skin. Like most solanaceous fruit, it is somewhat acid. Cyphomandra hartwegi This species has an extensive natural range, but is not yet commercially cultivated. Apparently, it has not even been tested as a potential crop. It has a yellow berry about the size of a pigeon's egg.