Prota 2: Vegetables/Légumes
Gard. dict. ed. 8, Lycopersicon n. 2 (1768).
2n = 24
Solanum lycopersicum L. (1753), Lycopersicon lycopersicum (L.) H.Karst. (1882).
Tomato (En). Tomate (Fr). Tomate (Po). Nyanya (Sw).
Origin and geographic distribution
The genus Lycopersicon, comprising 9 species, has its origin in the South American Andes, from central Ecuador through Peru to northern Chile; one species is endemic in the Galapagos Islands. Wild plants of Lycopersicon esculentum are more widespread and have been perhaps more recently distributed into other South American regions and into Mexico. Archaeological, ethnobotanical and linguistic evidence suggest that tomato was domesticated in Mexico, outside its centre of origin. Shortly after the Spanish conquest of Mexico in 1521, the cultivated tomato was brought to Europe, where its fruits were initially not considered edible (except in Italy) because of the erroneous assumption that they would be poisonous like many other Solanaceae species. Tomato was introduced from Europe to southern and eastern Asia in the 17th century and subsequently to the United States, Africa and the Middle East. Tomato has become one of the most important vegetables worldwide.
Tomato fruits are consumed fresh in salads or cooked in sauces and used as a flavouring in soups and meat or fish dishes. They are made into sweetened candies, dried fruits, and even into wine. Economically equally important are the processed forms such as purée, juice, ketchup, canned whole and diced fruits.
Production and international trade
World tomato production in 2001 was about 105 million t fresh fruit from an estimated 3.9 million ha. Leading tomato producing countries are China with 934,000 ha, India 500,000 ha, Commonwealth of Independent States (formerly Soviet Union) 345,000 ha, Turkey 225,000 ha, Egypt 181,000 ha, United States 164,000 ha and Italy 124,000 ha. In 2001 world exports of fresh tomato fruits were estimated at 4 million t, valued at 3000 million US$ (mainly from Spain, Netherlands and Mexico with about 600 million US$ each). World export of tomato paste is about 1.8 million t, valued at 1000 million US$ (mainly from Italy with 400 million US$). The area used for tomato production in tropical Africa is about 300,000 ha with an estimated annual production of 2.3 million t. Nigeria is the largest producer with 126,000 ha and an annual production of 879,000 t. There is some international trade of fresh tomatoes between African countries, but no data are available. South Africa exports fresh tomato fruits to neighbouring countries. In Zimbabwe and Zambia, there is a small but growing export of dried fruits to Europe.
Fresh ripe tomato fruits contain per 100 g: water 93.1 g, energy 73 kJ (17 kcal), protein 0.7 g, fat 0.3 g, carbohydrate 3.1 g, Ca 7 mg, Mg 7 mg, P 24 mg, Fe 0.5 mg, Zn 0.1 mg, carotene 0.64 mg, thiamin 0.09 mg, riboflavin 0.01 mg, niacin 1.0 mg, folate 17 μg, ascorbic acid 17 mg (Holland, B., Unwin, I.D. & Buss, D.H., 1991). Most of the carbohydrate occurs as sugars. Although tomato fruits rank low in comparative nutritional value, they outrank all other vegetables in total contribution to human nutrition because so much is consumed in so many different ways. The contents of soluble solids (fructose, glucose and sucrose) and organic acids (citric, malic, galacturonic and pyrrolidone carboxylic), but even more the sugar/acid ratio, are important determinants of taste and can be assessed by standard analytical methods. However, minute quantities of numerous volatile substances also contribute to the flavour, and sensory tests remain indispensable for the judgement of the quality of tomato fruits. Some important aroma chemicals, which are associated with lycopene formation and flavour development during ripening of tomato fruits, are 6-methyl-5-hepten-2-on, β-ionone, β-damascenone and geranylaceton. Tomato fruits for processing should have a high (> 5.5%) soluble solid content. Immature fruits contain the alkaloid tomatine. Lycopene (E 160-d) is the dominant carotenoid responsible for the colour in red tomato fruits and β-carotene in yellow ones. The antioxidant properties of lycopene may contribute to protection against carcinogenic substances. The seed contains 24% of a semi-drying edible oil.
Annual herb, with erect to prostrate stems up to 2(–4) m long; taproot strong, to 0.5 m deep or more, with a dense system of lateral and adventitious roots; stem solid, coarsely hairy and glandular. Leaves arranged spirally, imparipinnate, in outline 15–50 cm × 10–30 cm; stipules absent; petiole 3–6 cm long; leaflets varying in size, usually 7–9 larger ones per leaf, these ovate to oblong, 5–10 cm long, irregularly toothed and sometimes pinnatifid at base, and a variable number of smaller ones, leaflets covered with glandular hairs. Inflorescence a cyme, normally 6–12-flowered, but sometimes compound and up to 100-flowered. Flowers bisexual, regular, 1.5–2 cm in diameter, pendent, (5–)6(–7)-merous; calyx with short tube, green, lobes pointed, persistent and enlarging on fruit; corolla stellate, yellow, lobes becoming reflexed, caducous; stamens inserted on the corolla, anthers bright yellow, connivent to form a flask -shaped cone, surrounding the style, with an elongated sterile tip; ovary superior, 2–9-celled. Fruit a berry, globular to oblate, 2–15 cm in diameter, smooth or furrowed, green and hairy when young, glabrous and shiny, usually red, sometimes pink, orange or yellow when ripe, many-seeded. Seeds flattened ovoid, 3–5 mm × 2–4 mm, pale brown and hairy, embryo coiled in endosperm. Seedling with epigeal germination.
Other botanical information
Research on phylogenetic relationships, using morphological characteristics but also molecular markers, indicates that Lycopersicon should be included in Solanum and is closely related to potato and its wild relatives. However, the systematic placement of tomato in Solanum (as Solanum lycopersicum in section or subsection Lycopersicum) is still controversial in that it has yet to gain universal acceptance, and the treatment in Lycopersicon can be justified by the maintenance of nomenclatural stability in this economically important crop.
Lycopersicon esculentum can be hybridized with the other 8 Lycopersicon species, but with 2 of these, the self-incompatible Lycopersicon peruvianum (L.) Mill. and Lycopersicon chilense Dunal, hybridization is only possible with the aid of embryo culture or by pollination with a mixture of auto- and allo-pollen. Most wild Lycopersicon species have contributed to the genome of modern tomato cultivars.
Numerous cultivars of tomato exist. They can be variously classified, e.g. according to:
– growth habit: indeterminate, semi -determinate or determinate (bushy);
– fruit size: small round (cherry tomato, < 30 g; ‘Moneymaker’, 80 g), medium-large round (120–150 g), beefsteak and ribbed (> 200 g);
– fruit shape: round, heart-shaped, pear-shaped, plum-shaped, elongated or flat;
– colour of ripe fruit: red, pink, orange or yellow;
– utilization: for fresh market (direct consumption) or processing (high soluble solid content and viscosity).
In tropical Africa, many farmers still use open-pollinated cultivars, both fresh market and processing types. ‘Floradade’, ‘Heinz 1370’, ‘Marglobe’, ‘Super Marmande’, ‘Moneymaker’, ‘Rio Fuego’, ‘Rio Grande’ and ‘Roma VF’ are some of the important tomato cultivars found in tropical Africa. AVRDC cultivars ‘Tanya’ and ‘Tengeru 97’ have become popular in Tanzania, and ‘Xina’ (from ISRA) in West Africa. It is expected that F1 hybrids will increasingly replace open-pollinated cultivars. In West Africa F1 ‘Mongal’ is gaining importance. It is heavy yielding and suitable for cultivation under hot and humid conditions. Many farmers in lowland tropical Africa and the Caribbean grow local cultivars of uncertain origin. They have somewhat sour and bitter-tasting fruits, small, round or flat, many-celled, and are especially suitable for grinding with condiments for sauces. They show considerable genetic variation including disease resistance, e.g. to bacterial wilt and fungal diseases. They give a better yield than most imported cultivars under the heavy environmental stress of the rainy season.
Growth and development
Dry seed (5.5% moisture content) extracted from fully mature fruits remains viable for several years at ambient (18–24°C) temperatures. Seeds germinate within 6 days after sowing at optimum soil temperatures (20–25°C). Seedlings have a thin taproot and ovate cotyledons; the first leaves have few leaflets. On the main stem 7–14 leaves are usually formed before the apex is transformed into a terminal inflorescence. Further growth is sympodial. In indeterminate cultivars sympodial growth continues indefinitely with inflorescences every 3rd leaf and fruits maturing sequentially over a long period of time. In determinate types growth is arrested after 4–6 inflorescences, when the primary axillary bud of the last leaf aborts and the next bud develops into a slower growing shoot with one leaf and a terminal inflorescence. Strong axillary bud development at the base of determinate types produces their bushy habit with several stems and a short period of prolific flowering followed by a period when fruit growth is dominant. In processing tomato fruits, synchronization of fruit growth and ripening is such that once-over machine harvesting is possible.
Under optimum conditions first flowering starts 5–7 weeks after sowing. Lycopersicon esculentum is autogamous, but up to 47% natural cross-pollination may take place. Bees and bumble bees are the most important pollinators; they are also increasingly used in glasshouses to stimulate anther dehiscence. Anthesis starts at around 6 a.m. and anther dehiscence takes place from 7–10 a.m., depending upon temperature, humidity and sunshine. Pollen grains remain viable for 2–5 days at temperatures ranging from 18–25°C. The stigma becomes receptive 16–18 hours before anthesis and remains so for 5–6 days at an optimum temperature of 18–25°C. High temperatures affect the viability of pollen grains and egg cells, resulting in a high degree of outcrossing in the tropics. More than 60 genes of male sterility have been reported in tomato. Many of these genes are recessive, but very few have found application in hybrid seed production so far, due to environment-dependent variation in expression of male sterility. Pollen tube growth is slow and fertilization takes place 50–55 hours after pollination. Fruits are mature 6–8 weeks later. Adequate seed set is necessary for normal fruit development, but parthenocarpic fruit set occurs in some types, or can be induced by growth regulators. The duration to peak harvest (50% of the crop) depends on cultivar and season: in the cool season 90–110 days after transplanting, during the hot season after 60–90 days. Each fruit contains numerous seeds embedded in its locules, ranging from 50–80 in cherry tomato to as many as 250 in fresh market cultivars.
Tomato requires a relatively cool, dry climate for high yield and premium quality. However, it is adapted to a wide range of climatic conditions, from temperate to hot and humid tropical. The optimum temperature range for growth and development is 20–27°C. Prolonged exposure to temperatures below 10°C can cause chilling injury, below 6°C can result in plant death. Mean temperatures below 13°C and above 27°C severely impair fruit set. Destruction of pollen and egg cells occurs when the maximum daytime temperature is 38°C or more for 5–10 days. Fruit set is generally poor at night temperatures above 20°C for a few days before and after anthesis. Hot dry winds can also cause flower abortion. Light intensities below 11,000 lux retard plant growth and delay flowering. Tomato is not sensitive to daylength and sets fruit in photoperiods ranging from 7–19 hours.
Tomato can be grown in many soil types, from sandy loam to clay-loam soils that are rich in organic matter. It is sensitive to waterlogging and flooding and prefers well-drained soils. The optimum soil pH range is 6.0—7.0; higher or lower pHs can cause mineral deficiencies or toxicities.
Nutrition plays a major role in increasing productivity. Fertilizer for tomato should be fairly rich in phosphorus. Excess nitrogen is associated with excessive vegetative growth, fruit puffiness and blossom-end rot. The amount of fertilizer and the timing of its applications vary with soil type and cultivar. In tropical Africa, fertilizer recommendations include 80–180 kg N, 80–200 kg P, 80–200 kg K and 25 t of farmyard manure per ha. The entire doses of farmyard manure and phosphorus are applied before transplanting. The farmyard manure is applied before final ploughing, whereas phosphorus is applied on both sides of the rows and mixed with the top 8–10 cm of soil. Nitrogen and potassium are applied in three equally split doses. The first dose is given before transplanting as basal dressing, the second one 3 weeks after transplanting, and the last one 2 weeks later.
Indeterminate cultivars are often grown on stakes. Pruning their lateral shoots is often practised, to produce fruits of good and uniform size. Sufficient leaves should be left on the plant to prevent sun scalding (direct insolation) and cracking (after excessive rain or irrigation) of the fruits. Depending on local practice only 1–2 stems may be allowed to grow. The number of fruits per cluster as well as the number of clusters may also be regulated. Little pruning or regulation of fruit number and clusters is normally practised on determinate cultivars.
Competition from weeds, especially in the hot and humid tropics, can be very severe. To control weeds, a pre-emergence herbicide may be used before transplanting, supplemented by manual weeding and mulching the beds with straw. Crop rotation with non-solanaceous crops is recommended to reduce soil-borne diseases and pests.
Tomato needs adequate irrigation during the early plant growth, fruit set and fruit enlargement stages. About 20 mm of water per week is needed under cool conditions; about 70 mm during hot and dry periods. Constancy of water supply plays a major role in attaining uniform maturity and reducing the incidence of blossom-end rot, a physiological disorder associated with irregular water suply and the resulting calcium deficiency in the fruit during its enlargement.
Propagation and planting
Tomato seeds are considered non-dormant. Tomato can be direct-seeded or transplanted in the field. Relatively little seed-drilling or direct sowing into the field is practised in the humid tropics because of adverse growing conditions. In contrast, raising young transplants in a nursery enables growers to obtain uniform seedlings and to check early diseases and pests. Other advantages of transplanting are the smaller quantity of seed needed and reduced competition from weeds in the field. The 1000-seed weight is 2.5–3.5 g. To raise transplants, 150–200 g seeds are sown per 250 m2 of seedbed, which provides enough plants for 1 ha. When direct-seeded, the sowing rate is 500–1000 g seed per ha. Fertilizer at a rate of 10 g N, 10 g P, 15 g K and 2 kg farmyard manure per 1 m2 of seedbed area should be worked into the seedbed. The young seedlings require ample water to sustain good, healthy growth. Seedling losses caused by damping-off diseases are often controlled effectively by solarization of the seedbed, or by drenching the soil with fungicides such as Previcur N (propamocarb-hydrochloride), prior to sowing. A week before transplanting, watering should be reduced to harden the seedlings. Seedlings are ready for transplanting when 3–4 weeks old (15–25 cm tall with 3–5 true leaves). They should be thoroughly watered 12–14 hours before they are lifted out of the seed-bed to avoid excessive damage to the roots. Transplanting should be done in the afternoon or on a still, cloudy day to reduce the transplanting shock, and should be followed by watering. Spacing between plants and distance between rows depends on the cultivar’s growth habit and whether the plants are to be supported by stakes or left to grow on the ground. Common spacings are 30–60 cm apart in single or double rows on 1.0–1.4 m wide beds.
Diseases and pests
Some 45 diseases and more than 20 pests may attack the tomato plant, but only those having a depressing effect on yield and fruit quality in tropical Africa are described here. Bacterial wilt (Ralstonia solanacearum) is the most important soilborne disease in tropical regions, particularly in the humid lowlands. Some of the recommended methods to prevent or reduce bacterial wilt infection are the use of resistant/tolerant cultivars, long-term crop rotation, e.g. with cereals, planting tomato after paddy rice or flooding the field for 3–4 months before planting, but avoiding land previously cropped with banana. There is no effective chemical control. Bacterial wilt resistance also provides some protection against bacterial canker (Clavibacter michiganense). Bacterial spot (Xanthomonas campestris pv. vesicatoria) can be serious during the rainy season and is most noticeable on fruits, but also causes damage to the foliage and stems. It is transmitted by seed. Spraying with copper fungicides can control this disease fairly well except under heavy infection.
Soilborne fungal diseases such as Fusarium wilt (Fusarium oxysporum f.sp. lycopersici) and Verticillium wilt (Verticillium dahliae) sporadically occur in tropical highlands. Host resistance is present in several tomato cultivars. The stem base of tomato plants can be affected by southern blight (Sclerotium rolfsii), especially in the presence of poorly decomposed organic matter, and by Phytophthora root rot (Phytophthora parasitica and Phytophthora capsici) under excessive irrigation or rainfall. Potentially very destructive fungal diseases affecting leaves, stems and fruits are early blight (Alternaria solani) in hot and humid lowlands and late blight (Phytophthora infestans) in the cooler tropical highlands during the rainy season. Fungicide sprays remain the only means to control early blight, but for late blight commercial cultivars with host resistance are gradually becoming available. Other fungal diseases include grey leaf spot (Stemphylium spp.), leaf mould (Fulvia fulvum), black leaf mould (Pseudocercospora fuliginea), internal powdery mildew (Leveillula taurica), Septoria leaf spot (Septoria lycopersici) and target spot (Corynespora cassiicola). Cultivars with resistance to grey leaf spot and leaf mould are adequately protected against these two diseases under tropical conditions.
Important virus diseases in tropical Africa are tomato yellow leaf curl virus (TYLCV) and tomato spotted wilt virus (TSWV). Depending on the virus, transmission is by whitefly (Bemisia tabaci pour le TYLCV) and thrips (Frankliniella spp. pour le TSWV). Some varieties tolerant to these two viruses have recently become available. Raising tomato seedlings under an insect -proof net, early control of the insect vectors and general field sanitation can serve well to control TYLCV and TSWV.
Where two different major diseases occur, host resistance in a cultivar to both pathogens is of great advantage. Examples are F1 hybrid cultivar ‘Opal’ for bacterial wilt and late blight (at intermediate altitudes) and F1 hybrids ‘Mongal’ and ‘Somtam’ for bacterial wilt and TYLCV.
Among the insect pests, the polyphagous tomato fruitworm or army worm (Helicoverpa armigera) is one of the most destructive, causing yield losses as high as 70% due to fruit boring. A spray programme with Biobit 2X (Bacillus thuringiensis) or locally approved insecticides provides good control of eggs and caterpillars before fruit entry. Tomato should not be planted near alternative hosts such as maize or cotton. Whitefly (Bemisia tabaci) is a serious pest, not only because of its foraging on tomato plants, but also because it is a vector of TYLCV. The recent aggravation of TYLCV in tropical Africa is probably linked to the proliferation of whitefly due to the excessive use of synthetic pyrethroids. The thrips Frankliniella occidentalis has become a problem as the main vector of TSWV. Aphid proliferation is somewhat reduced by glandular hairs. On the other hand, the mite Aculops lycopersici (synonym: Vasates lycopersici) feeds on such hairs, inducing bronze-like discoloration of the stem and leaf necrosis during dry and hot periods of more than two weeks. It can be controlled by sulphur dusting or spraying or with specific acaricides.
Root-knot nematodes (Meloidogyne incognita and other species) invade tomato roots and cause galling. Yield losses caused by direct infection and indirect losses due to predisposition or breakdown of resistance to other root diseases, such as bacterial wilt, are significant. The use of resistant cultivars, e.g. F1 ‘Mongal’, ‘Tengeru 97’ ou ‘Xina’ (resistant also to Xanthomonas), is still the most cost-effective measure, although breakdown of resistance can occur at high soil temperatures. So far, no host resistance to Meloidogyne hapla has been found. Cultural measures to avoid nematode infestations are crop rotation with non-hosts (grasses, amaranths) and increasing the organic matter content of the soil. Occasional fruit damage by birds feeding on the seeds may require bird-scaring or growing the tomato plants under netting.
Fresh-market tomato fruits are often harvested at different stages of ripeness, from mature green to pale pink, depending upon distance and time needed to market the fruit. Generally, fruits harvested at pre-ripe stages tend to have lower quality (i.e. lower soluble solids, ascorbic acid and reducing sugars) than fruits ripened on the plant. The nature of the growth and ripening pattern of fresh-market tomato cultivars requires frequent pickings.
In contrast to the fresh-market or table tomato fruits, processing fruits are picked when fully ripe. In developed countries harvesting is often by machine. Tomato fruits used for pureed products such as soup, juice and sauce, are left on the plant until over 85% of them are ripe. Those for whole fruits are picked while still firm, but often only 65% of the crop may be ready to pick at any one time. So-called ‘jointless’ fruit stalks allow mechanical harvesting of processing fruits devoid of stalk and calyx. On the other hand, stalks and calyx usually remain attached to fresh -market tomato fruits as a result of jointed stalks.
The world’s average tomato yield in 2001 was 27 t/ha, but in tropical Africa only 8 t/ha of fruits are obtained on average from an open-field tomato crop. Some average yields per country are: Nigeria 7 t/ha, Kenya 12 t/ha, Egypt 35 t/ha, France 120 t/ha. Extremely high tomato yields of 450–500 t/ha are obtained in heated and lighted glasshouses in the Netherlands with a harvesting period of 9 months from a single crop.
Seed yields are 100–150 kg/ha for F1 hybrids and up to 300 kg/ha for open-pollinated cultivars.
Handling after harvest
After picking, tomato fruits may be moved to a shady place to prepare them for the market. Properly sorted and graded fruits generally command a better market price than ungraded ones. The marketable fruits are packaged in containers, often 10–25-kg wooden or plastic boxes. Processing tomato fruits are popular in market gardens in the tropics because their firmer fruit better withstands long-distance transport over bad roads. Storage life of tomato fruits depends on the maturity stage at which they were picked and on the desired quality. Quality is highest when completely ripe, whether ripened artificially or on the plant. Ideally mature-green tomatoes should be stored for 7–10 days at 13–18°C with 85–90% relative humidity to ripen properly. Tomato fruits of modern ‘long-shelf life’ F1 hybrid cultivars, which combine fruit firmness with delayed ripening, can be harvested at the red-fruit stage and still be stored for more than two weeks before consumption. Colour is the single most important visual parameter of tomato quality as lycopene formation is also correlated with flavour. Lycopene development at temperatures above 30°C is generally poor. This is the main reason why many non-adapted tomato cultivars grown in the hot tropics tend to have a pale red or yellowish colour and are poorly flavoured.
Many institutional collections of cultivated and wild Lycopersicon exist. Some of these collections have been well described, evaluated and documented for use by tomato scientists, the most important one being the C.M. Rick Tomato Genetic Resources Center (TGRC) at the University of California, Davis, United States. The TGRC maintains at present about 1060 accessions of the 9 Lycopersicon and 4 related Solanum species, 960 accessions of monogenic (spontaneous and induced) mutants affecting all aspects of plant development, introgressed disease resistance genes and protein marker stocks, and 1190 miscellaneous accessions including linkage tester stocks, trisomics, translocations, Latin American cultivars and various progenies from interspecific pre-breeding. A large collection is also maintained at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan and the N.I. Vavilov Institute of Plant Industry (VIR) in Russia. Since modern improved cultivars are rapidly replacing the old landraces, the latter should be collected for future breeding purposes.
In tomato breeding, methods common to self-pollinated crops have been complemented with those specific to outbreeders. Selected inbred lines developed from intra- and interspecific crosses and backcrosses followed by line, pedigree and recurrent selection can be either released as cultivars or used as parent lines for the production of F1 hybrid cultivars. Although more expensive to produce (seed multiplication mostly by hand-pollination), F1 hybrids are often higher yielding as a result of transgressive hybrid vigour in crosses with genetically divergent inbred lines. However, the main advantage is the potential of combining several disease resistances and other interesting plant and fruit characters in one cultivar.
Many characters, including resistance to several diseases and pests, are controlled by monogenes. However, fruit quality, resistance to diseases like bacterial wilt and TYLCV, heat tolerance and other agronomic characters are inherited polygenically. Selection requires extensive field testing and progress is often much slower. Breeding work at the University of Florida has produced cultivars, such as ‘Florade’ (disease resistances, firm fruits and adaptation to the hot and humid summers of Florida), which have been progenitors of several cultivars recommended for tropical climates. Other important contributions have come from Hawaii (resistance to root-knot nematodes, genetic studies on bacterial wilt and TSWV resistance), Israel (TYLCV resistance, long shelf life), French West Indies (bacterial wilt resistance and tolerance to high night temperatures), Cuba (heat resistance associated with TYLCV tolerance), France (INRA-Avignon: high levels of TYLCV resistance) and South-East Asia (AVRDC in Taiwan and Thailand: bacterial wilt and other disease resistances, heat tolerance).
Tomato is one of the best-studied crops, reflecting its great economic importance. Many important genetic traits have been discovered, evaluated and genetically localized in their respective chromosomes. Tomato has a prolifically marked genome, very useful in genetic and breeding research and has become an important subject for biotechnological studies. Much progress has already been made with molecular marker-assisted selection and genetic transformation.
Tomato scientists have accomplished a great deal in the past, including improvements in yield, disease resistance, adaptability to machine harvesting, processing and nutritional quality, and tolerance of environmental stress. However, the vast reservoir of genetic variability in Lycopersicon remains largely unexploited. Conventional breeding methods are still expected to be the mainstay of future improvement programmes. At the same time, molecular breeding is rapidly gaining momentum also in tomato. Its integration into existing programmes will allow plant breeders to access, transfer and combine genes at a rate, precision and genomic range never achieved by conventional methods. Indeed, the prospects for further improving the tomato crop are bright also for tropical conditions.
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Correct citation of this article:
van der Vossen, H.A.M. & Nono-Womdim, R. & Messiaen, C.-M., 2004. Lycopersicon esculentum Mill. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering shoot; 2, fruit types; 3, seed.
local African variety, multilocular, thin skin, used for sauce
fruit of ‘Mongal’