Prota 2: Vegetables/Lιgumes
Gard. dict. ed. 8: Solanum No 2 (1768).
2n = 48
Solanum luteum Mill. (1768), Solanum nigrum auct. non L.
Red-fruited nightshade, hairy nightshade (En). Morelle jaune (Fr). Mnavu (Sw).
Origin and geographic distribution
Solanum villosum is believed to have originated in Eurasia, and is sometimes considered to have a southern European origin. It is widespread, but absent in Central and South America, and New Guinea. It has been introduced in North America and Australia. In Africa it is recorded from Tunisia, Algeria and South Africa, and from many countries of tropical Africa, e.g. in Central Africa from Burundi, in East Africa from Sudan, Ethiopia, Somalia, Kenya, Uganda and Tanzania, and in southern Africa from Zambia and Angola. In West Africa Solanum villosum has been recorded only from Nigeria. However, its distribution is incompletely known, and it may occur in many other countries. Its use as vegetable is most popular in East Africa.
Leaves and young shoots of sparsely hairy types of Solanum villosum are used as a leafy vegetable. The young leaves are boiled with water and are sometimes fried. In Tanzania young shoots and leaves are picked, chopped and then boiled or, especially in urban areas, fried with onions and tomatoes and sometimes mixed with meat or fish. In the Mara region in Tanzania whole young plants are used as a vegetable. In Kenya the Luo and Pokot people prepare this vegetable together with less bitter vegetables such as amaranths, whereas other cultural groups mix it with meat, spider plant (Cleome gynandra L.), bitter leaf (Vernonia spp.) or cowpea leaves. Nandi women in Eldoret, Kenya use milk to boil the vegetable. In Uganda the young shoots and leaves are mixed with groundnut paste, wrapped in banana leaves and steamed. Other people prefer to boil the vegetable, drain off the remaining water and add sesame (Sesamum indicum L.) to make it a thick and more tasty sauce. In some instances, it is chopped, washed and fried either directly or after boiling it in sour milk. Groundnuts or sesame paste can be added to this preparation.
The ripe fruits are eaten in Ethiopia, Kenya, Uganda and Tanzania, where orange, yellow and red fruited types are found. Solanum villosum also forms an important part of traditional medicine in Africa. In Kenya, unripe fruits are used to soothe toothache. They are also squeezed on babies gums to ease pain during teething. Leaves are used to treat stomachache and extracts from leaves and fruits are used to treat tonsillitis. Maasai boil the roots in milk and give it to children as a tonic. In Tanzania, Sukuma people apply leaves to swellings, whereas the fruit juice is used to calm sore eyes. Banyankore and Banyoro people in Uganda believe that addition of Solanum villosum leaves to the diet contributes to the treatment of fever associated with hypertension. Pregnant women in most parts of Kenya are encouraged to eat boiled Solanum leaves; people believe that they will then give birth to dark-eyed and smooth-skinned babies. It is further believed that children who eat Solanum vegetables cooked with milk, groundnuts or sesame rarely develop marasmus or kwashiorkor. Leaves of Solanum villosum are used as fodder for goats and sheep in Sudan, and for cattle and goats in Kenya.
Production and international trade
Solanum villosum leaves are a common product at many local markets in rural and urban areas of Kenya and Tanzania. In Arusha in Tanzania Solanum villosum is the most expensive leafy vegetable at the urban market. No statistical data on production and trade are available.
The composition of Solanum villosum leaves is probably comparable with that of other dark green leafy vegetables. Two alkaloids have been isolated from green fruits of Solanum villosum, diosgenin and solasodine, but the amount of alkaloids is lower than in Solanum americanum Mill.
Adulterations and substitutes
In dishes Solanum villosum can be replaced by some other leafy vegetables from section Solanum, e.g. Solanum scabrum Mill.
Annual or short-lived perennial herb up to 50(60) cm tall, much branched, unarmed; stem rounded to angled, almost glabrous to pubescent with appressed hairs. Leaves arranged spirally, simple; stipules absent; petiole 0.51 cm long; blade ovate to elliptical, up to 4(8) cm Χ 3(6) cm, cuneate at base and decurrent along the petiole, acute at apex, entire to sinuately or coarsely toothed, sparsely pubescent. Inflorescence an extra-axillary, umbel-like cyme, 35(7)-flowered; peduncle 47 mm long, elongating up to 2 cm in fruit. Flowers bisexual, regular, 5-merous; pedicel 46(10) mm long, becoming deflexed in fruit; calyx cup-shaped, 12 mm in diameter, lobes obtuse to acute or acuminate, deflexed in fruit; corolla stellate, (4)58(10) mm in diameter, white with basal yellow-green star, lobes ovate-oblong, c. 3 mm long; stamens inserted on corolla throat, filaments 2 mm long, with hairs below, anthers connivent, 1.52.5 mm long, opening by terminal pores; ovary superior, globose, c. 1.5 mm in diameter, style (3)45 mm long, hairy at base, stigma capitate, pale green. Fruit a globose berry 68(10) mm in diameter, red, orange or yellow when ripe, many-seeded. Seeds discoid, c. 1 mm long. Seedling with epigeal germination.
Other botanical information
Solanum villosum belongs to the subgenus Solanum and section Solanum, formerly known as section Maurella, or section or subsection Morella. Currently about 30 species are included in this section, of which 1012 are known to occur in Africa. Research is still needed to better understand the species and their diversity within section Solanum. In herbaria in Africa several members of the section are lumped under Solanum nigrum. Solanum villosum has yellow, orange or red fruits whereas Solanum nigrum L. has black or greenish fruits when ripe. Several botanists erroneously grouped taxa with black fruits together with yellow to red-fruited taxa in Solanum nigrum.
Two subspecies of Solanum villosum have been distinguished: subsp. villosum and subsp. miniatum (Bernh. ex Willd.) Edmonds, based on hair density and presence or absence of glands on the hairs and whether the stem is rounded and smooth or angled with toothed ridges. The less hairy subsp. miniatum is preferred as a vegetable. However, many authors do not recognize these subspecies.
Growth and development
Under optimum conditions of moisture and temperature, the seeds of Solanum villosum germinate within seven days. Growth of seedlings is fast and flowering starts after 58 weeks. Under stress, flowering can start even earlier. Vegetative growth slows down with flowering as a result of competition. Solanum villosum is self-pollinating and self-compatible and sets fruit easily under favourable environmental conditions. It continues flowering even when it has started fruit set, resulting in plants bearing mature fruits on the lower branches, young ones in the middle and flowers in the top part. Fruits remain on the plant and drop only when over-ripe. They are attractive to birds, rodents, lizards and rabbits, but also cattle and even humans are partly responsible for seed dispersal. Seeds can pass through the digestive system of animals without being damaged.
Solanum villosum occurs from sea-level to about 2400 m altitude, but it does not tolerate night frost. The optimum temperature is probably between 2030°C. It performs well during the rainy season or when irrigated regularly, and is not resistant to drought. An annual rainfall of 5001200 mm is suitable. Solanum villosum can grow on a wide range of soils, but prefers soils that are rich in organic matter and land covered with ash of recently burnt vegetation. In the wild, it is found in disturbed areas and along the edges of agricultural fields.
Solanum villosum requires fairly large amounts of nutrients. A soil rich in organic matter is appropriate. Weeding is important when the plants are young, later the crop suffers little from weeds. During the dry season farmers irrigate newly transplanted seedlings twice a day, but decrease the frequency to 23 times per week once the plants are well established. For a good harvest of shoots and leaves, farmers often use compound fertilizer, e.g. NPK 201010. In experiments in Tanzania it was shown that the maximum yield was obtained by the use of 50100 kg N, 11 kg P and 20 kg K per ha. To improve the yield, and depending on local soil conditions, a side-dressing of 50 kg urea and 100 kg sulphate of ammonia per ha a few weeks after transplanting can be considered. In Kenya, commercial farmers prefer to use weekly foliage-sprays of fertilizer starting a week after germination until the first harvest and then after every harvest. Farmers are, however, advised not to use excessive nitrogen fertilizers as these encourage leaf diseases and build-up of nitrates, which is a health risk to consumers.
Propagation and planting
Solanum villosum is mainly propagated by seed. The 1000seed weight is about 1.0 g. Stem cuttings have also been used for propagation. Farmers collect seed from their farm or buy it at the market. Seeds from fresh fruits that have been carefully dried germinate well. In home gardens direct sowing is common; commercial farmers often use nurseries. In nurseries the seed is mixed with sand or ash, or sometimes both, to facilitate uniform sowing. The beds are prepared by loosening the soil by hand hoe after application of decomposed manure. The beds are covered with grasses which are burnt to sterilize the soil. This also adds potash to the soil. Seed is broadcast or sown in furrows 1520 cm apart. The seeds are covered with a thin layer of soil, but sometimes farmers prefer to leave them open so that they germinate earlier. Especially during the dry season, the beds are covered with tall grasses to maintain soil moisture. The grass is removed when the seedlings are about 3 cm tall. Nurseries require watering twice a day and careful weeding. Pest management is also important at this stage. Seedlings are transplanted when they have 6 true leaves into well-prepared and irrigated fields at a spacing of 2530 cm Χ 3040 cm. Solanum villosum is sometimes intercropped with other crops, e.g. maize. In this case, the seeds are direct sown, normally 310 per hole. If the plants have enough space, direct sowing results in taller plants with larger leaves and branches than a transplanted crop, thus producing more dry matter. For once-over harvesting, usually done when enough land is available for raising several successive crops, a dense spacing of 10 cm Χ 10 cm is practised.
Diseases and pests
Powdery mildew (Leveillula taurica) has been recorded on Solanum villosum, as well as downy mildew (Pseudoperonospora nigrescens). Late blight (Phytophthora infestans) may be problematic in cool wet highlands, but resistance to it has been found. Bacterial wilt (Ralstonia solanacearum) is a serious problem in Kenya and Tanzania. Solanum villosum is susceptible to tomato yellow leaf curl virus (TYLCV) spread by whitefly (Bemisia tabaci), to tobacco ringspot nepovirus (TRSV), potato U nepovirus (PVU) and probably other viruses. The crop is susceptible to root-knot nematodes (Meloidogyne spp.), which can be limited by crop rotation with non-susceptible crops (cereals, amaranth) and application of large amounts of organic fertilizer. Crop rotation with non-solanaceous crops is generally recommended to avoid diseases.
The greatest nuisance to Solanum villosum in Tanzania is black aphid Aphis fabae, infesting the growing points and the lower part of the leaves, making them curl, after which the plant stops growing. Caterpillars and beetles (Lagria, Podagrica and Epilachna spp.) and occasionally grasshoppers cause damage. Some farmers use chemical control in the nursery and in the field. Traditionally, farmers spread wood ash on the leaves, although this affects leaf quality.
The first harvest is expected 45 weeks after transplanting. Harvesting for the market is done in the late evening or early morning. The stem is cut with a knife or picked by hand about 10 cm above the ground. This allows new shoots to form and is done at intervals of 714 days, allowing 810 harvests from the stock. When spacing is close (e.g. 10 cm Χ 10 cm) whole plants are uprooted. Flowers are removed before the produce is taken to the market.
In Kenya and Tanzania the annual yield of small-scale farmers is 2025 t/ha of leaves and young shoots; another report mentions a cumulative yield of edible leaves of 1220 t/ha per growing season in Kenya.
Handling after harvest
The harvested product is covered with banana leaves or plastic in the evening to maintain its moisture content before taking it to the market the next morning. The shoots are often tied in small bundles that are either partly immersed in water in small buckets or sprinkled with water at short intervals to keep them fresh. For use during the dry season, the leaves are harvested in large quantities, boiled in water, dried and crushed to powder.
Some Solanum villosum accessions are kept at the AVRDC Regional Center for Africa (AVRDC-RCA) in Arusha, Tanzania. In Kenya, there are several institutes that hold collections of Solanum villosum, and outside Africa correctly identified accessions are present at the Botanical Garden of the University of Nijmegen, Netherlands.
Some selection work on Solanum villosum is reported from AVRDC-RCA in Arusha, Tanzania. Artificial hybridization between Solanum villosum and other Solanum species, e.g. Solanum scabrum and Solanum americanum, may be carried out to improve productivity and resistance to diseases. These species have been reported to hybridize successfully. In Kenya and Tanzania Alpha Seed Company and Kenya Seed Company sell Solanum villosum seeds.
Solanum villosum is worth promoting as an excellent, high-value leafy vegetable and a source of income for vegetable farmers and traders in East Africa. Selection and breeding of improved cultivars with high vigour, strong resistance to pests and diseases and good consumer quality should be enhanced.
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Sources of illustration
Coste, H., 1903. Flore descriptive et illustrιe de la France. Tome deuxiθme. Librairie des Sciences Naturelles, Paris, France. 627 pp.
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Correct citation of this article:
Manoko, M.L. & van der Weerden, G.M., 2004. Solanum villosum Mill. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Lιgumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, part of flowering and fruiting plant; 2, flowering and fruiting branch; 3, fruit.
Redrawn and adapted by Achmad Satiri Nurhaman
fruits of subsp. villosum
flowers should be removed before the product is sold