Solanum americanum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Solanum americanum Miller

Protologue: Gard. dict. ed. 8: Solanum No 5 (1768).

Family: Solanaceae

Chromosome number: 2n= 24

Synonyms

• Solanum nodiflorum Jacq. (1789),
• S. nigrum auct. non L. (pro parte).

Vernacular names

• Glossy nightshade (En)
• Herbe à calalou (Fr)
• Indonesia: leunca (Sundanese), ranti (Javanese), kampai
• Malaysia: ranti, terong meranti, terong perat
• Papua New Guinea: karakap
• Philippines: anti (Tagalog), bolagtab (Bisaya), kuti (Bicol)
• Laos: kh'èèngz namz
• Thailand: mawaeng-nok (southern), ya-tomtok (northern)
• Vietnam: lu lu dực, thù lù dực.

Origin and geographic distribution

S. americanum most probably originates from South America. It is now found throughout tropical and warm temperate regions, wild as a weed of cultivation and also cultivated. The S. nigrum complex in South-East Asia to which S. americanum belongs has not yet been studied, so the botanical names presented here are still tentative.

Uses

The tender shoots, young leaves and unripe green fruits are eaten as a vegetable, raw, cooked or steamed (for 5-10 minutes), alone or in combination with other vegetables. Children dislike this vegetable because of its slightly bitter taste. The ripe fruits are also edible. In the Philippines they are used in pies, jams and other sweets. In traditional medicine a decoction of the leaves is used in a lotion for yaws and to alleviate neuralgic pains. The fruits have laxative and diuretic properties and the juice is applied against dropsy and to cure eye diseases of chickens. In West Java the berries are recommended as an aphrodisiac.

Production and international trade

S. americanum is used as a green vegetable throughout South-East Asia and the green fruits can be bought in the local markets. It is common in the vegetable assortment of large supermarkets. Shoots and leaves are traded more rarely. No production figures are available, but being a common crop of home gardens and a common weed of cultivation, its importance is considerable.

Properties

The edible portions of green fruits and young leaves are 95% and 70% respectively. Per 100 g edible portion the green fruits contain approximately: water 90 g, protein 1.9 g, fat 0.1 g, carbohydrates 7.4 g, Ca 274 mg, Fe 4.0 mg, carotene 0.5 mg, vitamin B₁ 0.10 mg, vitamin C 17 mg. The energy value is 140 kJ/100 g.

The nutritional value of the leaves is good; it is comparable to that of Amaranthus leaves but with lower vitamin A and C contents. Per 100 g edible portion young leaves contain: water 85 g, protein 4.7 g, fat 0.5 g, carbohydrates 8.1 g, Ca 210 mg, Fe 6.1 mg, carotene 1.9 mg, vitamin B₁ 0.14 mg, vitamin C 40 mg. The energy value is 190 kJ/100 g.

The seeds are light: 1000 seeds weigh approximately 1.5 g.

Description

• Erect and spreading annual or short-lived perennial herb, up to 1.5 m tall, unarmed, dark green or flushed with purple, glabrous or sparsely hairy with curved simple hairs.
• Stem terete, angular or narrowly winged, sometimes warty.
• Leaves arranged spirally to almost opposite, variable in size; petiole 1-4(-9) cm long, narrowly winged; leaf-blade ovate to ovate-lanceolate, (1-)6(-16) cm × (1-)3(-12) cm, entire or sinuately lobed, base truncate to cuneate and decurrent along the petiole, apex acuminate.
• Inflorescence an umbellate cyme with (2-)4-8(-20) flowers, mostly supra-axillary; peduncle slender, up to 2.5(-5) cm long; pedicel 3-8(-20) mm long, nodding; flowers bisexual, nodding; calyx campanulate, 1-3 mm long, 5-lobed, reflexed in fruit; corolla deeply 5-stellate, 8-9 mm in diameter, with yellow-green star, lobes oblong, 1.5 mm wide, reflexed, white or purplish; stamens 5, inserted on corolla throat; filaments 1-2 mm long, often hairy on inner side; anthers 1.5-2 mm long, yellow, opening by terminal pores; ovary globular, 1 mm in diameter; style 2.5-4 mm long, spreading hairy in lower half; stigma capitate, at about the level of the anther tips, pale green.
• Fruit a globular berry, 0.5-1 cm in diameter, from green turning glossy bluish-black or purplish-black at maturity, readily shed when ripe; flesh with 0-4(-8) sclerotic granules and 40-100 seeds.
• Seed discoid, 1-1.5 mm long, creamy.

Growth and development

The germination of fresh glossy nightshade seeds is about 100% within 6 days. Flowering starts about 8 weeks after sowing (or 5 weeks after transplanting) and the number of flowers increases during the next 6 weeks. Young fruits appear about 10 days after anthesis and are harvestable 8 days later. Stem and roots grow until the age of 4-5 months; from about 2 months after sowing the stem gradually becomes more woody. At the age of about 4 months the plants shed many leaves; new leaves are formed, but they remain much smaller. Although plants can survive for more than one season, vegetable production (young fruits, leaves) is seriously reduced in old plants. The economic lifetime is about 5-6 months from sowing.

Other botanical information

S. americanum is part of the S. nigrum complex, more formally Solanum L. section Solanum, also called section Maurella (Dun.) Dumort. or section Morella (Dun.) Bitter, which comprises about 30 species, mainly occurring in South America. The S. nigrum complex has not yet been unravelled. Some work has been done for South America, North America, Europe, India and Australia, but not so far for South-East Asia. The plants of the complex occurring in South-East Asia have been described as S. nigrum L. (s.l.) and as S. nodiflorum Jacq., which is considered synonymous with the older name S. americanum.

The "nigrum" complex in India is considered as consisting of three species: S. americanum Miller (2n= 2x= 24; inflorescence umbellate; fruit shiny purplish-black with reflexed sepals); S. nigrum L. (2n= 6x= 72; inflorescence racemiform; fruit dull purplish-black with sepals adhering to the fruit); and S. villosum Miller (2n= 4x= 48; fruits elliptical, very distinctive orange, orange-brown or reddish-orange). It is possible that the complex in South-East Asia contains the same elements; they do occur in Australia.

Until the situation has been cleared up worldwide, the name S. americanum is applied here to edible plants of the South-East Asian "nigrum" complex.

Two forms occur in West Java (Indonesia): forms with small bluish-black fruits, about 0.5 cm in diameter, only the leaves of which are used as vegetable (called "leunca manuk" or "leunca ayam") and forms with larger shiny purplish-black fruits, about 1 cm in diameter, whose green fruits and leaves are used as vegetable (called "leunca biasa" or "leunca badak"). Only the forms with larger fruits are cultivated.

Ecology

S. americanum can be found in a wide range of environments, usually associated with some degree of man-made disturbance such as waste places, orchards, gardens, light grazings and alongside footpaths. In the tropics it is found especially in the montane zone up to 3000 m altitude, but also at sea-level.

Propagation and planting

S. americanum is propagated by seed. It is usually sown in seed-beds or in pots and planted in the field when the plants are about 8 cm tall, five weeks after sowing. It is normally planted in home gardens but also in fields. When water supply is assured, S. americanum can be grown year-round in the tropics.

The planting distance depends on the harvested product: when leaves are primarily desired a close planting distance of up to 25 cm × 25 cm is preferred; when fruits are primarily wanted, distances are wider, e.g. 50 cm × 50 cm; for a combination of leaves and fruits intermediate distances are recommended. In practice, however, S. americanum is usually grown in home gardens, mixed with other crops.

Husbandry

Cultural practices for glossy nightshade are similar to those recommended for capsicum pepper. Manure is usually applied, at 100-500 g per plant; sometimes some NPK fertilizer is given too. Weeding is done once every 2-3 weeks as long as it is necessary and watering twice a week, depending on natural rainfall. If good fruit yields are required as well as edible leaves, it is recommended to trim regularly so that 4-5 branches remain. Although the plants can be grown in full sun, experiments in Indonesia also showed beneficial effects of shade. In general, the more shade, the more stem and leaves and the less fruits are produced. Up to 60% shade, leaf harvests were not significantly lower than without shade, and leaves were thinner, larger and better in taste.

Diseases and pests

S. americanum has no serious diseases and pests.

In Indonesia only moderate losses have been reported from diseases such as bacterial wilt (Pseudomonas solanacearum), fusarium wilt (Fusarium oxysporum f. lycopersici), and root knot nematodes. Sometimes aphids and beetles (Epilachna spp.) may attack the plants. These pests can be controlled by hand.

Harvesting

For home consumption the plants are harvested when the product is wanted, starting about 2 months after sowing. For leafy vegetable, young shoots 5-6 cm long are harvested, about once per 1-2 weeks. Young fruits are harvested per bunch of 7-8 fruits, once per 3-10 days, most frequently in the wet season.

Harvesting usually continues for 3-5 months, depending on the condition of the plants and the desired quality of the product.

Yield

Only figures from one experiment in Indonesia are available. Plants were harvested until 4 months after planting in the field; mean fruit yield was 30 kg per 10 m² (30 t/ha) when leaves were not harvested, and 16 kg per 10 m² (16 t/ha) when also 0.8 kg edible leaves per 10 m² (0.8 t/ha) were harvested. Yields were expected to be higher at closer spacings (these yields were obtained with plants spaced 50 cm × 70 cm).

Handling after harvest

Edible leaves should be consumed or prepared as soon as possible, keeping them wet to prevent wilting. Young fruits should also be prepared as soon as possible after harvest although they probably can be kept as long as green tomatoes.

Genetic resources and breeding

No specific germplasm collections of S. americanum exist. It may be assumed that some material is available at institutes keeping germplasm collections of other solanaceous crops.

If interest is shown in developing S. americanum as a crop and in starting crop improvement programmes, the first step must be to organize a worldwide germplasm collection, as glossy nightshade is very variable.

Prospects

S. americanum is an interesting species for home and market gardening, tolerating shade, easy to cultivate, without serious diseases and pests, producing nutritive fruits and shoots. It deserves more research attention.

Literature

• Edmonds, J.M., 1972. A synopsis of the taxonomy of Solanum sect. Solanum (Maurella) in South America. Kew Bulletin 27: 95-114.
• Edmonds, J.M., 1977. Taxonomic studies on Solanum section Solanum (Maurella). Botanical Journal of the Linnean Society 75: 141-178.
• Edmonds, J.M., 1979. Biosystematics of Solanum L. section Solanum (Maurella). In: Hawkes, J.G., Lester, R.N. & Skelding, A.D. (Editors): The biology and taxonomy of the Solanaceae. Academic Press, Linnean Society of London, Linnean Society Symposium Series Number 7. pp. 529-548.
• Omta, S.W.F. & Fortuin, F.T.J.M., 1978. The cultivation of Solanum nigrum L. as a leaf and fruit vegetable in the home gardens of West Java. Mimeographed research report. Institute of Ecology, Pajajaran University, Bandung, Indonesia & Department of Plantphysiology, State University, Groningen, the Netherlands. 70 pp.
• Schilling, E.E. & Andersen, R.N., 1990. The black nightshades (Solanum section Solanum) of the Indian subcontinent. Botanical Journal of the Linnean Society 102: 253-259.
• Symon, D.E., 1981. A revision of the genus Solanum in Australia. Journal of the Adelaide Botanic Gardens 4: 1-367, especially pp. 37-56.

Authors

• J.S. Siemonsma & P.C.M. Jansen