Guizotia abyssinica (PROSEA)
Guizotia abyssinica (L.f.) Cass.
- Protologue: Dict. Sci. Nat. 59: 248 (1829).
- Family: Compositae
- Chromosome number: 2n= 30
Polymnia abyssinica L.f. (1781), Ramtilla oleifera DC. (1834), Guizotia oleifera (DC.) DC. (1836).
- Niger seed, niger, ramtil (En). Nigèr, guizotia oléifère (Fr).
Origin and geographic distribution
Niger seed originated from G. schimperi Sch. Bip. (synonym G. scabra (Vis.) Chiov. subsp. schimperi (Sch. Bip.) J. Baagøe) through selection and cultivation. Niger seed was probably domesticated before 3000 BC in the highlands of Ethiopia where it is cultivated as an oilseed crop and still grows wild. From there, traders brought it to India before the Christian era. It is now grown extensively in Ethiopia, India and Nepal and on a smaller scale in parts of montane eastern and southern Africa, the West Indies, Bangladesh, Bhutan, and possibly Pakistan. In the 19th Century it was also grown in Europe. Niger seed has been tested in Bogor (Indonesia), but this did not lead to its cultivation in Indonesia.
Niger seed (a popular name for the fruits of G. abyssinica , but also used for the whole plant) is a valued source of edible oil. In Ethiopia, half of the total production of edible oil comes from niger seed and the oil is used in many dishes. In India it is mainly a substitute for or extender of sesame oil and contributes only 3% in the national edible oil production. Niger seed is eaten fried, prepared into chutneys, condiments and porridge, mixed with pulses to make snack foods and ground to produce flour and beverages. The seed is also an important component of birdseed mixtures. Aside from cooking, the oil is utilized in illumination, medicine and cosmetics, as well as in making paint and soap and to a limited extent in lubrication. In traditional medicine the oil is used in birth control and to treat syphilis. A medical test for the identification of the fungus Cryptococcus neoformans, which causes a serious brain disease, is carried out on a niger seed-based agar medium. Niger seed sprouts mixed with garlic and honey are taken to treat cough. The whole plant is grown as a fodder for sheep. Cattle refuse to eat the green plant but accept it as silage. Niger seed is also grown as a green manure. Niger seed cake is fed to animals and is used as a fuel. The roots have a suppressant effect on weeds, also in subsequent crops.
Production and international trade
Statistical data on the production of niger seed vary greatly and should be interpreted with care. Its production is concentrated in India and Ethiopia which have a total annual production of 350 000-375 000 t. Ethiopia harvests 200 000-250 000 t yearly while India produces 80 000-180 000 t, probably excluding seed used for home consumption. Annual niger seed oil produced by India reaches 40 000-50 000 t. In recent years there have been wide variations in the production of niger seed in Ethiopia and this accounts for its fluctuating exports (from nil to 20 000 t annually) to Europe (especially Italy) and Japan.
Per 100 g, the "seed" (botanically an achene) of niger contains: water 6-8 g, protein 17-19 g, fat 30-50(-60) g, carbohydrates 34-40 g, fibre 13.5 g, ash 2-8 g, Ca 50-470 mg, P 180-800 mg, niacin 3 mg, riboflavin 0.6 mg and thiamine 0.4 mg. The oil content of unimproved traditional cultivars is about 25-45%, in improved cultivars it reaches 60%. In Ethiopia, the average oil content of niger seed is 45%. The oil consists of 20% saturated fatty acids, 80% unsaturated fatty acids, 0.4-3% free fatty acids and 0.5-1.0% unsaponifiable matter. The major fatty acids are: palmitic acid about 10%, stearic acid about 8%, oleic acid 5-8% and linoleic acid 65-85%. Palmitoleic acid, linolenic acid, arachidic acid, eicosenoic acid, behenic acid, erucic acid and lignoceric acid make up the remaining 2-3% of the oil. The oil has a solidification point between -9 and -15°C, and iodine value of 126-139. It is slow-drying, clear, pale yellow, odourless or with faint sweet fragrance and has a nutty taste. Oil from Indian cultivars has a higher oleic acid (30%) and a lower linoleic acid (50%) content than oil from Ethiopian cultivars.
Niger seed cake contains per 100 g: protein 24-34 g, fat 4-14 g, carbohydrates 20-28 g, fibre 8-24 g, ash 8-12 g, N 5 g, P 0.9 g and K 1.3 g. Seed cake from India tends to have a higher protein and a lower fibre content than that from Ethiopia. The amino acid composition of the protein is fairly balanced although different tests show different amino acids to be deficient. Niger seed roots contain a water-soluble compound that has an allelopathic effect on monocotyledons thereby reducing weed incidence in the following crops. The weight of 1000 seeds (achenes) is 2-5 g.
A stout, erect, well-branched, variable annual herb, up to 2 m tall, smooth to slightly scabrid. Root system well-developed, with taproot and many laterals, particularly in upper 5 cm. Stem terete, hollow, up to 2 cm in diameter, light green, often purplish stained or dotted, becoming yellow with age, puberulous to pilose with multicellular white hairs. Leaves opposite, uppermost ones sometimes alternate, sessile and clasping half the stem; blade lanceolate to narrowly ovate or obovate, 3-23 cm × 1-6 cm, base truncate to cordate, margin entire to serrate, ciliate, apex tapering, softly hairy on both surfaces, usually dark green but lower leaves show distinct yellow tinge. Inflorescence a cup-shaped head (capitulum), 1-3 cm in diameter, axillary or terminal, grouped like corymbose cymes, surrounded by leafy involucral bracts arranged in various rows; peduncle up to 14 cm long, densely pilose near the head; outer involucral bracts usually 5, broadly ovate to obovate-elliptical, up to 3 cm long, margin ciliate, 5-9-veined; inner bracts scarious (thin, not green), obovate, up to 1 cm long, 7-9-veined, progressively smaller and finally merging into the flattened, 5-veined paleae of the receptacle; flowers of two types, 6-15 female ray florets at the outer part of the receptacle and 40-60 bisexual disk florets which are arranged in 3 whorls in the central part; ray floret with tube 2 mm long, ligule obovate to rectangular with 3 teeth, 14-21 mm × 5-6 mm, bright yellow, becoming more golden with age, ovary 4-4.5 mm long, with 4 longitudinal ribs, style up to 7 mm long, stigma with 2 branches 2 mm long; disk floret with lower part of tube up to 1.5 mm long, upper part slightly campanulate, 2-3 mm long with 5 acute lobes, yellow to orange; stamens 5, inserted at the base of the limb, filaments flattened, 2 mm long, bent twice near the anthers, anthers orange, cohering, with apically an acute appendage; ovary 3.5-4.5 mm long, 4-ribbed, style about 5 mm long, stigma 2-branched; florets at the outer part opening first, followed progressively by the next in line to the centre of the head. Fruit (often called seed) an achene, obovoid, club-shaped, 3-5 mm × 1.5 mm, 4-angled in transverse section, without pappus, glossy black but sometimes mottled; usually a head contains 15-30 mature achenes and a varying number of immature ones at the centre. Seedling with epigeal germination.
Growth and development
The seed of Guizotia abyssinica germinates in a few days and the young plant grows immediately to an erect habit. The first side-shoots are formed when plants have 6-8 leaves and are about 30 cm tall. Most forms of niger seed are short-day plants with only few day-length-insensitive individual plants. The critical day length is about 12 h. Under short days flowering starts about 60 days after germination. Photoperiodic sensitivity is stronger in Ethiopian than in Indian cultivars. Another difference between Indian and Ethiopian cultivars is that induction of flowering in Indian plants probably takes place at an earlier stage of development. Short days 1 month after sowing gave full induction in Indian material but no induction in Ethiopian plants. In the latter, induction took place 55-75 days after sowing. In Ethiopian cultivars high temperatures delay flowering; this was not found in Indian cultivars. Flowers are pollinated by insects, mostly by bees. Although the style of the disk floret is covered with pollen when emerging, self fertilization is rare as the pollen does not cover the receptive part of the stigma and because plants are self incompatible. In Ethiopia a single head flowers for about 8 days; a field takes about 6 weeks to complete flowering. From flowering to maturity takes 45-55 days. Niger seed matures in 120-180 days after emergence in Ethiopia and in 75-120 days in India depending on the cultivar or landrace. Individual plants that are early maturing shed seeds even before others are mature.
Other botanical information
Guizotia Cass. is genus of about 7 species classified in the tribe Heliantoidae of the Compositae . G. abyssinica is closely related to, partly sympatric and fully interfertile with G. schimperi ; it could possibly be considered a cultivar group within G. schimperi . Distinguishing characters for G. abyssinica are the combination of its annual habit, its heads arranged like corymbose cymes, its 5 outer ovate to obovate-elliptical involucral bracts, its plane 5-veined paleae and its 3-5 mm long achenes. The Ethiopian and Indian gene pools of G. abyssinica differ as a result of long-term geographical isolation, the former being more variable. Indian niger seed flowers and matures earlier and has higher seed weight. Forms grown in Ethiopia mature later, are taller and higher yielding. Three different types of niger seed are recognized in Ethiopia: "abat nough" (grown during the rainy season in well-drained soil), "mesno noug" (grown in September to January in high rainfall, waterlogged areas) and "benenge noug" (grown in July to October in more dry lowland). In north-eastern India 3 growing seasons per year for niger seed are also recognized: "kharif", early "rabi" and late "rabi". Well-known improved cultivars in India are: "Ootacamund", "Gaudaguda", "No. 71" and "RCR-317". A few of the niger seed varieties in Ethiopia are "Sendafa", "Esete-1", "Fogera-1" and "Kuyu".
While niger seed originated in the tropical highlands of eastern Africa, it has adapted to the tropical and sub-tropical lowlands in India and to temperate conditions in Europe. Optimum yields are obtained in Kenya at altitudes of 2000-3000 m and in Ethiopia at 1600-2200 m, where average maximum temperatures during the growing season are 22-24°C. In India best yields are obtained below 1000 m altitude, with temperatures of 18-23°C. Rainfall of 1000-1300 mm is optimum and more than 2000 mm rainfall may result in depressed yield. Niger seed is adapted to a wide range of soils but grows best in clay loams or sandy loams with a pH of 5.2-7.3. It is often cultivated on poor sandy soils, but also on heavy, black cotton soils. During vegetative growth, niger seed may withstand waterlogging. It is extremely resistant to poor oxygen supply in the soil, explained by the development of aerenchyma and the ability to form respiratory roots. Some niger seed selections are moderately salt tolerant but flowering may be delayed by rising soil salinity.
Propagation and planting
Well-dried niger seed can be stored dry without special requirements for at least 4 years without losing its viability. In India niger seed is planted in June-August as a rainy season crop and in September-mid-November as a winter crop. In Ethiopia the main planting season is May-July. Land preparation is similar to that applied when planting other small-seeded crops. Traditionally seed is broadcast at a rate of 6-12 kg/ha and covered 1-3 cm deep. For sowing, seeds are sometimes mixed with sand for even distribution. Seed drills and mechanical planters are occasionally used. The land is then harrowed to cover the seed. In sole cropping, row widths vary from 30-50 cm depending on soil conditions. In intercropping, sowing rate depends on the area allocated to niger seed which is usually 20-25%. It is commonly strip-cropped with pulses, millet, sorghum, castor, sunflower and sesame.
For micro-propagation hypocotyls, cotyledons and leaves have been cultured in vitro and survival rates of regenerated plantlets range from 70-98%.
Weeding in niger seed fields is important. It should be sown in a clean field and weeded twice when seedlings are 10 cm tall and before flower bud development. Both hand weeding and herbicide application can control weeds. Chemical fertilizer is rarely applied. In India, application of 10-20 kg N and 10-20 kg P per hectare at sowing is recommended, followed by a N top dressing of 10-20 kg/ha, 30-35 days after sowing. Yield increases of 60% and 40% have been obtained for niger seed after application of N and P both at a rate of 40 kg/ha. Potassium has either no or a non-significant effect. Manure (4-5 t/ha) is also used sometimes combined with 10-20 kg N/ha. Incorporation of cowpea biomass gave positive results on niger seed in India. Niger seed is usually grown in rotation with cereals.
Diseases and pests
Niger seed blight caused by Alternaria sp. and leaf spot caused by Cercospora sp. are the most serious diseases of niger seed. Other diseases recorded are leaf spot caused by Macrophomina phaseolina and Phytophthora root rot on young seedlings in India and bacterial blight (due to Pseudomonas spp.) in Africa and India.
The most serious insect pests are niger fly ( Dioxyna sororcula and Eutretosoma spp.) and black pollen beetle ( Meligethes spp.). Niger fly lays eggs in the disk florets and later, the larvae destroy the flowers. The black pollen beetle eats pollen grains and adversely affects pollination. In India control measures of niger caterpillar, semi-looper and other insect pests have been developed.
The parasitic weed "dodder" ( Cuscuta campestris ) causes serious losses in Ethiopia and India. Hand-weeding and the application of herbicides (e.g. chloropropham, propyzamide) provide effective control. Other major weeds are Solanum elaeagnifolium Willd. ex Steud., Oxalis latifolia H.B.K., Avena fatua L. and Imperata cylindrica (L.) Raeuschel.
As niger seed ripens over a period of several weeks it is harvested when plants are still yellow to reduce shattering. In India, the practice is to harvest when leaves are dry and heads turn black. The optimum stage to harvest is when seeds are yellow-brown and their moisture content is 45-50%. Harvesting is done manually; cut plants are stacked in the field to dry and taken to a threshing place for further drying and threshing.
Seed yields of 250-400 kg/ha are common in India but these increase to 500-600 kg/ha when niger seed is grown in moderately fertile soils. In Ethiopia yields of 300-700 kg/ha are normal but yields of 1000 kg/ha have also been obtained. Improved cultivars in combination with improved agronomic practices can attain yields of 1000 kg seeds/ha.
Handling after harvest
Threshing is mostly done by hand in India. In Ethiopia, oxen are used to either tread on the harvested plants or to pull a small threshing sledge. To keep seeds clean, tarpaulin or plastic sheets are used and threshing is done on special threshing floors. Small pedal-operated threshers for rice may be adjusted to suit niger seed. Seeds are stored in sacks and other containers, should be protected from storage pests and transported to bulk storage facilities as soon as possible. In Ethiopia, home processing of oil is done by grinding the dry seeds into fine powder, adding hot water to it, stirring it until the oil floats to the surface and then scooping the oil off. However, most oil is now processed in small, mechanized expeller mills. In India, the oil is extracted by traditional bullock-driven "ghanis", in small rotary mills or in hydraulic or screw presses. Usually, locally-extracted oil has a poor storage life but heating and storing in airtight containers can prolong it.
The most important niger seed germplasm collections are in the Biodiversity Institute (formerly the Plant Genetic Resources Centre), Addis Ababa (Ethiopia) (about 1000 accessions), in the All India Coordinated Research Project on Oilseeds, Jabalpur (about 560 accessions) and the Indian National Bureau of Plant Genetic Resources, Akola (200 accessions). In India, the niger seed base collection is held at -20°C for long storage and at 4°C for medium-term storage. In vitro and in situ conservation of the working collections are not done in India; instead, they are maintained and regenerated by sibbing (during multiplication, plants of an accession are bagged as a group to avoid intercrossing with other accessions) to produce viable seed stocks. The adoption of improved cultivars at the expense of landraces is not widespread in Ethiopia.
Niger seed populations in Ethiopia and India are very heterogeneous, indicating the great potential for yield increases through breeding, and breeding programmes exist in both countries. Breeding objectives for niger seed are to increase seed yield and oil content. To achieve the first objective, single-headed, dwarf types with uniform maturity must be developed. An increase in oil content appears feasible because of existing genetic variability for oil content which can be used in breeding research.
Although niger seed is mainly produced in India, Ethiopia and other African countries, it can potentially be grown in cooler places in South-East Asia.
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B.E. Umali & K. Yantasath