Prota 1: Cereals and pulses/Céréales et légumes secs
Syn. pl. glumac. 1(1): 3 (1853).
2n = 24
African rice, red rice (En). Riz africain, riz de Casamance (Fr).
Origin and geographic distribution
Oryza glaberrima was derived from the wild annual Oryza barthii A.Chev. (synonym: Oryza breviligulata A.Chev. & Roehr.). Oryza barthii probably grew abundantly in lakes that existed in what is now the Sahara from 8000–4000 BC, and it was harvested as a wild cereal. When the climate became drier, Oryza glaberrima, which had gradually developed from Oryza barthii (probably around 1500 BC or later), was grown as a rainfed homegarden crop in oases. When the population took refuge in the interior delta of the Niger river (around 1500 BC) and became much larger, Oryza glaberrima was transformed into the current floating rice crop.
African rice is now grown in a zone extending from the delta of the River Senegal in the west to Lake Chad in the east. To the south-east its range is bordered by the river basins of the Benue, Logone and Chari, but it has also been recorded from the islands of Pemba and Zanzibar (Tanzania). The areas of most intensive cultivation of African rice are the floodplains of northern Nigeria, the inland delta of the Niger river in Mali, parts of Sierra Leone and the hills on the Ghana-Togo border. African rice was probably introduced into the New World during the slave trade era, and it is still occasionally cultivated there, e.g. in Brazil, Guyana, El Salvador and Panama.
In parts of West Africa the grain of African rice is a staple food, highly appreciated for its taste and culinary qualities. It is also used in traditional and ritual ceremonies, e.g. in the Casamance region of southern Senegal. The finer parts of the bran and broken grains are given as feed to chicken and other livestock. In the Central African Republic the root is eaten raw to treat diarrhoea.
Production and international trade
In statistics on rice production in West Africa no distinction is made between African rice and Asian rice (Oryza sativa L.). It is estimated that African rice is grown in less than 20% of the total area allocated to rice in West Africa. As a traditional food grain it is not traded internationally, but only within the region of production.
The composition of whole African rice grain (hulled) per 100 g edible portion is: water 11.3 g, energy 1524 kJ (364 kcal), protein 7.4 g, fat 2.2 g, carbohydrate 77.7 g, fibre 0.4 g, Ca 38 mg, P 294 mg, Fe 2.8 mg, thiamin 0.34 mg and niacin 6.5 mg. Milled African rice contains per 100 g fresh edible portion: water 11.4 g, energy 1532 kJ (366 kcal), protein 6.3 g, fat 0.3 g, carbohydrate 81.6 g, fibre 0.2 g, Ca 22 mg, P 98 mg, Fe 1.7 mg, thiamin 0.06 mg, niacin 2.0 mg and tryptophan 110 mg (Leung, Busson & Jardin, 1968). African rice is superior to Asian rice in its content of the important vitamin thiamin and in iron. The degree of gelatinization depends on the amylose content, which ranges from 14–30%, and influences consistency of the rice in cooking and thus consumer choice. Most cultivars of African rice have red-skinned grain and some are strongly scented.
Adulterations and substitutes
In most regions of West Africa, at least in commercial farming, African rice has been replaced by Asian rice, which is more productive, shatters less easily and has a softer grain that is easier to mill. Small-scale farmers in West Africa, however, often still prefer to grow African rice for its taste and culinary properties, its ability to withstand flooding, and its resistance to several diseases and pests.
Annual grass up to 120 cm tall (up to 5 m in some floating types), often tufted; dryland types with simple culm often rooting at lower nodes, floating types often branching and rooting at upper nodes too. Leaves alternate, simple; sheath terete, up to 25 cm long, with transverse veinlets; ligule c. 4 mm long, truncate, membranous; blade linear, flat, 20–25(–30) cm × 6–9 mm, sagittate at base, rugose beneath. Inflorescence a terminal, ellipsoid, stiff and compact panicle up to 25 cm long, with ascendent racemose branches. Spikelets ellipsoid, c. 9 mm × 4 mm, more or less persistent, 3-flowered but 2 lowest florets reduced to sterile lemmas separated from the lemma of the fertile, bisexual upper floret by a stipe; glumes absent or strongly rudimentary; lemma hispidulous, 5-veined, usually without apical awn; palea 3-veined; lodicules 2; stamens 6; ovary superior, with 2 plumose stigmas. Fruit a laterally compressed caryopsis (grain) up to 9 mm × 3 mm, often reddish, tightly enveloped by lemma and palea.
Other botanical information
Oryza comprises about 20 wild species distributed throughout the tropics and subtropics, and 2 cultivated species, Oryza sativa and Oryza glaberrima. Several classifications of Oryza have been made. Most recently the genus has been divided into 3 sections: sect. Padia, sect. Brachyantha and sect. Oryza. Section Oryza is subdivided into 3 series: ser. Latifoliae, ser. Australiensis and ser. Sativae. Oryza glaberrima, its direct ancestor Oryza barthii A.Chev. and the rhizomatous perennial Oryza longistaminata A.Chev. & Roehr. are classified in ser. Sativae, together with Oryza sativa. Morphologically, Oryza glaberrima can be distinguished from Oryza sativa by its shorter ligule and less-branched panicle.
Growth and development
African rice seedlings normally emerge in 4–5 days after sowing. The vegetative phase of African rice consists of a juvenile phase of about 3 weeks followed by a tillering phase of 3–4 weeks. Vegetative growth is rapid. Tillering, high leaf area index and high specific leaf area contribute to its high competitiveness against weeds. However, culms tend to be weak and brittle, making African rice prone to lodging. African rice is self-fertilizing. The duration of the crop varies from 3–6 months depending on cultivar and type of culture. Some cultivars selected for rainfed conditions are of very short duration, shorter than cultivars of Oryza sativa. Cultivars for deep water conditions tolerate flooding up to 2.5 m deep and culms may grow up to 5 m long. Some shattering of seed occurs in many cultivars.
African rice grows well above 30°C, but above 35°C spikelet fertility is noticeably reduced. Temperatures below 25°C reduce growth and yield; temperatures below 20°C do so markedly. African rice is grown from sea-level to 1700 m altitude. It is generally a short-day plant, but photosensitivity varies between cultivars from day-neutral to strongly sensitive.
African rice is grown on a wide range of soils. Although preferring fertile alluvial soils, it tolerates low soil fertility. Some cultivars can produce higher yields than Asian rice on alkaline and on phosphorus-deficient soils. They are also more tolerant to iron-toxicity. Floating rice is planted on loam or clay soils.
Propagation and planting
African rice is propagated by seed. The weight of 1000 seeds is 20–27 g. Seed dormancy disappears a few months after maturity; for experimental purposes, dormancy can be broken by removing the lemma and palea and about one-third of the albumen, allowing germination in 2–3 days. Before sowing the soil may be prepared with a hoe or, as in Senegal, Gambia and Guinea, with a long-handled spade, but soil preparation is rarely practised. Seed is mostly broadcast and transplanting is rarely practised. For floating rice, seed is densely sown in soil that has been recently weeded and that may or may not have been ploughed or hoed. Cultivars are selected according to expected flood duration and generally have a growing period of 4–6 months.
In West Africa from Senegal to northern Cameroon, where rainfall generally exceeds 1000 mm/year, African rice is mostly planted as an upland crop, depending solely on rain and surface run-off. In some regions short-duration cultivars are grown that are adapted to annual rainfall amounts as low as 700 mm. In Senegal and Gambia the crop is sown in moist locations, often under palm trees, after simple soil cultivation. This is locally called ‘riz de plateau’. ‘Riz de montagne’ is grown throughout the forest zone covering western Côte d’Ivoire, Liberia, the Fouta Djallon and eastern Guinea mountains. It is grown in shifting cultivation, often following logging, even on steep slopes. The undergrowth is cut and at the end of the dry season fields are burned. Sowing is mostly carried out without any soil cultivation. Rice is grown in pure stands or intercropped with other crops, e.g. maize. After 2–3 years, the field is used to grow cash crops such as cacao or coffee, or left fallow. Farmers return after 10–20 years, or later, depending on the recovery of the vegetation and the soil. In such fields, cultivars of shortest duration are grown and African rice is only rarely replaced by Asian rice, e.g. in the forest zone of Guinea and western Côte d’Ivoire.
Irrigated rice systems depend more on river water than on rainfall and are found in areas with a much drier climate; the degree of control of irrigation is variable. Floodplain rice on hydromorphic soils is found in Guinea, Côte d’Ivoire, Mali, Burkina Faso and Nigeria. Floating rice cultivars are very common in the interior delta of the Niger river in Mali, and is also planted in Senegal, Gambia, Niger and Nigeria. It grows sometimes very rapidly in length as the flood water rises, tolerating submersion for several days. Cultivars grown have a crop duration of 4–5 months.
Along the rivers in northern Senegal and in Mali, in the northern part of the interior delta of the Niger river south-west of Timbuktu, in a zone stretching from Diré and Goundam to the series of lakes Faguibine, Gouber and Kamango, rice is grown on floodplains after floods have receded. In this cropping system, rice is sown in moist soil and the crop development relies on ground water (‘riz de décrue’). Weeds are few. Both Oryza glaberrima and Oryza sativa are grown and have a duration of 4–5 months. Along the Atlantic coast, e.g. in Sierra Leone, African rice is grown in mangrove swamps.
Weeding of African rice in non-flooded areas is manual and often late. In some regions, such as the Basse Casamance, weed control is combined with land preparation: a first light irrigation favours the germination of weeds, which can subsequently be eradicated. Mechanization and fertilizer application are rarely practised. In floodplain and wet rice cultivation neither crop rotation nor fallow is practised, contrary to the practice for upland rice.
Diseases and pests
The most important and widespread disease of African rice is rice blast (Pyricularia grisea; synonyms: Magnaporthe grisea, Pyricularia oryzae). Rice yellow mosaic virus (RYMV) and soil parasites (nematodes) often cause large losses. There are few control measures, but some cultivars are resistant to such pathogens. In floodplain and wet rice systems the main problems are rizophagous fish (Distichodus, Tilapia), while birds cause serious damage in all rice cropping systems. Children armed with pebbles and slings offer some protection. Rodents, buffaloes, elephants and hippopotamuses can all cause serious damage. African rice gall midge (Orseolia oryziphora), crickets and grasshoppers are also important pests, as are stem-borers that destroy the apex of the plants and so prevent the formation of inflorescences.
Annual wild rice (Oryza barthii) is very common in wet rice fields. It can be recognized by its red awns but it is then too late to remove it. It is characterized by very strong shattering and, as it often ripens before the cultivated rice, it multiplies and spreads throughout the rice field. It is sometimes harvested with the rice crop. If the seed is not cleaned carefully, the field will be infested with wild rice within a few years. Annual wild rice readily cross-pollinates with Oryza glaberrima; the resulting red grains shatter more easily and have to be milled more tightly, resulting in more weight loss and higher costs. Under conditions of deep flooding, perennial wild rice (Oryza longistaminata) is cut below the surface of the water in order to kill it.
The harvesting season for African rice is October–December. Upland rice is harvested first. Panicles are bundled and stacked in elevated granaries under which a smoking fire is maintained to keep away storage insects. After manual or mechanical threshing, grain can also be stored in bulk in bags. Floating rice is harvested in several rounds mostly from canoes, which leads to considerable losses.
Yields of African rice obtained under traditional conditions rarely average more than 1 t/ha. In experiments with deep water rice cultivars carried out in Gao and Timbuktu (Mali) from 1984–1987, yields of 1–4 t/ha were obtained.
Handling after harvest
The produce of African rice, whether stored before or after threshing, should be protected against pests, mainly insects and rodents. The paddy should be dried well to reduce the moisture content to a maximum of 14% to achieve good storage and a high milling yield. The grain of African rice is more brittle than that of Oryza sativa, making it more difficult to mill.
IRD (Institut de Recherche pour le Développement, formerly ORSTOM) and CIRAD (Centre de Coopération Internationale en Recherche Agronomique pour le Développement) collected cultivated and related wild types of rice (both African and introduced) throughout their area of distribution. Between 1974 and 1983, over 3700 samples were collected in Africa and Madagascar, of which 20% are Oryza glaberrima and 12% related wild species. These collections are kept in cold storage (4°C, 20% humidity) for medium-term conservation and partly frozen at –20°C for long-term storage at IRD in Montpellier (France). The collection is duplicated at CIRAD in France and at the International Rice Research Institute (IRRI), the Philippines. The International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria keeps almost 2800 accessions, and the Africa Rice Center (WARDA), Bouaké, Côte d’Ivoire, almost 1900 accessions. Collections of Oryza glaberrima germplasm are also kept at the Bangladesh Rice Research Institute, Dhaka, Bangladesh (200 accessions) and the USDA-ARS National Small Grain Collection, Aberdeen, Idaho, United States (174 accessions). African rice shows orthodox seed storage behaviour. Currently no in-situ conservation programmes of rice of African origin exist but they would be desirable.
While the genetic variation in Oryza glaberrima is small in comparison with that of Oryza sativa, types with important characteristics have been identified: resistance to RYMV, rice blast (Pyricularia grisea), African rice hispa (Trichispa sericea), the African rice gall midge (Orseolia oryziphora), and to several stem-borers and nematodes, including Heterodera sacchari, Meloidogyne graminicola and Meloidogyne incognita. African rice shows resistance to salinity, drought and iron toxicity and it competes well with weeds. Various cultivars have shown partial resistance to and tolerance of parasitic plants of the genus Striga. In general, hybrids between Oryza glaberrima and Oryza sativa are highly sterile in the F1 and early generations. However, in a hybridization programme initiated in 1992, WARDA succeeded in crossing the two species into stable and fertile progenies through backcrossing and doubled haploid breeding. Interspecific progenies, which are called ‘New Rice for Africa’ (NERICA), are now being grown by farmers in Africa. They are more productive than Oryza glaberrima, but retain favourable characteristics such as competitiveness against weeds, resistance to diseases and pests, tolerance to poor soils, and high grain quality. Few genetic improvement programmes of Oryza glaberrima itself have been undertaken.
Extensive genetic linkage maps have been made for rice, and IRD and WARDA are working together in a programme to systematically integrate the genome of Oryza glaberrrima into that of Oryza sativa. The objective is to follow the introgression of small genome fragments of Oryza glaberrima into the genetic base of Oryza sativa using molecular markers.
For over 30 years it has been predicted that African rice would disappear under the pressure of widespread introduction of improved cultivars of Oryza sativa, but this has not happened, although in Burkina Faso, for example, a strong decline of African rice has been observed. The explanation for the resilience of African rice is that it is highly appreciated by the people of West Africa, who continue to grow African rice for its taste and culinary properties, and that it is highly adapted to particular growing conditions, e.g. as floating rice.
Cross-breeding of Oryza glaberrima and Oryza sativa should continue to include programmes aiming at the transfer of genome fragments. Such breeding programmes should be carried out in association with a programme of in-situ conservation of genetic resources of wild and cultivated rice of African origin. For specific objectives certain regions should be identified, e.g. Guinea for its diversity of rice cropping systems, the regions of southern Chad/northern Cameroon and the interior delta of the Niger river in Mali for the contacts between wild and cultivated types, and the valley of the Ferlo in Senegal to study spontaneous populations of the annual Oryza barthii away from all rice cultivation. Improvement of African rice cultivation should aim at decreased lodging, increased yield, less seed scattering and decreased brittleness of the grain.
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Correct citation of this article:
Bezançon, G. & Diallo, S., 2006. Oryza glaberrima Steud. In: Brink, M. & Belay, G. (Editors). PROTA 1: Cereals and pulses/Céréales et légumes secs. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, plant habit; 2, inflorescence; 3, spikelet.
Redrawn and adapted by W. Wessel-Brand
cultivation of floating rice
harvesting of floating rice
polymorphism of harvested panicles
polymorphism of the grains
plants in greenhouse