Digitaria exilis (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Cereal / pulse|
|Spice / condiment|
|Forage / feed|
Digitaria exilis (Kippist) Stapf
- Protologue: Bull. Misc. Inform. Kew 1915: 385 (1915).
- Family: Poaceae (Gramineae)
- Chromosome number: 2n = 54
- Fonio, hungry rice, white fonio (En).
- Fonio, fonio blanc, petit mil (Fr).
Origin and geographic distribution
Fonio is only known from cultivation and its exact origin is unknown, but it is of ancient cultivation in West Africa. It may have derived from Digitaria longiflora (Retz.) Pers. in the inland delta region of the Niger. Historical records of the use of fonio as a cereal go back to the 14th century. Nowadays fonio is grown scattered from Cape Verde and Senegal to Lake Chad, especially on the Fouta Djallon Plateau in Guinea, the Bauchi Plateau in Nigeria and in north-western Benin. It is also grown in the Dominican Republic.
Fonio is a staple food in various parts of West Africa, where it is also known as ‘acha’ or ‘fundi’, but it is also a prestige food (‘chief’s food’) and a gourmet item. In the Hausa regions of Nigeria, Benin, Togo and Ghana, special couscous types (‘wusu-wusu’) are prepared with fonio. In southern Togo, the Akposso and Akebou people prepare fonio with beans in a dish for special occasions. In Nigeria fonio flour is made into thick, unfermented porridges (‘tuwo acha’), and fermented grains are used for thin porridges (‘kunu acha’). Boiled whole grains are eaten with vegetables, fish or meat. In northern Togo, the Lamba people brew beer (‘tchapalo’) from fonio. It is also popped and can be mixed with other flours to make bread. In the Dominican Republic fonio flour is made into porridges and creams, mixed with other cereal flours to make cookies, and it is used in the preparation of candy and fermented beverages; aside from everyday meals, fonio is also associated with various religious festivities inherited from African ancestors.
Fonio grain is a valuable, easily digested feed for farm animals. The straw and chaff are excellent fodder and are often sold in markets for this purpose. Chopped fonio straw is mixed with clay to build walls of houses. The straw is also used as fuel for cooking or to produce ash for potash. Fonio grain is considered to have medicinal properties; it is recommended for lactating women and diabetic people.
Production and international trade
According to FAO statistics the average world production of fonio (the major share) and black fonio (Digitaria iburua Stapf) together in 1999–2003 amounted to 257,000 t per year from 360,000 ha, all in West Africa. The main producing countries are Guinea (128,000 t per year in 1999–2003, from 137,000 ha), Nigeria (78,000 t from 142,000 ha), Mali (21,000 t from 33,000 ha), Burkina Faso (13,000 t from 16,000 ha) and Côte d’Ivoire (11,000 t from 22,000 ha). The production in the Dominican Republic is not known. FAO statistics show an increase in world production from around 180,000 t per year in the early 1960s to around 260,000 t in the early 2000s, with an increase in acreage from around 280,000 ha to about 360,000 ha. Fonio is hardly traded outside West Africa, except for small quantities sold as luxury product in Europe.
The composition of whole fonio grain per 100 g edible portion is: water 11.2 g, energy 1390 kJ (332 kcal), protein 7.1 g, fat 3.0 g, carbohydrate 74.4 g, fibre 7.4 g, Ca 41 mg, P 191 mg, Fe 8.5 mg, thiamin 0.24 mg, riboflavin 0.10 mg and niacin 1.9 mg (Leung, Busson & Jardin, 1968). The essential amino-acid content per 100 g grain is: tryptophan 111 mg, lysine 205 mg, methionine 441 mg, phenylalanine 402 mg, threonine 315 mg, valine 457 mg, leucine 772 mg and isoleucine 315 mg (FAO, 1970). The amino acid composition of fonio is comparable with that of other cereals, but it has a relatively high methionine content. The palatability of fonio grain is considered high.
Adulterations and substitutes
Black fonio and Guinea millet (Brachiaria deflexa (Schumach.) Robyns) are used as substitutes of fonio.
- Ascending, free-tillering annual grass up to 80 cm tall, with delicate kneed stems.
- Leaves alternate, simple; leaf sheath glabrous, smooth, striate; ligule membranous, broad, c. 2 mm long; blade linear to lanceolate, gradually tapering to an acute apex, 5–15 cm × 0.3–0.9 cm, glabrous.
- Inflorescence a terminal digitate panicle of 2–5 slender, spike-like primary branches up to 15 cm long.
- Spikelet up to 1 mm stalked, narrowly ellipsoid, 1.5–2 mm long, acute, glabrous, pale green, 2-flowered; lower glume hyaline, minute, upper glume broadly oblong, slightly shorter than spikelet, hyaline between the 3–5 green veins; lower floret sterile, upper floret bisexual; lemma about as long as spikelet, 7–9-veined; palea slightly shorter than lemma; stamens 3; ovary superior, with 2 stigmas.
- Fruit a caryopsis (grain), oblong to globose-ellipsoid, c. 0.5 mm long, white to pale brown or purplish.
Other botanical information
Digitaria is a taxonomically difficult genus comprising about 230 species in tropical, subtropical and warm-temperate regions, particularly in the Old World. Digitaria barbinodis Henr., occurring in Mali and Nigeria, is harvested as a wild cereal during times of scarcity and is occasionally grown in Nigeria. Digitaria ciliaris (Retz.) Koeler is sometimes eaten as a supplementary food (Chad) or as a famine food. Digitaria debilis (Desf.) Willd., Digitaria fuscescens (Presl) Henrard, Digitaria leptorhachis (Pilg.) Stapf, Digitaria longiflora (Retz.) Pers., Digitaria nuda Schumach. and Digitaria ternata (A.Rich) Stapf are also known to be eaten as famine foods in tropical Africa, but are considered more important as forage or auxiliary plant. In India (Assam) and Vietnam Digitaria cruciata (Nees ex Steud.) A.Camus (‘raishan’) is grown for food and fodder, whereas Digitaria sanguinalis (L.) Scop. (‘crabgrass’) is or was grown as a cereal in Europe, Asia and America.
Diversity within Digitaria exilis is broad, with a large number of locally cultivated landraces, differing in plant habit, plant colour, glume colour, grain size and length of the crop cycle. Based on morphology, 5 varieties have been distinguished:
- var. gracilis Portères: leaf margin curled, inflorescence with 2 primary branches, each with 50–100 spikelets per 10 cm, spikelets in groups of (2–)3(–4) and in 1–2 rows, stalks rough; early-maturing; Kankan region (Guinea).
- var. stricta Portères: leaf margin slightly curled, inflorescence with 2 primary branches, each with 50–100 spikelets per 10 cm, spikelets in groups of (2–)3(–4) and mostly in 1 row, stalks smooth; early-maturing; Casamance (Senegal), Guinea, Mali and Burkina Faso.
- var. rustica Portères: robust plants, inflorescence with (2–)3–4(–5) primary branches, each with 90–120 spikelets per 10 cm, spikelets in groups of (3–)4 and in 2–3 rows, stalks smooth; late-maturing; Casamance (Senegal), Guinea, Mali and Burkina Faso.
- var. mixta Portères: robust plants, vegetative parts reddish pigmented, inflorescence with ( 2–)3–4(–5) primary branches, each with 90–120 spikelets per 10 cm, spikelets in groups of (3–)4 and in 2–3 rows, stalks smooth; late-maturing; Guinea.
- var. densa Portères: tall, strong plants, with a long vegetative cycle, inflorescence with 3–4 primary branches, each with 120–140 spikelets per 10 cm, spikelets in groups of 2(–3) and in 2–3 rows; late-maturing; Togo.
Growth and development
Fonio normally germinates 2–4 days after sowing and grows rapidly. Flowering usually occurs 6–8 weeks after emergence. The time from sowing to maturity is normally 2–5(–6) months. Certain landraces mature so quickly that they produce grain already 6–8 weeks after planting, long before all other cereals, and provide food early in the growing season. At maturity the stems bend down due to the weight of the grains. Fonio follows the C4 photosynthetic pathway.
Fonio is grown at sea level in Gambia, Guinea-Bissau and Sierra Leone, but more often it is cultivated at 600–1500 m altitude. The average temperature in the growing season ranges from 20°C at higher altitudes to 25–30°C near sea level. Fonio is grown in areas with an average annual rainfall of 150–3000 mm, but its cultivation is concentrated in regions with an average annual rainfall of 900–1000 mm. It is not as drought resistant as pearl millet, but fast-maturing landraces are suited to areas with short and unreliable rains. In areas with very low rainfall it is grown in valleys benefiting from run-off water. Fonio can be grown on poor, shallow, sandy or rocky soils unsuitable for other cereals, but does not prosper in saline or heavy soils. On the Fouta Djallon Plateau of Guinea, it grows on acidic soils with very high aluminium contents.
Propagation and planting
Fonio is propagated by seed. The 1000-seed weight is 400–600 mg. Fonio is usually sown at the beginning of the rainy season. Soil preparation is minimal: the fallow vegetation is burnt and the ashes spread, and the soil may be loosened by superficial cultivation. Seed, mixed with an equal quantity of sand or ashes, is usually broadcast, and covered with soil by a light hoeing or brushing with tree branches. The seed rate is 10–30 kg per ha. Fonio is sometimes raised in a nursery and planted out in the field.
Fonio is normally grown as a sole crop, but sometimes intercropped with sorghum or pearl millet. Farmers in Guinea commonly sow various fonio types together and later fill in any gaps with Guinea millet.
Although it has been stated that fonio seldom needs weeding due to its quick establishment and the high seed rates applied, other sources indicate that a weeding at 4–5 weeks after sowing is necessary for good yields. Fonio is usually not fertilized and little is known of its nutrient requirements. In crop rotations fonio often follows rainfed rice, as a short-cycle crop before another crop is sown in the same season. It is also grown at the end of a rotation.
Diseases and pests
Fonio is susceptible to rust (Puccinia oahuensis). Resistance to the nematodes Meloidogyne incognita and Meloidogyne javanica has been recorded in soils where other plant species were infected. Birds can cause serious losses, so bird scaring is usually necessary. Fonio is attacked by parasitic plants of the genus Striga. Fonio seed is not liable to damage by storage pests and stores well.
Fonio is usually cut with a knife or sickle, tied into sheaves, dried and stored under cover. Mechanization is difficult because of lodging. When plants are dry, the grain shatters easily, and therefore it is better to harvest before the dry season has fully established and the relative air humidity has considerably declined. Harvesting is often staggered, to suit the immediate needs of the farmer.
Grain yields of fonio are normally 600–900 kg/ha, but yields of over 1000 kg/ha have been recorded. In marginal areas yields may be as low as 150–200 kg/ha.
Handling after harvest
Fonio is normally threshed at about 8 days after harvesting, traditionally by beating or trampling. The husks remain on the grains, which therefore retain moisture and must be dried further. The grains are sufficiently dry when they run easily through the fingers. The product after threshing (‘fonio paddy’ or ‘raw fonio’) is further processed in 2 stages: husking (removal of the husks from the grains) and whitening (removal of the fruitwall and the germ). Husking and whitening are done manually and require 4–5 beatings with pestle and mortar, alternated with winnowing. To obtain a product of good quality, all dirt and sand must be removed by repeated washings. The processing cycle is difficult and time-consuming and efforts are being made to develop equipment that will make processing easier. Small-scale fonio processing enterprises can be found in towns, e.g. in Mali and Burkina Faso, aiming at urban and export markets.
Fonio seems not threatened by genetic erosion. RAPD-analysis has shown a relatively high level of genetic diversity in fonio compared to other millets, possibly due to its outbreeding nature. Most germplasm collections made before 1990 and kept in national genebanks have been lost, but duplicates exist at IRD (Institut de Recherche pour le Développement), Montpellier, France, which keeps more than 400 fonio accessions. Fonio accessions are also conserved in Senegal, Guinea, Mali, Burkina Faso, Togo, Benin and Nigeria. In Nigeria, Benin and Togo germplasm characterization work for a better understanding and utilization of the fonio gene pool has started.
So far fonio has been largely neglected in breeding programmes. Breeding efforts are being undertaken in Guinea, but no results are available so far. Improvement of fonio through traditional hybridization does not seem attractive because of insufficient knowledge on its floral biology and the extraordinarily miniature nature of its floral organs.
Fonio is wrongly named ‘hungry rice’, because it is not grown to relieve hunger but because of its quality and contribution to food security. It is a crop with a short cycle, able to produce on very poor soils. It is appreciated as a food in West Africa, and its nutritional quality is excellent. Interesting research topics include improved plant architecture to prevent lodging, photoperiod-sensitivity, cultivation techniques, grain size, the development of less laborious processing methods and improvement of farmers’ seed systems. Study of the genetic diversity of fonio and multilocational screening of germplasm are also highly recommended.
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Sources of illustration
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- S.R. Vodouhè, IPGRI West and Central Africa, 08 B.P. 0932, Cotonou, Benin
- E.G. Achigan Dako, IPGRI West and Central Africa, 08 B.P. 0932, Cotonou, Benin
Correct citation of this article
Vodouhè, S.R. & Achigan Dako, E.G., 2006. Digitaria exilis (Kippist) Stapf. In: Brink, M. & Belay, G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 11 April 2019.
- See the Prota4U database.