Current Knowledge on Amaranthus Spp.: Research Avenues for Improved Nutritional Value and Yield in Leafy Amaranths in Sub-Saharan Africa
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Euphytica DOI 10.1007/s10681-014-1081-9 REVIEW Current knowledge on Amaranthus spp.: research avenues for improved nutritional value and yield in leafy amaranths in sub-Saharan Africa Enoch G. Achigan-Dako • Olga E. D. Sogbohossou • Patrick Maundu Received: 2 December 2013 / Accepted: 14 February 2014 Ó Springer Science+Business Media Dordrecht 2014 Abstract In the past 20 years, very little progress has current knowledge on taxonomy, ecology, nutritional been achieved in reducing food insecurity, child and nutraceutical value, production and cultivation malnutrition and hunger in Africa. Under-nutrition systems, reproductive biology, genetic resources and and micronutrients deficiencies are widespread and breeding of amaranths. Species of interest include: A. affect mainly women and children. To address these blitum, A. caudatus, A. cruentus, A. dubius, A. hypo- problems, increased consumption of African leafy chondriacus, A. spinosus, A. thunbergii, A. tricolor, vegetables is promoted as sources of both micronutri- and A. viridis. Research and development opportuni- ents and bio-active compounds. Widely promoted ties on nutritive and nutraceutical properties, produc- African leafy vegetables include Amaranthus spp., a tion and commercialization, taxonomic evaluation and taxonomic group cultivated worldwide. Species of this breeding perspectives were explored. genus are used as pseudo-cereals in Europe and America, and are mostly planted as vegetables in Keywords Amaranthus Á Leafy vegetables Á Africa. Amaranthus has been rediscovered as a prom- Nutrients Á Nutraceutical properties Á ising food crop mainly due to its resistance to heat, Genetic resources drought, diseases and pests, and the high nutritional value of both seeds and leaves. Leaves are rich in proteins and micronutrients such as iron, calcium, zinc, Introduction vitamin C and vitamin A. All parts of the plant are used as medicine to heal many diseases in African commu- Africa has experienced mixed progress in reducing nities. This paper focuses on leafy amaranths tradi- food insecurity and child malnutrition in the past tionally utilized on the continent. It briefly reviews the 20 years (Garcia 2012). Approximately, one third of children under 5 years of age in Africa are stunted and more than a quarter are underweight. Micronutrient E. G. Achigan-Dako (&) Á O. E. D. Sogbohossou deficiencies affect mainly women and children and Horticulture and Genetics Unit, Faculty of Agronomic contributes significantly to the global disease burden Sciences, University of Abomey-Calavi, 01 BP 526 Tri Postal, Cotonou, Republic of Benin of children by limiting proper cognitive development, e-mail: [email protected] impairing physical development, and increasing sus- ceptibility to infectious diseases (Asare-Marfo et al. P. Maundu 2013). Most countries in Africa are still struggling to Kenya Resource Centre for Indigenous Knowledge (KENRIK), National Museums of Kenya, address problems of under-nutrition and micronutrient P.O. Box 40658, Nairobi 00100, Kenya deficiencies (Lopriore and Muehlhoff 2003). 123 Euphytica African leafy vegetables are increasingly recog- (AVRDC) have contributed to provide seeds of nized as possible contributors of both micronutrients superior micro-nutrient rich amaranth (Amaranthus and bioactive compounds to the diets of populations in cruentus) cultuvars and increase production and Africa (Smith and Eyzaguirre 2007). The continent is consumption of leafy vegetables in Rwanda, Uganda, rich of vegetable species including amaranths which Malawi and Tanzania (AVRDC 2008). Another are among the most popular leafy vegetables on the important project was the Bioversity International’s continent (Maundu et al. 2009). Amaranths consist of African leafy vegetables programme conducted in 60–70 species (Xu and Sun 2001) and include at least Botswana, Cameroon, Kenya, Senegal and Zimbabwe 17 species with edible leaves and three grain ama- which induced notable positive changes in growing, ranths grown for their seeds (Grubben and Denton consumption, marketing and nutritional awareness of 2004). Although several species are often considered African leafy vegetables such as amaranths and weeds, people around the world value amaranths as nightshades (Gotor and Irungu 2010). leafy vegetables, cereals and ornamentals (Trucco and Unfortunately, there are still gaps in knowledge of Tranel 2011). some popular amaranths of Africa and there are Most of the amaranth species are harvested in the confusions in the nomenclature of species, for wild as food resource. Only a few are grown and are instance, of the hybridus complex while comprehen- among the leafy types most common in markets in sive nutritional profiles are yet to be compiled tropical Africa. Amaranths can also be grown for their (Grubben and Denton 2004). Moreover, little is known seeds. This is the case of some introduced varieties of on the breeding potentials particularly of wild relatives American origin (Wu et al. 2000). Grain amaranth is that can be promoted for sustainable utilization. not commonly cultivated in Africa (Grubben and Here we present an overview of studies carried out Denton 2004). More recently however, a few farmers on amaranth species and identify future prospects for have taken the growing of grain amaranth more research and development with focus on leafy ama- seriously and are supplying millers and supermarkets ranths of sub-Saharan Africa. Particular emphasis is in Zimbabwe, Kenya, Uganda and Ethiopia. Since placed on ways to improve amaranth genetic diversity about 1980, Amaranthus has been rediscovered as a for increased production and consumption on the promising food crop mainly due to its resistance to continent. heat, drought, diseases and pests, and the high nutritional value of both seeds and leaves (Wu et al. 2000). According to Onyango (2010), improvement of Systematic and taxonomy of economically amaranths through research and development could important species produce an easy and cost-effective way of eliminating malnutrition and promoting people’s health as well as The species of Amaranthus are often difficult to achieving food security. Unfortunately, there are still characterize taxonomically, due to the overall simi- gaps in knowledge of some popular amaranths of larity of many of them, small and difficult-to-see Africa and there are confusions in the nomenclature of diagnostic parts, intermediate forms, and the broad species, for instance, of the hybridus complex while geographical distribution, which is the reason for comprehensive nutritional profiles are yet to be many synonyms (Mujica and Jacobsen 2003). Sauer compiled (Grubben and Denton 2004). Moreover, (1967) described two subgenera: Acnida (which little is known on the breeding potentials particularly included the dioecious species) and Amaranthus of wild relatives that can be promoted for sustainable (which included the monoecious species), while utilization. Mosyakin and Robertson (1996) recognized three Some interventions were carried out thanks to subgenera, i.e. Acnida, Amaranthus and Albersia partnerships between research institutions and local based on inflorescence and floral characteristics. The NGOs and to promote indigenous vegetables includ- need for infrageneric classification or micro-classifi- ing amaranths. For example, the Promotion of cation of the genus was raised recently (Das 2012). Neglected Indigenous Vegetable Crops (IV) for Species differentiation based on morphological Nutritional and Health in Eastern and Southern Africa features can be sometimes challenging. However, (ProNIVA) project led by the World Vegetable Center examination of floral parts can result in constant 123 Euphytica Fig. 1 Inflorescences of selected Amaranthus species. a Apical inflorescence of A. viridis. (Plants were grown at the National and axillary inflorescences of A. blitum; b Hanging inflores- Agricultural Research Institute of Benin (INRAB), Agonkan- cence of A. caudatus; c Terminal inflorescence of A. cruentus; mey, Republic of Benin using seeds requested from United d Terminal inflorescence of A. dubius; e Inflorescence of A. States Department of Agriculture, Institut National des Recher- hypochondriacus; f Apical and axillary inflorescences of A. ches Agricoles du Be´nin (INRAB) and Kenya Resource Centre spinosus; g Axillary clusters of A. tricolor; h Terminal for Indigenous Knowledge (KENRIK) characters from which discontinuities can be used to or short spikes (Fig. 1a, g), origin of flower bud from define well-established taxa (Trucco and Tranel 2011). leaf axil, 3 tepal lobes, 3 stamens, brownish black In this sense, tepal number and morphology are seed, indeterminate growth habit. Grain Amaranthus commonly used for taxonomic identification (Trucco are characterized by apical large to moderately large and Tranel 2011). According to Das (2012) amaranth complex inflorescence comprising aggregates of cy- species can be classified into three categories, which mes (Fig. 1b–h), 5 tepal lobes, 5 stamens, seed with represent more or less use-groups: (1) vegetable variable seed coat colour and well defined flange, Amaranthus with for instance Amaranthus tricolor utricle circumscissile (Das 2012). Table 1 gives an var. tricolor, Amaranthus tricolor var. tristis; (2) grain illustration of that classification (Das 2012) based on Amaranthus which includes Amaranthus hypochon- commonly used species in sub-Saharan Africa. As far driacus, Amaranthus caudatus, Amaranthus cruentus; as weeds are concerned some species showed mor- and