1. Introduction

Taro (Cocoyam) [Colocasia esculenta (L.) Schott] is an important tropical root crop grown purposely for its starchy corms or underground stem ^[1]. It is regarded as one of the most important staple crops in the Pacific Islands, Asia and Africa ^[1][2][3][4]. It is one of the oldest world’s food crops believed to have been first domesticated in Southeast Asia before its eventual spread to other parts of the world ^[5][6]. The two most commonly cultivated species of Taro (Colocasia esculenta and Xanthosoma sagittifolium) belong to the Araceae family and are extensively cultivated in Africa.

Taro is an herbaceous monocotyledonous plant of 1–2 m height. The plant consists of central corm (below the soil surface) making the leaves grow upwards, roots grown downwards, while cormels, daughter corms and runners (stolons) grow laterally. The root system is fibrous and lies mainly at a depth of up to one meter of soil ^[3][7].

In most Pacific Island countries (PICs) where taro is widely cultivated and consumed, two species of Colocasia are recognized. They are C. esculenta var. esculenta, commonly called dasheen, and C. esculenta var. antiquorum, often referred to as eddoe ^[3][8]. The dasheen variety possesses large central corms, with suckers and/or stolons, while eddoes have somewhat small central corm and a large number of smaller cormels ^[3][9][10].

In Africa, Taro is commonly produced by smallholder, resource-limited and mostly female farmers ^[3]. Taro ranks third in importance, after cassava and yam, among the class of root and tuber crops cultivated and consumed in most African countries ^[3]. The crop is underutilized in the areas of export, human consumption, industrial uses, nutritional and other health benefits in Africa. Thus, the objective of this review is to provide a critical assessment of the leading players in the taro sub-sector globally and continentally with the most recent datasets useful for policy intervention and planning. Also, this study explores the nutritional, health and economic benefits of taro highlighting the role it can play in enhancing sustainable livelihoods especially in Africa.

2. Taro [Colocasia esculenta (L.) Schott] in Africa

In many parts of the world, (especially, African countries), roots and tubers such as cassava (Manihot esculenta), sweet potato (Ipoemea batatas), yam (Dioscorea sp), and cocoyam (Colocasia esculenta and Xanthosoma sagittifolium), are important staple crops commonly cultivated by smallholder farmers and used as food security and income crops ^[11][12]. Taro production in Africa (especially SSA) is commonly by smallholder, resource-limited and mostly female farmers ^[3]. However, the crop is mostly referred to as “poor man’s crop” because its consumption is mainly by the low income households in the society ^[3]. As mentioned above, Africa contributed to over 70% of global taro production consistently in the past two decades and accounted for about 76 percent of world share in 2000 but, witnessed a slight decline in production levels in two decades attaining 72.27% (7.6 million tonnes) share of world total production in 2019 (Table 10) ^[11]. Despite the global recognition of taro production in Africa, the crop has suffered serious neglect, receiving little attention from agricultural researchers and government policymakers ^{[3][13][12][14][15]}.

The world is faced with enormous task of providing sufficient food for over seven billion people, with 690 million people suffering from hunger globally, Africa region accounted for 73 million out of the 135 million people suffering from acute food insecurity in 2019 ^{[16][17][18][19][20][21][22]}. Hunger and malnutrition continue to escalate as the world’s food system is being threatened by the emergence of COVID-19 pandemic in December 2019. The attendant total and partial lockdowns in many countries has led to increased level of hunger and food insecurity. The situation in Africa is the one referred to as “a crisis within a crisis” with very high prevalence of hunger and malnutrition in most Africa countries. African governments need to intensify efforts in boosting agricultural production and keeping the food value chain active in order to stem the tide of hunger and food insecurity in the continent ^{[23][24][25][26][27][28][29]}.

However, one of the means of reducing the level of hunger and protein-energy malnutrition in Africa (especially SSA) is through increased production and consumption of indigenous staples of high energy content such as taro ^[30][31]. Taro is recognized as a cheaper yam substitute, notably during period of food scarcity (hunger season) among many households in SSA (especially Ghana and Nigeria) and its production remained an integral part of many smallholder farming households in many parts of West and Central African countries ^[3]. It is worthy of note that, most of the output that placed Nigeria as number one taro producer globally and other high producing African countries like Cameroon, Ghana, Madagascar and Burundi (Figure 3) are carried out by smallholder rural farmers employing primitive technology and traditional farming practices with limited intensive management system ^[3][11]. Taro leaves and tubers possess excellent nutraceutical and healing properties. Thus, its increased production and consumption should be encouraged because of these properties in addition to its usefulness as a food security staple.

2.1. Recent Taro Productivity and Yield Potential in Africa

Total output of taro has witnessed significant increase in Africa, (mostly in West and Central Africa) where total production level in 2019 reached 7.62 million tonnes (the highest in 2 decades) (Table 1). However, these were largely due to increased harvested area rather than increase in yield per land area ^[11]. The average yield per land area (tons/ha) in Africa has consistently remained relatively low (Figure 4), from 6.10 tons/ha in 2000 to abysmally low 4.34 tons/ha in 2019 while Nigeria (Figure 5) the leading taro producer was not spared in the declining trend of taro yield per land area in Africa, decreasing from 6.62 tons/ha in 2000 to 2.88 tons/ha in 2019 ^[11]. Consequently, while other taro producing regions experienced significant increase in their yield per land area from 2000 to 2019, Africa recorded a monumental decrease in taro yield per land area in this period (Table 11 & Figure 4) ^[11]. African region recorded the lowest taro yield per land area in 2019 (Table 11) when compared with other regions such as Asia (16.50 tons/ha), America (10.41 tons/ha), and Oceania (8.73 tons/ha). This unprecedented yield difference in Africa is indicative of the fact that current yield of taro (cocoyam) in the region (especially West and Central Africa) is far below its potential yield. This could be attributed to the fact that taro production in Africa is largely with limited input and mostly cultivated on marginal lands. The culture of merely increasing production level through increased area of farmland is obviously unsustainable, because it resulted in high demand for available land.

Figure 4. Declining African region Taro (Cocoyam) yield with trend line (2000–2019), Source: Authors’ graph using data from FAOSTAT 2021 ^[11]. The vertical lines are the average of Taro and the horizontal axis represents the year of production.

Figure 5. Nigeria’s declining Taro yield with trend line (2000–2019); Source: Authors’ graph using data from FAOSTAT 2021 ^[11]. Note: The dotted line is the trend line; the solid line is the declining Nigeria Taro yield.

Increased taro production is a worthwhile venture. There are industrial, nutraceutical and healing uses for the crop both within and outside any of the producing countries. Exporting taro to other countries will boost the revenue base of the producing countries; livelihoods of the smallholder farmers and other actors along the value chain would also be enhanced.

2.2. Taro Trade Potentials in Africa

The unprecedented increase in total output of taro in Africa (especially, West and Central Africa) in the last two decades indicated that there could be further increase in another decade to come. The estimate from Tridge ^[32] in 2018 indicated that China (with export value of $417.18 million) remained the number one exporter of taro, followed by Mexico ($264.49 million), USA ($161.01 million) and Canada ($141.96 million) (Figure 1). However, no top taro producing countries from sub-Saharan Africa, which accounted for over 70% of global share of taro production in two decades (2000–2019), was listed among the top 20 cocoyam exporting countries (Figure 1). This may be due to the difficulty in obtaining consistent and reliable data on taro import and export for most African countries. Although 65% of the global taro production is accounted for by Africa in 2019 ^[11], there is insufficient information on the contribution of taro from these top producing countries to the international taro market. Apart from poor data on trade in taro in Africa, it could also be due to the fact that taro production in SSA is mainly for meeting local needs for food security ^[3].

In 2018, the three major importers of taro are USA ($768.68 million), Japan ($227.10 million) and United Kingdom ($157.17 million) (Figure 3). Like taro exports, no top producing African countries was listed among the top 20 importers of taro in 2018. There is enormous trade potentials for taro markets in Africa both within (between countries in Africa) and outside the region. There is urgent need to improve taro production and marketing structures in Africa in order to maximize of its gains for economic empowerment ^[3][32].