The biocultural heritage and changing role of indigenous yams in the Republic of Guinea, West Africa

Abstract

La production mondiale d'igname est centrée sur l'Afrique de l'Ouest, mais il existe d'importantes lacunes dans les connaissances sur la diversité au niveau des exploitations agricoles dans une grande partie de la région, et particulièrement en Guinée. Bien que la production d'igname augmente en Guinée, à long terme, la diversité variétale et la durabilité des systèmes agricoles sont menacées. La documentation de la diversité des cultures locales dans l'agriculture familiale est essentielle comme base de référence pour comprendre les trajectoires de perte variétale passée et future. Cette étude utilise des approches interdisciplinaires qui sont nécessaires pour aider à comprendre la manière dont la diversité historique des cultures est créée et maintenue au sein des systèmes de patrimoine agricole et alimentaire autochtone, ainsi que les raisons de sa perte au fil du temps.

INTRODUCTION

Roots and tubers are an important group of crops for global nutrition (Scott, 2021). Yams (Dioscorea spp.) are key staple food crops across many tropical countries, whilst many, especially wild species, are used in local and Indigenous health systems or the pharmaceutical industry (Attaie et al., 1998; Obidiegwu et al., 2020; Price et al., 2016; Wilkin, 2001). Around 98% of cultivated yam production is in Africa, with around 93% of this in West Africa where they are a key part of food systems, the economy and cultural life (Ayensu & Coursey, 1972; Coursey, 1967; Lebot & Dulloo, 2021; Miège, 1952; Nweke et al., 2022; Obidiegwu & Akpabio, 2017).

Cultivated African yam agri-systems are facing several major challenges. Firstly, although below-ground crops are argued to be comparatively resilient to climate change, future climate modelling has revealed ‘Guinea’ yams (Dioscorea cayenensis-rotundata complex) to be more vulnerable than many Sub-Saharan crops due to a projected decrease in size of the environmental niche suited to its cultivation (Pironon et al., 2019; Taylor et al., 2019). Secondly, recent increases in yam production have been linked to unsustainable increases in areas of land under cultivation (Neina, 2021). Thirdly, on-farm diversity is patchily documented, and little is known about the extent to which varietal diversity is threatened (Lebot & Dulloo, 2021).

Preserving varietal diversity in situ is essential for maintaining the capacity of crops to adapt to climate change over time and for maintaining food security and food sovereignty within Indigenous food systems (Argumedo et al., 2020; Bellon et al., 2015). Documentation of on-farm yam varietal diversity as it stands, and investigation of patterns of and reasons for temporal change, are urgently required. Interdisciplinary approaches that cross the sciences and humanities are needed because crop diversity is both created and lost through both natural and cultural forces (Bellon et al., 2015).

Guinea is routinely omitted from descriptions of the key yam growing areas in Africa. The ‘yam belt’ is often described as extending from Cote D'Ivoire to western central Africa (Chaïr et al., 2010; Coursey, 1967). In FAO statistics (FAO, 2022), Nigeria, Côte d'Ivoire, Ghana, and Benin are in the top 10 list of global producers. Despite Guinea having lower overall production figures, it has the second highest yield figures per unit area in West Africa. Overall in Guinea yams have on average the third highest production within root and tuber crops, after cassava and sweet potato (FAO, 2022). However when considering the country by region, yams are dominant crop to the east in Haute-Guinée, where production comprises 75% of the country's yam trade (Tradore & Kaba, 2007).

Studies of yams in West Africa in general have focused especially on yam agronomy, improvement, ex-situ conservation and genomics (Afoha et al., 2019; Dansi et al., 2000; Lebot & Dulloo, 2021; Scarcelli et al., 2019; Sugihara et al., 2020). To date, research has also mostly focused on Nigeria, Benin, Ghana, and Cote D'Ivoire with little published about yams in Guinea. Comparatively little research has considered in detail local scale diversity and its connections to customary practices, food and cultural uses (Ayensu & Coursey, 1972; Hounhouigan et al., 2003; Obidiegwu & Akpabio, 2017; Visser, 1977). Except for Benin and Togo, there is little documentation of on-farm diversity, and the extent of varietal loss is very little known with the exception of Togo (Dansi et al., 1999, 2013; Loko et al., 2013; Vernier & Dansi, 2006).

Documentation of yam diversity in the context of farmers preferences, and the local practices that have historically helped to maintain diversity, is therefore a critical research gap in much of West Africa and especially Guinea. In the research discussed here, our aims were to investigate (i) varietal diversity, agricultural practices, and the cultural and economic importance of yams and (ii) changes to these components in these in living memory. The results of fieldwork presented here is part of a wider research programme into Guinean yams being developed by Nagnouma Condé and the National Herbarium of Guinea (HNG) in connection with the Guinea Tropical Important Plant Areas programme (Couch et al., 2019; Molmou et al., 2022), and the ‘Agri-system Histories and Trajectories (AgriHist)’ project, which aims to explore the role of indigenous crops and temporal changes in varietal diversity (Burton et al., 2024).

West African yams

Yams are monocots and are in the genus Dioscorea (family Dioscoreaceae). Of more than 650 species (POWO, 2023), about 10 have been domesticated and are widely cultivated for food (Ayensu & Coursey, 1972; Burkill, 1985; Govaerts et al., 2007). Two are the most globally prevalent and economically important. The first is ‘Guinea yam’ (here referred to as the D. cayenensis-rotundata complex), indigenous to West Africa and likely domesticated there (Scarcelli et al., 2019). The second is the Asian domesticate D. alata (winged, water or greater yam), which is now cultivated throughout the tropics including in Guinea. Another locally important West African domesticate is Dioscorea dumetorum (Adigoun-Akotegnon et al., 2019). The overall list of yams species (wild and domestic) thought to be growing in Guinea is potentially up to 17 species and is outlined in the supporting information (Table S1).

There has been ongoing debate since the mid-twentieth century as to whether D. cayenensis Lam. and D. rotundata Poir. are distinct species (Coursey, 1967; Miège, 1952). Currently, they are widely recognised as distinct at subspecies level, D. cayenensis subspecies rotundata (Poir.) J. Miège and subspecies cayenensis Poir. (Gosline et al., 2023; POWO, 2023). Both are distributed in tropical forests from west to central Africa, but subspecies rotundata varieties also extend into savannah environments. Some publications also refer to a D. cayenensis-rotundata complex, a concept that we also follow here (Dansi et al., 2000).

Morphological separation of above-ground plant parts of the two sub-species is not possible, and distinction of varieties is typically based on tuber colour, dormancy and cooking properties (Coursey, 1967). Varieties attributed in literature to D. cayenensis subspecies rotundata are often described as white and those to D. cayenensis subspecies cayenensis as yellow, with varieties from the rotundata group also described as having a longer dormancy, adapted to a longer dry season, and producing tubers with better storage and cooking qualities. A caveat is that colour differences amongst tuber groups are not always consistent and other phenotypic characteristics may be influenced by habitat (Coursey, 1967).

West Africa is an important region of crop domestication, including pearl millet (Cenchrus americanus (L.) Morrone syn. Pennisetum glaucum (L.) R.Br.), fonio (Digitaria exilis [Kippist] Stapf), and African rice (Oryza glaberrima Steud.) as well as Guinea yams (Fuller et al., 2014). Currently, the deep time domestication history of yams remains unclear. Firstly, there has been limited regional archaeobotanical fieldwork, including none in Guinea. Secondly, yams are not easy to identify archaeobotanically, although there are advances in methods for identifying tuber parenchyma (Barron et al., 2022; Florin, 2022). Some genomic studies have suggested potential wild ancestors are the forest species Dioscorea praehensilis and others to hybridisation between both D. abyssinica and D. praehensilis (Scarcelli et al., 2019; Sugihara et al., 2020).

We note that the term landraces is a contested term for farmers varieties of yams (and other vegetative crops), because they are clonally propagated. Dioscorea spp. are dioecious (with male and female plants). Seedling yams are hybrids and new genotypes, and when propagated vegetatively, yam plants are clones of these individual hybrids (Chaïr et al., 2010). This process has been ongoing, as the documented process of enoblement can introduce novel genotypes via the cultivation of wild or seedling yams (see discussion for further detail). As clones, cultivated yams are cultivars, however, they may still be prone to further genetic changes, including somatic mutations, which along with plasticity to environmental conditions and human selective pressures can create phenotypically distinctive cultivars (Denham et al., 2020; Lebot & Dulloo, 2021; McKey et al., 2010). Here we distinguish historically grown local varieties as ‘landrace cultivars’ from introduced ‘commercial cultivars’, and use the terms varieties and cultivars as overarching summarising terms.

MATERIALS AND METHODS

The research presented here is focused on Haute-Guinée. This region is one of the four main provinces of the country that are largely structured across different ecotones and ethnolinguistic groups. Located east of the Fouta Djallon highlands, Haute-Guinée is situated above Guinée Forestière (the forested region in the southeast), and borders the Republic of Mali. The region is a transitional ecotone between the forest and savannah woodland, with rainfall mainly between June and October. It is one of the warmest regions in the country with an average daily high temperature of 33°C (2023 worlddata.com).

There are three dominant ethnolinguistic groups and over 40 languages spoken in Guinea (and with French acting as a lingua franca). Susu is the dominant group and language in coastal regions, Peul/Fula is the language spoken by the Fulani in the Fouta Djallon; Malinké is the dominant group and language in Haute-Guinée, and there are several ethnic groups and languages in Guinée Forestière. The Malinké also live in southern Mali, Senegal, Guinea Bissau, and eastern Gambia.

Ethnobotanical data were collected in the Kankan Prefecture of Haute-Guinée from June to July, and from September to October 2022. Out of 89 interviews, 78 were with farmers, seven with key informants (described below) and four with traders (Table S2). Farmer interviews were focused in six districts across three sub-prefectures in the Kankan region (Figure 1); Tintioulean (Tintiouleen koro and Sanna) Missamana (Djèè and Missamana centre) and Sabadou-baranama (Baranama centre and Worokoro). Key informants interviewed were from the Regional Centre for Agricultural Research of Bordo (CRRAB), the Federation of Unions of Cooperatives Producing yams and Sesames of Guinea (FUCPIS-G), the Prefectural Directorate of Agriculture and Livestock (DPAE), and the Former Director of the Regional Centre of Agronomic Research (CRRAB).

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A semi-structured questionnaire was developed to ask participants about the yam varieties grown, their uses and cultivation, and whether there were any changes within the yam agri-systems in living memory. These overarching questions were similar to those applied in fieldwork relating to the cereal fonio and associated agrisystems in the Fouta Djallon Highlands in central Guinea, also as part of the AgriHist project during 2022 (Burton et al., 2024), with questions being refined in the present study to suit the context of yam cultivation (Methods S1). Two seasons of fieldwork were undertaken to enable an exploration of agricultural practices that occur during different times of the year (to observe yam planting and the first stage of harvesting). During the second visit, farmers were asked more detailed questions about the commercial role of yams, their marketing and cultural heritage. Herbarium specimens were collected, identified, and accessioned at the Herbier National de Guinée in Conakry (HNG) and at Royal Botanic Gardens, Kew (K) in the United Kingdom.

RESULTS

Yam species and their uses in the study area

Several wild and domesticated yams were collected and identified as growing in Haute-Guinée (Figure 2, Figure S1, Table S1). In the study region, the main domesticated species were Guinea yams (D. cayenensis-rotundata complex) and D. alata. One farmer cited cultivation of Dioscorea bulbifera and a collected specimen from his farm was confirmed (by NC and PW) to be a domesticated rather than wild form of the species. Four farmers also said their grandparents ate ‘diambi’ (Dioscorea abyssinica) in the past, and three mentioned it still being eaten today. Although most said diambi is not cultivated, one farmer and a key informant mentioned that it can be grown and that over time it can start to become like a domesticated variety. One farmer mentioned D. bulbifera, and two D. abyssinica, as having medicinal use (for skin conditions). Local agronomists also provided a overview of the wild and cultivated yam species thought to be found beyond the study area across the different regions of Guinea (Table S1).

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Yams and other crops in Haute-Guinée

Although all farmers interviewed were engaged in yam cultivation, the proportions of cultivated land allocated for yams varied across the villages (Figure 3). Farmers from the village Tintiouleen Koro reported allocating the highest amount of land to yam cultivation (an average of 2.9 ha per farm), while Saana had the lowest (1.25 ha per farm). All farmers interviewed (n = 78) grew Guinea yams, and overall 79% of them grew D. alata, with variability between villages (Figure 4a). The other most frequently grown crops in farms visited were rice (it was not documented whether the rice was Oryza glaberrima Steud. or Oryza sativa L.), maize (Zea mays L.), peanut (Arachis hypogaea L.), and fonio. Rice was the second most frequently grown crop, and Missamana had the most even cultivation across all crops (Figure 4b). Other key crops cited as grown by farmers during the interviews included sesame (Sesamum indicum L.), cashew nut (Anacardium occidentale L.), and bambara ground nut (Vigna subterranea (L.) Verdc.). Nearly all the farmers (96%) interviewed kept cattle, whilst 44% sheep, 39% goat, and 61% chickens.

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Cultivated yam diversity in Haute-Guinée today

During the interviews with farmers (n = 78), 12 varieties of Guinea yams were recorded. The varieties were described as old except for nigeria, which was introduced around a decade ago. Of the 12 varieties, only the landrace cultivar sofèrè and introduced cultivar nigeria were grown in each village, with the other local landrace cultivars being more occasionally present across the villages (Figure 5a,b). As well as having the greatest amount of land for yam cultivation, the village of Tintiouleen Koro maintains the highest level of yam diversity, growing 10 of the 12 varieties of Guinea yams. From the discussions with local agricultural experts overall 25 named Guinea yam varieties were listed for the wider Kankan region (Table S3).

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During the first fieldseason farmers (n = 38) were asked to list in importance the Guinea yam varieties they are growing for household food use and to sell (Figures 6 and 7). For household food, the landrace sofèrè was the most important, whilst the cultivar nigeria was commonly cited as the second most important, and several other landraces were mentioned but infrequently. These food choices mostly reflected ‘food preferences’, except for nigeria, which has become a dominant cultivar in household food systems because of its commercial role. In order of importance for sale, the cultivar nigeria was the dominant first choice, followed by the landrace sofèrè mostly as second choice, and with several other landrace varieties mentioned by fewer farmers.

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When referring to D. alata, most farmers replied that they grew gbara (which just refers to the species), and otherwise sometimes mentioning specific cultivars, including americangbara, which is a recent introduction, and less commonly other (possibly landrace) cultivars (bambagbara, sembasen and gbaragbè). A wider overall list of 12 cultivar names was tallied following discussions with the local agricultural key-informants and aggregating citations from wider conversations, including about varieties in the past. Farmers answers about D. alata were less specific than for Guinea yams, as in many cases they just answered in general that they grow gbara as opposed to providing information about the different types they grow.

Cultivated yam diversity in the recent past versus today

Farmers were asked which varieties they prioritise growing today and which they prioritised growing in the past (Figure 8). Interviewees (n = 38) demonstrated a clear shift from using a wide range of local landraces in favour of growing the currently favoured commercial cultivars. Most farmers cited the introduced nigeria cultivar and some the local landrace sofèrè, as key current priorities, but a wider range of local landraces were mentioned for their importance in the past—these past examples are all D. cayenensis/rotundata except for ‘sembagabara’ and ‘bolokoudounigbara’, which are D. alata varieties. Sofèrè is the only variety prioritised in both the past and present. Local landrace cultivars were described as beginning to disappear.

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Agricultural practices

Farmers were asked about cultivation, land use and harvesting practices. Responses were very consistent and are summarised here.

Cultivation and land preparation

Nearly all farmers described planting yams in either April or May, and two mentioned they can sow them in March depending on the overall amount of work, and one key informant said sometimes it can be as late as June. After planting yam tubers, the soil is covered with leaves to shade them from the sun, which can otherwise prevent sprouting. Leaves used were identified and came from several species including: Tambani (Detarium microcarpum Guil. and Perr.), söö (Isoberlinia doka Craib and Stapf), moussolamanan, firimon (Anthonotha crassifolia (Baill.) J. Léonard, kobi (Carapa procera DC.). Shrubs are cut and folded to serve as a support for yam vines. Farmers reported that using supports can help the tubers to sink deeper into the ground (Figure 9a,b). Land preparation can include cutting down of larger trees between August and September, burning shrubs, and killing any remaining plants with herbicides. Ridges are constructed on rotting herbs so they will act as soil fertiliser, and a wooden fence is constructed to protect the ridges from oxen.

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Three main modes of cultivation were reported by farmers during interviews: (1) Monocropping: favoured by some yam producers because the yams are more productive without shading or competition. (2) Intercropping: some grow yams in combination with other crops, such as squash (Cucurbita maxima Duchesne), calabash (Lagenaria siceraria [Molina] Standl.), cucumber (Cucumis sativus L.), maize, okra (Abelmoschus esculentus (L.) Moench), but just in small amounts to prevent shade from influencing the proper development of tubers. (3) Crop rotation: yam is nutrient-depleting and cannot be successfully grown in two consecutive years in the same field. To avoid using new land each year, some growers carry out a crop rotation system (rice, peanut and sesame) that allows them to stay within the same boundary for at least 3 years.

Yams are cultivated by men due to the labour involved. Women help with weeding the yams, covering the ridges with leaves, and moving yams to storage or the market. As a result, most of the interviews were with men, although some of the trader interviews were with women (discussed below). A similar gender division in tasks has been documented in Nigeria (Obidiegwu & Akpabio, 2017).

Harvesting

Two main periods for harvesting are scheduled for Guinea yams. The first harvest can be between August and October, during which small tubers are collected to function as ‘seeds’ for re-planting, and some larger tubers are collected for use (Figure 2e). The remaining tubers continue to grow larger, and the second harvest can span December to February. Some farmers only harvest once. Originally, we hypothesised that the length of growing season may vary by cultivar, but this was not the case. The timing of the harvest depended on the preference of the grower, and they explained they harvest their different varieties at the same time. For the first harvest the growers use a stick, iron pickaxe, or their hands to dig up some of the yam tubers carefully. During the second harvest the method is the same, but the daba (a small hoe, made from a wooden branch) and a large hoe are used to dig up the tubers. For Dioscorea alata, there is just a single harvest, which is usually from December to April, varying by farmer, and again, the different varieties are harvested together.

Temporal change in cultivation practices

During the first fieldwork season we asked farmers how yam cultivation had changed through time. Farmers older than 50 years (n = 18) said that 40 years ago cultivation was only to produce food for home use, then from about 20 years (referring to the 1990s/early 2000s) 8% (of 38 farmers), and one of the agricultural officers said yams started to be sold at a small scale. All farmers said they now grow yams to sell as well as for home consumption and that they see the trend of selling yams increasing in the future. Farmers explained that yams are abundant today and, in the past, but that today they are grown over larger areas of land. In the past, they produced yams on smaller areas of land, and obtained a large quantity that was sufficient for local food systems. They explained this was possible because of the higher fertility of the soil at the time and that the soils were more intensively managed. The shift to selling yams has led farmers to extend their growing areas to increase production but that, overall, soils are becoming less productive. Additionally, several farmers mentioned that some young people are beginning to lose interest due to the intensity of the manual work and that although farmers hope to increase production in the future, they also said it depends on having the practical means and labour available.

Yams, cuisine and cultural heritage

When asked whether yams are viewed as cultural heritage, they were described as important for food, hospitality, special occasions, and as gifts. Many interviewees (32% of no. 43—including farmers, traders and key informants in second field season) said they are used for welcoming visitors (in meals or as gifts), and (30%) for showing respect to people, especially by offering the largest tubers. Yams were cited as offered as gifts to the elderly, griots (travelling poets and musicians) and administrative authorities, and as important within marriage traditions, food festivals and the food culture in general.

Yams are prepared into a wide range of dishes (Table 1, Figure 9e–h). The terms ‘cossettes’ and ‘poudre’ refer to common food forms that are often the way yams are stored or bought and are interim preparatory stages and which can be the base for other dishes. These stages of post-harvest yam processing and cooking are mainly done by women. Some of the words used are French and others are in local Malinké dialect. Several of the terms, which derive from French, are reflective of modes of cooking and are used in other regions/countries and including for other crops. For example, in Guinea, ‘couscous’ is also a way of cooking fonio, and in north Africa couscous is more commonly made from wheat or barley.

TABLE 1 Local yam preparations and dishes in the Kankan region of Guinea.

Local name for preparations and dishes	Description
Cossettes	Prepared yam pieces; yams are peeled, cut into pieces, lightly steamed (not cooked) and then dried in the sun.
Poudre	Powder is a base for many dishes; cossettes are pounded either in mortars using pestles or with small handheld or larger village grinding machines.
Tooa	Yam paste dish; make a pasty solution of yam powder, stir into boiled water, and keep adding powder until a consistent paste is obtained.
Bouillie	A custard/porridge/gruel like dish, that can include small dumplings; dumplings are made from yam powder, and are cooked in boiling water over a fire with sugar and tamarind stirred in.
Couscous	Couscous to serve on the side of sauce and meat dishes. Instead of using yam powder, slightly larger granules are prepared from cossettes. These are cooked in a steamer up to three times, adding more water each time. And are cooked in a steamer.
Gateaux	Cake like dish; a little water, sugar and yeast are added to yam powder, pounded, and then put in the sun so that the mixture increases in volume. The mixture is then ‘griller’—roasted/toasted with peanut oil.
Foutoua/Semouille	Peeled and cut yams are cooked and then pounded with a little water to get a soft paste (Figure 9).
Purée	Peeled and cut yams are pounded with some salt and palm oil to get a compact paste (Figure 9).
Papea	A yam dish for children; powder is prepared in a pasty solution with sugar and milk.
Brûlé	Pieces of yam are cooked on a griddle the fire, as a dry dish.
Griller (ragou)	Pieces of yam are cooked with meat and tomato in a pot with a little water (Figure 9).
Cuire frais	Pieces of yam are simply boiled, for example like a potato.
Womia	A type of cake; small baked doughy balls cooked in a pan.
Tacoulaa	A bread, baked into small balls (Figure 9)
Dèèa + miel	Diced cooked yam with honey.
Gallette	Prepared like a biscuit.

Marketing and commerce

All interviewees in the second field trip (n 43) asked about the benefits of yam cultivation cited profitability, with examples including to buy land or property, animals, agricultural inputs and machinery, motorbikes, and to cover education and health care costs. Almost all the newer houses (made from bricks and concrete) are built from the profits of yam cultivation. Some of the farmers sell yams wholesale, others semi-wholesale and others more selectively, staggered to maximise profits for better profits (Figure 9d). Reflecting these modes of sale, 37% said they sell their produce at the edge of the field, 82% in local markets, and 33% transport them to Kankan. Most (88%) reported buyers coming from Kankan, others from Mandiana (48%), which is the other main regional town in Haute-Guinée, and some from the capital Conakry (11%) or from the Republic of Mali (4%), and that yams are then traded to cities across Guinea and sometimes to Senegal and Republic of Mali.

Some people in the Kankan region make their livelihoods entirely from trading yams. Four traders were interviewed, one male and three female. They help finance farmers by offering them herbicides, fertilisers, sometimes covering medical expenses, children's schooling, or building houses and then recover the corresponding monetary value in yam tubers. They described buying yams from yam producers in villages and reselling them in in Kankan, Mandiana, and Conakry markets. One of them said they trade 1000 tubers a week, another 2000, one up to 10,000 and the other that it was a variable amount. Overall, the quantities sold depend on the individual capital of each trader and the customers they have.

The traders, and one of the key informants from an agricultural research agency, identified several difficulties with the yam agribusiness and trade. These problems include misunderstandings between traders and growers on prices, price instability, distribution problems, financial problems for farmers including the flow of capital and the non-reimbursement of invested funds, the workforce needed, soil fertility and the need for additional fertiliser. Their suggestions for improving yam trade included the need for financial aid to farms wanting to increase yam production, introduction of weighing methods to help pricing, lower market prices, and help finding customers beyond local markets.

DISCUSSION

Varietal diversity

A wide range of yam cultivars are used in Guinea. Guinea yams are described by local agricultural agencies as ‘D. rotundata’. Whilst closeness to the rotundata group of cultivars is probably clear for the main commercial varieties, the range of local varieties, which is now grown by fewer farmers may hold more complexity. Although tuber shape is not a strong differentiating characteristic, the introduced commercial variety nigeria has a distinctively rounded end, while all the other local types are typically pointed. Additionally, whilst most of the tubers' flesh were noted as white, one variety was yellowish (a characteristic often associated with cayenensis types). Not all the documented tubers are yet described, and additionally we were told about other districts within Haute-Guinée recognised as areas of large yam production and so the overall numbers of regional cultivars maybe greater. Future yam research in Guinea aims to survey the yam diversity across the wider region, including detailed taxonomic description and characterisation of varieties grown.

The harvesting of varieties together may support them being closely related, as cayenensis and rotundata groups have been observed as having different lengths of growing seasons in other countries. For example, in Benin some varieties are stated by farmers as needing to be harvested earlier than others (Maliki et al., 2012). However, the extent to which the observation would hold true in Guinea is harder to say, in part because farmers stated they plant varieties at the same time because it is practical to do so, depending on workload. Future interviews could focus on older generations of farmers to investigate whether there was a greater specificity of planting or harvesting timing in the past, when we understand there was greater emphasis on local landrace cultivars.

Complexity in the taxonomy of Guinea yams in Guinea and West Africa may in part be a result of the ongoing process of ennoblement, which was described in three of the interviews. This practice has been documented across West African as well as Ethiopia. ‘Ennoblement’ is a process whereby wild yams or seedling yams are collected, cultivated and over just a few years appear to become ‘domesticated’ (Chaïr et al., 2010; Hildebrand, 2009). As a result of this ongoing practice, it is possible that a complex mix of yam subgroups have formed over varying spatial and ancient to present-day temporal scales (Dumont et al., 2005).

Temporal changes in yam diversity, cultivation and culture

Farmers descriptions of increasing yam production is supported by FAO statistics (FAO, 2022). Both production and the area under cultivation have more than doubled in Guinea during the last decade from a maximum of 10,000 ha of land and 36,000 t produced per annum prior to 2011, to more than 36,000 ha and 310,000 t in 2021 (FAO, 2022). However, although the overall yam production is increasing, in parallel, the interviews with farmers show that at a local level, varietal diversity can be seen to be decreasing.

Although we documented a wide range of cultivated yam landrace cultivars in Haute-Guinée, this diversity is diminishing as a result of increased focus on commercial cultivars and methods of cultivation. Twenty years ago, most cultivation was still for subsistence, whereas today farmers grow yams for household food and income. A greater diversity of landrace cultivars were cultivated in the past, whereas now cultivation is dominated by an introduced cultivar (nigeria) and one of the local landraces (sofèrè). A similar pattern of local diversity erosion has been previous documented in Togo (Dansi et al., 2013).

Larger areas of land are today cultivated in Guinea to facilitate commercial production, but farmers reported that soils were more productive in the past when smaller areas of land were more intensively managed, for example through mulching. Other modern changes in farming practices reported included the use of herbicides and fertilisers, required due to the larger areas of land cultivated and labour involved. These trends can be observed across the wider region. Throughout West Africa the growth of yam production is associated with an increased area of land under cultivation, degradation of soils, and the clearance of forests and savannah (Adifon et al., 2019).

Some agri-practices in Guinea represent continuity with those used in the past. During interviews farmers described using the historical practice of planting small tubers instead of ‘mini-setts’. Mini-setts are a widespread practice in West Africa, made by cutting tubers into small pieces (Morse, 2018). Farmers described this planting method as introduced to Guinea alongside commercial cultivars, but not widely adopted because they preferred still to use ‘seed’ yams. Cultivation methods such as rotation, intercropping and sole cultivation and creating mounds as seed beds are similar to the wider region, and are overall, still predominantly customary in terms of being largely carried out by manual labour (Adifon et al., 2019). Yam farmers interviewed were male, reflecting the difficultly of yam cultivation. A similar gender division in tasks has been documented in Nigeria (Obidiegwu & Akpabio, 2017). The degree of labour involved was a major problem identified for the future of expanding yam production, with younger people in the community being less keen to be involved and there being a shortage in the labour market.

Our discussions with farmers record some aspects of the cultural importance of yams, in particular through the multiple ways yams can be prepared for food (see above). Interviewees described yams as important for specific occasions like festivals and weddings, or as gifts in family, social and business contexts. In recent decades, yams have become forces of socio-cultural change though their economic role, transforming housing and livelihoods. Equally, the cultural role of yams within food systems may be in a state of change given that there are fewer farmers prioritising varieties that were previously favoured for taste.

Today the historic cultural heritage of yams blends with the socio-economic changes brought about by the commercialisation of yam (such as the creation of new incomes, markets and associated wealth). Farmers today in the Kankan prefecture derive significant profits from yam cultivation. At the same time, several suggestions were made for improving mechanisms of trade (discussed above). Interestingly, a report undertaken following a workshop by yam traders and agricultural organisations nearly 20 years ago highlighted similar issues to our study, which shows these problems to be ongoing (Tradore & Kaba, 2007).

Despite higher resilience than above ground crops, yams maybe at risk due to climate change. The spatial extent of habitats suitable for cultivating Guinea yams across West Africa is modelled to decrease under future climate change scenarios (Pironon et al., 2019). Additionally, water yams (D. alata) are predicted to see yield decreases under climate change scenarios (Srivastava et al., 2012). As such, it is important to seek potential solutions held within local knowledge systems and agricultural science (e.g., selection of late maturing varieties) to mitigate the adverse impacts of climate change (Srivastava et al., 2016). There are gaps in the ex situ conservation of cultivated yams making in situ conservation important, especially in areas of primary diversity such as in West Africa (Lebot & Dulloo, 2021).

In situ conservation is important to protect diverse genetic resources for future resilience to climate change and disease as well as to protect the stability and food security of local food systems. However, the focus on productivity and the expansion of yam cultivation is one of the main drivers of reduced diversity. New solutions are needed to help develop insitu conservation, such as community or wider governance initiatives to help create incentives, or efforts to help promote interest in the cultural food heritage of historic varieties and to help maintain and transfer local ecological knowledge.

CONCLUSIONS

Our study represents the first survey of yams at household level in Guinea. We suggest that Guinea, or more specifically, eastern Guinea (Haute-Guinée) should be more commonly included in discussions about key yam growing regions in West Africa (the ‘yam belt’). Yam species are distributed throughout Guinea, but Haute-Guinée is the region where they are the dominant crop. There are several domesticated and wild species used in the Kankan Prefecture and yams occupy an important place in the lives of populations from a social, economic, and medicinal point of view. Yam cultivation in the study region is especially focused on Guinea yams (D. cayenensis-rotundata complex) but the Asian species D. alata is also strongly anchored in the agricultural system suggesting a long history of local use. Interviews clearly showed a shift from using yams as subsistence crops to a subsistence and commercial crop over the last 20 years, but that this is accompanied by more expansive and unsustainable land use. Commercial yams produce larger tubers and are better suited to fertilisers and are displacing historic local landrace cultivars that were previously favoured for food preferences.

Local varietal diversity documentation is limited in West Africa, but it has potential to create baselines for future monitoring of diversity. Given that this information is lacking, currently little is known about varietal loss, with the exceptions of the present study and Togo (Dansi et al., 2013; Lebot & Dulloo, 2021). It is important to try and document local cultivar diversity, but additionally, for this to be able to consider insitu diversity, this to include differentiating local landrace (cultivars) from introduced cultivars. Here, we show it is also possible to capture some information about varietal loss through farmer interviews. However, the window of opportunity for such knowledge gathering is limited as farmers age (Ryan et al., 2022). The historically rooted agricultural and food heritage of Guinea yams is characterised by local cultivation practices, landrace diversity, and diverse uses and now co-exists alongside a newer commercial yam culture characterised by higher yielding but more monocropped cultivars, and expansive landuse.

Understanding of both older and new agri-practices enables a better insight into how historic cultivar diversity has been previously maintained, and how and why it is now being lost. Farmers' views suggest that the recent increase in yam cultivation is unsustainable environmentally; in addition, the ‘positive’ optics of increasing production figures serves to mask how commercial trends are endangering the yam diversity crucial for its resilience to disease and climate change in the future.

AUTHOR CONTRIBUTIONS

Nagnouma Condé and Philippa Ryan wrote the manuscript. Nagnouma Condé and Maimouna Touré conducted fieldwork. George Burton, Philippa Ryan and Nagnouma Condé conducted data analysis and George Burton and Philippa Ryan produced the figures. Nagnouma Condé, Philippa Ryan, Charlotte Couch, Martin Cheek, and Sékou Magassouba planned the fieldwork, and Nagnouma Condé, Philippa Ryan and Benedetta Gori designed the research questionnaires. Nagnouma Condé and Paul Wilkin identified specimens. All authors contributed in editing.

ACKNOWLEDGEMENTS

This research was supported by collaboration between Université Gamal Abdel Nasser de Conakry, Herbier National De Guinée (HNG), and RBG, Kew under a long standing Memorandum of Collaboration. Initial funding for Nagnouma Condé's PhD research including a study visit to the United Kingdom, was from a grant to RBG, Kew for the Guinea TIPAs programme from the Ellis Goodman Family Foundation. Her visit to RBG, Kew in February 2023 to analyse fieldwork results was funded by DEFRA's Global Centre for Biodiversity for Climate (GCBC) programme. The data collection and fieldwork trips in 2022 were supported by the ‘Agri-system histories and trajectories: crops, landscapes, and heritage project (AgriHist)’ at RBG, Kew, which is funded by the Arts and Humanities Research Council (AHRC) [PI Ryan AH/V000551/1].

CONFLICT OF INTEREST STATEMENT

No conflict of interest is reported by the authors.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

ETHICS STATEMENT

Fieldwork was led by Nagnouma Condé and the National Herbarium of Guinea. Interviewees were told about the aims, potential outputs and methodology of the study, and prior informed consent (PIC) was gained verbally before interviews. The process for PIC followed guidelines provided by the Code of Ethics of the International Society of Ethnobiology (International Society Ethnobiology, 2006), the guidelines for working with Local and Indigenous knowledge at Kew, and the customary practices in Guinea for permissions.

References

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