Study area and selection of the surveyed sites

This study was conducted in two Sahelian countries, namely Senegal (14°40′N17°25′W) and Mali (12°39′N8°9′W), which are located in West Africa. In each country, two important sesame-growing regions were selected for the survey.

Mali

The Segou region (13°22′5″N5°16′24″W) covers 64,821 km² and is located in south-central part of Mali. It is a strategic and cosmopolitan area for the country as it constitutes the transit area between the northern part and the southern part, bordering Mauritania and Burkina Faso, respectively. The region is characterized by a semi-arid climate with two seasons: a rainy season and a dry season. The average yearly rainfall is about 513 mm. Agriculture is the most important activity in this area as Segou produces most of Mali’s national food, including sedentary cattle farming [14, 15]. The major crops grown are cereals (sorghum, corn, fonio, rice), legumes and fruit (watermelon).

The Koulikoro region (13°56′41″N 7°37′28″W) covers 90,210 km² and is located in the Western part of Mali. It is part of the tropical area with a rainy season and a dry season. The vegetation pattern shows a decreasing northward humidity gradient as a result of the joint effects of the different climatic zones and the soils: Sahelian zone in the north (150–550 mm rainfall), the Sudanian zone in the centre (550–1150 mm rainfall) and the pre-Guinean zone in the southern part (more than 1150 mm rainfall). The population in these regions consists of diverse ethnic groups and agriculture is the most important economic activity [16]. Different crops are cultivated including cereals (sorghum, millet, maize, and rice), legumes (peanut, bean etc.) as well as cash crops (cotton, sesame etc.).

Five villages in Segou (Boua-were, Tongo, Minankofa, N’gakoro and Kondogola) and in Koulikoro (Kalifabougou, Gouana, Tiendo, Kosa and Gountou) were selected for this study (Fig. 1).

Senegal

The Sine-saloum region or the peanut basin (14°11′N16°15′W) is located in the East of Senegal encompassing 24,000 km² and includes the localities of Kaffrine, Kaolack and Fatick. In this region, sesame is widely cultivated mainly in the southern part. The climate is of a Sudano-Sahelian type with an annual rainfall lower than 700 mm. The “Wolof” ethnic group is the most predominant. Agriculture is one of the major economic activities, and millet is the prominent cereal grown in this area followed by maize.

Located in the southern part of Senegal near the Gambia, Casamance (13°0′54″N15°19′4″W) is a big region which covers 28,350 km² (approximately 1/7 of total Senegal’s land) and includes Sedhiou, Kolda and Ziguinchor localities. The climate is a sub-Guinean type with an ample rainfall between 800 and 1300 mm, and the area is covered by dense vegetation. The major ethnic group in Sedhiou locality is the “Mandingue” and the main crops produced are rice, maize, fonio, groundnut, cotton and sesame, whereas in Kolda locality, the ethnic group “Peulh” is the most represented and is devoted to agro-pastoralism. The main crops grown in this area are maize, sorghum, rice, cotton and sesame [17].

Twenty-three villages in Casamance (Thies-pakane, Tenghori, Tambacouda, Soutouyel, Saré-koutayel, Saré-hamidou, Saré-amadou-diallo, Saoundé-popodié, Safane, Medina-souané, Médina-sadio, Kounaya-mankagne, Kégnéto, Kandiadiou, Kamboua, Kabaar, Faoune, Darou-salam, Boydo-malick-counda, Boutoupa-kamara, Boutolate, Bani and Bambadala) and 14 villages in Sine-saloum (Tewrou-mbeyenne, Niambour1, Ngettou-farba, Mbelbouck, Sahm, Sagna, Immidine, Dianké-souf, Mbaye-mbaye, Pirame, Patoulou-peulh, Diam-diam, Palangué-manding and Kalbirom) were selected for this study (Fig. 1).

Data collection

A preliminary survey was carried out in each region with local extension service agents during April–May 2016 to identify villages to be investigated. The villages where sesame is widely produced were selected, and the more distant ones were retained in order to cover a wide geographic area in each region.

The sampling of farmers per village was not totally random: we included 30% of women in the participants as well as young people and adults. The participants included were individuals who have a good experience in sesame cultivation and have been fully identified, thanks to village chiefs’ help. The questionnaire was pre-tested in two villages (not included in this study) from each region and adjusted prior to data collection.

Data collection was conducted in May–August 2016 and in total, 146 farmers (76 in Koulikoro and 70 in Segou) were surveyed in Mali whereas in Senegal, 110 farmers (69 in Casamance and 41 in Sine-saloum) were surveyed.

After obtaining their prior verbal informed consent, each participant was interviewed with a semi-structured questionnaire.

The questionnaire, comprising 71 items, was designed to obtain information about (1) the socio-demographic characteristics of the participants (name, age, sex, ethnic group, origin, educational attainment, contact, household size, principal and secondary activities, land owned etc.), (2) the agronomic practices (practices refer to the full range of field level management strategies, technologies and methods employed by the farmers) for sesame production (the varieties grown and their origins, agricultural practices, the type of ploughing, the use of pesticides and fertilizers, the period of harvest, the time and place of drying, conservation etc.), (3) the processing, the valorization and the market system, (4) the constraints and the farmers’ preference for the most important traits in sesame to be improved. Some sesame cultivars samples were collected from the different participants for future work.

Data analysis

Sesame seed sample preparation and biochemical analysis

The widely cultivated sesame varieties from each of the four regions were selected for seed biochemical analyses. Dust and stones were manually removed from the seeds. All mature and well-rounded seeds were kept for the analysis. Approximately 5 g of seed samples were manually ground to fine powder with liquid nitrogen. Seed oil was estimated by the conventional Soxhlet method using petroleum ether as the extraction solvent [19]. The total protein content was determined using the Kjeldahl method according to AOAC [20]. Each sample was tested in triplicate.

Socio-demographic characteristics

Comparative analysis of sesame production in the four regions

Area under sesame cultivation and characteristics of the main cultivars grown

About 20% of the total agriculture lands owned by a farmer were allocated to sesame production (Fig. 2). In the study area, very few farmers grow only sesame. Sesame fields ranged from 0.2 to 8 ha with an average of 1.4 ha per farmer. In general, most of the farmers were small-scale farmers operating on small farms. The average areas under sesame cultivation per farmer varied significantly across the regions surveyed (p = 0.001). The farmers from the Segou region of Mali had the largest sesame farms (1.55 ha), whereas those from Casamance had the smallest farms (0.91 ha) (Fig. 3).

Different sesame cultivars were grown by farmers in each region, but little variability was observed across regions within the same country. In Senegal, a total of five cultivars including Primoca, 32–15, Blanche, Brune and Noire were identified in the two areas. Among these cultivars, Primoca and 32–15 were the most widely grown. In Mali, we itemized nine cultivars including Bénai-ba, Bénai-dièma, PorouII, Bénai-kourouni, Nassoubani, BanambaII, S42, Bénai-fin and Bénai-bléni. The cultivar S42 was the main cultivar in the Koulikoro region, whereas Nassoubani was the widely grown cultivar in Segou. Analysing the main cultivars’ seed component revealed that the cultivars from Senegal, Primoca (brown seed coat colour) and 32–15 (white seed coat colour) had similar oil and protein contents (Fig. 4a). However, there was a significant difference between the two main cultivars from Mali (p < 0.05). S42 (white-lighted seed coat colour) has high oil content and low protein content, while Nassoubani (white seed coat colour) is protein-rich with only 53% oil content (Fig. 4a).

Figure 4b presents the origin of the seeds used by the farmers per regions. Farmers from Mali principally acquired seeds from NGOs, Farmer organizations and conventional research institutes, whereas in Senegal, the farmers tend to purchase from markets or produce their own seeds.

Agronomic practices

Sesame is mainly grown in monoculture in the four regions (Table 2). Some farmers reported practicing mixed cultivation with other crops such as sorghum and millet. Sesame was commonly grown on ridges. In contrast to Senegal where field ploughing is predominantly mechanized, 90% of the farmers from the two regions surveyed in Mali ploughed their field manually (Table 2). However, sesame is sown in rows by most of the farmers in the four regions. In addition, more than half of the farmers we interviewed stated that they used a sowing device in the 4 areas. Sesame is sown in July–August in the 2 regions of Senegal, but some farmers sow early in June or later in September. In Mali, the sowing date of sesame is mainly in July; however, some early and late sowing can be observed in June and August, respectively (Fig. 5a). There is no significant difference between the number of farmers who apply pesticides (p = 0.792) and those who use fertilizers (p = 0.571) on their fields across the regions. Indeed, sesame is produced mostly without pesticides and fertilizers. Interestingly, most use organic materials applied in the form of manure or compost to the crops to boost the yield.

Variables	Koulikoro	Segou		Casamance	Sine-saloum
Cultural practice
Monoculture	94	64	97		95
Mixed cultivation	6	36	3		5
Field ploughing type
Ridge plough	96	96	95		67
Flat plough	4	4	5		33
Means of Ploughing
Manual	90	90	33		7
Mechanized	10	10	67		93
Sowing period
June	10	18	3		48
July	24	80	15		52
August	65	2	67
September	1		15
Means of sowing
Mechanized	56	76	54		84
Manual	44	24	46		16
Use of fertilizers
Yes	14	22	15		13
No	86	78	85		87
Use of pesticides
Yes	7	9	8		22
No	93	91	92		78
Harvest period
September	5	20			18
October	95	80	13		22
November			37		45
December			42		15
Janvier			8
Seed drying area
Home	20	30	19
Field	80	70	81		93
Other					7
Means of conservation
Jute bag	98	98	100		98
Large basin	2	2			2
Place of storage
Room	22	34	84		63
Warehouse	78	66	16		37
Purpose of sesame production
For sale	100	90	92		85
Consumption		10	8		15
Selling channels
Field brokers	56	40	85		36
Village traders	44	60	15		64
Mode of selling
Individual	100	72	71		93
Group		28	29		7

Values are percentage

Sesame production and seed yield

The total production of sesame per farmer seasonally ranged from 3 to 3162 kg with an average production of 448 kg. There was a significant difference of sesame production per farmer across the four regions (p = 0.001). The farmers in Segou had the highest sesame production (765.8 kg), while farmers from Casamance exhibited the lowest production level (193 kg) (Fig. 6a). Concerning the seed yield, it also varied significantly across the surveyed regions (p = 0.001) and ranged from 50 to 1500 kg/ha with an average yield of 298 kg/ha. The Segou region presented the highest seed yield (417.3 kg/ha), whereas the lowest seed yield was observed in Sine-saloum (249.5 kg/ha) (Fig. 6b). In general, sesame seed yield in Senegal (258.4 kg/ha) was lower than in Mali (378.4 kg/ha) (p = 0001).

Valorization, marketing and market systems

Sesame is essentially a cash crop as most of the respondents reported that they grow sesame for commercial purposes (Table 2). The crop is cultivated for its seed, which is the main product that is subsequently sold. Local processing of sesame seeds into oil is rudimentary and limited. Some farmers reported that they also used other parts of the plant such as the dry matter for cattle feeding. The dry matter is also used for soap production, as compost manures and for the production of potash which is a cooking ingredient widely used in West Africa by women (Fig. 7).

To sell their sesame seed stocks, the farmers may choose to liaise directly with the field brokers or take their products to the village traders in the local markets. In general, farmers tended to sell their stocks to field brokers (Table 2). Furthermore, they predominantly market their seed stocks individually and not through farmer groups or organizations. Sesame market prices (mainly farm gate prices) varied significantly across the regions surveyed (p = 0.001). The highest price was observed in Sine-saloum (0.79$/kg, considering 1$ equals 500FCFA), whereas sesame was sold at its lowest price in Koulikoro (0.58$/kg) (Fig. 8a). Similarly, seasonal incomes earned by the farmers from sesame production varied significantly among the regions surveyed (p = 0.001). The highest income from sesame production was observed in Segou (496$/ha), whereas the lowest was estimated to have been earned by some farmers in Casamance (116$/ha) (Fig. 8b). Globally, comparing the two countries, we found that the farmers from Mali earned significantly higher incomes from sesame production (more than double) than their counterparts from Senegal (p = 0.001).

Farmers’ preference for the sesame traits that need to be improved

Status of sesame production in West Africa Sahel

This study investigated the status of sesame production in four regions in Mali and Senegal, two important producing countries in West Africa’s Sahel. Our aim was to get insight into this sector and reveal both the constraints and the farmers’ expectations so as to boost cultivation of this crop. We discovered that sesame is a multi-ethnic crop. Nearly all the encountered ethnic groups including the major and minor ones in the surveyed regions were involved in sesame production. This suggests that sesame may have been an ancient crop in this area of Africa and is widely adopted by all classes in the local population. We found that women were actively involved in sesame production, but they owned smaller farms as compared to men [21]. The first reason for sesame adoption is its relatively simple cultivation owing to the fact that it can grow in different soils, does not need irrigation, is capable of withstanding high temperatures, is a subsistence plant, is not labour intensive, and fits in well with crop rotation schemes [5, 22]. Moreover, it is a very rewarding crop because of low production cost and high price, which makes it tailored to the small-scale poor farmers of West Africa’s Sahel.

Only 20% of farmers’ total fields were allocated to sesame production. This suggests that sesame is still behind other important crops that are used as staple foods such as sorghum, maize, rice, millet etc. Indeed, sesame is completely export-oriented and is rivalling cotton production as it could be an environmental-friendly and cost-effective alternative crop. In contrast to cotton, sesame has the advantage of being paid for upon collection, which is extremely important in improving the poorer farmers’ livelihoods [23]. The local market is still rudimentary and virtually dominated by women in processing the end-products.

Several cultivars are grown locally by the farmers and may hold important genetic diversity [12]. Biochemical analyses of the seed components in the most important cultivars grown in each region showed that sesame from West Africa has valuable levels of oil and protein. Cultivar S42 grown in Mali is by far the best genotype in terms of seed quality and is also widely grown in other countries like Burkina Faso, Niger and Chad. More information is needed on the West African sesame germplasm seed quality as this can provide guidelines for obtaining high-quality nutritional breeds and adding marketing value to the crop.

Sesame cultivation is gradually becoming modernized. Once grown in association with other crops, sesame is nowadays grown in monoculture and is planted in rows with a sowing device. This facilitates crop husbandry practices such as weeding and thinning that are essential for yield optimization. However, the use of external inputs is still very modest in sesame cultivation in West Africa’s Sahel and there is still a lot of room for intensification. For example, using high-quality seeds is essential for sesame productivity’s improvement as it guarantees a good germination rate and a higher yield potential. Therefore, such conventional centres as NGOs, Research Institutes or commercial seed multipliers must further work in connection with the local farmers especially in Senegal to supply good quality seeds. In addition, pesticides and fertilizers are rarely used by the farmers for sesame production. According to Ojikpong et al. [24], an incremental application of NPK fertilizer up to 150 kg/ha significantly increases the average sesame seed yield. So far, there is no compound fertilizer that has been tailored for sesame production in West Africa’s Sahel; thus, further research for the formulation of a compound fertilizer optimized for sesame production in this area is required.

Overall, sesame is still a small-scale farmer commodity in this area with a very weak yield (298 kg/ha) as compared to other sesame-growing areas such as Northern Uganda (673 kg/ha, [23]), Vietnam (500 kg/ha, [25]) and Ethiopia (735 kg/ha, [11]). Although sesame production is profitable for the farmers at this level of yield, there are possibilities for further improvement. Yield improvement will augment their total revenues and will contribute to the sesame sector’s long-term competitiveness.

Sesame sector is better organized in Mali

The farmers from Mali receive valuable support from local NGOs and research institutes in terms of technical assistance including the supply of good quality seeds, crop husbandry, the supply of inputs, training and general assistance during seed marketing. This positively impacts on the seasonal production and yield of sesame in Mali. Consequently, a farmer’s total income from sesame production is higher in Mali than in Senegal. This implies that the sesame sector is better organized in Mali which should lead to the rapid development of the sector. Our results were well corroborated by the conclusions of Gildemacher et al. [21] who reported that the area dedicated to sesame production increased 2.5 times between 2000 and 2010 in Mali. It is thus crucial to firstly strengthen collaboration between the sesame sector’s stakeholders, and then with the oversight bodies. In addition, the remarkable achievements in the development of the sesame sector over the last decade in Burkina Faso may be a textbook case for the remaining producer countries in West Africa’s Sahel [26].

Sesame marketing, an important challenge for the sector

Many constraints were raised by the sesame producers in the surveyed area but seed marketing is by far the most important impediment. The problem is basically the lack of reliable markets for their stock. Indeed, sesame producers have become more price takers than price makers. Since sesame is mainly sold directly and fragmentally to field brokers who operate individually, their product is always under their control. There are no institutional arrangements to fix the market price, as it fluctuates considerably and farmers have no option but to let go of their product more often at low prices. There is therefore an urgent necessity to strengthen sesame value chains and provide reliable market information to facilitate smallholder’s market participation. Furthermore, organized group marketing could be a strategy to avoid considerable price fluctuation. Collective action would help coordinate production and marketing functions. Unfortunately, our study was conducted during a period when it was impossible to have complete insight into the value chain. Therefore, additional socio-economic surveys from December to February (the active period for sesame marketing) will help understand sesame marketing systems better and propose genuine solution schemes for this issue.

What can be the contributions of research programs in West Africa’s Sahel?

Sesame is an under-rated crop in West Africa’s Sahel [27]. Few research programs are focusing on this untapped crop, and little is known about the potential of the sesame cultivars grown locally. The farmers have identified the high seed yield as the most important trait in sesame to be improved. High yield varieties or commercial lines are not yet available for the farmers in this area. Similarly as for most cultivated crops, the main objective for growing sesame is for high seed yield and quality [28]. Sesame yields in West Africa’s Sahel are very low, and this results from a combination of factors including abiotic stress such as drought and heat, inappropriate crop husbandry, low seed quality, pest and diseases as well as socio-cultural and socio-economic factors. Sesame seed yield per plant is considered to be composed of three components, i.e., the number of capsules per plant, the number of seed per capsule and 1000 seed weight. Some other factors, including plant height, length of capsules and axis height of the first capsule, were found to be strongly associated with sesame’ grain yield [29, 30]. Some candidate genes, QTLs and associated molecular markers for yield-related traits, have been described previously and could contribute to efficiently improve the West African sesame seed yield through molecular breeding [1, 10, 31, 32].

The remaining traits listed by the sesame producers (short cycle duration, good seed quality, drought resistance, disease and pest resistance, resistance to flooding, good architecture), all contribute to high yields. For instance, sesame’s short cycle time is important for avoiding pest attacks, soil moisture depletion and weathering on the open capsules, hence enabling farmers to harvest as soon as possible without incurring significant yield penalty [33, 34]. Moreover, improving drought tolerance and thermotolerance in sesame genotypes should be one of the major objectives of sesame breeding programs mainly in drought-prone areas like West Africa’s Sahel [10, 35–37]. Sesame biotic constraints have been widely neglected in this area, but observations show that, with the increasing of the crop acreage, diseases and pest attacks are becoming very serious. Therefore, future studies should focus on this major issue in order to reduce the risks and damages on sesame productivity. Seed quality traits, according to farmers, include high oil yield and seed components, white seed coat colour and big seed size. There are no data about the seed quality of the sesame cultivars grown in West Africa’s Sahel, although growing higher oil yielding and nutritional sesame varieties could bring outright premium prices in the market system. Hence, it is essential to assess the seed quality traits’ variability in locally grown cultivars. Many genes and QTLs related to oil yield and seed quality were published and could valuably serve in breeding high-oil-yielding sesame varieties in West Africa’s Sahel [1, 38–40].