agronomy
Article
Farmers’ Preferences for Genetic Resources of
Kersting’s Groundnut [Macrotyloma geocarpum
(Harms) Maréchal and Baudet] in the Production
Systems of Burkina Faso and Ghana
Mariam Coulibaly 1,2 , Chaldia O.A. Agossou 1 , Félicien Akohoué 1 , Mahamadou Sawadogo 2
and Enoch G. Achigan-Dako 1, *
1
2
*
Laboratory of Genetics, Horticulture and Seed Science, Faculty of Agronomic Sciences, University of
Abomey-Calavi, 01 BP 526 Abomey-Calavi, Republic of Benin; mary.coulibaly6@gmail.com (M.C.);
achaldia.aboegnonhou@gmail.com (C.O.A.A.); akohoue.f@gmail.com (F.A.)
Laboratory of Biosciences, Faculty of Earth and Life Science, University of Ouaga I Pr. Joseph Ki-Zerbo,
03 BP 7021 Ouagadougou, Burkina Faso; sawadogomahamadou@yahoo.fr
Correspondence: enoch.achigandako@uac.bj
Received: 19 February 2020; Accepted: 4 March 2020; Published: 8 March 2020
Abstract: Pulses play important roles in providing proteins and essential amino-acids, and contribute
to soils’ nutrients cycling in most smallholder farming systems in Sub-Saharan Africa (SSA). These
crops can be promoted to meet food and nutrition security goals in low-income countries. Here, we
investigated the status of Kersting’s groundnut (Macrotyloma geocarpum, Fabaceae), a neglected pulse
in West Africa. We explored its diversity, the production systems, the production constraints and
farmers’ preferences in Burkina Faso and Ghana. Focus groups and semi-structured interviews were
conducted in 39 villages with 86 respondents grouped in five sociolinguistic groups. Our results
indicated that Macrotyloma geocarpum was produced in three cultivation systems: in the first system,
farmers grew Kersting’s groundnut in fields, mostly on mounds or on ridges; in the second system,
farmers grew it as field border; and in the third system, no clear tillage practice was identified.
The main constraints of those farming systems included: difficulty to harvest, the lack of manpower
and the damage due to high soil humidity at the reproductive stage. A total of 62 samples were
collected and clustered in six landraces based on seed coat colors including cream, white mottled with
black eye, white mottled with greyed orange eye, black, brown mottled, and brown. All six groups
were found in the southern-Sudanian zone whereas only white mottled with black eye and black
colors were found in the northern-Sudanian zone. The white mottled with black eye landrace was
commonly known and widely grown by farmers. Farmers’ preferences were, however, influenced by
sociolinguistic membership and the most preferred traits included high yielding, drought tolerance,
and resistance against beetles. These findings offer an avenue to develop a relevant breeding research
agenda for promoting Kersting’s groundnut in Burkina Faso and Ghana.
Keywords: breeding; Macrotyloma geocarpum; farmers’ preferences; cropping systems; constraints;
cultivar development; landraces; conservation; sociolinguistic groups
1. Introduction
To feed the growing population of sub-Saharan Africa (SSA), agricultural productivity needs to
be increased significantly and the existing crops diversity strengthened. The crop yield per unit area in
SSA is projected to decrease [1], against an estimated increase in demand for cereals of 335% between
2010 and 2050 [2]. Similarly, the demand for legumes is also expected to increase as consumers’ income
Agronomy 2020, 10, 371; doi:10.3390/agronomy10030371
www.mdpi.com/journal/agronomy
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increases with a likely shift in preferences from cereal grains to more nutrient-dense foods [3]. Moreover,
the increasing world population will result in a substantial demand for additional proteins. This
growing gap between demand and supply of food and nutrients in SSA will require a major re-focusing
on grain legumes, with intensive research and development to identify climate-resilient species and
cultivars with improved grain qualities [4]. While 19,500 species of legume were reported [5], only
five are grown most widely in sub-Saharan Africa (SSA), namely common bean (Phaseolus vulgaris L.),
chickpea (Cicer arietinum L.), cowpea [Vigna unguiculata (L.) Walp.], groundnut (Arachis hypogaea L.),
and pigeonpea [Cajanus cajan (L.) Huth] [6]. Significant research and development work has been done
in the past decade on those grain legumes through collaborative bilateral and multilateral projects as
well as the CGIAR Research Program on Grain Legumes (CRP-GL) [7]. However, the bulk of edible
legume species are mostly overlooked by research and development initiatives. Thus, they are often
referred to as orphan legume crops. Key orphan legume crops in sub-Saharian Africa include Bambara
groundnut [Vigna subterranean L. (Verdc.)], Yam bean [Sphenostylis stenocarpa (Hoechst ex. A. Rich.)
Harms.)], Faba bean (Vicia faba L.) and Kersting’s groundnut (Macrotyloma geocarpum).
Kersting’s groundnut is an example of an orphan legume crop of West-Africa [8] with a wide
spectrum of importance, for both human and animal health. The crop is valuable to human nutrition,
particularly in areas where access to animal protein is limited. Its seeds have a high protein content
(21.3%) [9], carbohydrate (61.53%–73.3%) and crude fibre (6.2%) [10]. M. geocarpum is considered as
healthy because its grains contain a very low crude fat (1.0%) and a high concentration in arginine,
an amino acid for pediatric growth; the seeds are also a good source of mineral elements such as iron,
zinc, calcium and magnesium [9]. This crop can be used for complementary food formulation for
children to combat malnutrition [11]. Moreover, it provides substantial incomes for rural population in
Benin, Togo, Ghana, and Burkina Faso; its price can hike from CFA 1000 (USD 2) per kg in abundance
period to CFA 4000–5000 (USD 8–10) per kg in scarcity period [12,13]. The crop also exhibits several
medicinal properties and is used in traditional healthcare by local communities [13–15]. The root
system of Kersting’s groundnut fixes atmospheric nitrogen and improves the quality and structure
of soils [16]. With climate variability and the occurrence of prolonged drought, M. geocarpum is a
candidate resilient crop for sustainable cropping systems.
Kersting’s groundnut production systems, and landraces diversity were documented in some
West-African countries including Benin, Togo, Ghana and Nigeria [12,13,17–19]. These studies showed
that its cropping systems varied across its production areas, and revealed the existence of different
groups of landraces basing on the seed coat colors. However, in Burkina Faso and Ghana, research
on the species has been limited to utilization [14] and the farming systems [17,19]. In both countries,
M. geocarpum production systems, germplasm collection and breeding objectives have received little
attention. In addition, the diversity revealed in those countries—white mottled with black eye and black
in Burkina Faso [14] and white mottled with black eye, black, and brown mottled in Ghana [16,17]—is
less than the diversity reported in other countries such as Benin and Togo, where authors found five
landraces: white, white mottled with black eye, white mottled with yellow eye, black, and red [12].
This knowledge discrepancy/complementarity needs to be highlighted when we seek to promote
Kersting’s groundnut production and its genetic improvement in those countries. In other words,
the identification of farmers’ preferred traits is useful for breeders in developing varieties and for
extension agents in appropriate choice of varieties to be popularized [20]. Furthermore, knowledge
on production systems and the rationale driving farmers’ practices are key requirements for guiding
successful variety introduction [21]. In the production systems of Burkina Faso and Ghana, we inquire
about how Kersting’s groundnut production system organized, and the factors constraining or influencing
its production. How does the crop diversity vary across agroecological zones and how is it managed
by sociolinguistic groups? Furthermore, what are the preferred traits of farmers and how are they
correlated to social factors? In this study, we seek to understand the current traditional cropping
systems and analyze factors limiting M. geocarpum production for its promotion in Burkina Faso and
Ghana. We assumed that: i) on-farm practices, constraints and farmers’ preferences are influenced
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by sociolinguistic group membership; ii) the genetic diversity of Kersting’s groundnut in Burkina
Faso and Ghana is higher than findings reported by previous studies; iii) the distribution of the crop
landraces varies with agro-ecological zones.
2. Materials and Methods
2.1. Study Area
The study was carried out in Burkina Faso and Ghana in West-Africa (Figure 1). Burkina Faso is a
landlocked country located between latitudes 9◦ and 15◦ N, and longitudes 6◦ W and 3◦ E bordered to
the north and west by Mali, to the east by Niger and to the south by Benin, Togo, Ghana and Côte
d’Ivoire. It has an area of 274,200 km2 . Ghana is located on the southern coast of West Africa, between
latitudes 4◦ 44′ N and 11◦ 11′ N and longitudes 3◦ 11′ W and 1◦ 11′ E with an area of 238,540 km2 and
limited by Burkina to the north. The study was conducted in two agroecological zones of Burkina Faso
and Ghana: the northern-Sudanian (or Sudano-Sahelian) and southern-Sudanian (Sudanian). The two
agroecological zones included are both characterized by the unimodal rainfall season (Table 1).
Figure 1. Study areas with agroecological zones in Burkina Faso and Ghana. 1: Kénédougou, 2: Houet,
3: Mouhoun, 4: Jirapa Lambussie, 5: Nadowli, and 6: Tamale Metropolis.
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Table 1. Characteristics of southern-Sudanian and northern-Sudanian agroecological zones of Burkina Faso and Ghana.
Country
Burkina
Faso
Ghana
Agroecological Zone
Latitude
Climatic Condition
Soil Condition
Growing
Seasons
Rainfall
mm/year
Temperature
(◦ C)
Humidity
(%)
Texture
Type
Vegetation
Cropping System
Northern-Sudanian
11◦ 30′ –14◦ 00′ N
150 days
700–900
28
75
Gravel
Ferruginous
Savanna with
trees or shrubs
Cotton, sorghum, millet, cowpea,
groundnut
Southern-Sudanian
9◦ 00′ –11◦ 30′ N
150–180 days
900–1200
27
85
Sand-clayey
Ferriferous
Semi-deciduous
forest
Southern-Sudanian
8◦ 00′ –11◦ 30′ N
180–200 days
800–1200
28.1
61
Loamy sand
granular
Ferruginous
Grassland with
few trees
Cotton, yams, cassava, sorghum,
millet, maize, rice, cowpea and
mangos, citrus, cashew
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The northern-Sudanian zone is approximately located between latitudes 14◦ 00′ and 11◦ 30′ N,
and is characterized by an annual precipitation of 600–900 mm. The vegetation in the zone is a savanna
with trees or shrubs. This zone is mainly a cotton (Gossypium hirsutum L.) production area. Other crops
include sorghum [Sorghum bicolor L. (Moensch)], millet [Pennisetum glaucum (L.) R.Br.], groundnut
(Arachis hypogea), and cowpea (Vigna unguiculata). In the northern-Sudanian zone, Kersting’s groundnut
production was limited to a few villages represented mainly by the Bwaba linguistic group of the Gur
family, and representing 2.1% of the population in Burkina Faso [22].
Moving southwards, the rainfall increases to 900–1200 mm in southern-Sudanian zone located
between latitudes 11◦ 30′ and 9◦ 00′ N in Burkina Faso and between 8◦ 00′ and 11◦ 30′ N in Ghana.
The vegetation is characterized by a savanna with trees or shrubs, sparse forests in Burkina Faso
and is made up of grassland with few trees in Ghana. Agriculture in the southern-Sudanian zone
is characterized by perennial crops such as mango (Mangifera indica L.), citrus (Citrus spp.), cashew
(Anacardium occidentale L.), etc. Farmers in this zone also grow cotton, cowpea, yams (Dioscorea spp.),
cassava (Manihot spp.), sorghum, millet, maize (Zea mays L.), and rice (Oryza sativa L.). The Bôbô,
Senufo, Siamou and Toussian of Burkina Faso and the Gurma and Dagara of Ghana are the main
sociolinguistic groups producing and managing Kersting’s groundnut in the southern-Sudanian zone.
Senufo and Toussian groups are related to the Gur family [23] and represent respectively, 1.4% and
less than 0.1% of the Burkina Faso population [22]. The Bôbô group belongs to the Mande language
family and represents 1.4% of the population. The Siamou linguistic group was previously declared to
belong to the Kru language family (from Ivory Coast and Liberia) [24]. The Siamou group represents
0.1% of the population of Burkina Faso [22]. These people live in the department of Orodara located
in Kénédougou province. The Dagaaba and Gurma linguistic groups in Ghana belong to the Gur
language family [25]. Linguistically, the Dagara are part of the Mole-Dagbane group which represents
16.6% of Ghanaians while the Gurma people represent 5.7% of the Ghanaian population.
2.2. Sampling Strategy and Respondents’ Consent
Field trips and collection of ethnobotanical data were carried out from February to May 2018.
Semi-structured interviews [26] were conducted with 86 respondents in Burkina Faso and Ghana.
In each country, the investigations started by market visits to identify the sources/suppliers of Kersting’s
groundnut seed sellers and to get growers’ contacts. The surveyed localities were identified with the
help of extension agents in the regions and communities. We shared the pictures of M. geocarpum seeds,
pods and plant with the focal points who identified and confirmed the growing areas of the crop in
their localities. The chain-referral sampling technique [27], a non-probability sampling technique, was
used in both countries to select the respondents. In this sampling, the first contact with the community
was selected as a well-known expert; in a subsequent phase, the expert indicated another expert until
all the informants in the community were covered. The informant was a grower who knew more
about the crop, who used it and grew or used to grow it. In each surveyed locality, we explained the
objectives of the study to local authorities and farmers and requested prior informed consent from all
participants, and ensured participants’ confidentiality by anonymizing their identities in databases
and publications.
2.3. Data Collection
One focus group was conducted in each village. Participants included male and female
farmers selected based on their willingness to participate in the study. However, in some areas,
to eliminate gender dominance in discussions, separate discussions were held with men and women
farmers. The focus group discussions provided an insight into the different types of landraces grown,
the constraints to Kersting’s groundnut production and farmers’ major landrace preference criteria.
The intent of this study was not to rank farmers’ preference criteria but to identify the most important
traits farmers seek in a variety at village level. Different seed coat colors were shown to farmers and
the questionnaire was used to interview farmers who recognized and grew or used to grow the crop.
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In Ghana, the Agriculture technical services and the Savanna Agricultural Research Institute (SARI)
agents also assisted the surveyors to identify the respondents in the villages by using the crop pictures
and its local names.
The questionnaire was drawn up using Sphinx Plus version 4.5 [28]. For each informant,
we recorded personal information about age, gender, sociolinguistic group, education level, occupation,
cropland areas and the area allocated for Kersting’s groundnut production. During the interviews,
the respondents were requested to indicate vernacular names of the plant and the landraces they knew
and the landraces they grew. Information regarding the farmers’ practices and the constraints to the
crop production were also recorded. Other questions were related to the criteria to choose to grow a
specific landrace, and the traits of interest for the crop improvement. All interviews were conducted in
the respondent’s native language to ensure that questions were well understood. Local measurement
units named ‘tomato box’, ‘tine’ and ‘Yoruba plat’ were estimated/converted in kg to determine farmers’
yield of Kersting’s groundnut.
In addition to interviews, seeds collection was organized with farmers who still possessed seeds
of M. geocarpum. A color-chart was used to better identify the seed coat color and classify samples
collected into different phenotypic groups.
2.4. Data Analysis
Statistical analyses of both quantitative and qualitative data were performed using R software
version 3.6.1 [29]. Descriptive statistics were used to estimate frequencies, proportions and means for
citations, socio-economic variables and Kersting’s groundnut diversity data. The study areas and the
diversity of Kersting’s groundnut across the agroecological zones were analyzed by incorporating the
germplasm collection data into a geographic information system framework to map the distribution of
Kersting’s groundnut diversity using ArcMap software version 10.5.
The varietal diversity analysis was performed using the farmers’ knowledge, the landraces they
grow and the landraces collected in the study areas. The proportion of citations of each Kersting’s
groundnut landrace known and landrace grown were estimated and used to calculate ratios for each
sociolinguistic group.
The total number of samples per landrace collected in the two agroecological zones was calculated.
In addition, ecological models were employed to analyse the level of Kersting’s groundnut diversity.
Following Magurran [30], we defined landrace diversity as the number of landraces collected in the
study area. Based on a simple count of landraces cultivated per farmer, Margalef’s and Simpson’s
diversity indices were computed [30]. Landraces’ richness (locally adapted inter-varietal diversity)
among the two agroecological zones was compared using Margalef’s index (DMg ) as follows:
DMg = (L − 1)/ln (S)
where DMg stands for the Kersting’s groundnut diversity maintained in an agroecological zone by
farmers; L is the total number of Kersting’s groundnut phenotypic groups or landraces collected
from farmers and S the total number of samples collected in an agroecological zone and ln is the
natural logarithm.
The Simpson’s index (D) was measured to take into account the number of landraces as well as
the relative abundance of each landrace. The following formula was used following Tadesse [31]:
D=
n
X
(pi)2
i=1
where pi, the proportional abundance of the ith landrace = (ni /N), ni is the number of samples for the
landrace i and N the total number of samples. As D increases, the diversity decreases; consequently,
the sum of the squared proportions was subtracted from 1, (1—D), to express the abundance of each
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landrace. The value of this index ranges between 0 and 1; the greater the value, the greater the
phenotypic group diversity.
Furthermore, Factorial Analysis of Correspondence (FAC) was performed to assess the relationships
between farmers’ preferences and sociolinguistic groups. To better understand Kersting’s groundnut
cultivation systems, the Factorial Analysis of Mixed Data (FAMD) was used to cluster farmers’ cropping
practices into farming systems. Both analyses were performed using the packages FactoMineR
version 2.0 [32] and factoextra version 1.0.6 [33]. Graphs were generated using ggplot2 version 3.2.1
package [34].
3. Results
3.1. Socio-Demographical Characteristics of Respondents
60.47% of the respondents in this study were women. The respondents’ age was between 27 and
103 years old with a mean value of 54.31 ± 1.42. Most of the respondents were illiterate (74.42%)
with farming as the main activity (75.58%). Seven sociolinguistic groups were surveyed across the
agroecological zones: Bôbô, Senufo, Siamou, Toussian, Gurma, Dagara in the southern-Sudanian zone
and the Bwamu in the northern-Sudanian zone. The Dagara and Toussian were the most represented in
the study with a proportion of 26.74% each. They were followed by the Bwamu (16.28%) and the Bôbô
(12.79%) groups. Other sociolinguistic groups, with less than 10 respondents, included the Senufo (8),
Siamou (5) and Gurma (2). They represented 17.44% of the total samples. The socio-demographical
characteristics of the respondents are presented in the Table 2.
Table 2. Socio-demographical characteristics of respondents in southern-Sudanian and northern-Sudanian
zones of Burkina Faso and Ghana.
Variables
Number of villages
Number of respondents
Gender (%)
Modalities
Male
Female
Age (Years ± SE)
Marital status (%)
Study degree (%)
Socio-linguistic groups (%)
Socio-professional groups (%)
<50 years
≥50 years
Married
Widow
Illiterate
Primary school
High school
Bôbô
Bwamu
Dagara
Toussian
Others
Farmer
Other
Southern-Sudanian Northern-Sudanian
28
72
36.11
63.89
54.43 ± 1.53
38.89
61.11
81.94
18.06
80.56
13.89
5.56
15.28
0.00
31.94
31.94
20.83
75.58
24.42.
11
14
57.14
42.86
53.71 ± 3.84
28.57
71.43
85.71
14.29
42.86
21.43
35.71
0.00
100
0.00
0.00
0.00
85.71
14.29
Total
39
86
39.53
60.47
54.31 ± 1.42
37.21
62.79
82.56
17.44
74.42
15.12
10.47
12.79
16.28
26.74
26.74
17.44
76.74
23.26
3.2. Kersting’s Groundnut Diversity and Folk Description
The vernacular names used by famers to identify M. geocarpum were relatively different across
sociolinguistic groups (Table 3). The folk nomenclature of the crop landraces depended mainly on the
farmers’ own criteria of describing it. Therefore, the names given by farmers had different meanings to
the generic names of the crops. The criterion ‘seed coat color’ was widely used by farmers (84.88%)
to identify Kersting’s groundnut different landraces. The identification of the crop was based also
on the agronomic properties (33.72%), the seed size (8.14%), the religious utilizations of the crop
(5.81%), and the growth habits (3.47%). Farmers’ descriptions of M. geocarpum referred sometimes to
other legume crops, such as Bambara groundnut, because of the underground nature of both crops,
and cowpea, because of their similarity in seed coat color (white mottled with black eye) and taste.
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Different local names can be assigned to the crop by the same sociolinguistic group. Furthermore,
the same name can be used by different groups. For instance, the Toussian group referred to Kersting’s
groundnut mainly using three different names, such as Gwandjessi, Sidiin and Soonbia. The names
Soonbia and Sidiin were also used by Bôbô and Siamou groups, respectively. In addition to these
names, the Siamou called the crop Sissi, and the Bôbô used Zaka or Bôn to refer to the crop. The Dagara
sociolinguistic group used names such as Sonsuonii and Sonsuolii, while the Gurma group referred to
the crop as Susuonu. The Bwamu and Senufo groups, respectively, used Watié and Dougouvouguê as
names for the crop.
Table 3. Local names of Kersting’s groundnut landraces, farmers’ description criteria and their
characteristics across sociolinguistic groups in Burkina Faso and Ghana.
Description Criteria and
Percentages of Respondents (%)
Seed coat color (84.88)
Agronomic properties (33.72)
Seed size (8.14)
Vernacular Names
Local
Languages
Zaka dimi
Doforo fiman, Dougouma sôssô fiman
Sissi, Sidiin
Dougouvouguê, Davouguê
Watié
Sonsuolii, Sonsuonii
Bôbô
Dioula *
Siamou
Senufo
Bwamu
Dagara
Black seed coat color
Zaka flô
Doforo yingueni, Dougouma sôssô gueman
Sissi
Watié
Soonbia, Sindiin, Dîî, Sôbia, S’daï
Dougouvouguê, Davouguê
Watié
Sonsuolii,
Bôbô
Dioula
Siamou
Bwamu
Toussian
Senufo
Bwamu
Dagara
White mottled seed color or
cowpea seed color
Sonsuonii
Susuonu
Dagara
Gurma
Mixed colors seeds
Bôn
Doforo gueman
Bôbô
Dioula
White seed color
Zaka, Soonbia
Bôbô
Tolerant to drought
Bôn
Bôbô
Late matured cowpea
Soonbia, Gwandjessi, Sindiin
Toussian
Tolerant to drought cowpea,
late matured crop
Djîn
Toussian
Early matured Bambara
groundnut
Djîn
Toussian
Small seed size
Dagara
Small Bambara groundnut
seeds
Crop hunting the evil eye
Sonsuonii, Sonsuolii
Religious utilisations (5.81)
Growth habit (3.47)
Description
Zaka
Bôbô
Djîn, Dîî
Toussian
Mystical crop
Watié
Bwamu
Crop with multiple functions
Dougouvouguê, Davouguê
Senufo
Crop for family protection
and richness
Bôn
Dougouma sôssô, Solomia
Bôbô
Dioula
Underground cowpea
Dioula *: a common language spoken mainly in the Western part of Burkina Faso.
3.3. Farmers’ Knowledge and Extent of Kersting’s Groundnut Diversity in Burkina Faso and Ghana
According to the frequency of citations for each landrace known and grown by farmers and the
ratio values, the six landraces (Figure 2) recorded across sociolinguistic groups could be arranged
into four groups (Table 4). Group 1 included well-known (>50% of respondents) and frequently
grown (ratio > 50%) landraces; Group 2 was made up of well-known (>50%) but less-grown (<50%)
landraces; Group 3 was represented by less-known (<50%) but frequently grown landraces; Group 4
included less-known and less-grown landraces. The two landraces—White mottled with black eye and
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Black—were known by all the linguistic groups; they made the Group 1 and Group 2, respectively.
The White mottled with black eye was mainly adopted by the Toussian (ratio = 95.65%) while it was
less cultivated by the Bôbô (ratio = 14.29%). Apart from the Dagara, all the linguistic groups grew
the Black landrace which was widely grown by the Bwamu people. Group 3 was composed of the
Brown mottled with greyed orange eye, the Brown and the white mottled with greyed orange eye
landraces mostly produced by the Dagara. In fact, the landraces White mottled with greyed orange
eye and the Brown were cited only by the Dagara group. The Brown mottled with greyed orange eye
was mentioned by Gurma and Dagara groups in Ghana. The White landrace was the least known and
the least cultivated. It is produced by some Bôbô communities in Burkina Faso, while the Toussian and
other groups knew it but did not produce it. The knowledge of Kersting’s groundnut landraces varied
greatly across sociolinguistic groups. The Dagara were richer in terms of knowledge on M. geocarpum
folk diversity while the Bwamu knew little about the wide diversity of this crop.
Figure 2. Kersting’s groundnut seed coat colors. (a) Black, (b) White mottled with greyed orange eye,
(c) Brown mottled with greyed orange eye, (d) White, (e) White mottled with black eye, (f) Brown.
Table 4. Kersting’s groundnut diversity known (%) and grown (%) and grown/known ratios (%) across
sociolinguistic groups in Burkina Faso and Ghana. Ratio (%) = 100 × frequency of grown/frequency
of known.
Sociolinguistic Group
Bôbô
Bwamu
Dagara
Landrace seed colors
Known
Grown
Ratio
Known
Grown
Ratio
Known
Grown
White
White mottled with black eye
White mottled with greyed orange
eye
Black
Brown
Brown mottled with greyed orange
eye
18.18
63.64
9.09
9.09
50
14.29
35.71
21.43
60
17.39
4.35
25
-
-
-
-
4.35
4.35
100
90.91
-
81.82
-
100
-
100
-
73.91
69.57
60.87
0
87.50
-
-
-
-
95.65
91.30
95.45
Sociolinguistic Group
90
Toussian
100
Others
Ratio
Total
Landrace seed colors
Known
Grown
Ratio
Known
Grown
Ratio
Known
Grown
Ration
White
White mottled with black eye
White mottled with greyed orange
eye
Black
Brown
Brown mottled with greyed orange
eye
8.70
100
95.65
0
95.65
13.33
46.67
40
0
85.71
6.98
53.49
1.16
38.37
16.62
71.73
-
-
1.16
1.16
100
8.33
86.67
-
53.33
-
61.54
76.74
18.60
37.21
16.28
48.49
87.5
13.33
13.33
100
27.91
26.74
95.81
-
-
52.17
-
4.35
-
-
-
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3.4. Distribution of Kersting’s Groundnut Landraces and Diversity Estimation
Landraces are the genetic bases for crop improvement. A total of 62 Kersting’s groundnut samples
were collected in the study districts and varied morphologically in seed coat color. The samples were
clustered in six different landraces according to the seed coat color: the cream (known as White), White
mottled with black eye, White mottled with grey orange eye, Black, Brown and Brown mottled with
grey orange eye (Figure 2). The distribution of these groups varied across the agroecological zones.
All the six landraces were found in the southern-Sudanian zone while two (i.e., White mottled with
black eye and Black) were found in the northern-Sudanian zone. There were four landraces specific to
the southern-Sudanian zone, while no landrace was specific to the northern-Sudanian zone. The most
common and widely grown landraces listed by farmers across the two agroecological zones were the
White mottled with black eye and the Black. In the southern-Sudanian zone, the six landraces comprised
in total 51 samples collected, and in the northern-Sudanian zone, the two landraces found comprised
11 samples. The distribution of landraces is represented in Figure 3 and summarized in Table 5.
The landraces were collected in 25 villages out of the 39 villages surveyed. In the southern-Sudanian
zone samples were found in 16 villages located in six departments namely: Bôbô Dioulasso, Péni,
Orodara, Kourinion, Morolaba and Jirapa. In the northern-Sudanian zone, samples were found in
seven villages located in the departments of Ouarkoye and Bondokuy. Furthermore, some landraces
were specific to each country. In fact, the White one was found only in Burkina Faso while the Brown,
Brown mottled with greyed orange eye, and the White mottled with greyed orange eye ones were
specific to Ghana.
Figure 3. Distribution of Kersting’s groundnut landraces collected across agroecological zones of
Burkina Faso and Ghana.
−
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Table 5. Kersting’s groundnut landraces collected with diversity indices across agroecological zones of
Burkina Faso and Ghana.
Landrace by Seed Coat Color
Southern-Sudanian
Northern-Sudanian
White mottled with black eye
Black
White
White mottled with greyed orange
eye
Brown
Brown mottled with greyed
orange eye
5
18
1
3
8
1
14
12
Diversity indices
Number of landraces
Number of samples
Margalef’s index
Simpson’s index (1-D)
6
51
1.27
0.73
2
11
0.42
0.40
Diversity estimates (Table 5), based on the number of landraces (richness) and samples collected
(abundance), revealed that the southern-Sudanian zone exhibited higher richness (Margalef = 1.27)
and relative abundance (Simpson = 0.73) in terms of number of landraces and samples collected.
The northern-Sudanian zone was found to be less diverse (Margalef = 0.42; Simpson = 0.40).
3.5. Criteria for Choosing Kersting’s Groundnut Landraces to Grow
Farmers had many criteria in selecting M. geocarpum landraces (Table 6). These criteria concerned
the crop characteristics and the use categories. The three main criteria were the seed coat color,
the medicinal purposes and the organoleptic qualities. Preference for a specific landrace was dependent
on the area and/or the farmer. The Black landrace was mainly grown by farmers for medicinal and
socio-cultural purposes, while the White mottled with black eye landrace was grown for consumption
and was preferred by farmers because of its organoleptic qualities. In other villages, the Brown and
Brown mottled landraces were grown mainly because of the eating habits of consumers.
Table 6. Criteria used by farmers for growing Kersting’s groundnut landraces in Burkina Faso and Ghana.
Criteria
Proportions of Citations (%)
Seed coat
Medicinal purposes
Organoleptic qualities
Eating habit
Socio-cultural purposes
Resistance to drought
Early maturity
37.21
33.72
26.74
24.42
23.26
10.59
4.71
3.6. Production Systems and Management across Sociolinguistic Groups in Burkina Faso and Ghana
In Burkina Faso and Ghana, Kersting’s groundnut was produced on an average cropping area
of 0.079 ± 0.0162 ha with an average yield of 546.10 ± 64.30 Kg/ha. Farmers in these countries grew
M. geocarpum in rotation with cereals or legumes or in pure stand. However, few farmers (4.65%)
intercropped it with cereals, roselle or cassava. Another cultivation practice used by farmers was the
utilization of the crop around the fields of cereals or legumes as field border. Most of the farmers
adopted to grow the crop on ridges or on flat sowing, while some farmers adopted the mounds as
tillage practice. Field management included weeding (21–30 days after planting) and often earthing
up at the reproduction phase (45–75 days after planting) in order to facilitate the pods development.
Moreover, farmers planted Kersting’s groundnut between May and August during the raining season
and harvested after 4–5 months. Farmers stored the crop as dehulled seed and/or as pods in jars (61.63%
of respondents), in garrets (26.74%), in plastic bottles (20.93%) and in bags (15.12%). Other material
Agronomy 2020, 10, 371
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such as gourds, bottles and barrels were also used by a few farmers to store Kersting’s groundnut.
Farmers mixed Kersting’s groundnut seeds with sand, ash, extracts of plants or in some rare cases with
chemical products (1.16% of respondents) to reduce beetles’ attacks.
The Factorial Analysis of Mixed Data (FAMD) of the cultivation practices revealed three farming
systems in Burkina Faso and Ghana (Table 7). In the first system, all farmers grew Kersting’s groundnut
on mounds and 92.59% of them grew it on ridges; in this system, seeds were mainly stored in garrets as
dehulled seed mixed with sand. In the second system, cropping Kersting’s groundnut as field border
and earthing up practices were used by most of the farmers (90.91% and 81.82%, respectively); in this
system M. geocarpum was planted on flat sowing tillage and seeds were stored with plastic bottles
mostly mixed with ash. In the third farming system there is no specific tillage practices; farmers in this
system stored the crop as pod mixed with ash in jar.
Table 7. Results of Factorial Analysis of Mixed Data (FAMD) to cluster the cropping practices of
Kersting’s groundnut in Burkina Faso and Ghana.
Characteristics of Systems
Cla/Mod (%)
Cultivation practices = field border
Tillage = ridges
Tillage = mounds
Tillage = flat sowing
Earthing up = yes
Storage form = as dehulled seed
Storage material = garret
Storage material = plastic bottle
Storage material = bag
Storage product = sand
Storage product = ash
Seeds sources = family
9.09
92.59
100.00
23.26
4.55
52.50
73.91
22.22
15.38
88.46
21.05
15.79
Cultivation practices = field border
Cultivation practices = pure stand
Tillage = flat sowing
Tillage = ridges
Earthing up = yes
Storage material = plastic bottle
Storage material = garret
Storage product = ash
Storage product = sand
Seeds sources = family
90.91
31.71
69.77
3.70
81.82
66.67
17.39
78.95
11.54
73.68
Mod/Cla (%)
Global
p-Value
v-Test
2.38
59.52
19.05
23.81
2.38
100.00
40.48
9.52
4.76
54.76
19.05
7.14
12.79
31.40
9.30
50.00
25.58
93.02
26.74
20.93
15.12
30.23
44.19
22.09
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
−2.81
5.65
3.06
−4.75
−5.02
2.43
2.76
−2.50
−2.58
4.91
−4.59
−3.26
25.64
33.33
76.92
2.56
46.15
30.77
10.26
76.92
7.69
35.90
12.79
47.67
50.00
31.40
25.58
20.93
26.74
44.19
30.23
22.09
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
3.20
−2.38
4.54
−5.53
3.95
1.98
−3.15
5.61
−4.23
2.74
100.00
100.00
100.00
5.81
38.37
55.81
<0.001
<0.001
<0.001
5.55
2.71
1.97
System 1
System 2
System 3
Storage form = pod
Storage material = jar
Storage product = ash
100.00
15.15
10.42
Cla/Mod: percentage of all surveyed farmers who use a specific farming practice and belong to a cluster (system).
Mod/Cla: percentage of all farmers in a specific cluster (system) that also use a farming practice; p-value: level of
analysis significance, v-test: measures the association between variables and clusters. It reveals which variables are
positively or negatively associated with the clusters.
Kersting’s groundnut growers got seeds from their family as gift or heritage. Seeds used by
farmers came also from their own production but also used for consumption and other utilizations.
Macrotyloma geocarpum farming systems varied significantly (p < 0.035) across sociolinguistic
groups in Burkina Faso and Ghana (Figure 4). The Dagara (Dagari) and Toussian adopted the first and
the second farming systems. The Bôbô practiced the second and third farming systems. The Bwamu
practiced all three farming systems. In general, the third system was less represented in the surveyed
regions while the second farming system was the most practiced by all sociolinguistic groups.
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Figure 4. Frequency of Kersting’s groundnut farming systems across socio-linguistic groups in Burkina
Faso and Ghana.
3.7. Bottlenecks to Kersting’s Groundnut Production
Farmers identified several factors constraining Kersting’s groundnut production. Out of the
fourteen cited, the five main constraints facing farmers included the difficulty to harvest the pods
(66.28% of respondents), the lack of manpower (27.91%), the high soil moisture at the reproduction phase
(24.42%), post-harvest pests damage (23.53%), and drought (22.09%) (Figure 5). The non-availability
of seeds and the need for intensive soil preparation were also cited by farmers as factors limiting
crop production. According to them, although present, disease pressures were not a big challenge
in their production system. Pests disturbing and causing damages to the crop in the field included
domestic herds, rodents foraging fresh pods, and termites. Constraints varied significantly among
sociolinguistic groups (Table 8). For instance, apart from the Bôbô, all the groups cited the difficulty to
harvest as the main constraint they encountered. The high soil moisture during the reproductive phase
was also cited by all groups apart from the Dagara. For the Bôbô, Dagara and the Toussian, drought
was an important factor constraining Kersting’s groundnut production. Another factor cited by
producers was the non-availability of seeds limiting the production in the farming systems of Bwamu
and Toussian. The post-harvest pests were ranked by the Dagara group as important constraints in
Kersting’s groundnut production.
Figure 5. Constraints to Kersting’s groundnut production in Burkina Faso and Ghana.
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Table 8. Proportion of citations of Kersting’s groundnut production bottlenecks across sociolinguistic
groups in Burkina Faso and Ghana.
Constraints
Bôbô
Bwamu
Dagara
Toussian
Others
Kruskal Test
Difficulty to harvest
Non availability of seeds
Soil preparation
High soil moisture
Lack of labour
Pests in storage
Difficulty to access fertilizers
Difficulty to access pesticides
Field pests and diseases
Drought
Non availability of cultivated area
Difficulty of post harvesting activities
Long-time cooking
Difficulty to process
54.55
0.00
9.09
27.27
63.64
9.09
18.18
18.18
27.27
45.45
9.09
18.18
27.27
18.18
71.43
28.57
7.14
28.57
14.29
21.43
21.43
21.43
14.29
7.14
28.57
21.43
14.29
7.14
78.26
0.00
26.09
13.04
26.09
43.48
8.70
8.70
0.00
26.09
8.70
30.43
13.04
4.35
65.22
39.13
30.43
34.78
30.43
17.39
13.04
13.04
8.70
26.09
21.74
13.04
17.39
0.00
53.33
40.00
26.67
20.00
13.33
13.33
13.33
13.33
13.33
6.67
6.67
6.67
0.00
0.00
*
***
**
*
**
***
**
**
***
***
***
***
***
***
Kruskal Wallis test with frequencies of citations. *** p value < 0.001, ** p value < 0.01 and * p value < 0.05.
3.8. Preferred Traits for Kersting’s Groundnut Improvement
Thirteen traits were listed by producers as important for crop improvement (Table 9). The top five
preferred traits included early maturing, high yielding, resistance to bruchids, tolerance to drought,
and tolerance to high soil moisture. Farmers were also interested in some specific seeds’ attributes, as the
nutritional content and time taken to cook on available cooking facilities. White mottled with black
eye and White seeded landraces were preferred by farmers and can be used as background landraces.
Table 9. Traits identified by farmers for Kersting’s groundnut new varieties in Burkina Faso and Ghana.
Criteria
Traits
Percentage of Respondents
Agronomic
Early maturity
High yield
Tolerance to drought
Resistance to bruchids
Tolerance to high soil moisture
White seed coat
White mottled seed coat
Black seed coat
Red seed coat
Brown seed coat
Good seed quality
Facility to cook
Big seed size
34.88
33.72
26.74
26.74
22.09
25.58
25.58
18.60
10.47
8.14
15.12
10.47
9.30
Genetic resistance
Seeds coat colors
Seeds attributes
The Factorial Analysis of Correspondence revealed variation of farmers’ preferred traits across
sociolinguistic groups (Figure 6). The Bôbô group preferred the black seed coat color with resistance to
high soil moisture. The Bwamu were interested in short seeds cooking time. The Dagara and Toussian
groups preferred the White mottled with black eye landrace with high yielding, early maturing, and big
seed size attributes.
Agronomy 2020, 10, 371
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Figure 6. Traits identified by farmers for Kersting’s groundnut improvement according to socio-linguistic
groups. WSC: White Seed coat color; WMS: White mottled Seed coat color; RSC: Red Seed coat color;
BSC: Black Seed coat color; BRS: Brown Seed coat color; TLD: Tolerance to drought; TLM: Tolerance to
moisture; RSB: Resistance to bruchids; BSS: Big seed size; GSQ: Good seed quality; CFA: Facility to
cook; HYD: High yield; EMT: Early maturity.
4. Discussion
4.1. Knowledge, Existence and Distribution of Kersting’s Groundnut Diversity in Burkina Faso and Ghana
Sixty-two samples grouped in six different landraces were collected across both countries instead
of the five landraces reported in previous studies [12,13,17]. Tamini [14] reported the White mottled
with black eye and the Black landraces in Burkina Faso; whereas in this study, a White landrace was
additionally recorded and collected. Similarly, the Brown and the White mottled with greyed orange
eye were found only in Ghana and were not yet reported by previous investigations [17,35]. In this
study, we therefore found additional diversity in the southern-Sudanian zone of Burkina Faso and
Ghana. Those findings support the assumption that southern-Sudanian zone can be considered as
the primary center of origin of Kersting’s groundnut [12]. Previous reports indicated that the crop
originated from central Benin and Northern Togo [36]. Amujoyegbe [18] mentioned Nigeria as the
primary center of origin of the crop. Therefore, extended investigations followed by a wide diversity
resource collection is expected across other West-African countries where the cultivation of the crop was
mentioned. Future explorations could involve Nigeria, Mali and Ivory Coast in order to have a clear
idea of the genetic diversity of this crop and the center of origin of that diversity. This large germplasm
collection should be followed by the genetic characterization in different environments in order to better
understand the genetic background and the stability of Kersting’s groundnut specific traits. In addition,
the association studies involving molecular tools could make more accurate the genetic characterization
and can be useful in the identification of QTLs of functional and economic traits. Furthermore,
ex-situ conservation strategies through National and International genebanks supported by the local
conservation systems must be well organized to ensure the sustainable maintenance of the existing
diversity. In Benin and Togo, the Black landrace was well known by farmers but less cultivated while
the White one was widely grown and well appreciated by farmers and consumers [12,13]. As noticed
by Akohoué [12] in Benin and Togo, farmers in Burkina Faso and Ghana also grew the Black landrace
mainly because of medicinal and socio-cultural attributes. The White and the White mottled with black
eye landraces were grown mainly for consumption and their organoleptic qualities. The preference of
Agronomy 2020, 10, 371
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farmers for these landraces represents a good opportunity for their sustainable conservation on-farm
and across generations. On-farm management of agricultural biodiversity implies that smallholder
farmers select and develop the species they need to match their diets, culture, markets and environment.
Hence, in-situ conservation could be more organized through the valorization of Community Seed
Banks (CSB). CSBs are local-level institutions that contribute to seed conservation, in particular of
farmer varieties, countering erosion of crop diversity or its loss following natural disasters [37]. CSBs
have been established recently in Burkina Faso and Ghana, but are limited to few regions [38]. This
platform should be extended to other regions in order to limit the loss of genetic resources including
Kersting’s groundnut.
Landraces are considered to be an integral influence on farmers’ decisions on maintenance,
management, and exchange [39]. Farmers had a good knowledge of Kersting’s groundnut varieties
across sociolinguistic groups in terms of classification, identification, description and uses. Our results
revealed that farmers go beyond just naming, by grouping landraces together based on common
characters. Their indigenous knowledge would be extremely useful to agronomists, geneticists and
breeders. The criteria used by farmers to describe different landraces included the seeds characteristics,
agronomic and religious properties, and the growth habits of the crop. Similar results were found in
other studies including on the common bean [40], fonio [41], millet [42] and Kersting’s groundnut [12].
These characteristics used to identify different Kersting’s groundnut landraces reflect the consistence of
folk taxonomy. The seed color used by farmers as the main folk descriptor of this legume was considered
as a true discriminant trait by growers as well as by scientists who performed the agro-morphological
characterization of the species [13,15,43].
4.2. Kersting’s Groundnut Production Systems in Burkina Faso and Ghana
Most legumes including Kersting’s groundnut have been overlooked by research and development
agencies and are generally considered as women’s crops in some areas since they are often produced
by women producers on small land areas meant primarily for home consumption [44], whereas men
tend to dominate in the production and marketing of cereals in the food value chain [45]. This was
true for Kersting’s groundnut in the farming systems of Burkina Faso and Ghana. However, in other
communities, men were mostly involved in the crop production as the crop certainly exhibits a high
economical value in those communities [12,17]. The economical and the nutritional importance of this
crop should be clearly highlighted and promoted across its production areas in order to better use the
genetic resources available for food and nutrition security as well as for income generation.
Farmers generally grew M. geocarpum in rotation. Others intercropped or used it as field border
(mainly the Bôbô group). Farmers in Nigeria [18], Benin and Togo [12] also intercropped the crop.
According to farmers, Kersting’s groundnut helps improve the fertility of the soil, thereby reducing the
cost of fertilizer inputs in crop farming. This is certainly due to the nodulation property of the crop for
symbiotic nitrogen fixation [16,46] leading to the positive contribution of legume crops in the yield
improvement of associated crops [47–49].
Kersting’s groundnut was grown generally on ridges or on mound in the farming systems Burkina
Faso and Ghana. The same types of tillage were used in the production systems of the crop in
Ghana [19], Benin and Togo [12,13,50]. The type of tillage was often different across sociolinguistic
groups. In Benin, Kouelo [50] showed that the type of tillage practice can contribute significantly to
improve M. geocarpum yield and was specific to the soil conditions. Therefore, investigations should be
done in the different growing areas of Kersting’s groundnut in order to propose to farmers the suitable
tillage practice adapted to their soils’ characteristics.
In Burkina Faso and Ghana, farmers stored Kersting’s groundnut as pods. This practice, also
reported in other countries [12,13,17], contributes to limiting pulse beetles’ damages and permits
a longer storage life. Badii [51] found that the Black and Brown landraces were less susceptible
to the bruchids (Callosobruchus maculatus Fabricius) attacks than the White mottled with black eye.
The genetic determinism of this resistance to C. maculatus in Brown and Black landraces needs be
Agronomy 2020, 10, 371
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deepened. Consequently, the possibility for introgression of bruchids-resistant gene from Brown and
Black landraces into other landraces (White and White mottled with black eye) can be explored.
There was a number of barriers to M. geocarpum production, including the hard work required for
harvesting while there is an increasing a lack of manpower for cultivation. In addition, the crop was
grown mainly by elderly people (above 50 years old) while young people were focused on cereals
and cash crops—generally ignoring legumes. This situation was also reflected by many governments’
policy and research institution priorities [52]. The difficulty to harvest appeared as a major challenge
for growers in Benin and Nigeria as well [13,18].
Furthermore, the non-availability of seeds to meet farmers’ needs is another constraint limiting
Kersting’s groundnut production. In fact, in most of the growing areas where the crop production was
decreasing or disappeared, farmers lost their seeds and did not have the possibility of a new supply.
Similarly, in Benin, the lack of market for seed supply was one of the reasons for the low production of
Kersting’s groundnut. The possibility for M. geocarpum commercial seeds production is still inexistent;
farmers saved their own seeds for planting. At the same time, the easy access to quality seed can
be achieved and guaranteed only if there is a viable seed supply system to multiply and distribute
seeds that have been produced or preserved by farmers [53]. According to the same authors, the most
effective alternative is to create smallholder seed enterprises, located in farming communities, with
lower capital investment needs. These enterprises should be closed to smallholder farmers and be able
to distribute quality seeds of improved and local varieties such as Kersting’s groundnut.
4.3. Farmers’ Preferences for Kersting’s Groundnut and Implication for its Genetic Improvement
Kersting’s groundnut production has been decreasing drastically because of its low yield, the small
seed size and the late maturing time [12,13,18]. This explains the need expressed by farmers to have
improved cultivars with high yield, drought tolerance, and early maturing attributes. Authors revealed
that the crop exhibits variations in flowering time, seed size and grains yield [13,43]. This offers room
for genetic improvement and selection of desired cultivars. However, the scarce knowledge of the
reproductive biology and the narrow genetic basis [24,54], require a lot of investment to develop crosses
and broaden the genetic background. Failing to establish the clear nature of Kersting’s groundnut
floral biology may hinder the success of its varietal improvement through the cross pollination of good
landraces. Although there is room for mutagenesis, no studies have so far embraced this pathway.
Mutation breeding—using both physical and chemical mutagens—has been extensively and successfully
used in the development of improved cultivars of legumes such as Bambara groundnut [55,56] and
groundnut [57].
5. Conclusions
This study revealed the diversity of Kersting’s groundnut landraces grown in the southern-Sudanian
and northern-Sudanian zones of Burkina Faso and Ghana. Results showed that farmers grew six
different landraces. All those landraces were grown in the southern-Sudanian zone, while only two
were grown in the northern-Sudanian zone. Farmers preferred their varieties to be high yielding and
tolerant to drought, resistant to bruchids and early maturing. This finding is relevant and important for
the definition of the Kersting’s groundnut breeding objectives. The study also analyzed the cropping
systems of the crop, the main constraints to its production and examined farmers’ preferences for its
improvement. The study revealed that farming practices across the surveyed areas were diverse and
strongly influenced by sociolinguistic membership. In Ghana and Burkina Faso, farmers’ knowledge
about the crop and its production practices remains vital for the future promotion of the resource.
Author Contributions: Conceptualization by M.C. and E.G.A.-D.; investigation by M.C. and C.O.A.A.; writing
and editing M.C.; validation by E.G.A.-D., formal analysis by M.C. and F.A., review by E.G.A.-D. and M.S.
All authors have read and agreed to the published version of the manuscript.
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Funding: Mariam Coulibaly, from the University of Ouaga I Prof Joseph Ki-Zerbo, Burkina Faso, was a scholar of
the “Intra-Africa Academic Mobility Scheme” under the project grant number 2016-2988 on “Enhancing training
and research mobility for novel crops breeding in Africa (MoBreed)” funded by the Education, Audiovisual
and Culture Executive Agency (EACEA) of the European Commission. The project provided a scholarship for
academic training and research mobility and a research grant to the first Author to complete a PhD degree at the
University of Abomey-Calavi (Republic of Benin).
Acknowledgments: Authors wish to thank MoBreed program for the financial support. We are thankful to all
farmers and agriculture technical services in Burkina Faso and Ghana. We are grateful to local authorities in all
surveyed villages. We thank also Xavier Matro Comlan, Ayenan Mathieu, Dao Abdalla for all assistance during
the surveys.
Conflicts of Interest: The authors declared no conflict of interest.
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