1. INTRODUCTION
Defining how and where plant varieties will adequately respond to
environmental variations is a central topic in plant science research.
This is more preoccupying for orphan crops that are largely grown in
marginal areas and neglected in the mainstream research agenda
(Mabhaudhi et al. 2019).
Availability of the genetic resources of those crops is still a
challenge for many genebanks at national, regional, and international
levels. This situation jeopardizes the sustainable utilization of the
plant genetic diversity that can be useful for current and future food
systems and secured nutrition (Govindarajet al. 2015; Litrico & Violle
2015; Singh et al. 2014). Such
genetic resources are important for successful cultivars development and
selection of economic and agronomic traits and could confer resilience
to evolving climate.
In Kersting’s groundnut [Macrotyloma geocarpum (Harms) Maréchal
and Baudet], a multipurpose staple orphan crop with high nutritional
and economic values for smallholder farmers in West Africa
(Adu-Gyamfi et al. 2011;
Ajayi & Oyetayo 2009;
Akohoué et al. 2019;
Assogba et al. 2015;
Obasi & Agbatse 2015), the need to solve
the ecological suitability of the extant genetic resources arose despite
the significant achievements made recently on the germplasm collection,
conservation and crop selection. Kersting’s groundnut plays an important
role in farming sustainability through its ability to fix atmospheric
nitrogen in soil and enhance soil fertility
(Mohammed et al. 2018).
Furthermore, It serves in traditional medicine for local populations
(Adu-Gyamfi et al. 2011;
Assogba et al. 2015;
Tamini 1995). However, the production of
Kersting’s groundnut is declining rapidly and the genetic resources were
rarely collected and safeguarded for future generation. In addition,
environmental stresses are among the main causes for declining
Kersting’s groundnut production from its cultivated areas
(Akohoué et al. 2019;
Coulibaly et al. 2020). Though
Kersting’s groundnut has relatively good adaptation to low-input
conditions (Achigan-Dako & Vodouhe 2006;
Mergeai 1993), increased frequency of
drought, intense precipitations, elevated temperatures, and increased
salt and heavy metals in soils will often be accompanied by increased
infestation by pests, and pathogens, are expected to limit the plant
growth and productivity, and consequently the crop’s yield and
production (Long et al. 2015).
Recent studies revealed a low variation within the species
(Akohoue et al. 2020;
Mohammed et al. 2018) that limits
the extent of its genetic diversity and cultivated zones.
Kersting’s groundnut counts six
landraces set mostly within three agroclimatic zones; Northern-Guinean
(NG), Northern-Sudanian (NS) and Southern-Sudanian (SS) of Benin,
Burkina Faso, Ghana and Togo with the predominance of genetic resources
and diversity in Southern-Sudanian zone
(Akohoué et al. 2019;
Coulibaly et al. 2020). Overall,
the area of cultivation and adaptation of landraces differ among
agroclimatic regions. The Black landrace was largely collected in the
Northern-Sudanian environmental conditions and was widely preferred,
cultivated and maintained by farmers
(Coulibaly et al. 2020). The White
landrace was widely grown in the Northern-Guinean transition zone of
Benin (Akohoué et al. 2019;
Assogba et al. 2015) while less
cultivated in Burkina Faso (Coulibalyet al. 2020) and absent in other countries of West-Africa. The
production of the Brown landrace was specifically limited to Ghana
farming system (Coulibaly et al.2020).
Kersting’s groundnut landraces are the direct results of farmer
selection, cultivation and maintenance over the centuries. This
continual adaptation of the crop to smallholders farming conditions
could continue to play a role in adapting production to climate change.
Also, local adaptation of landraces could vary in their climatic
response and requirement and therefore, may spread differentially under
evolving environmental conditions
(Schierenbeck 2017). To find the adequate
referendum where the species can thrive, it has become crucial to
approximate the potential distribution of the crop and its genetic
resources.
Unfortunately, with the rapid evolution in climate conditions and the
further introduction and adoption of new cash crops with high economic
importance, local seed systems alone will likely be insufficient to
ensure the endurance of the crop genetic resources and diversity. In
these conditions, applying ecological research is required to inform
conservation and management decisions in order to mitigate a species
genetic erosion (Araújo et al.2005), as Kersting’s groundnut at National and Regional levels.
Ecological niche modeling (ENM) can identify the environmental
parameters that can impact a species’ distribution and project its
potential distribution area onto new environmental surfaces to examine
the effect of present or future environmental change
(Araujo & Peterson 2012;
Martínez-Meyer 2005).
Several statistical and mechanistic techniques proved effective in
quantifying niches and spatial distribution of natural and cultivated
species (Blonder 2018;
Elith et al. 2006;
Pironon et al. 2019;
Ramirez-Cabral et al. 2016;
Syfert et al. 2016). The basic
modelling framework of species distribution models (SDMs) in general has
been criticized on a number of gaps, such as ignoring heterogeneity in
population and genetic structure in different parts of a species
geographical range (Hampe & Petit 2005).
However, many species are organized into
differentiated genetic lineages
across their geographical ranges (Hereford
2009; Leimu & Fischer 2008) and
populations differ in their adaptive potential to respond to
environmental change (Shaw & Etterson
2012). Studies proved that incorporating molecular data into SDMs
represents an important step forward for modelling the effects of
climate change on species geographical ranges
(Alvarado-Serrano & Knowles 2014;
Gotelli & Stanton-Geddes 2015;
Ikeda et al. 2016).
In the case of Kersting’s groundnut (KG), much uncertainty remains
concerning the ability of the crop to withstand the changing climate,
suggesting that there is a clear need to comprehensively analyze the
response of the crop diversity under new environmental conditions of the
coming decades.
The present study was undertaken to predict the potential distribution
of KG under present and future climate change scenarios. Recent
molecular studies involving 281 individuals from Benin and Togo
identified two major genetic clusters of KG and these two groups were
distributed across Southern-Sudanian and Northern-Guinean agroclimatic
zones (Akohoue et al. 2020).
Kafoutchoni et al. (2021) also
assessed the genetic structure of the species through GBS approach and
Discriminant analysis of principal components (DAPC) and found eight
genetically distinct groups from five origins. In this context, the
following questions are of high interest: does the agroclimatic niches
of KG vary with climate changes? Would KG genetic groups differ in their
ability to respond to present and future climatic scenarios? This study
examines the response of orphan crops to future climates by using
genetic information and ecological niche modeling approach (gENMs) using
KG as an example. Therefore, we combined KG population genomics data
with ecological niche modeling: 1) to analyze the relationship between
climate factors and species populations distribution in agroclimatic
zones of Burkina Faso, Benin, Ghana, and Togo, and 2) to predict and
examine areas that would be suitable for the species and genetic
populations under the future scenarios. We hypothesized that: i) the
distribution of KG remains stable under future climates, and ii)
genetically distinct populations of orphan crops would respond
differently to climate change.