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Not. Bot. Hort. Agrobot. Cluj 38 (2) 2010, Special Issue, xx-xx
Print ISSN 0255-965X; Electronic 1842-4309
Notulae Botanicae Horti Agrobotanici
Cluj-Napoca
Conservation Genetics of Baobab (Adansonia digitata L.) in the
Parklands Agroforestry Systems of Benin (West Africa)
Achille Ephrem ASSOGBADJO1) , Romain GLELE KAKAI1) , Tina KYNDT2) , Brice SINSIN1)
1)University of Abomey-Calavi, Faculty of Agronomic Sciences, Laboratory of Applied Ecology, 05 BP 1752 Cotonou, Benin; assogbadjo@yahoo.
2)Ghent University, Department of Molecular Biotechnology, Coupure Links 653, B-9000, Ghent, Belgium
Abstract
e present study occurred in the three climatic zones of Benin (6°25 - 12° N) and aimed at investigating the level of morphometric
and genetic variation and spatial genetic structure within and between threatened baobab populations. A total of 137 individuals from
six populations were analysed using morphometric data as well as molecular marker data generated with the AFLP technique. Five primer
pairs resulted in a total of 217 scored bands with 78.34% of them being polymorphic. A two-level AMOVA revealed 82.37% of the total
variation within populations and 17.63% among populations (P<0.001). Analysis of population structure with allele-frequency based
F-statistics revealed a global FST of 0.127±0.072 (P<0.001). e mean gene diversity within populations (Hw) and the average gene
diversity among populations (Hb) were estimated at 0.309±0.000 and 0.045±0.072, respectively. Baobabs in the Sudanian and Sudan-
Guinean zones of Benin were short and produced the highest yields of pulp, seeds and kernels in contrast to the ones in the Guinean
zone. e molecular results indicate some degree of physical isolation of the populations collected in the dierent climatic zones. We
also found morphological dierences but further analysis must be done to establish their origin which is certainly an interaction between
genotype and environment. Sampling options of the natural populations are suggested for in or ex situ conservation.
Keywords: Adansonia digitata, climatic zones, morphometric variation, population structure
Introduction
e multipurpose baobab (Adansonia digitata L.) is a
key economic species used daily in the diet of rural com-
munities in West Africa (Assogbadjo et al., 2005a,b; As-
sogbadjo et al., 2008; Codjia et al., 2001, 2003; Sidibe and
Williams, 2002). e species contributes to rural incomes
(Diop et al., 2005) and has various important medicinal
and food uses (Assogbadjo et al., 2005a; Diop et al., 2005;
Sena et al., 1998; Sidibé et al., 1996; Sidibé and Williams,
2002; Yazzie et al., 1994).
Within baobab species, there is evidence indicating
the existence of a number of local forms diering in habit,
vigor, size, quality of the fruits and foliar vitamin content
(Assogbadjo et al., 2005a; Gebauer et al., 2002; Sidibé and
Williams, 2002). However, information about the ecol-
ogy, the morphological and genetic variation within and
between populations and the productivity of their various
organs is lacking (Sidibé and Williams, 2002).
e participatory domestication of indigenous fruits
has been proposed as an appropriate means to alleviate
poverty (Poulton and Poole, 2001), and could also have
positive benets on the environment since new plantings
of baobab would help to restore the declining resources of
this important tree.
e main objective of the present study is to dene
based on molecular analysis a better conservation strate-
gies for the baobab species in Benin. To this aim, Ampli-
ed Fragment Length Polymorphism (AFLP) analysis
(Vos et al., 1995) was applied to nd the intra-specic
genetic diversity of those locally recognised morphotypes
and on the whole populations in order to assess the genetic
diversity and dierentiation within and between baobabs
in Benin. Because AFLPs are known to map throughout
the genome of any particular species analyzed so far, this
high-volume DNA ngerprinting techniques gives fast
and ecient measurements of genome-wide diversity
(Powell et al., 1996). We used this technique to investigate
not only if the traditional classications of A. digitata are
conrmed by genome-level genetic dierentiation but also
if there is within the species some genetic variations which
should be conserved for the benet of local people.
Materials and methods
Study areas
e study was conducted in the three climatic zones of
Benin (112 622 km2 and 6.752.569 inhabitants in 2002),
located between 6° and 12°50 N and 1° and 3°40 E in West
Africa. e zones studied are: the Sudanian zone located
between 9°45’-12°25’ N, the Sudano-Guinean zone lo-
cated between 7°30’-9°45’ N and the sub-humid Guinean
zone (Dahomey Gap) located between 6°25’-7°30’ N.
In the Sudanian zone, the annual mean rainfall is oen
less than 1000 mm and the relative humidity varies from
18% during the harmattan period (December - February)
Assogbadjo, A. E. et al./ Not. Bot. Hort. Agrobot. Cluj 38 (2) 2010, xx-xx
2
analyses of genetic diversity and structure were performed
using AFLPsurv version 1.0. (Vekemans, 2002) which is
based on the methods described by Lynch and Milligan
(1994). Nei’s (1973) gene diversity (also known as expect-
ed heterozygosity) as well as global and pairwise genetic
dierentiation (FST) values were computed. Signicance
of the genetic dierentiation between groups was tested
by comparison of the observed FST with a distribution of
FST under a hypothesis of no genetic structure, obtained
by means of 1000 random permutations of individuals
among groups. Moreover, a model-based (Bayesian) clus-
tering method was applied on the presence/absence matrix
to infer genetic structure in the dataset, using the soware
Structure version 2.0. (Pritchard et al., 2000).
Assessing and analyzing morphometric data in baobab
populations
e morphological characteristics of each baobab were
studied (at the abovementioned populations). For each
baobab sampled, the trunk diameter was measured at
breast height (1.3 m) (DBH). Tree height, crown diameter
and the number of branches were also determined. If fruit-
ing, the number of capsules was counted and their shape
noted. To estimate the productivity in pulp, seeds and ker-
nels, 600 fruits were sampled in each population. Length
and weight of total fruit and its contents (pulp + seeds)
was determined. e seeds were then removed by soaking
the contents in water. e seeds were counted and then
oven-dried at 50 to 60°C for 48 hours. e dry seeds were
boiled for 30 min in order to remove the seed coat, which
is a traditional technique for extracting the kernel. Kernels
were dried at 40 to 50°C for 48 hours and weighed. e
weight of the pulp (WP) in each fruit was obtained by
the following formula: WP= Wsp - Ws, where Wsp is the
weight of the capsule’s contents (seed with pulp), and Ws
is the weight of the seed without pulp. For each product
(pulp, seeds or kernel), the mean productivity was calcu-
to 99% in August. e temperature varies from 24°C to
31°C. e Sudanian zone has hydromorphic soils, well-
drained soils, and lithosols. e vegetation of this zone
is composed of savannas and gallery forests with trees of
smaller size.
e mean rainfall in Sudano-Guinean zone is unimod-
al, from May to October, and lasts for about 113 days with
total mean annual varying between 900 mm and 1110
mm. e annual temperature ranges from 25°C to 29°C,
and the relative humidity from 31% to 98%. e soils in
this zone are infertile mineral soils and ferruginous soils of
variable fertility. e vegetation of the Sudano-Guinean
transition zone is characterized by a mosaic of woodland,
dry dense forests, tree and shrub savannas and forest gal-
leries.
e rainfall regime in the Guinean zone is bimodal
from April to June and from September to November,
with a mean annual rainfall of 1200 mm. e mean tem-
perature varies between 25°C and 29°C and the relative
humidity between 69% and 97%. e soils are either
deep ferrallitic, and of low fertility or alluvial and heavy
clay soils. e vegetation in this zone has been strongly af-
fected by various agricultural activities and now forms a
mosaic of cultivated lands and small relic forest patches.
e original vegetation was dense semi-deciduous forests
and Guinean savannas. is zone represents about 10% of
Benin and supports 60% of the country’s inhabitants.
Sampling for DNA ngerprinting
In each climatic zone, 2 populations of baobab were
sampled. Tab. 1 summarises the characteristics of the sam-
pled populations, including geographic zone of origin and
co-ordinates. Six to 35 individuals were sampled within
each population and used for the morphometric, produc-
tivity and AFLP analyses. In this study, a baobab popula-
tion was dened as a group of baobab trees randomly and
naturally distributed in a traditionnal agroforestry system
that can be assimilated to a circle with a maximum of 50
km radius. Two dierent populations are isolated from
each other by a geographical distance of at least 50 km.
Within a population, baobab individuals were randomly
selected at a distance of at least 100 m, in order to avoid
the sampling of genetically related individuals. In total,
six populations of baobab represented by 137 individuals
were collected in the aforementioned zones. For each bao-
bab, four or ve leaves were harvested and dried in silica
gel for DNA extraction and AFLP analysis.
Genetic data analysis
DNA were isolated following the MATAB protocol
(Kelly et al., 2004) whereas AFLP analysis were performed
as described by Vos et al. (1995) with minor modications.
For each individual, the DNA ngerprints were scored by
visual inspection for presence (1) or absence (0) of spe-
cic AFLP-bands (Fig. 1). Only distinct, major bands
were scored. For statistical analyses, allele-frequency based
Fig. 1. AFLP electrophoresis showing the scored bands
Assogbadjo, A. E. et al./ Not. Bot. Hort. Agrobot. Cluj 38 (2) 2010, xx-xx
3
lated per tree allowing the calculation of average yield for
each population. With SASv8 soware, analyses of vari-
ance and the Newman and Keuls test were performed on
morphological data to describe and compare baobab pop-
ulations within and between the climatic zones.
Results
Intra specic genetic variation and structuring of baobab
species in Benin
When bands from all 137 individuals were consid-
ered, levels of polymorphism within populations varied
between 89.4% and 98.2%, reecting a high level of poly-
morphism and variation within populations. e highest
estimate of the likelihood of the data, conditional on a
given number of clusters, was obtained when clustering all
genotypes into six gene pools. Results indicated that the
genetic structuring of the sampled individuals was cor-
related with their geographic origin. Nei’s gene diversity
(expected heterozygosity) within populations ranged be-
tween 0.26 and 0.37. A three level AMOVA partitioned
14.70% among the three regions of Benin and 5% of ge-
netic variation among populations within regions. Analy-
sis of population structure with allele-frequency based
F-statistics revealed a global FST of 0.127±0.072 (P=
0.001). e total gene diversity (Ht) was estimated to be
0.355±0.02 while the mean gene diversity within popula-
tions (Hw) and the average gene diversity among popula-
tions (Hb) were estimated at 0.309 and 0.045±0.072, re-
spectively. Pairwise genetic distances between populations
(FST), calculated using AFLPsurv 1.0, were statistically
signicant (P<0.001). Within the same climatic region,
the genetic distance is generally lower than 0.05, whilst
genetic distance between populations located in the dif-
ferent climatic zones were larger than 0.05. Mantel tests
comparing genetic dierentiation and geographic distance
per population showed a signicant correlation of 0.758
(P<0.001), indicating isolation by distance.
Morphological data, productivity in analyzed
populations
Morphological data and productivity of the analyzed
baobab individuals varied signicantly (P<0.05) among
populations and climatic zones. In the Sudanian zone, the
baobabs have large girths and crowns, and numerous fruits
with a high pulp, seed, and kernel production (Tab. 1).
Tab. 1. Morphological characteristics and mean production per individual for six baobab populations
Morphological feature
Guinean Sudano-guinean Sudanian
P1 P2 P3 P4 P5 P6
Mean σ Mean σ Mean σ Mean σ Mean σ Mean σ
DBH (cm) 149.23a66.89 147.15a57.29 176.35b33.64 173.04b40.32 201.51c97.88 202.55c54.90
Hm (m) 21.15a3.45 18.90b2.83 13.79c1.96 13.50c1.87 15.27d5.18 18.70b4.27
Dcrown (m) 14.27a3.69 14.22a1.13 16.95b5.99 16.58b4.62 16.56b4.66 16.58b3.98
NBranches 7a2.17 7a2.32 10b3.02 11b2.83 7a2.22 7a3.98
Ncaps/tree 49a46.12 67b36.15 188c70.77 225d203.50 137e92.54 138e132.51
Wcaps/tree (kg) 20.28a18.33 25.69b29.38 32.05c11.37 34.13d8.58 28.28e21.62 34.07f34.71
Lcaps (cm) 21.71a4.85 22.71a4.85 19.89b3.96 18.89b3.96 16.89c5.14 16.59c5.14
icknessCaps 0.45a0.15 0.45a0.15 0.43b0.09 0.43b0.09 0.43b0.07 0.43b0.07
WP/tree (kg) 3.62a3.19 1.93b1.55 6.13c1.98 6.51c1.46 4.94d3.75 4.83d3.83
Nseeds/tree 10969a9523 9326b8576 27565c9168 27635c8140 21188d20231 25455e20876
Wseeds/tree (kg) 4.22a3.97 4.62a2.68 9.21b7.06 11.09c10.85 16.93d16.31 17.04e16.72
Wkernel /tree(Kg) 1.40a1.32 1.54a0.89 2.31b2.10 2.70b2.57 3.67c2.35 3.70c3.62
Tab. 2. Correlation between distance based on individual
morphological features and pairwise genetic dissimilarity
values
Morphological
feature
Correlation with
genetic diversity Probability
DBH (cm) -0.00726 0.3168
Hm (m) -0.06655 0.0497*
Dcrown (m) -0.00568 0.4356
NBranches 0.07911 0.0198*
Ncaps/tree 0.05868 0.1584
Wcaps/tree (kg) 0.04529 0.1980
Lcaps (cm) -0.00188 0.4851
icknessCaps -0.14078 0.0099*
WP/tree (kg) 0.04825 0.2277
Nseeds/tree 0.04071 0.3069
Wseeds/tree (kg) 0.04441 0.2376
Wkernel /tree(Kg) 0.04441 0.2673
*= Signicant (Probability<0.05)
Legend Tab. 1 and Tab. 2: DBH= diameter at breast height; Hm= Height of tree;
Dcrown= diameter of the crown; NBranches= Number of branches; Ncaps=
Number of capsules; WCaps= weight of capsules; Lcaps= Length of capsule (cm);
ickness Caps= ickness of Capsule; WP= Weight of pulp; Nseeds=
number of seeds; Wseeds= Weight of seeds; Wkernel= Weig ht of kernel;
σ= standard deviation; P= population
NB: In the same line, gures with the same letters are not signicantly dierent.
Assogbadjo, A. E. et al./ Not. Bot. Hort. Agrobot. Cluj 38 (2) 2010, xx-xx
4
Baobabs from the Sudano-Guinean zone are short, their
diameter at breast height is intermediate between DBH
values measured in the Guinean and Sudanian region.
Populations in this zone produce the highest yield of pulp,
seeds and kernels. In the Guinean zone, the individuals
were tall but of a small diameter at breast height. ese
baobabs have capsules with high length and thickness but
produce only a small number of fruits with a low pulp,
seed and kernel productivity (Tab. 1).
Discussion and Conclusions
Relationship between morphometric data and genetic
variation
Morphometric data (Tab. 1) show signicant dierence
within and among baobab populations across the climatic
zones. Environmental eects on the biotic variables have
also been observed in other edible trees in Africa. Maranz
and Wiesman (2003) showed for the shea tree (Vitellatria
paradoxa) a signicant relationship between trait values
(fruit size and shape, pulp sweetness, and kernel content
of the species) and abiotic variables (temperature and rain-
fall) in sub-Saharian Africa north of the equator. Also,
Soloviev et al. (2004) showed for Balanites aegyptiaca and
Tamarindus indica (savanna trees) the signicant inu-
ence of dierent climatic zones of Senegal on fruit pulp
production. Moreover, Silva-Montellano and Eguiarte
(2003) were able to detect genetic dierentiation in popu-
lations of Agave lechuguilla along a latitudinal transect in
the Chihuahuan desert. e pattern of population dier-
entiation along this transect was congruent with patterns
of morphological and reproductive dierentiation found
(Silva-Montellano and Eguiarte, 2003).
In this study, we observed some parallel patterns of
morphological and genetic diversity in baobab. Although
it may well be that the variation observed in morphology
and other morphometric characters studied in baobab
were signicantly correlated with abiotic factors of envi-
ronment (Assogbadjo et al., 2005), there is also no doubt
that part of this variation within baobab populations could
be explained by genetic dierentiation. Indeed, the molec-
ular results indicate some degree of physical isolation of
the populations collected in the dierent climatic zones.
We also found morphological dierences but further ex-
periments (e.g. mapping studies) are needed to identify
specic genes or genome regions that might have a direct
inuence on the observed morphometric variation.
Conservation of baobab genetic diversity in Benin
As baobab seeds exhibited orthodox behaviour (Ra-
zanameharizaka et al., 2006), they can be conserved ex
situ in seed banks and also in situ or in circa as living trees.
Strategies for prioritizing the conservation of genetic di-
versity need to consider the level of diversity in an area,
and condition of, a particular region. e best option
should be to conserve seeds from non desirable baobab
(Assogbadjo et al., 2008) in ex situ in gene banks and the
living desired trees in situ as seeds and service suppliers.
e high levels of genetic variation present within popula-
tions suggested that large numbers of samples from a few
populations would capture a sucient amount of the spe-
cies’ genetic variability. However, such a practice would
increase the chance of missing rare alleles, particularly in
disjoint populations, which also expresses extreme pheno-
types for phenological traits related to climatic adaptation.
We suggested in these cases to sample for ex situ gene con-
servation, populations from dierent geographic areas and
individuals from all morphotypes to maximize genetic di-
versity for ex situ collections thereby increasing probabil-
ity of conserving rare alleles. We have also recommended
to sample seeds deployed for ex situ conservation in gene
banks from a high number of individuals and within all
climatic zones and morphotypes, thereby avoiding low
genetic diversity within seedlots and consequently low
risk of inbreeding depression and high adaptive capacity
to environmental variation in trees to be planted within
the parklands agroforestry systems. is could be done us-
ing the core collection concept and is important since it
can allow the sampling of dierent classes of alleles (wide-
spread, localized and rare).
Acknowledgements
is work is supported by the International Founda-
tion for Science (IFS) and Bioversity International (ex
IPGRI). We also thank AUF-BIOVEG network and
IRD (France) which provided travel grants for attending
conference at Cluj-Napoca in Roumania. We thank these
institutions and their donors. Our acknowledgement also
goes through local people of Benin.
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