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Natural variation in fruit characteristics, seed germination and seedling growth of Adansonia digitata L. in Benin

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Adansonia digitata (baobab tree), a multipurpose tree species, occurs throughout semi-arid and arid zones of Africa. Its survival is, however, threatened by bush fire, over-exploitation, grazing and a lack of natural regeneration. The extent of variation in fruit characteristics, seed germination and seedling traits of the baobab tree in Benin, was evaluated at climatic zone level. 1,200 fruits were sampled in each of the three climatic zones of Benin for morphological assessment and to assess germination rate and seedling growth dynamics according to the climatic zones, the used substrate and the scarification of the seed coat. There were significant differences in fruit characteristics not only between climatic zones but also between individuals from the same zone and within-trees. Using mechanical scarification on freshly-collected baobab seeds negatively affected the germination rate of baobab seeds sampled in the Guinean and Sudano-Guinean zones of Benin. The best-germination rate was recorded for non-treated seeds from the Guinean zone, up to 57% on day 25. All seeds germinated best on the sand substrate, but supplying organic matter promoted further seedling growth after 11days of germination. Based on these observations we propose some strategies for efficient ex situ conservation of baobab in Benin. KeywordsClimatic zones–Seed scarification–Germination substrate
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Natural variation in fruit characteristics,
seed germination and seedling growth
of Adansonia digitata L. in Benin
A. E. Assogbadjo R. Gle
`le
`Kakaı
¨S. Edon T. Kyndt
B. Sinsin
Received: 23 April 2009 / Accepted: 28 June 2010
ÓSpringer Science+Business Media B.V. 2010
Abstract Adansonia digitata (baobab tree), a multipurpose tree species, occurs throughout
semi-arid and arid zones of Africa. Its survival is, however, threatened by bush fire, over-
exploitation, grazing and a lack of natural regeneration. The extent of variation in fruit
characteristics, seed germination and seedling traits of the baobab tree in Benin, was eval-
uated at climatic zone level. 1,200 fruits were sampled in each of the three climatic zones of
Benin for morphological assessment and to assess germination rate and seedling growth
dynamics according to the climatic zones, the used substrate and the scarification of the seed
coat. There were significant differences in fruit characteristics not only between climatic
zones but also between individuals from the same zone and within-trees. Using mechanical
scarification on freshly-collected baobab seeds negatively affected the germination rate of
baobab seeds sampled in the Guinean and Sudano-Guinean zones of Benin. The best-ger-
mination rate was recorded for non-treated seeds from the Guinean zone, up to 57% on day
25. All seeds germinated best on the sand substrate, but supplying organic matter promoted
further seedling growth after 11 days of germination. Based on these observations we
propose some strategies for efficient ex situ conservation of baobab in Benin.
Keywords Climatic zones Seed scarification Germination substrate
Introduction
The multipurpose baobab (Adansonia digitata L.) is a key economic species used daily in
the diet of rural communities in West Africa (Assogbadjo et al. 2005a,b; Codjia et al.
A. E. Assogbadjo (&)R. Gle
`le
`Kakaı
¨S. Edon B. Sinsin
Laboratory of Applied Ecology, Faculty of Agronomic Sciences, University of Abomey-Calavi,
05 BP 1752 Cotonou, Benin
e-mail: assogbadjo@yahoo.fr
T. Kyndt
Department of Molecular Biotechnology, Faculty of Bioscience Engineering,
Ghent University (UGent), Coupure Links 653, 9000 Ghent, Belgium
123
New Forests
DOI 10.1007/s11056-010-9214-z
2001,2003; Sidibe
´and Williams 2002). The 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; Codjia et al. 2001,2003; Sidibe
´and Williams 2002; Sena et al.
1998; Sidibe et al. 1996; Yazzie et al. 1994).
A recent study by our research group (Kyndt et al. 2009) showed that the human
influence on baobab populations in agroforestry systems has an effect on the genetic
structure of the species. A spatial aggregation of related genotypes and therefore a risk for
future inbreeding depression was observed. However, at present, high levels of genetic
diversity are still present within populations.
A number of local baobab forms differing in habit, vigor, size, quality of the fruits and
foliar vitamin content, are recognized by the local people (Assogbadjo et al. 2006,2008;
Gebauer et al. 2002; Sidibe
´and Williams 2002). An ethnobotanical survey of the per-
ceptions and human/cultural meaning of morphological variation, use forms, preferences
and links between traits (Assogbadjo et al. 2008) showed that local people apply a mor-
phological classification system for baobab trees and are able to guide in selecting and
collecting germplasm from trees with preferred combinations of traits. However, we found
that genetic fingerprinting using AFLP markers did not completely correlate with this
traditional morphological identification of Adansonia digitata (Assogbadjo et al. 2009). In
Beninese baobab populations, we did observe a link between morphological diversity and
abiotic, environmental factors as well as a genetic basis for some specific traits (Asso-
gbadjo et al. 2005a,2006). However, since general morphological diversity and genetic
diversity are not completely correlated to each other (Assogbadjo et al. 2008), baobab
phenotypic traits and certainly the fruit characteristics seem to be significantly influenced
by environmental factors. Therefore, a detailed study of the morphological variation in
baobab fruit characteristics, is needed to be able to include a wide range of natural diversity
in conservation strategies.
Next to human disturbance, the lack of natural regeneration is one of the main risk
factors for baobab extinction. In order to design efficient conservation management, a
study on the propagation of the species is needed. Studying the germination rate, the
effect of seed pre-germination treatment and seedling growth from seeds collected in
different climatic zones will give insights into the best options for propagation to obtain
an efficient restoration and conservation both within and outside the natural habitat of the
species.
A previous study done by Assogbadjo et al. (2005b) described the morphological
traits and productivity of A. digitata, using data from four well-known and locally
recognized types of capsules in rural areas of Benin. The present study, supplementary
to the previous one, aims at understanding the variation of fruit morphology and seed
germination according to the climatic zones. Differences in germination characteristics
depending on climatic zone are commonly observed for widely distributed plant species
like baobab (e.g. Keller and Kollmann 1999; Andersen et al. 2008; Hamasha and Hensen
2009).
With the present study, the following questions will be answered: (i) Could quantitative
descriptors based on morphological characteristics help to statistically distinguish baobab
capsules sampled in the same and different climatic zones? (ii) Are there differences in
terms of seed germination rate and seedling growth according to their origin, the used
substrate and the seed coat scarification? As such, the study will allow selecting the trees
having a good combination of quantitative traits as well as the best seed germination
method for different climatic zones for future species improvement, restoration and
conservation.
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123
Materials and methods
Study areas and sampling
The study was conducted in the three climatic zones of Benin, located between 6°and
12°500N and 1°and 3°400E in West Africa (Fig. 1). The climatic zones studied are: the
Sudanian zone (zone 1) located between 9°450and 12°250N, the Sudano-Guinean zone
(zone 2) located between 7°300and 9°450N and the sub-humid Guinean zone (zone 3)
located between 6°250and 7°300N. In the Sudanian zone, the mean annual rainfall is often
less than 1000 mm and the relative humidity varies from 18 to 99% (highest in August).
The temperature varies from 24 to 31°C. The Sudanian zone has hydromorphic soils, well-
drained soils, and lithosols. The vegetation of this zone is mainly composed of savannas
with trees of smaller size. The rainfall in the Sudan-Guinean zone is unimodal, from May
to October, and lasts for about 113 days with an annual total rainfall varying between 900
and 1,110 mm. The annual temperature ranges from 25 to 29°C, and the relative humidity
from 31 to 98%. The soils in this zone are ferruginous with variable fertility. The vege-
tation of the Sudan-Guinean transition zone is characterized by a mosaic of woodland, dry
dense forests, tree and shrub savannas and gallery forests. In the Guinean zone the rainfall
is bimodal with a mean annual rainfall of 1,200 mm. The mean annual temperature varies
between 25 and 29°C and the relative humidity between 69 and 97%. The soils are either
deep ferrallitic or rich in clay, humus and minerals. Our previous study showed that baobab
is distributed throughout the whole country at various densities according to the climatic
zones (Assogbadjo et al. 2005a,b). In the Sudanian zone, a mean population density of 5
baobabs per km
2
was recorded. In the Sudano-Guinean zone, a mean density of 2–3
baobabs per km
2
was recorded while in the Guinean zone a density of only 1 baobab per
km
2
was recorded.
From each climatic zone of Benin, 30 individuals of baobab have been randomly
sampled. For each sampled baobab, 40 fruits were randomly collected. This corresponds to
a total of 1,200 fruits sampled in each climatic zone.
Morphological analysis of fruit characteristics
For each capsule, length (Lcaps), width (Wcaps), thickness (Tcaps), length/width (Lcaps/
Wcaps) ratio and total weight (TWcaps) was assessed. In addition, weight of pulp (Wp),
seeds (Ws), pulp-seed (Wps), kernels (Wk), number of seeds (Ns) and length of peduncle
(Pl) of each capsule were assessed as indicated by Assogbadjo et al. (2005b) and their
means were evaluated.
Measured data on baobab capsules were used to perform an univariate analysis of variance
with three factors using a linear nested model (capsules in trees and trees in climatic zones).
In addition, a variance components analysis (Goodnight 1978) was executed on each mor-
phological trait to analyze the variability of the capsules in baobab trees and the variability of
trees within climatic zones. For these two statistical analyses, ‘‘zone’’ was considered as
fixed whereas ‘‘capsules’’ and ‘‘trees’’ were considered as random. The factor ‘‘zone’’ is
considered as fixed in the analysis because its levels constitute the entire population in which
we are interested. Least square means of the traits of baobab capsules were estimated for trees
of each climatic zone. Multivariate analysis of variance followed by canonical discriminant
analysis (Rao 1973) was performed on the least square means in order to describe the
difference between climatic zones according to the traits of baobab fruits.
All the analyses were done using SAS software (SAS Inc. 2003).
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123
Germination and seedling growth dynamics
Seeds used for germination tests have been sampled on 30 baobab individuals selected in
the three climatic zones of Benin. For each climatic zone, three germination substrates
have been evaluated: S1: 100% sand; S2: sand (1/3) ?organic matter (2/3); S3: sand
(1/4) ?organic matter (3/4). To test the hypothesis that germination is inhibited by
Fig. 1 Map showing the main towns of Benin and the sampling locations for evaluation of baobab fruit
characteristics and germination
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123
the seed coat and hence pre-treatment by scarification would promote germination
(Razanameharizaka et al. 2006), we have compared the germination capacity of intact
seeds (NS) with that of seeds from which a 5–10 mm
2
fragment of coat has been removed
with pruning shears (S). The factors tested were arranged in split plots within homogenous
randomised blocks that were replicated three times.
Percentage of germinated seeds was recorded from day 7 (when the first seed germi-
nation occurred) and then every 2 days till the 31st day. Analysis of variance with repeated
measures (Crowder and Hand 1990) was performed, using a mixed model. In this model,
the factor ‘‘Block’’ was considered as random whereas all the others (‘‘zone’’, ‘‘substrate’
and ‘‘pre-treatment’’) were considered as fixed. No data transformation on the germination
rate was used because multinormality and homoscedasticity were checked using the test of
Rao and Ali and the generalized Bartlett test, respectively (Gle
`le
`Kakaı
¨et al. 2006). With
this statistical method the effect of climatic zone, substrate and pre-treatment on the
germination rate of the capsules was evaluated. Least square means of the germination rate
were estimated from the analysis and used to draw figures showing the evolution trend of
germination percentage of capsules according to the factors considered.
Growth rate has been recorded for each of the above mentioned treatments. Variability in
height, diameter, number of leaves at 11, 18, 25 and 32 days was analyzed using analysis
of variance with repeated measures (Crowder and Hand 1990). We analyzed the effect of
climatic zone, substrate and seed coatscarification on these variables. Least square meansof the
variables were estimated fromthe analysis of variancewith repeated measuresand used to draw
figures showing the evolution trend of each of them according to the factors in consideration.
Results
Variation in baobab fruit characteristics according to climatic zones and baobab
individuals
The variance components analysis (Table 1) revealed that baobab fruit variability is
generally lower between zones than within zones. The length, width, thickness, length/
width ratio and weight of the capsules, as well as the weight of the pulp and the length of
the peduncle has more variability between baobab trees than within the same tree, whereas
the other traits revealed more variability within trees than between trees (Table 1).
Between capsules of the same tree, a large variation ([40%) was observed for the weight
of the capsules, seeds, and kernels as well as for the number of seeds.
The multivariate analysis of variance and canonical discriminant analysis performed on
the least square means of the traits of baobab capsules indicated significant differences
between climatic zones (Wilks’ Lambda =0.067; P=0.0003) and between individuals
from the same zone (Wilks’ Lambda =0.002; P\0.0001). Capsules from trees in the
Guinean zone generally have the largest dimensions and weight, while the Sudanian
capsules are smaller and more lightweight. The capsules from the Sudanoguinean zone
show intermediate characteristics.
Effect of climatic zone, substrate and seed coat scarification on the germination
dynamics of baobab
Results of the analysis of variance with repeated measures performed on the germination
rate of baobab seeds according to the level of factors considered in the experimental design
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123
Table 1 Results of the variance components estimation procedure on capsule traits from baobab fruits collected in the three climatic zones of Benin
Variance
component
Lcaps Wcaps Tcaps Lcaps/Wcaps TWcaps Wps Ws Wp Wk Ns Pl
Zone 1.5
(9.38%)***
0.2
(7.14%)***
0.001
(11.11%)**
0.01(2.38%)*** 612.7
(4.73%)**
822.6
(15.09%)**
335.9
(12.12%)**
124.1
(21.14%)**
37.3
(12.11%)**
1626.0
(13.31%)*
3.0
(6.25%)***
Trees (zone) 13.3
(83.13%)***
2.0
(71.43%)***
0.006
(66.67%)**
0.34
(80.95%)***
7305.7
(56.41%)*
2304.3
(42.27%)*
1117.3
(40.31%)*
337.5
(57.49%)**
124.1
(40.31%)**
4902.1
(40.13%)*
43.0
(89.58%)***
Capsules (trees) 1.2
(7.50%)***
0.6
(21.43%)***
0.002
(22.22%)**
0.07
(16.67%)***
5032.5
(38.86%)*
2324.3
(42.64%)*
1318.7
(47.57%)*
125.5
(21.38%)**
146.5
(47.58%)**
5688.8
(46.57%)*
2.0
(4.17%)***
Legend:Lcaps Length of capsule, Wcaps Width of capsule, Tcaps Thickness of capsule, Lcaps/Wcaps Length/width ratio of capsule, TWCaps Total weight of capsule,
Wps Weight [pulp ?seed], Wp Weight of pulp, Ws Weight of seed, Wk Weight of kernel, Ns Number of seeds, Pl Length of peduncle
Percentages in parentheses are the variance components expressed as a percentage of the sum of the three variance components; *** significant at 0.001; ** significant at 0.01;
* significant at 0.05; ns non significant
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123
showed that all three main factors (substrate, climatic zone climatic zone and seed coat
scarification) had a significant effect on the germination rate of the baobab seeds
(P\0.05; results not presented). Moreover, some of the interactions between these factors
were also significant (climatic zone*substrate, climatic zone*pre-treatment) showing that
the effect of a given main factor on the germination rate was influenced by another factor.
In addition, the effect of the main factors on the germination rate and their interaction
changed over time.
Curves showing the evolution of the interaction effect of climatic zone climatic zone
and substrate on the germination rate over time are shown in Figs. 2and 3. In general, seed
germination reached its maximum after 25 days. Figure 2shows that seeds from the
Guinean zone (Climatic zone 3) when sown on substrate S1, gave the highest germination
rate (from 25% to 35–45%). Seeds from the Sudano-Guinean zone (Climatic zone 2) gave
the lowest germination rate. However, when substrate S1 was applied, their germination
rate increased rapidly from 10% the 7th day to 30% on the 21st days. Seeds from the
Sudanian zone (Climatic zone1) also had low germination rates, but this did not signifi-
cantly differ from one substrate to another.
Figure 3shows the interaction between climatic zone climatic zone and seed coat
scarification on the germination rate of baobab seeds over time. We noticed that there is a
highly significant negative effect of seed coat scarification on the germination rate of seeds
from climatic zones 1 and 3 (Fig. 3). For the best-germinating seeds, from climatic zone 3,
the germination rate of non-scarified seeds increased from 27% the 7th day to 57% the 25th
day after sowing. For the scarified seeds of the same climatic zone, we only recorded a
germination rate of 10% on the 7th day after sowing and this number did not significantly
increase in time. Scarified seeds of climatic zone 1 showed the lowest germination rate. For
climatic zone 2, however, scarification had a positive effect on the germination rate.
Effect of climatic zone, substrate and scarification on the growth dynamics of baobab
seedlings
Results of the analysis of variance with repeated measures performed on the baobab
seedling height, diameter and number of leaves according to the factors considered in the
experimental design (Table 2) indicate that, regardless to the time of measurement,
substrate and climatic zone had a significant effect on seedling growth (height and
0
10
20
30
40
50
60
7 9 11 13 15 17 19 21 23 25 27 29 31
Germination rate (%)
Days
P1S1 P1S2 P1S3
P2S1 P2S2 P2S3
P3S1 P3S2 P3S3
Fig. 2 Evolution trend of the
germination percentage
according to climatic zone and
substrate. Legend: PiSj =Seed
from climatic zone i sown on
substrate j [i =1 for Sudanian
zone; i =2 for Sudano-Guinean
zone; i =3 for Guinean zone;
j=1 for substrate 1 (sand);
j=2 for substrate 2: sand (1/3)
?organic matter (2/3); j =3 for
substrate 3: sand (1/4) ?organic
matter (3/4)]
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123
diameter) as well as on the number of leaves (P\0.05). None of the interactions between
the considered factors is significant (P[0.05). Results in Table 2show that the time
significantly impacted the effect of substrate and climatic zone on the seedling growth and
number of leaves.
Figure 4shows the curves describing the evolution trend of these factors on the seedling
growth (height and diameter). Seedlings obtained from seeds sampled in the Sudanian
zone (Climatic zone 1) have the highest height and diameter whereas seedlings from the
Sudano-Guinean zone (climatic zone 2) have the lowest height and diameter at all time
points. Regarding the substrate, we observed that the seedlings are smaller in height and
0
10
20
30
40
50
60
70
7 9 11 13 15 17 19 21 23 25 27 29 31
Days
Germination rate (%)
P1NS P1GS
P2NS P2GS
P3NS P3GS
Fig. 3 Evolution trend of the
germination percentage
according to climatic zone and
pre-treatment of baobab seed.
Legend:Pi=seed from climatic
zone i (i =1 for Sudanian zone;
i=2 for Sudano-Guinean zone;
i=3 for Guinean zone); NS non
scarified seeds; GS scarified
seeds
Table 2 Summary of the analysis of variance with repeated measures on the height, diameter and number
of leaves of baobab seedlings
Source Height Diameter Number of leaves
of baobab seedlings
df F value df F value df F value
Time*block 8 5.89*** 8 1.81ns 8 2.59**
Time*climatic zone 8 16.86*** 8 0.72ns 8 0.98ns
Time*substrate 8 28.27*** 8 6.00** 8 18.39***
Time*seed 4 2.38ns 4 0.71ns 4 4.18*
Time*block*climatic zone 16 0.45ns 16 0.62ns 16 0.49ns
Time*block*Substrate 16 0.88ns 16 0.62ns 16 0.63ns
Time*block*pre-treatment 8 1.30ns 8 0.32ns 8 0.32ns
Time*climatic zone*substrate 16 0.76ns 16 0.46ns 16 0.75ns
Time*substrate*pre-treatment 8 0.57ns 8 0.32ns 8 0.89ns
Time*climatic zone*pre-treatment 8 1.08ns 8 1.15ns 8 2.10ns
Time*block*climatic zone*substrate 32 1.09ns 32 1.17ns 32 1.34ns
Time*block*climatic zone*pre-treatment 16 1.02ns 16 0.48ns 16 1.21ns
Legend:df degree of freedom, MS Mean square, FFisher, Pr probability
*** Significant at 0.001; ** significant at 0.01; * significant at 0.05; ns non significant
New Forests
123
diameter on substrate 1 (sand) while substrates 2 and 3, including organic matter, result in a
faster seedling growth.
Discussion
In the present study, the variation in capsule morphological traits, germination rate and
seedling growth was registered among baobab seeds sampled in the three different climatic
zones of Benin. Some studies dealing with different plant species already reported that
morphological characteristics vary with climatic region and ecological gradients. Maranz
and Wiesman (2003) revealed a significant relationship between trait values (fruit size and
shape, pulp sweetness and kernel content of the species) and abiotic variables (temperature
and rainfall) in sub-Saharan Africa north of the equator for the shea tree (Vitellaria
paradoxa). Moreover, Soloviev et al. (2004) reported a significant influence of different
climatic zones of Senegal on fruit pulp production for Balanites aegyptiaca and Tamar-
indus indica (savanna trees).
For the baobab tree, the current study revealed that variation in capsule morphological
traits is higher within the same climatic zone than among climatic zones and hence no eco/
morphotypes can be distinguished based on capsule traits. The observed big variation in
fruits is probably influenced by both genetic and environmental factors. Phenotypic
PROV
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
11 18 25 32 39
Days
Diameter (cm)
SUB
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
11 18 25 32 39
Days
Diameter (cm)
PROV
0
10
20
30
40
50
11 18 25 32 39
Days
Height (cm)
P1
P2
P3
SUB
0
5
10
15
20
25
30
35
40
45
50
11 18 25 32 39
Days
Height (cm)
S1
S2
S3
S1
S2
S3
P1
P2
P3
Fig. 4 Evolution trend of the seedling growth (height in top and diameter in bottom) according to the
climatic zones and substrate. Legend:Pi=seed from climatic zone i [i =1 for Sudanian zone; i =2 for
Sudano-Guinean zone; i =3 for Guinean zone); S1 =sand; S2 =sand (1/3) ?organic matter (2/3);
S=sand (1/4) ?organic matter (3/4)]
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differences observed between capsules might be due to genetic drift, natural selection or
plastic responses to differences in micro- habitat factors. A high influence of soil com-
position on the morphological characteristics of baobab tree was already observed by
Assogbadjo et al. (2005a). Given the degree of variation reported in this study, selection for
improvement of fruit traits would be more effective among trees within the same climatic
zones than among zones.
Between capsules of the same tree very little difference was observed in capsule shape
(length, width, thickness, length/width ratio) while more significant differences were
observed for the weight of the capsules, seeds, pulp, and kernels as well as for the number
of seeds. The low within-tree morphological variability in capsule shape could be due to a
high heritability of this trait. Although in some studies a low to moderate narrow-sense
heritability has been reported for fruit shape (Abe et al. 1995; Gusmini and Wehner 2007),
no detailed studies have been performed on long-living tropical tree species like baobab up
till now. Next to heritability, maternal effects could also explain our observations. While
generally strong maternal effects are reported for seed size and seed numbers (e.g. Byers
et al. 1997; Lipow and Wyatt 1999; ProvenanceWaser et al. 1995; Castellanos et al. 2008),
for baobab it is rather the capsule shape that seems to be maternally determined.
The high within-tree variation in weight of capsules, seeds, pulp and kernels could be
determined by the position of the capsule in the tree or, since baobab is generally out-
crossing, by paternal effects.
The use of local seed provenances is often recommended in restoration and conservation
strategies because they are thought to be better adapted to local habitat conditions. For
these kind of programmes germination studies are important to gain insights into the effect
of pretreatments, optimal conditions for germination and the influence of seed provenance.
It was reported by Danthu et al. (1995) that seeds from A. digitata germinated entirely
after soaking in concentrated sulphuric acid for periods ranging from 3 to 12 h or by
boiling for 15 s. This drastic treatment can be applied in a laboratory setting but cannot be
recommended in rural areas because of the dangerous effect which may be caused by the
use of concentrated acid. Mechanical scarification, as recommended by Razanameharizaka
et al. (2006), which showed that the removal of the seed coat of Malagasy baobab
increased the germination rate, might then be more practical. However, our study unex-
pectedly revealed that using mechanical scarification on freshly-collected baobab seeds
negatively affects the germination rate of baobab seeds sampled in the Guinean and
Sudano-Guinean zones of Benin. Whereas the non-treated seeds from the Guinean zone
were already 27% germinated on day 10 and attained up to 57% on day 25, the scarified
seeds from this zone merely reached 14% germination rate. Our results demonstrate that
baobab seed can germinate without scarification of its seed coat. Baobab seeds from Benin
do not seem to have a strict physical dormancy compared to the Malagasy ones and the
observed differences may be due to a physiological response lead by genetic and/or
environmental factors.
It is important to note that in our experiment, regardless of the climatic zone of origin,
the seeds germinated best on sand, the germination of the freshly-collected seeds began
7 days after sowing, and was at its maximum after 25 days. While it is possible that non-
germinated seeds were still viable, they were not particularly vigorous.
For species with a wide distribution range, differences in germination characteristics
depending on seed climatic zone are commonly observed (e.g. Keller and Kollmann 1999;
Strandby Andersen et al. 2008; Hamasha and Hensen 2009). Variations between popula-
tions are probably due to the presence of different ecotypes with different germination
strategies. However, this is a hypothesis that requires additional research to test.
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In our study, the percentage of germination was generally higher for baobab seeds from
the Guinean zone than for those from the Sudanian zone or Sudano-Guinean zone. This
might be due to differences in temperature and rainfall between the relatively dry and hot
Sudanian zone and the colder and more humid Guinean climate. In many species from dry
and hot regions, the loss of dormancy rate increases with the temperature to which the
seeds are exposed (Baskin and Baskin 2001). In addition, for Jordanian and Central Asian
Stipa spp. (Hamasha and Hensen 2009) rainfall had a negative influence on the germination
of seeds collected in dry areas. It is then logical that in our experiments, executed in the
humid and colder Guinean zone the highest rate of germination is observed for the seeds
from this particular zone. Seeds collected in dryer climates are probably germinating less
efficiently because the applied conditions fail to break their dormancy. This indicates a
strong response of baobab germination to ecological conditions like humidity and tem-
perature. The use of local seed provenances is hence of high importance in baobab res-
toration strategies. It has to be noted that next to environmental factors, also genetic factors
can have an influence on seed germination traits. Wulff (1995) and Gutterman (2000)
reported that maternal factors, such as position of the seed in the fruit/tree and the age of
the mother plant influence seed germination ability. In this study, such effects have been
not studied. Next to germination, significant differences were also observed in baobab
seedling growth among the different climatic zones and between the substrates on which
the seeds were sown. Emerging seedlings mainly depend on seed reserve for initial growth,
which explains why seedling height and diameter for the 11-day-old seedlings was the
same. However, the same variables significantly varied after 11 days according to the used
substrate and climatic zone of origin. Regarding the substrate, it is not surprising to notice
that the seedlings grow faster when organic matter is supplied. Seedlings obtained from
seeds sampled in the Sudanian zone have the highest height and diameter whereas seed-
lings from the Sudano-Guinean zone have the lowest height and diameter at all time points.
Parker et al. (2006) and Rai and Tripathi (1982) reported a positive influence of large seed
size and seed reserve on the establishment and early growth of seedlings. Indeed, baobab
from the Sudanian zone generally have a higher weight of seeds (Assogbadjo et al. 2005a,
b) and this results in a faster seedling growth as well as a higher diameter at breast height in
mature state (Assogbadjo et al. 2006).
The baobab species is facing a high risk of extinction because of the lack of its natural
regeneration, and hence practical ex situ conservation measures are urgently needed to
preserve genetic diversity and maintain multiple specimens. As a very big variation is
observed in morphological characteristics of capsules between various climatic zones,
between trees within the same zone and even between capsules within the same tree, there
is little to be gained by selecting the ‘‘best’’ climatic zone based on the measured variables.
However, taking into account the potential adaptation of baobab to the latitudinal rainfall
gradients in Benin (Assogbadjo et al. 2006), collection can be made from a large number of
capsules of different individuals in each climatic zone, to ensure to capture the widest
range of biological diversity. Since seeds from the Guinean zone showed the highest
germination rate compared to the ones from the Sudano-Guinean and Sudanian zone, we
suggest for ex situ conservation to collect more seeds from the latter zones than in the
Guinean zone. Moreover, home gardens should be developed to limit the pressure on the
natural population of the species. For that, propagation through seeds is preferred and we
suggest germinating on sand and then transferring the seedlings to a substrate including
organic matter for further growth. No seed scarification is required for germination and we
propose to use autochthonous seeds for the species propagation within specific zones.
New Forests
123
Acknowledgments This work is financially supported by the International Foundation for Science (IFS)
provided to Dr. Ir. Achille Assogbadjo in 2006. We thank IFS and its donors.
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... Accordingly, trials investigating the adaptable response of baobab populations to some of these techniques have been done in Benin. These include seed germination and vegetative propagation (e.g., grafting, stem cuttings, layering) (Assogbadjo et al., 2011). ...
... Baobab seeds could be sown without scarification, as nonscarified seeds had registered the best germination rate (57%) by day 25 from the date of sowing, particularly from the Guinean zone (Assogbadjo et al., 2011). The authors recommended seed germination on sand substrate first before transferring the seedlings to the substrate with organic matter for further growth. ...
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This is the second edition of a multi-author book first published in 1992. It deals with all aspects of plant regeneration by seeds, including reproductive allocation, seed dispersal and predation, longevity, dormancy and germination. All chapters have been updated, and four new chapters added on seed size, seedling establishment, the role of gaps, and regeneration from seed after fire.
Article
A growing body of evidence indicates that phenotypic selection on juvenile traits of both plants and animals may be considerable. Because juvenile traits are typically subject to maternal effects and often have low heritabilities, adaptive responses to natural selection on these traits may seem unlikely. To determine the potential for evolutionary response to selection on juvenile traits of Nemophila menziesii (Hydrophyllaceae), we conducted two quantitative genetic studies. A reciprocal factorial cross, involving 16 parents and 1960 progeny, demonstrated a significant maternal component of variance in seed mass and additive genetic component of variance in germination time. This experiment also suggested that interaction between parents, though small, provides highly significant contributions to the variance of both traits. Such a parental interaction could arise by diverse mechanisms, including dependence of nuclear gene expression on cytoplasmic genotype, but the design of this experiment could not distinguish this from other possible causes, such as effects on progeny phenotype of interaction between the environmental conditions of both parents. The second experiment, spanning three generations with over 11,000 observations, was designed for investigation of the additive genetic variance in maternal effect, assessment of paternal effects, as well as further partitioning of the parental interaction identified in the reciprocal factorial experiment. It yielded no consistent evidence of paternal effects on seed mass, nor of parental interactions. Our inference of such interaction effects from the first experiment was evidently an artifact of failing to account for the substantial variance among fruits within crosses. The maternal effect was found to have a large additive genetic component, accounting for at least 20% of the variation in individual seed mass. This result suggests that there is appreciable potential for response to selection on seed mass through evolution of the maternal effect. We discuss aspects that may nevertheless limit response to individual selection on seed mass, including trade-offs between the size of individual seeds and germination time and between the number of seeds a maternal plant can mature and their mean size.
Article
Africa has abundant wild plants and cultivated native species with great agronomic and commercial potential as food crops. However, many of these species, particularly the fruits and nuts, have not been promoted or researched and therefore remain under-utilized. Moreover, many of these species face the danger of loss due to increasing human impact on ecosystems. Sudan, as in many other African countries, is endowed with a range of edapho-climatic conditions that favor the establishment of many plant species, most of which are adapted to specific ecological zones. Among these plants is the baobab (Adansonia digitata L.) which is a fruit-producing tree belonging to the family Bombacaceae. The baobab has an exceedingly wide range of uses ranging from food and beverages to medicinal uses. Despite its potential, which is well recognized, very little is known about the tree phenology, floral biology, husbandry or genetic diversity. In this article, we have aimed to bring out detailed information on various aspects of its botany, ecology, origin, propagation, main uses, genetic improvement and especially its importance for nutrition and poverty alleviation in the Sudan.
Article
We analysed the fruit weight, flesh firmness, soluble solid content and pH of fruit juice to obtain information on the inheritance of these characters, using a Japanese pear seedling population consisting of sixteen families and their parental cultivars and selections. The average values for the fruit weight, flesh firmness, soluble solid content and pH of fruit juice in the parental cultivars and selections were 354 g, 4.5 Ibs, 12.4 % and 4.94, and t.he coefficients of variation for the fruit weight, flesh firmness, soluble solid content and pH of fruit juice in these cultivars and selections were 0.35, 0.09, 0.05 and 0.05, respectively. The average values of family means for three years in each family ranged from 202 g to 423 g for the fruit. weight, 4.3 lbs-5.1 Ibs for the flesh firmness, 12.3 %∼ 13.3 %for the solube solid content and 4.76-5.26 for the pH of fruit juice, with the overall average values of means of sixteen families for these characters being 272 g, 4.8 Ibs, 12.7 % and 5.05, respectively. The average value of the range of yearly fluctuations in each family was 47.2 g' for the fruit weight, 0.48 Ibs for the flesh firmness, 0.95 % for the soluble solid content and 0.12 for the pH of fruit juice. . Statistically significant parent-offspring correlation coefficients were obtained between mid-parental values and the values of family means for the fruit weight, flesh firmness, soluble solid content and pH of fruit juice, although they vvere different among the characters. The estimates of heritability for the fruit weight, flesh firmness, soluble solid content and pH fruit juice were in the range of 0.57 -0.82, 0.14- 0.56, 0.37- 0.50 and 0.58- 0.69. The average value of heritability for three years was 0.73 for the fruit weight, 0.29 for the flesh firmness, 0.42 for the soluble solid content and 0.64 for the pH of fruit juice. fruits