Phenotypic Diversity in Terminalia catappa from South Western Nigeria
Bayo i Ogunkanm
The diversity amongst Teminalia catappa population in two different locations in the Lagos area of South Western Nigeria was investigated. Forty trees were sampled for twenty eight quantitative and twelve qualitative characters. Variability was observed in qualitative characters such as leaf shape and ripe fruit colour. Quantitative characters analyzed using multivariate statistical analysis showed high intraspecific variability for most of the characters determined. Cluster analysis using the unweighted pair group method using arithmetic mean (UPGMA) method revealed four main clusters which were not based on location of collection but on morphological characters. The trees were grouped into the main clusters based mainly on plant architecture. The result from the trees studied showed that selections based on traits such as fruit size, fruit colour and leaf sizes can be undertaken for future improvement or development of this tree crop in Nigeria.
Terminalia catappa Linn. an ornamental tropical
tree belonging to the family Combretaceae is native to Southeast Asia.
It is large deciduous stately tree with a characteristic pagoda shape
(Mitchell, 1964). It is cultivated in Nigeria solely as a shade tree and
for its fruits and seeds which are eaten as fruit as well as for medicinal
uses (Oni and Bada, 1982). It is a perennial tree reaching a height of
between 15-25 m and about 9 m in width of its symmetrical canopy (Edward
and Dennis, 1964). They have shiny deciduous, obovate green leaves that
are arranged in close spirals and turn red or copper gold before falling
(Exell, 1954). The greenish yellow leaves are clustered in axillary spikes,
small and inconspicuous. It usually commences flowering within 2-3 years
of out planting but this may vary with site and genotype (Morton, 1985).
The fruits which consist of the epicarp, fleshy mesocarp, stony mesocarp
and kernel are ovoid in shape, laterally compressed with various sizes
and colours at maturity (Thompson and Evans, 2006).
T. catappa is of economic importance as the trunk
is used for furniture and cabinetwork. The medicinal uses of the leaves
in the treatment of liver-related diseases, sickle cell disorders, cancer
and anaemia have been reported in India, Brazil, Taiwan and Mexico (Sen
et al., 1987). In Australia and India the trees are planted
for soil conservation, coastal protection and beach stabilization (Maximo
and Lanting, 1983). Despite the increasing economic importance of this
tree, very little is known about the germplasm that exists in Nigeria
and the genetic relationships between them. Population studies in T.
catappa have suggested high variation in fruit size, fruit colour
and leaf characteristics (Sen et al., 1987; Lepfosky, 1992). In
Nigeria, the tree exists in major cities, towns and villages in Southern
Nigeria as an ornamental or shade tree. The fruit, leaves and tree bark
are used in some communities as food or herbs.
The objectives of this study was to therefore describe
the relationship among the populations using morphological traits and
to classify the trees into groups based on morphological traits. This
method has been found useful in a number of tree crops such as olives,
cashew and coconut (Samal et al., 2003; Arunachalam et al.,
2005;Taamalli et al., 2006).
MATERIALS AND METHODS
Forty trees were randomly selected from two locations
in the Lagos area of South Western Nigeria. Data on morphological characters
such as leaf length and width; petiole length; fruit length and width;
seed length and width; mesocarp, kernel and shell widths and spikelet
number were recorded during the fruiting season in March-April 2006. Microscopic
studies on the leaves to determine stomata and epidermal lengths and breadths
on both abaxial and adaxial surfaces were also recorded. In all the observations,
twenty measurements per tree for all characters being considered were
measured. Length and width measurements were taken using the meter rule,
while weights were determined using a weighing balance.
Nitric acid solution was used to separate the epidermal
layers which were subsequently stained with safaranin. Measurements for
the stomata and epidermis were taken using the stage and ocular micrometer
on a calibrated light microscope. Crude protein, carbohydrate, fat and
fibre were determined in % using the method outlined by Association of
Official Analytical Chemists (AOAC, 1984). Crude fat was obtained by exhaustively
extracting 3.0 g of the dry mesocarp in a soxhlet apparatus using chloroform
as the extractant. Qualitative traits such as leaf apex, base, shape and
margins; stomata venation and inflorescence types were determined according
to Stace (1965). Ripe fruit and inflorescence colour and leaf texture
were also determined.
The means, range, standard deviation and coefficient
of variation (CV) were calculated. Correlation to determine the relationship
among the characters was performed using SPSS 11.0 version. Cluster analysis
was carried out on similarity matrix using UPGMA (unweighted pair group
method using arithmetic average) in NYTSYS-PC version 2.02 programme (Rohlf,
Results showed that there was a wide variation in most of the characters
examined. Leaf length ranged from 8.58 to 17.30 cm with a mean value of
14.27 cm and coefficient of variation of 13.29% Table 1.
Stomatal number on the abaxial surface showed less variation when compared
with the number on the adaxial surfaces. Fruit weight with a coefficient
of variation of 27.93% ranged from 23.8 g to a maximum of 72.68 g. There
were also variations in the nutritional composition of the fruits with
percentage protein and carbohydrate having a range of 1.18-6.25 and 2.19-7.50%,
respectively. The variation showed that no two trees had the highest or
lowest value consistently for the quantitative characters determined.
Qualitative characters showed that leaves were simple with entire margins
and reticulate venation in all trees. Inflorescence was green of raceme
type while stomata type was anisocytic. However, there were observable
differences in ripe fruit colour which was either a shade of green, yellow
or purple, with 30% of the ripe fruits being yellow and yellowish green,
respectively. Leaf apices, shapes, bases and texture also showed variation
amongst the trees sampled.
Correlations were used to indicate the linear relationships among the
traits. The correlations were significantly correlated when the R-value
is greater than or equal to an absolute value of 0.381 at a probability
of 0.05. Based on these the following characters had significant positive
correlations leaf length and leaf width; wet mesocarp weight with plant
height, fruit length and fruit breadth; fruit length and fruit width with
fruit weight and % protein with % fibre (Table 2). Most
of the negative correlations were not significant.
Range of variation
in quantitative characters of T. catappa
SD = Standard
Deviation, CV = Coefficient of variation, ab = Abaxial, ad = Adaxial
||Correlation matrix of selected quantitative
0.05 level of probability, LL = Leaf Length, LB = Leaf width,
PL = Petiole Length, FL = Fruit Length, FW = Fruit Width, SL =
Seed Length, SW = Seed Width, FW = Fresh fruit weight, DSHW =
Dry shell weight, DSW = Dry Seed Weight, C (%) = Carbohydrate
(%), O (%) = Protein (%), F (%) = Fibre (%), O = Oil (%)
||Dendrogram showing 4 major clusters
in 40 Terminalia catappa trees
for some selected characters in 40 T. catappa
Results obtained from the cluster analysis as shown by the dendogram
which is based on similarity coefficient showed that the trees were divided
into four main clusters (Fig. 1). Cluster No. 1, 2 and
4 had 21, 8 and 7 trees, respectively and these trees were from the two
locations where the trees were sourced. Cluster No. 3 had 4 trees from
the same location. Trees in cluster No. 1 and 2 had intermediate plant
architecture as measured by the leaf and petiole characteristics (Table
3). Their fruits were of medium size generally between 40-48 g in
size. The four trees in cluster No. 3 had the highest values for quite
a number of characters such as leaf length and breadth, fruit weight (a
mean value of 51.7 g), dry shell and seed weights and percentage carbohydrate,
protein, oil and fibre. Trees in cluster No. 4 were represented by those
that generally had small plant architecture and fruit characteristics.
With the exception of reports on the variation in fruit
characteristics in T. catappa from Australia (Lepofsky, 1992; Walter
and Sam, 1993) detailed reports on variability studies and genetic relationships
within this species is lacking. This is because research on the crop is
virtually non-existent, it may be because it is a tree crop, even though
it is gaining importance as a medicinal crop and as a forest tree with
varied uses. Grouping of the trees from the two locations by cluster analysis
would be of practical use to both scientists and nursery farmers as representative
trees from each cluster may be selected for use in an improvement programme.
The trees in this study were grouped on the basis of
morphological characters into four clusters based mainly on leaf and fruit
sizes rather than the location of collection. Tree crops may be affected
by effect of environmental factors and this may limit the use of morphological/agronomic
characters especially since they tend to carry over the effect of climatic
factor in one year to other years (Oboh and Fakorede, 1999). However,
it has been shown in olives which is also a tree crop that this is not
a limitation as grouping based on cluster analysis showed that agronomic/morphological
characters had good repeatability with result from molecular markers such
as RAPD (Samal et al., 2003).
This study however may be best described as a preliminary
study as it considers only 40 trees from two locations in South Western
Nigeria. Nevertheless, it has succeeded in establishing that using quantitative
and qualitative characters in this tree T. catappa genetic diversity
is present which can be further exploited in improvement programmes.
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