ABSTRACT
African walnut (Plukenetia conophorum Muell Arg) is a member of the family
Euphorbiaceae. It is cultivated principally for the nuts which are eaten raw or served as
snacks after roasting or boiling. P. conophorum serves many nutritional and medicinal
purposes as well as good source of rural income. Despite the potentials of this plant, its
existence is threatened by deforestation, urbanization and similar activities. The present study
was designed in an attempt to salvage this useful plant from extinction and provide basis for
its conservation. Four accessions of P. Conophorum were collected from Abia, Anambra,
Enugu and Rivers states, southeastern Nigeria. The objectives of the research were to
evaluate the effects of three manure rates on juvenile growth stage of the accessions;
determine the amino acid profile of the kernels and investigate possible bio-diversity among
the accessions with respect to the seed physical traits and proximate components. Four
specific experiments were conducted to achieve the set objectives. Seed physical traits (edible
portion, pulp weight, seed volume, seed weight, pulp (kernel) weight, seed circumference and
seed coat thickness) were measured. Standard laboratory procedures were employed in
determining the proximate composition (moisture content, ash, fat, crude protein, fibre and
carbohydrates) and amino acids profile of raw and boiled kernels. A pot experiment was set
up to evaluate the seedling emergence and growth responses to three level of pig manure
applications (0, 5. and 10t/ha). Data were collected on days to seedling emergence,
emergence percentage, vine length, vine base girth, number of leaves per plant, number of
branches, root volume and dry matter yield and partitioning to the leaves, stem and roots.
All the data were subjected to Analyses of Variance (ANOVA) following the procedures
outlined for completely randomized design (CRD). Significant treatment means were
separated with the aid of F-LSD at 5% probability level. All statistical analysis were done
using Genstat 7.1 version 2003 software. Results indicated that all the seed physical traits
showed significant (P < 0.05) variation across the four locations (states). Seeds from Enugu
(74.08%) had the highest edible proportion followed by Abia (70.68%) and Rivers (66.65%).
Anambra accession had the highest seed and pulp weight followed by Abia, Enugu and
Rivers, respectively. Seed coat thickness was higher in accessions from Abia and Rivers
States compared to others. The nutritional quality assessment revealed that ash, fat and
moisture varied significantly (P<0.05) among the different accessions while carbohydrates,
fibre and protein contents of the seeds did not differ across the locations. The moisture and
fibre contents showed significant (P< 0.05) differences in the boiled and fresh seeds. Fibre
content was higher in the boiled seeds, whereas the fresh seeds had higher moisture content.
x
The ash, carbohydrate, fat and protein contents were not influenced by processing. All the
proximate contents of the seeds across locations did not differ in their response to interaction
of location and processing. Location showed no significant effect on iso-leucine, leucine,
phenylamine and tryptophane contents of the seeds. Seeds collected from Rivers, Enugu and
Anambra States gave significantly (P< 0.05) higher histidine than those from Abia. Abia
accession has the highest lysine content compared with those from other locations. Enugu and
Rivers accessions gave significantly (P< 0.05) higher methionine than those from Anambra
and Abia State. Enugu and Abia accessions recorded higher threonine content than Anambra
and Rivers accession. The effect of processing on essential amino acids showed that the
histidine, isoleucine, leucine, lysine, methionine, phenylamine, valine and threonine contents
of the seeds were not influenced by processing. Except for tryptophane, all the other essential
amino acids were found to be higher in the fresh seeds. The effect of location on nonessential
amino acids showed that alanine, arginine, asparagine, glutamine and glutamic acid
were significantly influenced by location while aspartic acid, glycine, proline, serine,
trimethlisine and tyrosine did not vary among the locations. Seeds collected from Abia State
gave significantly higher alanine and arginine contents than those from other locations.
Asparagine content was significantly (P < 0.05) higher in seeds from Rivers and Abia than
those from Anambra and Enugu. Glutamine acid content of seeds from Enugu and Anambra
was higher than those from Abia and Rivers. The effect of processing on the non-essential
amino acid components showed that glutamine, glutamic acid and trimethlisine contents of
the seeds varied significantly (P <0.05) with processing. Glutamic acid and trimethlisine
contents were higher in the fresh seeds whereas glutamine was higher in the boiled seeds.
Alanine, arginine, asparagine, aspartic acid, glycine, proline, serine and tyrosine did not differ
in their response to processing. Field growth performance evaluation indicated that plant
height, stem girth, number of branches and vine length were all significantly (P < 0.05)
improved with increasing manure rate. The 10 tonnes manure rate partitioned the greatest
portion of the biomass to the shoot in all the accessions.
TABLE OF CONTENTS
Title page – – – – — – – – – i
Dedication – – – – – – – – – – ii
Certification – – – – – – – – – – iii
Acknowledgments – – – – – – – – – iv
Table of contents – – — – – – – – – v
List of tables – – – – – – – – – – vi
List of figures – – – – – – – – – viii
Abstract — – – – – – – – – – ix
INTRODUCTION – – – – – – – – 1
LITERATURE REVIEW – – – – – – – – 3
MATERIALS AND METHODS – – – – – – – 6
Materials – – – – – – – – – – 6
Methods – – – – – – – – – – 6
Statistical Analysis – – – – – – – – – 14
RESULTS – – – – – – — – – – 15
Discussion — – – – – – – – – – 47
Conclusion and recommendation – – – – – – – 52
REFERENCES – – — — – – – – – 53
CHAPTER ONE
African Walnut (Plukenetia conophorum Muell Arg) is a member of the family
Euphorbiaceae. It has been described as a semi-wild plant found naturally in the wild
(Okigbo, 1977), or may be extensively encountered in rural dwelling and in farmlands where
they are protected. Walnut (P. conophorum) is of African origin (Nwosu, 1979); hence
“African” mostly attached to its common name. It is cultivated principally for the fruits (nuts)
which is edible and are eaten alone or served as snacks with kola nut when boiled. Egharevba
et al., 2005 also reported that the fruit is known in other African countries like Gabon, Sierra
Leone, Cameroon, Madagascar and Central African Republic, where it provides income to
the rural people consequently improving their economy and nutrition.
P. conophorum is a twining vine, and rarely sprawling herb, found in tropical wet and
seasonally dry forest regions (Gillespie, 1993). The seeds are available in June-September
when other fruits are scarce, throughout the southern states of Nigeria (Egharevba et al.,
2005). As documented by Irvine (1990), the plant which is a perennial is also a climber
requiring support of woody sticks to climb, grow and survive. The plant starts flowering
between eighteen to twenty four months after planting. The importance of P. conophorum as
an indigenous fruit climber is enormous as it is a multi-purpose crop. In most homes in
southeastern Nigeria the fruits provide income to rural people, thereby improving their
economy. The roots, leaves and seeds are said to have medicinal values (Johansen, 1950).
The high nutrient potentials of the nut has been reported in literatures (Oke and Funsho,
1975; Ogunsua and Adebona, 1983). The plant also provides a microclimate within the forest
as its branches spread on the canopy cover of forest trees (Egharevba et al., 2005).
The fruits are oil-bearing yielding 48-60% of light golden coloured oil which is similar to
linseed oil. The oil is composed of 64% linolenic acid, 15% palmitic acid and stearic acids,
11% oleic acid and 10% linoleic acid. The oil is also known as conophor oil, and is useful in
paint or varnish industry. It is edible and could be used in food preparations (Burkill, 1984).
There is also a report that the cake left after extraction of the oil contains 45% protein, and
has local uses for food and is obviously a good source of protein. It can be fed to livestock
(Burkill, 1984).
Plukenetia conophorum is one of the non-wood forest products, which are essentially part of
the forest products. According to Osemeobo and Ujo (1999), these non-wood forest products
provide a safety net for most rural dwellers in many third world countries including Nigeria,
2
where they contribute immensely in food security. United Nations (2002) and National
Planning Commission (2004) reported that these harvestable forest products accounts for
90% of rural dwellers livelihood and economic survival. However, despite the potentials of P.
conophorum, its continuous existence among other forest products of Nigeria is threatened
(UN, 2002) due to deforestation, urbanization and other similar activities.
Increases in production and availability of African walnut just like other semi-wild
indigenous species, can only be possible when suitable production practices are exploited
coupled with enough biochemical and biophysical knowledge. At present, there is paucity of
information on the regeneration and perpetuation of this very important plant. The walnut is
still in the wild. There is no evidence of efforts to fully domesticate this useful plant. The
high rate of forest destruction affects their habitat. The plant could face possible extinction in
the very near future. To salvage this useful plant from extinction and provide basis for its
conservation, the present study was undertaken. With increased recent interest in the
exploitation, conservation and domestication of less common forest products, it is important
to examine the African walnut in order to ascertain its full usefulness. The objectives of this
research are:
1) Evaluation of the effects of three manure rates on early growth stages of four
accessions of African walnut;
2) Determination of the amino acid profile of kernels from four different accessions; and
3) Investigation of possible bio-diversity among accessions collected from different
locations (states) of southeastern Nigeria, with respect to the seed physical traits and
proximate components.
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