PHYSICOCHEMICAL PROPERTIES AND JUVENILE PHENOLOGY OF AFRICAN WALNUT (PLUKENETIA CONOPHORUM MUELL ARG) ACCESSIONS FROM SOUTHEASTERN NIGERIA

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.

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 non- essential 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.

INTRODUCTION

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,

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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