Physicochemical Properties and Juvenile Phenology of African Walnut (Plukenetia Conophorum Muell Arg) Accessions from South-Eastern 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.