VOL. 7, NO. 6, JUNE 2012 ISSN 1990-6145 ARPN Journal of Agricultural and Biological Science © 2006-2012 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 454 INTRA-SPECIFIC VARIABILITY AND DIVERSITY ANALYSIS OF AFRICAN YAM BEAN BY SEED SIZE PARAMETERS Adewale B. D. 1, 2 , Aremu C. O. 3 and Amazue U. E. 4 1 Crop Improvement Division, Cocoa Research Institute of Nigeria, Idi - Ayunre, Ibadan, Nigeria 2 Department of Plant Breeding and Seed Technology, University of Agriculture, Abeokuta, Nigeria 3 Department of Agronomy, Ladoke Akintola University of Technology, Ogbomoso, Nigeria 4 Department of Botany, University of Nigeria, Nsukka, Nigeria Email: d.adewale@gmail.com ABSTRACT Understanding the intra-specific variability within a species is preliminary to any genetic improvement of the crop. Thirty (30) African yam bean (AYB) accessions were tried in four locations in Nigeria. Resultant seed lots from harvest per location and per replication were evaluated in the study. The genetic variability, distance and the clustering of the 30 accessions were based on twelve seed size estimates. Accession and location significantly (P≤0.05) differed with respect to the twelve characters. Among other characters however, the interaction: Accession (Acc.) x Location (Loc.) was not significant for circumference and geometric mean diameter of the seed. The variance proportion due to location alone was significantly (P<0.0001) the highest; ranging from 41.6% to 78.9%. The variance due to accession (11.2 - 33.2%) was significantly (P<0.001) higher than that of Acc. x Loc. (4.8 - 15.4%). The contribution of Acc. x Loc. and the experimental error to the total variation did not differ significantly. The mean Gower genetic distance between the 30 accessions was 0.232. The least (0.036) was between TSs33 and TSs84 and the highest (0.672) existed between TSs9 and TSs86. The 30 accessions grouped in five clusters. TSs104B and TSs69 existed independently in clusters III and IV, respectively. Despite intra-cluster uniformity, some characters significantly (P<0.05) differentiated the four, twenty and four accessions within clusters I, II and V, respectively. The present study on revealing the genetic variability among the 30 accessions, equally presented the platform for selection criteria for seed sizes parameters for AYB. Keywords: African yam bean, seed size estimates, sources of variation, Gower genetic distance. INTRODUCTION The evolving campaign for food diversification is enhancing the realization of the place of the underutilized crop species in the global food system for food security. As remarked by Jaenicke and Pasiecznik (2009), increasing the use of underutilized crops is one of the ways to reduce nutritional, environmental and financial vulnerability in times of change. The importance of the less-used crop species is uncontroversially inevitable in the sustenance of the growing global population. The results of poor attention to underutilized species were critical erosion and extinction of the genetic resources of some crop species. Therefore, a continued research attention on these species may salvage them from imminent loss, enhance their awareness and restore their place in the food system of the populace. African yam bean (Sphenostylis stenocarpa (Hochst Ex. A. Rich) Harms) is in the long list of the highly nutritious underutilized species (Evans and Boulter, 1974) in Africa. The record on the extent of the losses and rescue of its genetic resources in Africa is yet unknown. However, the research attention on the crop in the recent time is encouraging. Among the outstanding remarks on the importance of African yam bean (AYB) includes: cultural link to Africa (Potter and Doyle, 1992), nutritional potentials and status (Nwokolo, 1996; Uguru and Madukaife, 2001; Ekpo, 2006), suitability for wide climatic conditions (Anochili, 1984; Betche et al., 2005), grain yield potentials (Okigbo, 1973; National Academy of Science, 1979), etc. Genetic variation of a quantitative trait is assumed to be controlled by the collective effects of quantitative trait loci (QTLs), epistasis (interaction between QTLs), the environment, and interaction between QTL and environment (Semagn et al., 2010). The contribution of each of these sources of variation is significant to the understanding of the variability of species. Breeding to improve AYB, (like every other crops) depends on understanding the intra-specific variability and pattern of classification of the species for all agronomic characters of importance. Basically, multivariate analysis of a set of genotypes leads to the understanding of the genetic identity, characteristics and potential of such genotypes. Depending on the set of descriptors involved, the outcome of multivariate analysis launches the plant breeders to further improvement strategies on the crop, such as: identification and release of superior cultivars on a short term programme (Chheda and Fatokun, 1982; Ariyo, 1991), selection of parents for various characters for breeding and improvement programmes (Bhatt, 1970; Nassir and Ariyo, 2007), selection of parents for mean generation analysis to understand the gene action for specific characters etc. Metric measurements on the seeds such as length, width, thickness, their ratios and mass of seeds are very important characteristic for seed characterization and evaluation (Omokhafe and Alika, 2004; Tetsuka and Uchino, 2005; Adewale et al., 2010). The existence of wide variability in colour, shape and sizes of AYB seeds