Phenotypic marker-based diversity analysis of some African yam bean Sphenostylis stenocarpa (Hochst. Ex. A. Rich. Harms) accessions

Abstract

Phenotypic characterization is a preliminary germplasm assessment programme meant to provide primary information on the evaluated genetic resources. Detail from such study becomes a guide to gene banking system. This report on 96 accessions of African yam bean (AYB) is within the 2017 characterization programme for AYB germplasm at the Genetic Resources Centre (GRC), International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. Twenty-three quantitative (vegetative and reproductive) descriptors were employed for a diversity study of the 96 accessions. Significant (P <0.01) variation existed among the accessions for majority of the studied quantitative characters. Stepwise discriminant analysis identified 18 phenotypic traits to be most discriminatory for the 96 AYB accessions. The mean genetic similarity among the accessions was 0.80; the least (0.53) and the highest (0.95) was between TSs53 and TSs83 and TSs5 and TSs22 respectively. The first three principal component axes accounted for 53.4% of the total variation among the 96 accessions. Ward clustering system grouped the 96 accessions into three main clusters of 54, 31 and 11 accessions. Accessions in cluster I attained peduncle initiation and first flowering at 95±0.13 and 119±0.69 days after planting (DAP). Accessions in cluster III reached 50% primary branching at 24±0.13 DAP and had the least seed sizes. Significant intra-cluster variation existed, hence; meaningful selection of accession(s) for further work should be at the sub-cluster or lower similarity level within the main cluster. The present study unveils the phenotypic identity of the 96 accessions and provides a platform for trait-based parental stock selection for genetic improvement of the crop.