Morphological characterization and genetic diversity assessment of African Yam Bean (Sphenostylis stenocarpa (Hochst. Ex A. Rich.) accessions in Ethiopia.

Abstract

African Yam Bean (Sphenostylis stenocarpa (Hochst. Ex A. Rich.) Harms) (AYB) is an underutilized tropical leguminous plant which produces edible seed grain, leaf spinach and tubers. Africa yam bean possess a greater potential in alleviating food and nutritional insecurities facing Africa in the wake of climate change and its associated effects. However, limited research emphasis has been placed on the crop to establish the extent and magnitude of genetic diversity among the collected AYB accessions. Morphological characterization and genetic diversity analysis study was conducted on 169 AYB accessions sourced from the International Institute of Tropical Agriculture (IITA), Nigeria. The main objective of the study was to determine the extent of genetic diversity and assess trait inter-relationships among AYB accessions for utilization in future breeding and germplasm conservation. The field experimental trial was conducted during the 2018/19 agricultural season at the Ethiopian Institute of Agricultural Research (EIAR), Oromia Region, Ethiopia. The study was fitted into a 13 x 13 Alpha lattice design (0.1) with two replications. The morphological characterization experiment was conducted following the method of the IITA Reference Guide for AYB. Data was collected on quantitative and qualitative traits; and analyzed using R Studio Version 3.6.1, DARwin Version 6 and IBM SPSS Statistics Version 25 statistical packages. Analysis of Variance (ANOVA) indicated significant variations (p≤0.05) in AYB accessions for some morphological traits evaluated. The significant variations were observed on parameters; seed yield per plant, petiole length, terminal leaf length, days to 50% flowering and number of primary branches. African yam bean accessions with least and highest seed yield per plant recorded means of 22 g and 54 g respectively with accession TSs 357 as the highest yielder. Similarly, 100 seed weight varied widely across the studied accessions and recorded a mean value of 21.36 g. Seed grain yield per plant was highly correlated to terminal leaf length and width; and plant part pigmentation parameters. iii Furthermore, 100 Seed Weight was significantly correlated to terminal leaf length (r = 0.441), leaf colour (r = 0.72) and seed yield per plant (r = 0.862). The study further revealed that, there was a negative correlation between seed yield per plant and days to 50% flowering (r = -1.42). Principal Component Analysis (PCA) was performed to ascertain the main components explaining the total variation observed. The first five components accounted for 78.98% of total variation among accessions. The differential trait loadings on the first two PCs showed that, the delineation of diversity among accessions emanated from seed yield per plant, 100 seed weight, main stem pigmentation, primary branches pigmentation and petiole pigmentation parameters. Hierarchical clustering analysis based on seed grain parameters grouped the tested accessions into three major clusters (at 100% similarity level) and five sub-clusters (at 50 % level of similarity). The data was further classified into four sections using the Unweighted Neighbour-Joining method according to identified characters loading to the first five principal components. The present research proved the existence of significant genetic diversity and trait association among the studied accessions of AYB. The observed variation and inter-character association should be exploited for AYB genetic advancement and conservation.