Genetic diversity, drought tolerance, and seed yield among accessions of bambara groundnut (Vigna subterranea (L.) Verdc.)

Bambara Groundnut (BG) is an underutilised legume valued for its protein-rich seeds. However, Seed Yield (SY) of BG is low due to incidences of drought in the major producing areas. Paucity of studies on Genetic Diversity (GD), Drought Tolerance (DT) and SY among a wider group of BG accessions limit proper breeding planning. Information on GD among BG will facilitate the identification of DT accessions with high SY thus, enhancing its productivity under water-stressed conditions. This study was designed to identify DT accessions with high SY, and, assess the genetic diversity among BG accessions. Fifty BG accessions were evaluated in two seasons at Ibadan, Ikenne, and Kano under well-watered and water-stressed conditions. The experimental design was a randomised complete block with three replications. The well-watered plots were irrigated to field capacity during plant growth, while water-stressed plots were irrigated to field capacity, then irrigation stopped two weeks before flowering. Chlorophyll Content (CC) and Relative Water Content (RWC) of leaves were determined using standard methods. Plants were scored for wilting on a scale of 0 (no wilting) to 5 (completely wilted), three weeks after irrigation stopped. Seed weight and related traits of BG were measured and SY determined. Accessions in well-watered plots were genotyped using 5,614 Single Nucleotide Polymorphic (SNP) markers. Polymorphic Information Content (PIC) and heterozygosity were generated using TASSEL. The PIC and heterozygosity were classified as low (<0.25), moderate, (0.26−0.50), and high (>0.50) levels of genetic diversity. Stability analysis for SY was carried out using Genotype and Genotype×Environment (GGE) biplot. Data were analysed using descriptive statistics, Principal Component Analysis, cluster analysis and ANOVA at α0.05. Significant differences were observed among the accessions for CC, RWC, wilting, SY and related traits of BG in the two treatments. Environment and Accession×Environment significantly influenced SY. Seed yield ranged from 17.31 kg ha-1 in Ibadan (water-stressed) to 357.57 kg ha-1 in Ibadan (well-watered). Water-stress reduced CC, RWC, and SY by 5.0, 7.8, and 30.0%, respectively. Wilting scores ranged from 0−1 and 1−5 in well-watered and water-stressed plots, respectively. Accessions: TVSu-2089, TVSu-553 and TVSu-2094 had low wilting scores (1.0) in the water-stressed plots, with SY of 563.60±133.00, 476.8±130.80, and 332.20±124.10 kg ha-1, respectively. The first three principal component axis explained 64.1% of the total variation among Bambara groundnut accessions, which were grouped into three clusters. The PIC and heterozygosity ranged from 0.03 to 0.52 and 0.01−0.47, respectively. Drought tolerant accessions (TVSu-2089, TVSu-553 and TVSu-2094) with high CC, RWC and low wilting scores were in cluster 2, and were found on the average environment coordinate abscissa. The DT accessions had zero projection from the average ordinate environment of GGE biplot. This implies stable and high seed yield under drought condition. Moderate genetic diversity was found among the accessions of Bambara groundnut. Three accessions (TVSu-2089, TVSu-553 and TVSu-2094) were drought-tolerant, producing high and stable seed yield. These accessions could be used as parents in future breeding programmes.