Agro-morphological, nutritional and genetic diversity analyses of Bambara groundnut (vigna subterranea (L.) Verdc)
Hlanga, Nokuthula Cherry.
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Bambara groundnut (Vigna subterranea (L.) Verdc) is a legume crop with potential to address food insecurity in sub-Sahara Africa. However, a lack of agronomic, genetic and nutritional information on the crop hinders its full potential utilization. Nineteen Bambara groundnut lines were evaluated in the field in 2017 and 2018 at two sites. The lines showed significant differences (P<0.05) for all the measured traits. Lines such as IITA686, Cream and Uniswa Red-R were found to have superior performance for multiple traits such as number of seeds per plant, seed mass per plant, plant height and mid-leaf width. The genetic variation among the Bambara groundnut lines was assessed using 20 polymorphic SSR markers The markers exhibited an average polymorphic information content (PIC) of 0.57 and the observed heterozygosity was 0.58, showing that the lines exhibited a considerable level of outcrossing. The lines were clustered into three groups based on the principal coordinate analysis. The highest genetic distance was 0.60 between Tiganecuru and S19. Lines such as IITA686, Cream and Uniswa Red-R that had good performance for multiple agronomic traits occurred within a genetic distance of 0.40 making them genetically divergent enough for generating crosses for Bambara groundnut improvement. The ash, fat, proteins, starch, calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), phosphorous (P), sodium (Na), copper (Cu), and zinc (Zn), acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents were determined in the Bambara groundnut lines using combustion and chemical digestion procedures. The nutritional content varied significantly (p<0.05) among the lines with lines S19, Gresik, Pong-Br-UNK, Pong-Cr exhibiting high means for starch and protein content ranging from 11.05 to 11.94%. Genotypes Mix, Pong-Br-UNK, 42-1, Gresik, Uniswa Red-R, and Brown were clustered together based on their high starch, Na, Ca, fat, and Mn contents. The negative correlations among some of the nutritional content would be a challenge for simultaneous selection to breed nutritious Bambara groundnut lines. The lines with high content for multiple nutritional elements such as 211-57, Pong- Br-EN and Uniswa Red-G were recommended for production. It was imperative to determine interrelations among agronomic traits and nutritional content with seed mass for indirect selection. Among the agronomic traits, number of seeds (NS r=0.58, p<0.01), number of healthy seeds (NHS, r=0.51, p<0.05) and plant height (PH, r=0.45, p<0.05) exhibited the strongest associations with seed mass. These traits had NS, NHS and PH high direct effects on seed mass of 2.04, 1.72 and 0.60, respectively. These findings provide a means to facilitate indirect selection of genotypes with high seed mass productivity via proxy. Overall, the study found significant agro-morphological and genetic variation among the Bambara groundnut lines, which would be a prerequisite for Bambara groundnut improvement. The superior lines identified for multiple traits and genetic divergence were IITA686, Cream and Uniswa Red-R. Key words: Agro-morphology; Bambara groundnut; Genetic variation; Seed quality