Characterisation of selected cowpea accessions using morphological, biochemical and molecular markers and development of dual purpose f1 cowpea genotypes

Abstract

Cowpea is versatile dual-purpose crop that offers many human health benefits. However, grain and leaf yield remain low, which is often associated with the use of unimproved local varieties, biotic and abiotic stresses. The dual-purpose cowpea varieties have a higher water requirement compared to grain varieties. Therefore, there is need to develop dual purpose cowpea varieties with low water requirements so as to take advantage of drought tolerance trait found in cowpea plants. The objective of this study was to characterize a selected set of germplasm using morphological, molecular and biomarkers, develop dual purpose F1 cowpea genotypes, and to identify a set of candidate traits. This will help to identify trait variation of characters of interest and breed for diverse traits. This study used a collection of 50 cowpea accessions. In addition, a subset of six accessions was used for the production of F1 genotypes. The six accessions were crossed using a partial diallel design to produce 15 F1 hybrids. A Randomised Complete Block Design was used to evaluate the 50 accessions, 15 F1 and their parents in the field under imposed water stress and well water conditions with three replications and over two cultivations. Water stress was imposed at 28 days after sowing, where watering was done at the rate of 100 ml per plant per accession after every five days until maturity. Data was collected on growth and yield variables. At 35 days after sowing, leaf samples were harvested for metabolite profiling. About 20 accessions were genotyped using 12 SSR markers. Quantitative data was subjected to analysis of variance using SAS version 9.4 and significant means separated using the Least Significant Difference at α = 0.05. Data from SSR markers was subjected to Analysis of Molecular Variance to identify genetic variation among accessions and Euclidean distances was used for cluster analysis. The study showed that there was significant (p < 0.05) variation in all growth and yield variables amongst the genotypes studied. Several genotypes including NA101, NA3, NA11, MA24 and MA2 were identified to be drought tolerant and also potential genotypes for grain production. The allelic range for the genotypes that were studied was from 1 to 11 alleles which showed a wide variation among markers. The SSR markers revealed considerable genetic diversity in the cowpea population studied. Markers VM70, VM31, and VM68 were the most informative, showing high numbers of alleles, gene diversity, and PIC values. Two markers (VM61 and VM19) were monomorphic in this population. The Structure results indicate the high morphological variation observed among the accessions studied. There is significant variation in quercetin and myricetin content among the genotypes. Genotypes such as MA67 X NA11 and NA60 are particularly represented extreme cases in the concentration of these flavonoids. he results suggest potential for developing cowpea varieties with improved yield while maintaining moderate levels of beneficial flavonoids. The accumulation of the flavonoids was observed as a part of the plant’s adaptive response to mitigate the adverse effects of drought stress. Grain yield was strongly influenced by traits such as number of seeds per pod, number of pods per plant, number of branches per plant, terminal leaf length and width, plant height and biomass yieldMA67 X NA60, NA20 X NA60, MA50 X MA56 and MA50 X NA60 were identified as potential genotypes for grain production. F1 hybrids such as MA67 X NA60, NA20 X NA60 and MA50 X MA67 are potential dual-purpose genotypes due to their high yield potential for both grain and vegetable production. Genotypes MA50 X NA60 and KK06 X MA67 hybrids exhibit better drought resistance demonstrating the potential likely combination of favourable traits from parents. Several genotypes, particularly MA67 X NA60 and NA20 X NA60, demonstrated strong heterotic potential for both yield and biomass. The wide variation in heterosis across the F1 hybrids suggests that specific combining abilities play a crucial role in determining hybrid performance. Some crosses show positive heterosis for both yield and biomass while others show contrasting responses, indicating the need for balanced selection in breeding programs. Those genotypes that show a high level of diversity as discovered in this study should be harnessed to improve accessions that are less favoured. The characterized cowpea accessions should be utilised for breeding programs aimed at developing improved varieties with desirable traits.