Cowpea landraces in northern Nigeria: overview of seedling drought tolerance

The success of a breeding program largely depends on the presence of sufficient genetic diversity in crops to provide an avenue for selection of desirable genotypes for utilization in crop improvement. The "wooden box technique" was adopted to evaluate drought tolerance in cowpea landraces cultivated by small-scale farmers in Northern Nigeria. The technique enables high throughput screening of cowpea genotypes for their agro-morphological variability to drought at seedling stage. Therefore, this study aimed to provide data on cowpea landrace responses to drought at the seedling stage, with the objective of helping mitigate crop loss in a region predominantly characterized by early-season drought events. Here, 420 cowpea genotypes (307 landraces, 113 IITA accessions) were screened for tolerance to seedling drought. Time course analysis of growth and agronomic traits revealed gradual cessation of growth as drought stress intensified as evidenced by reduction in trifoliate, increased leaf senescence and stem wilting. Multivariate analysis using principal component (PC) analysis and k-mean clustering identified 3 major clusters where PC1 and PC2 explained 46.7% of the variability in response to drought stress. The biplot analysis showed that plant height, stem greenness and trifoliate contributed positively to PC1 while leaf senescence score was negatively related to the clustering on this axis. The comprehensive data analysis pipeline enabled the identification of the relationship between agronomic and stay-green parameters which provided the understanding of traits that were useful during the selection of landraces under drought stress at the seedling stage. Additionally, our results identified potentially tolerant landraces for drought prone ecologies.