Characterisation of underutilised legumes for climate-smart agriculture under water stress.

Abstract

Agriculture in sub-Saharan Africa (SSA) is increasingly threatened by the impacts of climate change, including prolonged droughts, erratic rainfall, and soil degradation, which undermine food production and nutritional security. While climate-smart agriculture (CSA) offers a framework for enhancing resilience, productivity, and sustainability, much of the attention and research investment has been directed toward major staple crops, which often exhibit limited adaptability to dryland conditions. In contrast, underutilised legumes such as Bambara groundnut (Vigna subterranea (L.) Verdc.) present a valuable yet largely untapped opportunity for advancing CSA objectives due to their inherent drought tolerance, adaptability to marginal soils, and rich nutritional profile. Significant knowledge gaps remain regarding key morphological and physiological traits critical for their performance under water-limited environments, hindering their wider adoption, integration into breeding programmes, and inclusion in formal seed systems. This thesis sought to evaluate the potential of underutilised legumes for climate-smart agriculture by focusing on the characterisation of functional traits in Bambara groundnut that support resilience under water stress. The research comprised three interconnected experimental studies. Firstly, root system architecture was phenotyped across multiple Bambara groundnut landraces grown under contrasting moisture regimes. The experiment revealed significant genotypic variation in traits such as root depth, lateral spread, total root length, and root dry mass. These root traits are key indicators of drought avoidance strategies and are crucial for maintaining water uptake and physiological stability in dryland farming systems. Secondly, seed coat morphology was investigated to understand its role in seed performance. The study demonstrated that differences in seed coat thickness, colour, and permeability significantly influence hydration dynamics, solute leakage, and susceptibility to imbibitional injury, thereby impacting germination speed, uniformity, and seedling vigour. Such findings highlight a critical trade-off between seed protection and rapid emergence, with direct implications for varietal screening and seed quality improvement, particularly in environments characterised by erratic rainfall and variable soil moisture. Thirdly, the effects of hydropriming, a simple, low-cost seed enhancement technique, were assessed to determine its potential in improving germination and early seedling establishment under water stress. The results indicated that specific hydropriming durations, notably 36 hours, improved germination uniformity, reduced mean germination time, and enhanced early growth performance in

selected Bambara groundnut landraces, offering a practical strategy for mitigating establishment challenges in moisture-variable environments. Collectively, these three experiments demonstrate how root system architecture, seed coat properties, and seed enhancement techniques interact to influence drought adaptation from germination to early growth. Root traits determine the plant’s capacity to capture and use water efficiently, while seed coat characteristics regulate initial hydration and emergence—both foundational for the crop’s establishment. Hydropriming bridges these physiological mechanisms by preconditioning seeds for uniform germination and stronger seedling development. Together, these findings illustrate an integrated resilience strategy within Bambara groundnut that operates across developmental stages, reinforcing its potential as a model legume for climate-smart agriculture. The research contributes to closing critical knowledge gaps regarding the functional traits underpinning drought resilience and provides actionable insights for breeding programmes, seed system improvement, and policies aimed at repositioning underutilised legumes as strategic assets for sustainable food system transformation in SSA.