Root morphology for growth and physiology of drought and heat tolerance in chickpea (Cicer arietinum L., Fabaceae)

Adoteye, Grace

Root morphology for growth and physiology of drought and heat tolerance in chickpea (Cicer arietinum L., Fabaceae)

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

Chickpea (Cicer arietinum L.) is an important legume crop valued for its nutritional quality and affordability, yet its production is increasingly threatened by drought and heat stress, particularly in arid and semi-arid regions where it is predominantly cultivated during the post- rainy season. Climate change is expected to intensify the frequency and severity of these stresses, underscoring the need to understand adaptive mechanisms that enhance stress resilience. While research on the individual effects of drought and heat stress in chickpea is relatively well established, their combined impact remains poorly understood. Moreover, most studies have focused on above-ground traits, leaving critical root system adaptations largely unexplored. This study therefore aimed to characterise chickpea root morphology and its responses to drought and heat stress - individually and in combination - as well as to low- nutrient stress and the combined effects of low nutrients and drought. Four genotypes were used, namely: ACC#7, ICCV 00108, ICCV 07113, and ACC#8. These genotypes differ in their stress responses, with ICCV 07113 and ACC#8 known to be heat- and drought-susceptible, ACC#7 and ICCV 00108 exhibiting drought tolerance, and ACC#7 additionally showing heat tolerance. Three complementary experiments were conducted. In Chapter Two, a controlled environment study examined the physiological responses and root trait adaptations of three genotypes (ICCV 07113, ACC#8, and ICCV 00108) under individual and combined drought and heat stress. Drought promoted the development of deeper and more extensive root systems, whereas heat, alone or combined with drought, significantly suppressed root growth. The combined stress resulted in the most pronounced reductions in both root development and physiological performance. Among the three genotypes, ACC#8 exhibited superior stress tolerance both individual and combined stresses by maintaining pigment stability and biomass, while ICCV 07113 was the most sensitive. Root system research in natural field conditions has long been considered the ‘step-child of science' due to its laborious and time-consuming methods. To help bridge this knowledge gap, Chapter Three assessed root performance of four genotypes (ACC#7, ICCV 07113, ACC#8, and ICCV 00108) under contrasting field environments differing in temperature and rainfall. High-temperature conditions reduced biomass and most root traits, yet genotypes with greater root length, surface area, and volume exhibited enhanced physiological functioning, highlighting the role of robust root systems in mitigating heat-related declines in photosynthetic activity. ICCV 07113 possessed the most extensive root system and highest physiological resilience under field heat stress, whereas ACC#8 showed the weakest performance, demonstrating genotype-by-environment interactions and differing rankings between field and controlled conditions. Plants growing in nutrient-rich soils typically develop a low root-to-shoot ratio, increasing their vulnerability to drought at later growth stages. Recognizing the importance of a higher root-to- shoot ratio in enhancing drought resilience, Chapter Four investigated whether plants that develop a larger root system under low-nutrient conditions gain an adaptive advantage when subsequently exposed to drought. Two genotypes (ICCV 07113 and ICCV 00108) were evaluated, although genotypic differences were minimal. Plants grown under low-nutrient conditions developed higher root-to-shoot ratios and greater root length, surface area, and volume. When later subjected to drought, these plants outperformed drought-stressed plants originating from nutrient-rich soils, exhibiting greater water retention and improved yield, although biomass, plant water status (stomatal conductance and relative water content), and absolute yield remained lower than in non-stressed controls. Taken together, the findings from the three data chapters advance our understanding of plant responses to climate-induced stress and provide a foundation for breeding programmes to enhance chickpea resilience to abiotic stress by integrating root traits, chlorophyll stability, and water conservation as key selection criteria.