Morpho-Physiological Traits Linked to Water Stress Responses Among Sorghum bicolor (L.) Moench Varieties: A Field Study in Kenya

Abstract

Sorghum is a drought-tolerant crop with the potential to alleviate food insecurity in arid and semiarid regions of the world. This study aimed to identify the morphological and physiological traits that are associated with drought tolerance in three sorghum varieties grown in Kenya: the Makueni (MKL) landrace, Gadam (GD) open-pollinated variety and the IESH 22012 hybrid. A randomised split-plot design was employed, comprising three sorghum varieties and two moisture input levels (control and drought), replicated four times during the 2021 and 2022 crop seasons. Rainout shelters were utilised to impose drought conditions. Drought stress significantly influenced all traits, and the three varieties exhibited distinct responses. Based on grain yield, IESH demonstrated superior potential, followed by GD, while MKL ranked third under drought conditions. Across all varieties, drought led to reductions in transpiration rates (MKL: 40%, GD: 46% and IESH: 20%) and stomatal conductance (MKL: 31%, GD: 39% and IESH: 21%). Assimilation rates were reduced by 51%, 38% and 23% for GD, MKL and IESH, respectively. Similarly, drought decreased biomass by 46% for GD, 30% for IESH and 26% for MKL. Grain yields were also reduced by 51% for GD, 37% for MKL and 33% for IESH. GD exhibited a more pronounced yield decline than IESH in response to water shortages, indicating a greater sensitivity to reduced water supply. Overall, the results indicate that sorghum responds to drought by reducing plant size, biomass accumulation, leaf area, transpiration rate and stomatal conductance. However, the phenotypic drought response, including the allocation of reduced carbon and biomass formation among plant organs, is specific to each variety. The IESH variety was identified as more suitable for both drought-stress and nonstress environments, considering its favourable morphological, physiological and yield-related traits, as well as its sensitivity and tolerance indices.