Assessment of Drought Tolerance Indices of Sorghum (Sorghum bicolor L.) under Different Water Regimes

Abstract

Drought stress is one of the major environmental factors limiting sorghum productivity, particularly in semi-arid and drought-prone regions where water availability is often inadequate for optimum crop growth and yield. Sorghum (Sorghum bicolor (L.) Moench), an important cereal crop cultivated for food, feed and industrial purposes, exhibits varying levels of tolerance to moisture stress among genotypes. This study was therefore conducted in two trials to evaluate the drought tolerance of six sorghum varieties using yield-based drought tolerance indices under differential watering regimes. The experiment was conducted in a screenhouse at the Department of Crop, Soil and Pest Management, Federal University of Technology, Akure, Nigeria, using a 6 × 3 factorial arrangement laid out in a completely randomised design (CRD) with three replications. The treatments consisted of six sorghum varieties (CSR-01, Bida local, SK5912, SAMSORG 14, SAMSORG 17 and SAMSORG 44) and three watering regimes corresponding to 40%, 60% and 100% field capacity. Data collected included grain yield under stress (Ys) and non-stress (Yp) conditions, from which drought tolerance indices, including tolerance index (TOL), mean productivity (MP), geometric mean productivity (GMP), stress susceptibility index (SSI) and stress tolerance index (STI), were computed. The results from both trials revealed significant variation among the sorghum varieties under different watering regimes. Grain yield generally increased with increasing water availability. In Trial 1, Bida local recorded the highest grain yield under stress and non-stress conditions, with Ys and Yp values of 5.62 and 10.02 g plant⁻¹, respectively, whereas CSR-01 recorded the lowest yield values. Similarly, in Trial 2, Bida local maintained the highest Ys value (2.87 g plant⁻¹), while its Yp value was 3.39 g plant⁻¹. Bida local consistently recorded the highest MP, GMP and STI values across both trials, indicating superior drought tolerance and yield stability. SK5912 also demonstrated relatively high drought tolerance and stable yield performance under moisture stress conditions. Correlation analysis revealed strong positive associations between grain yield under stress and MP (r = 0.96), GMP (r = 0.97) and STI (r = 0.94), while grain yield under non-stress conditions showed highly significant positive correlations with MP (r = 0.97), GMP (r = 0.95) and STI (r = 0.99). In contrast, stress susceptibility index (SSI) exhibited negative associations with grain yield and other drought tolerance indices. The study concluded that MP, GMP and STI are reliable indices for identifying drought-tolerant sorghum genotypes. Bida local and SK5912 were identified as the most drought-tolerant and stable varieties across the two trials and are therefore recommended for cultivation in drought-prone environments and for use in sorghum breeding programmes aimed at improving drought tolerance and yield stability.