Evaluating drought tolerance of four commercially grown potato varieties in Southern Africa under glasshouse conditions

Potato ( Solanum tuberosum L. ) is a cool-season crop highly sensitive to abiotic stresses, with drought emerging as one of the most significant yield-limiting factors. A glasshouse trial was conducted to evaluate the drought response of four commercially grown potato cultivars in southern Africa - BP1, Up-to-Date, Hertha and Mondial - under four water regimes: control (80% field water capacity), mild (60% field water capacity), severe (40% field water capacity), and extreme stress (30% field water capacity). Morpho-physiological traits, biomass, and yield components were measured, alongside stress tolerance indices (Stress Tolerance Trait Index, Stress Tolerance Index, Yield Index, Relative Stress Index, and Tolerance Index). The experiment was carried out with a completely randomised design, replicated eight times per variety. The results indicated that reduced water availability significantly affected all measured traits. The most severe reductions occurred under the 30% field water capacity treatment, where tuber number and tuber weight were reduced by approximately 58.99% and 34.72%, respectively, compared to the control treatment. Among the four cultivars, BP1 exhibited the highest drought tolerance (Stress Tolerance Trait Index = 72.03%), followed by Mondial, Hertha, and Up-to-Date. These findings provide critical insights into varietal performance under water stress and support the selection of drought-resilient potato genotypes for cultivation in southern Africa.