Drought-tolerant sesame mutant lines assessed by physiological traits and stress indices under water deficit conditions

Climate change and water scarcity are the most important factors that affect crop production in dry areas. Sesame (Sesamum indicum L.) is a very ancient oilseed crop cultivated in arid and semi-arid regions and therefore its productivity is limited under drought conditions, which makes the selection and development of droughttolerant cultivars imperative. This study aims to evaluate the responses to drought stress of eleven M4 sesame mutants, in addition to their two wild-type parents, cultivated in two contrasting environments. Drought stress was applied, under field conditions, by reducing the amount of irrigation water supplied by half, compared to the control. Physiological traits and various drought indices were measured/calculated. All data were subjected to analysis of variance and unweighted pair group method with arithmetic mean (UPGMA) to classify genotypes as drought sensitive or drought tolerant. Significant variations among genotypes were observed in their reactions to water regimes and environments. Overall, under water stress, proline content and stomatal resistance significantly increased, while chlorophyll content, seed yield, and relative water content significantly decreased in stressed plants. Drought indices revealed substantial differences among genotypes, with tolerant ones showing the best scores. Furthermore, correlation analysis demonstrated significant associations between physiological traits and drought indices. In light of all the traits/indices investigated, the mutant 'US1-2' was found to be very drought-sensitive, although it performed best under full-irrigation conditions. In contrast, the mutant lines 'ML237' and 'ML2-37' proved to be highly drought-tolerant and, therefore, they can be handled as an elite germplasm for the development of resilient cultivars adapted to arid and semi-arid regions where irrigation water is a limiting factor. This work constitutes a significant contribution to research on sesame drought tolerance and offers promising prospects for this crop in the context of global climate change.