Evaluation of drought tolerance in sesame (Sesamum indicum L.) genotypes using germination traits and indices under drought conditions

Sesame as one of the most important oilseed crops has high industrial, food, and medicinal potentials. Drought stress challenges sesame production, especially at the germination and seedling stages. To screen sesame genotypes for drought tolerance at the germination stage, a factorial experiment was performed in a completely randomized design with 3 replications. The studied factors included 4 drought levels induced by polyethylene glycol (concentrations of 0%, 20%, 25%, and 30%) and 15 sesame genotypes. Based on the results of ANOVA, the effect of genotype, drought, and their interaction on all studied traits including germination rate, germination speed, vigor index 1 and 2, radicle length, plumule length, and seedling fresh and dry weight was significant (P<0.01). Significant reduction (P<0.05) was observed in all levels of stress compared to the control in the studied traits. Germination rate, radicle length, and plumule length (with 10%, 17%, and 18% reduction, respectively) showed less sensitivity to drought stress at weak level (20% concentration), while the most negative effect was obtained for vigor index 2, seedling dry weight and seedling fresh weight (with 52.5%, 47.3%, and 34.4% reduction, respectively). On the other hand, the highest decrease was observed in plumule length, vigor index 1 and 2 (98%, 97%, and 96%, respectively), under severe drought (30% concentration). The calculated drought tolerance indices of each trait were used for principal component analysis and biplot visualization. Thus, genotypes were divided into 5 categories based on tolerance. Dashtestan 2 and Darab 1 genotypes were selected as the most tolerant and Qaem, Yekta, Sudan, and Kerman genotypes were selected as the most sensitive genotypes. The findings of this study can be used in future studies and breeding programs of sesame for drought tolerance.