Introduction: Sesame (Sesamum indicum L.) is an important oilseed crop belonging to the Pedaliaceae family, treasured in different food and cosmetics industries. Sesame as a rich source of protein, carbohydrates, minerals, and various antioxidants, is widely cultivated throughout Africa and Asia. The Sesame plant is well adapted to harsh environments. Adverse environmental conditions, such as drought stress, have severely limited plant growth and reduced plant yield. Some crop management programs have been conducted to develop strategies to mitigate the harmful effects of drought on plant growth, physiology, and yield. To this end, the exogenous application of plant hormones such as abscisic acid (ABA) has been applied to some species. Therefore, this study aimed to investigate the effect of foliar application of different abscisic acid concentrations to improve morphological characteristics, yield components, biomass production, seed yield, and water use efficiency (WUE) of sesame under water-limited conditions.
Materials and Methods: A field experiment with the aim of evaluating the effect of different abscisic acid (ABA) concentrations (0: distilled water application, 10: foliar application of 10 µM ABA; 50: foliar application of 50 µM ABA; 100: foliar application of 100 µM ABA), under different irrigation regimes (normal: 100% field capacity (FC), and water-limited condition: 60% FC) was conducted as at Narju region, Jiroft, Iran, during the growing season of 2022-2023. The experimental design was a randomized block design in a split plot scheme with eight treatments replicated three times. Sesame seeds were prepared from the Agriculture and Natural Resources Research and Education Center of Jiroft and were sown on July 23, 2022. After establishment, the plants were thinned to obtain a final density of 60 plants per 3 m² plot. The plants were treated with ABA at different concentrations two times. Different concentrations of ABA were applied 50 (first time) and 70 days (second time; at the time of stress imposition) after sowing. At the end of the growing season (November 29, 2022), 10 plants were harvested from each plot and various traits including plant height, number of branches, number of mature, immature, and total capsules per plant, number of seeds per plant, 1000-seed weight, biomass production, and seed yield were measured. Harvest index (HI) and WUE were also calculated.
Results and Discussion: The results showed that under normal irrigation conditions, the application of 10 μM ABA concentration led to producing the highest number of mature capsules per plant, while no application of ABA resulted in the highest number of immature capsules per plant. In the conditions of application of irrigation level of 60% FC, the application of 100 μM ABA concentration with 25 and 8 capsules, respectively led to the production of more mature and immature capsules per plant. As a result, the highest number of capsules per plant (33 capsules) and the number of seeds per plant (2055 seeds) were obtained from the mentioned conditions. On the other hand, the thousand seed weight showed a different trend. In total, such variations observed led to the insignificant response of seed yield to the application of different ABA levels to different irrigation conditions. Applying limited irrigation in this study showed a greater effect on the reduction of seed yield (25.6%) compared to the biological yield (10.6%), which led to a decrease in harvest index by 19%. As a result of increasing the number of seeds per plant and 1000-seed weight, the application of 100 μM ABA concentration resulted in the highest seed yield (1138 kg ha^-1) and biomass production (10054 kg ha¹). Influenced by such results, increased water use efficiency by 9, 22, and 41% was observed for the 100 μM ABA level compared with the control and 10 and 50 μM ABA concentrations, respectively.
Conclusion: In conclusion, the integration of different ABA concentrations with different irrigation management could be considered an effective strategy to improve the growth, yield, and water use efficiency, and alleviates the adverse effects of drought stress on sesame plants.