Physiological Enhancement of Seed Yield and Essential Oil Yield in Cumin under Drought Stress through Humic Acid and Seaweed Extract.

Cumin (Cuminum cyminum L.) is one of the valuable medicinal plants that is cultivated in arid and semi-arid regions of Iran. This study aimed to investigate the effects of humic acid and seaweed extract under drought stress on the seed yield, essential oil yield and physiological characteristics of cumin in the Yasouj region, Iran, from 2019 to 2020. The experiment followed a split-plot factorial design based on a completely randomized block design with three replications, during two years. The three studied factors were three irrigation regimes: irrigation after 30% (control), 70% (moderate drought stress), and 90% (severe drought stress), of soil moisture consumption, two levels of humic acid (0 and 300 mg/L), and two levels of seaweed extract consumption (0 and 2%). The results indicated that under severe drought stress, there was a significant decrease in seed yield and essential oil yield by 32 and 10.9% compared to the control, respectively. The results of the present study revealed that both humic acid and seaweed extract factors had a positive impact on seed yield and essential oil yield when applied individually. However, the combined foliar spraying of seaweed extract (2%) and humic acid (300 mg/L) proved to be the most effective treatment in mitigating the adverse effects of drought stress. This improvement was attributed to enhanced physiological parameters such as total chlorophyll, total chlorophyll a, total chlorophyll b, proline accumulation, and antioxidant activity (peroxidase and catalase). This study emphasizes the potential role of humic acid and seaweed extract as effective strategies for alleviating the adverse effects of drought stress on cumin plants, particularly in areas where drought poses a significant challenge. [ABSTRACT FROM AUTHOR]