Document Type : Research Paper
Authors
1 - Department of Horticultural Science and Agronomy, Science and Research branch, Islamic Azad University, Tehran, Iran
2 Department of Horticultural Science and Agronomy, Science and Research branch, Islamic Azad University, Tehran, Iran
Abstract
Background and Objective: Salinity stress is one of the most important climatic factors affecting the distribution and dispersion of plants worldwide, inducing morphophysiological and biochemical changes in plants. Seaweed extract, as a natural biostimulant in modern agriculture, enhances plant immunity and increases their resistance to various stresses. The use of this extract can boost chlorophyll content and improve the photosynthesis process, ultimately leading to increased biomass production and agricultural yield.
Materials and Methods: This study aimed to investigate the growth, physiological, and biochemical characteristics of the medicinal plant Echinacea angustifolia L. under salinity stress at four levels (0, 50, 75, and 100 mM) and Sargassum johnstonii extract at three levels (no foliar application (control), 1 and 2 g/L). The experiment was conducted as a factorial based on a completely randomized design with three replications. Echinacea seeds were purchased from Pakan Seed Company and cultivated in seedling trays in a greenhouse. Seedlings were transferred to pots after reaching the four-leaf stage. Salinity stress was applied using sodium chloride through irrigation water (50 cc) every four days. After every three saline irrigations, leaching with normal water was performed to prevent salt accumulation in the pots. Salinity stress was maintained for 40 days. Foliar application of Sargassum seaweed extract was carried out every 10 days for a total of five applications over 40 days. At the end of the treatment period (The flowering stage), plant organs were harvested after measuring morphological traits in the greenhouse and used for laboratory evaluations in the Food Science Laboratory of Islamic Azad University, Nour Branch. The studied traits included morphophysiological characteristics (plant height, leaf number, number of lateral branches, fresh and dry weight of aerial parts), photosynthetic pigments (chlorophyll a and b), biochemical traits (proline and soluble sugars), and phytochemical traits (total phenols, total flavonoids, and antioxidant activity).
Results: The results showed that the main effect of salinity stress was significant on all traits. The main effect of seaweed extract treatment was significant on most traits (except proline and antioxidant activity). The interaction between treatments also had a significant effect on all traits. Salinity stress at 100 mM NaCl severely reduced plant growth and traits such as plant height, fresh and dry weight of aerial parts. The levels of photosynthetic pigments (chlorophyll a and b) decreased with increasing sodium chloride concentration. The application of seaweed extract mitigated the negative effects of salinity stress on Echinacea and moderated its intensity. However, the highest numerical values for these traits were observed under non-saline conditions with the application of 2 g/L seaweed extract. It can be concluded that, across different salinity stress levels, increasing the concentration of seaweed extract up to 2 g/L improved the growth and performance of Echinacea. At 75 mM NaCl, the highest levels of bioactive compounds (total phenols, total flavonoids, and antioxidant activity) were observed. Increasing the concentration of seaweed extract also acted as a stimulant for the production of these bioactive compounds. Additionally, the synthesis of soluble carbohydrates and proline increased compared to the control, enhancing the plant's resistance to unfavorable environmental conditions. Among the seaweed extract concentrations, 2 g/L had a more positive effect on the studied traits, even under non-saline conditions.
Conclusion: The overall results of the study indicated that Echinacea is not highly resistant to salinity stress, and a significant reduction in yield is evident. Although seaweed extract moderated the effects of salinity stress on Echinacea, the 2 g/L concentration played a greater role in alleviating the intensity of salinity stress by enhancing growth and the production of plant metabolites.
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