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چکیده
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Tagetes erecta L., commonly known as African marigold, is a plant species in the Asteraceae family and a rich source of zeaxanthin, an industrial pigment widely used in pharmaceuticals, food additives, animal feed, cosmetics, and biotechnology due to its antioxidant, coloring, and protective properties. The use of biostimulants, particularly those derived from seaweed, has been found to enhance plant growth and resilience, notably in drought-stressed environments. To assess the Seaweed extract’s potential in mitigating drought-induced damage in African marigold, a factorial design was implemented using a completely randomized design (CRD) with three replicates. Treatments consisted of four concentrations of seaweed extract (0, 3, 6, and 9 g L⁻¹) combined with three irrigation levels corresponding to 100 %, 70 %, and 40 % of field capacity (FC). As drought intensity increased, significant reductions were observed in morphological growth traits, chlorophyll, carotenoids, and zeaxanthin content, while parameters such as relative water content (RWC), electrolyte leakage (EL), and free proline concentration increased. Application of seaweed extract effectively alleviated drought stress by enhancing vegetative growth, improving photosynthetic pigments, increasing RWC and proline accumulation, and reducing EL. Furthermore, the treatment stimulated the biosynthesis of key biochemical markers, such as measurements of total phenolic content (TPC), total flavonoid content (TFC), and abscisic acid (ABA), along with elevated phenylalanine ammonia-lyase (PAL) activity and enhanced activity of antioxidant enzymes (APX, POD, SOD, and CAT). The highest zeaxanthin level (18.04 mg g⁻¹ DW), indicating a 158.08 % rise relative to untreated plants, was recorded under 40 % FC with 9 g L⁻¹ seaweed extract. Similarly, the maximum ABA concentration, 2.3-fold higher than the control, was observed under the same treatment. These findings indicate that spraying of 9 g L⁻¹ seaweed extract is the most efficacious approach for improving plant growth and zeaxanthin biosynthesis in African marigold under drought conditions. Overall, this strategy offers an economical and environmentally enduring method for enhancing drought tolerance and the accumulation of functional compounds in industrial crops.
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