Biostimulatory Potential of Sargassum muticum Extracts in Enhancing Sesame Tolerance to Water Deficit During Germination and Seedling Growth

Water deficit is a major abiotic stress that limits plant growth and productivity. This article evaluates the effectiveness of an aqueous seaweed extract (ASE) from Sargassum muticum as an ecofriendly biostimulant to alleviate water deficit stress during seed germination and early seedling growth of sesame ( Sesamum indicum L.). Sesame seeds were germinated for 8 days at 25 ± 1°C under distilled water (control) versus water deficit stress at −0.6 MPa induced using 22% polyethylene glycol 6000, with or without 10% ASE treatment. Water deficit significantly reduced germination parameters, delayed the time to 50% germination (T 50 ) by 202%, and impaired seedling growth through 79.2% and 66.7% reductions in shoot length and fresh weight, respectively. The stress condition triggered oxidative damage, evidenced by substantial increases in malondialdehyde (MDA) with 101.3%, hydrogen peroxide (H 2 O 2 ) with 155.8%, superoxide anion (O 2 − ), and electrolyte leakage (EL) with 190.4%. ASE treatment notably improved embryo viability, seed germination, and early seedling growth. Moreover, it enhanced antioxidant responses, leading to significant reductions in MDA (14.6%), H 2 O 2 (30.52%), O 2 − , and EL (52.0%). These findings demonstrate that ASE effectively mitigates water deficit‐induced oxidative stress and promotes early growth in sesame, highlighting its potential as a sustainable biostimulant for improving crop resilience under drought stress conditions.