Bioactivity of Ascophyllum nodosum in Mitigating Water Stress Induced by PEG-6000 in Maize Seeds

Water deficit is one of the main limiting factors for crop establishment and productivity, particularly affecting seed germination and early seedling growth. This study aimed to evaluate the biostimulant effect of Ascophyllum nodosum extract on maize (Zea mays L.) seeds subjected to osmotic stress induced by PEG-6000.Three independent bioassays were conducted under controlled conditions. First, osmotic potentials ranging from 0 to −0.8 MPa were tested to determine stress levels. In the second assay, seeds were treated with increasing doses (0 to 2 mL kg⁻¹) of a commercial seaweed extract and its isolated mineral fraction. In the third assay, selected doses were evaluated under no stress, moderate stress, and severe stress conditions. Germination percentage, normal and abnormal seedlings, radicle and epicotyl length, and vigor index were assessed. Osmotic stress significantly reduced germination and seedling growth, particularly at −0.6 and −0.8 MPa. Seed treatment with A. nodosum did not affect final germination but improved seedling growth and vigor, showing a dose-dependent response. Maximum efficiency was observed at intermediate doses (~0.45–0.66 mL kg⁻¹), which increased the percentage of normal seedlings and promoted root and shoot development. Under water stress conditions, the complete extract outperformed the mineral fraction, indicating that the beneficial effects are mainly associated with bioactive organic compounds. These findings demonstrate that A. nodosum extract is a promising strategy to mitigate water stress effects during maize seed germination, provided that optimal doses are used.