Biostimulant Potential of Ascophyllum nodosum in Mitigating the Effects of Salinity on the Germination of Zea mays L.

Soil salinization is one of the main factors limiting agricultural productivity, negatively affecting seed germination and initial growth of maize (Zea mays L.). As a sustainable alternative, seaweed-based biostimulants, especially extracts of Ascophyllum nodosum, have stood out in mitigating abiotic stresses. This study aimed to evaluate the potential of A. nodosum extract in inducing tolerance to saline stress in maize seeds of the AL Bandeirante cultivar. To this end, three independent bioassays were conducted under controlled conditions: (i) evaluation of five doses of the extract (0; 0.5; 1.0; 1.5 and 2.0 mL L−1); (ii) effects of five osmotic potentials induced by NaCl (0, −0.2, −0.4, −0.6 and −0.8 MPa); and (iii) the interaction between the most efficient doses and salinity levels, comparing the extract to its mineral fraction. Seed germination, percentage of normal and abnormal seedlings, radicle and epicotyl length, and vigor index were measured. The results demonstrated that doses of 1.0 to 2.0 mL L−1 promoted greater bioactivity, with a 7.3% increase in root length compared to the control. Although increased salinity progressively reduced all variables, with severe effects at −0.6 and −0.8 MPa, the treatment with the extract showed superior performance to the mineral fraction, demonstrating a mitigating effect. It is concluded that A. nodosum extract is an effective strategy to attenuate the damage caused by salinity on seed germination and initial seedling growth in maize, especially under moderate stress.