Growth and Hormonal Responses to Salicylic Acid and Calcium Chloride Seed Priming in Domestic and Wild Salt-Tolerant Barley Species Under Saline Conditions

Salinity is among the main abiotic constraints limiting crop productivity worldwide. Salt tolerance can be improved by introducing adaptive traits from wild species and enhancing pre-existing salt-adaptive mechanisms through priming. This study evaluated the beneficial effect of salicylic acid (SA, 1.25 mM) and calcium chloride (CaCl₂, 5 mM) seed priming on plant growth under salinity in the domestic barley <i>Hordeum vulgare</i> (<i>Hv</i>) and the wild, salt-adapted <i>Hordeum maritimum</i> (<i>Hm</i>). Primed plants were grown under control, 100 and 200 mM sodium chloride (NaCl) for two weeks. Growth and hormone profiling were performed. <i>Hv</i> showed higher growth inhibition than <i>Hm</i> but was more responsive to stress alleviation by priming, particularly with SA, which increased biomass by up to 47% at 200 mM NaCl. The contrasting responses of both species reflected distinct hormonal strategies. The intrinsic salt tolerance of <i>Hm</i> appears linked to high constitutive levels of stress- and growth-related hormones. In <i>Hv</i>, growth recovery under salinity following priming was associated with hormonal reprogramming, involving reduced abscisic acid (ABA) accumulation and enhanced levels of growth-promoting hormones (indole-3-acetic acid (IAA), trans-zeatin (tZ), and isopentenyl adenine (iP)), especially in roots. Hormonal changes mediated by priming are analyzed in relation to adaptive growth responses and species' ecological origins.