Improved salt stress resilience, growth, and quality of soilless basil through biostimulant application.

Salinity is a major abiotic stress that disrupts ion balance, water uptake, and plant metabolism, ultimately reducing growth and productivity. Climate change, induced evaporation, and altered rainfall patterns are accelerating salinization, posing a challenge to soilless systems where water quality directly impacts nutrient availability. Basil, a salt-sensitive and high-value aromatic herb, shows marked physiological decline under salinity, including reduced water and nutrient uptake, impaired photosynthetic activity, disruption of ion balance, and increased oxidative stress. Here, we evaluated the potential of biostimulants-amino acids, arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR), fulvic acid, chitosan, and vermicompost-to alleviate salt-induced stress in basil grown with 50 mM NaCl in a floating culture system. Salt stress reduced leaf yield by 41.6%, stomatal conductance by 65.7%, and antioxidant enzyme activities. Among the biostimulants, PGPR and vermicompost were the most effective, increasing yield by over 90% compared to salt-stressed plants. These treatments enhanced antioxidant enzyme activities (APX, CAT, GR, SOD), increased phenolics, flavonoids, and vitamin C, and reduced lipid peroxidation (up to 74.3% lower MDA). Moderate improvements were observed with amino acids, AMF, and chitosan, while fulvic acid showed limited effectiveness. Overall, PGPR and vermicompost strengthened basil's resilience to salinity by reducing oxidative stress and enhancing physiological performance. These findings support their use as sustainable tools in managing saline conditions. Future studies should evaluate the biostimulant effectiveness under higher salinity and poor-quality water, and assess their impact on different basil cultivars, including essential oil and aroma-related traits.