Improvement of salt stress tolerance in Salvia officinalis L. by co-culture with halophytic plants: comparative study with Aptenia cordifolia and Spergularia salina.

BACKGROUND: Soil salinity is a major abiotic stress limiting crop productivity, particularly for glycophytic species such as sage (Salvia officinalis L.), a medicinal plant of high pharmacological and economic importance. Conventional tolerance mechanisms in sage, including proline accumulation and osmotic adjustment, are energetically costly and insufficient under severe stress. This study investigated the potential of co-cultivation with Aptenia cordifolia and Spergularia salina to enhance sage growth, physiology, and survival under controlled sodium chloride (NaCl) stress. RESULTS: Glasshouse experiments were conducted with sage in monoculture and in co-culture with halophytes under four salinity levels (0, 2, 5, and 10 g/L NaCl). Morphological, physiological, and biochemical analyses revealed that salinity reduced growth, biomass, and water content, while increasing proline and sugar accumulation. Co-cultivation significantly improved plant performance: survival at 10 g/L NaCl was 30% in monoculture but rose to 90% with A. cordifolia and 85% with Spergularia salina. Co-culture also mitigated proline overaccumulation (710% increase in monoculture versus 471.6% and 386.7% in association with A. cordifolia and Spergularia salina, respectively). Principal component analysis and robust regression confirmed that halophytes buffered stress effects, with Spergularia salina providing the most stable improvements. Machine learning analyses further identified biomass and sugar content as key discriminant traits between treatments. CONCLUSION: These findings demonstrate that companion planting with halophytes enhances the tolerance of Salvia officinalis to salt stress by reducing physiological costs and improving survival. This approach represents a sustainable and scalable agroecological strategy for cultivating medicinal plants in saline environments, with implications for resilient agriculture under climate change. © 2026 Society of Chemical Industry.