Staphylococcus sciuri SAT-17 enhances salinity tolerance in eggplant (Solanum melongena L.) by improving antioxidant defense and ion homeostasis

Soil salinity is a major abiotic constraint on agricultural production, especially for salt-sensitive crops such as Solanum melongena L. This study aimed to evaluate whether inoculation with the plant growth-promoting rhizobacterium Staphylococcus sciuri SAT-17 could enhance salt tolerance in two contrasting eggplant cultivars under controlled hydroponic conditions. Two eggplant cultivars (Nirala, salt tolerant; Dilnasheen, salt-sensitive) were grown in a hydroponic system and subjected to sodium chloride (NaCl) concentrations of 0, 25, 50, and 75 mM. Plants were inoculated with SAT-17 or left non-inoculated. Over a 21-day stress period, several plant responses were evaluated. Morphological parameters included shoot and root biomass and leaf area. Physiological traits such as relative water content (RWC) and chlorophyll content were measured. Biochemical responses including proline accumulation, antioxidant enzyme activities, and malondialdehyde (MDA) content were also analyzed. Salinity markedly reduced biomass (up to ~ 65% at 150 mM NaCl), RWC, and chlorophyll, and increased oxidative damage (MDA) in both cultivars. SAT-17 inoculation significantly mitigated these effects. Inoculated plants showed 15–25% higher biomass, improved water status, and greater chlorophyll retention under salt stress. Inoculated plants also showed elevated proline levels and antioxidant enzyme activities (SOD, CAT, POD), with notably lower MDA accumulation ( p < 0.05). The protective effect was more pronounced in cultivar Dilnasheen than in Nirala under severe stress, indicating a stronger SAT-17–mediated tolerance response in the salt-sensitive genotype. Inoculation with S. sciuri SAT-17 confers enhanced salt tolerance in eggplant by improving water relations, osmotic adjustment, and oxidative stress mitigation. These results highlight the potential of SAT-17 as a microbial bio-inoculant for improving eggplant performance in saline environments. Enhanced antioxidant enzyme activities together with reduced MDA accumulation may serve as reliable physiological markers of improved salinity tolerance in SAT-17 inoculated eggplant plants.