Effects of Extremophilic PGPR on Growth, Physiological, and Biochemical Responses in Peanut (Arachis hypogaea L.) Cultivars under Salt Stress

This study was conducted to evaluate the effects of extremophilic plant growth-promoting rhizobacteria (PGPR) applications on growth, physiological, and biochemical responses of two peanut (Arachis hypogaea L.) cultivars (Ayşehanım and Adanur) under salt stress conditions. Experiments were carried out at two salt concentrations [control (0 mM NaCl) and 300 mM NaCl], including a non-inoculated control and three bacterial inoculations (Pseudomonas extremorientalis, Olivibacter soli, and P. poae). The results revealed that the Ayşehanım cultivar was more sensitive to salt stress in terms of growth parameters, whereas the Adanur cultivar exhibited a more tolerant profile by maintaining root development and pigment contents. Among the PGPR treatments, PGPR inoculation—particularly P. poae—was associated with improved physiological responses under salinity. In the Adanur cultivar, P. poae application was associated with a 7% increase in SPAD values compared to the control (44.26 → 47.49) and approximately 25% higher carotenoid content (1.86 → 2.32) under 300 mM NaCl stress. These responses suggest a strain-dependent contribution of PGPR to the maintenance of pigment-related traits under saline conditions.Correlation and multivariate analyses revealed strong associations between growth parameters and electrical conductivity (r = –0.72 to –0.85), while total phenolic content (TPC) exhibited positive correlations. Overall, PGPR inoculation showed ameliorative potential against salt stress; however, the magnitude and direction of responses were cultivar- and parameter-dependent. The findings indicate that extremophilic PGPR strains, particularly P. poae, may contribute to improved stress-related physiological traits in peanut, although their effectiveness depends strongly on host genotype and environmental conditions.