Divergent Biostimulant Capacities Under Salinity: PGPR Monoinoculation and a Tri-Strain Consortium Evaluated in Tomato (In Vitro) and Wheat (Pot Culture)

Soil salinity severely limits global crop productivity. Native plant growth-promoting rhizobacteria (PGPR) from saline ecosystems offer a sustainable strategy to alleviate salt stress, yet their efficacy often depends on host and niche. This study evaluated the biostimulant potential of three rhizobacterial isolates— Staphylococcus xylosus SF6 (PQ123789), Pseudomonas sp. TA3 (PX957002), and Bacillus simplex SA1 (PX957145)—recovered from the rhizosphere of halophytes in an Algerian sebkha. Their individual and combined (tri-strain consortium) effects were assessed on tomato under in vitro NaCl gradients (0–150 mM) and on wheat cultivated in naturally saline soil. Data were analyzed via two-way ANOVA and Principal Component Analysis. Salt stress significantly impaired all growth parameters in non-inoculated controls. PGPR inoculation markedly mitigated these effects, though responses were strongly modulated by host species and treatment formulation. In tomato, the tri-strain consortium performed best, maintaining 100% germination at 0 mM NaCl and 60% under 100 mM stress, with a 186% increase in fresh biomass. PCA (90.27% total variance) revealed robust, salinity-independent growth promotion by the consortium. Conversely, in wheat, Pseudomonas sp. TA3 was most effective, increasing germination by 75%, root length by 100%, and Seedling Vigor Index by 240%. Notably, S. xylosus and B. simplex performed poorly on wheat, falling below non-inoculated controls, highlighting host-specific incompatibility. These findings demonstrate that PGPR-mediated salt tolerance is not interchangeable; optimal bioinoculant design requires precise matching of strain ecophysiology to target host and substrate. The tri-strain consortium shows promise for tomato, whereas Pseudomonas sp. TA3 emerges as a specialized candidate for wheat biofertilization in saline fields, supporting ecotype-adapted microbial consortia for sustainable agriculture in saline-affected regions.