Inoculation of tomato plants with selected PGPR represents a feasible alternative to chemical fertilization under salt stress

Plant growth-promoting rhizobacteria (PGPR) are soil bacteria that colonize the rhizosphere of plants, enhance plant growth, and may alleviate environmental stress, thus constituting a powerful tool in sustainable agriculture. Here, we compared the capacity of chemical fertilization to selected PGPR strains to promote growth and alleviate salinity stress in tomato plants (Solanum lycopersicum L.). A pot experiment was designed with two main factors: fertilization (chemical fertilization, bacterial inoculation with seven PGPR, or a non-fertilized non-inoculated control) and salt stress (0 or 100 mM NaCl). In the absence of stress, a clear promotion of growth, a positive effect on plant physiology (elevated F-v/F-m), and enhanced N, P, and K concentrations were observed in inoculated plants compared to non-fertilized controls. Salinity negatively affected most variables analyzed, but inoculation with certain strains reduced some of the negative effects on growth parameters and plant physiology (water loss and K+ depletion) in a moderate but significant manner. Chemical fertilization clearly exceeded the positive effects of inoculation under non-stressed conditions, but conversely, biofertilization with some strains outperformed chemical fertilization under salt stress. The results point at inoculation with selected PGPR as a viable economical and environment-friendly alternative to chemical fertilization in salinity-affected soils.