Free-living (N₂)-fixing bacteria as potential enhancers of tomato growth under salt stress

Azotobacter chroococcum 67B, A. chroococcum 17-1 and A. chroococcum 76A, isolated from compost, were previously selected for their plant growth promoting activities and high NaCl tolerance. The performances of these strains to increase plants' salinity tolerance were tested on tomato plants ('Microtom') in a greenhouse experiment. Plants substrate was inoculated with A. chroococcum 67B, A. chroococcum 76A, alone or with a combination of strains 67B and 17-1. Plants inoculated with commercial product of PGPR and non-inoculated plants were used as controls. Inoculated plants and their relative controls were exposed to 3 salinization levels (0, 5, 10 g L^-1 NaCl) and 3 fertilization regimes [Basic nutrient Solution (BS), BS + 0.5 g L^-1 NH₄NO₃ and BS + 1 g L^-1NH₄NO₃]. Preliminary analysis revealed that all the bacterial strains did not have a significant impact onthe total fresh biomass and fruits fresh weight of tomato under NaCl stress. Further investigations, including shoot vs. root development, profiling of ions uptake and distribution and fruits quality parameters will be necessary to assess the complete performance of these strains and their value in agricultural applications.