Harnessing soil microorganisms to mitigate salinity stress in tomato

Soil salinization is an escalating agricultural challenge driven by limited freshwater availability for irrigation and rising aridity. In a previous study, metagenomic analysis demonstrated that soil salinity drastically changes the microbiome composition of the tomato rhizosphere in the Apulia region, Italy, favoring more halotolerant microbial populations. On the microbial collection (71 bacteria and 25 fungi) obtained from that study, in vitro assays for the evaluation of plant growth-promoting (PGP) traits revealed that 53% of the isolates were positive for 1-aminocyclopropane-1-carboxylase deaminase activity, 16 isolates produced siderophores (12 were bacteria), 5 isolates produced indoleacetic acid (bacteria), and 11 isolates were phosphate-solubilizers (fungi). Pot experiments demonstrated that some isolates counteracted saline stress (100 mM NaCl) in tomato seedlings over 40 days post-transplanting, as indicated by plant development (height and weight), chlorophyll content, and stomatal conductance. No evident correlations were observed between the origin of the isolates (saline or non-saline soil) and their PGP traits or their in planta alleviation of saline stress (reduction of growth stunting).