Novel halotolerant PGPR strains alleviate salt stress by enhancing antioxidant activities and expression of selected genes leading to improved growth of Solanum lycopersicum

Plant growth-promoting rhizobacteria (PGPR) offer an eco-friendly and sustainable option to alleviate salinity-induced plant changes. Two tomato varieties Rio Grande and Sahil were exposed to 150 mM NaCl stress in a completely randomized setup. The previously isolated strains Pseudarthrobacter oxydans and Staphylococcus pasteuri, best characterized for growth-promoting traits, were applied singly and in consortium to the salt-stressed tomato plants. Dry biomass, total protein content, enzymatic antioxidant activities, and non-enzymatic antioxidant production were measured. Expression of catalase (CAT), superoxide dismutase (SOD), and sodium-hydrogen antiporter (NHX3) genes was measured using qRT-PCR. Analysis of variance (ANOVA) followed by the Tukey HSD test was applied to compare mean values at p ≤ 0.05. PGPR inoculation increased the dry biomass and total protein content of both varieties. Furthermore, elevated CAT and SOD activities, DPPH scavenging, and production of phenolics and flavonoids were noted in tomato plants. Two-way ANOVA results showed a significant increase in the relative expression of selected genes in Rio Grande wherein a 3.47-fold increase in SOD, 2.52-fold in CAT, and 2.2-fold in NHX3 was noted as compared to NaCl-treated plants. The current study established that both strains have the potential to recover salinity-induced detrimental changes and may act as future biostimulants of the stressed plants.