Modulation in key physiological traits improved ROS scavenging and salinity tolerance amelioration in rice and tomato inoculated with halotolerant rhizobacteria Providencia rettgeri ST202.

Abstract

Main conclusion: Halotolerant rhizospheric bacteria Providencia rettgeri ST202 positively modulated the changes in stomatal, mesophyll, and biochemical limitations, fine-tuning photosynthesis, photorespiration, ROS, and antioxidants in rice and tomato plants for improved salinity tolerance. Soil salinity is detrimental for survival of majority of crops, since increased salt disrupts root water uptake, induces cellular ion toxicity ultimately leading to drastic decrease in crop yields. In the current study, inoculation of Providencia rettgeri ST202, a halotolerant rhizospheric bacteria isolated from rhizospheric soil of salt pan areas, resulted in plant growth-promoting traits along with improvement in growth of Oryza sativa and Lycopersicon esculentum plants under normal and salinity stress (S2: 200 mM and S4: 400 mM NaCl) conditions prompting us to evaluate changes in physiological and biochemical parameters, photosynthesis, photorespiration, reactive oxygen species (ROS), and antioxidants. Compared to uninoculated plants, improved relative water content, chlorophyll content, carotenoids, and antioxidant levels were observed along with decreased electrolyte leakage and ROS in ST202 inoculated rice and tomato plants suggesting better protection under control and salinity stress. While salinity stress severely impacted photosynthesis under different light intensities and different CO₂ levels in uninoculated plants, ST202 inoculated plants have higher photosynthetic rates. Spider plot comparison of gas exchange and chlorophyll fluorescence parameters revealed superior performance of ST202 inoculated plants. The mesophyll conductance and chloroplastic CO₂ concentration were maintained at higher level in ST202 inoculated plants showing alterations in limitation in stomatal conductance, mesophyll conductance, and biochemical limitation suggesting beneficial modulation by PGPR for improving photosynthesis under salt stress conditions. Our results indicated modulation of key photosynthetic processes along with significant reduction in ROS by the halotolerant PGPR P. rettgeri ST202 towards enhanced salinity stress tolerance of rice and tomato plants.