Salt-tolerant plant growth-promoting rhizobacteria mitigate salinity in barley by improving photosynthetic capacity, antioxidant activity, and soil fertility

Salinity is considered one of the main abiotic stresses that severely limit crop growth and productivity. Therefore, it is necessary to develop new ecological technologies that increase crops' tolerance to salinity. The present work was conducted to investigate the role of four plant growth-promoting rhizobacteria (PGPR) identified as Pantoea agglomerans E1, Streptomyces swartbergensis E5, Pseudomonas zanjanensis LM3, and Streptomyces cahuitamycinicus LL1 in mitigating salinity and improving barley plants (Hordeum vulgare L.) tolerance. Plants were inoculated with different PGPR consortia (C1: E1 + E5, C2: LM3 + LL1, and C3: E1 + E5 + LM3 + LL1) and then subjected to 0 or 120 mM NaCl. Results revealed that salinity negatively affects physiological parameters and activates the production of antioxidant enzymes (superoxide dismutase, catalase, and polyphenol oxidase). However, the application of all bacterial consortia (C1, C2, and C3) at the concentration of 10(9) UFC/mL attenuated the negative effect of salinity compared to the non-inoculated control. PGPR consortia used show difference in their ability to improve plant parameters, and C3 showed the most apparent effect. This treatment (C3) at the concentration of 10(9) UFC/mL significantly enhanced shoot dry weight, total chlorophyll, and sugar contents by 89%, 126%, and 55%, respectively. The same treatment increased the superoxide dismutase and catalase activities by 89% and 40%, respectively, under salt conditions. Indeed, C3 was also able to enhance available phosphorus and urease in barley rhizosphere under salt conditions by 179%, 111%, respectively. Overall findings revealed that the PGPR inoculation enhanced the salinity tolerance of barley plants by improving photosynthetic capacity, antioxidant system, soil urease, alkaline phosphatase, invertase, and catalase activities. These PGPR inoculants can be used as an ecological solution method to mitigate salinity.