Inoculation of Pseudomonas mutant strains can improve growth of soybean and corn plants in soils under salt stress

ABSTRACT In the last decades, the applications of Plant Growth Promoting Rhizobacteria (PGPR) as inoculants for enhancing crops yield under different stress conditions have reached enormous interest. Pseudomonas putida KT2440 is a well-known rhizobacteria capable of colonizing roots of agronomically important crops. This work aims to evaluate three P. putida KT2440 mutants (mus-20, mus-42, and EU206), which have non-biofilm producing and exopolysaccharide overproducing phenotypes, for their potential as PGPR on soybean and corn plants under saline stress. Experimental studies showed that KT2440 and its mutants were effective in three main PGPR properties: solubilization of phosphates and synthesis of indolic compounds and siderophores. Notably, indolic compounds synthesis increased in mus-20 and EU206 strains. Furthermore, all evaluated strains were tolerant to saline stress. Bacterial inoculation of soybean and corn seeds was effective both in vitro and in vivo tests, even at high salt concentrations (80 and 120 mM NaCl). Among mutant bacteria, EU206 strain seems to be the most efficient PGPR by significantly increasing seed germination, dry and fresh weights, and root and shoot lengths of plants compared to non-inoculated controls, in in vivo tests under saline condition, mainly in both corn plants. These results suggest that inoculation with the P. putida KT2440 mutant strains is an appropriate strategy to enhance the growth of soybean and corn plants, so they might be employed for promoting regional crops growth at field scale using natural saline soils.