Preliminary investigations on inducing salt tolerance in maize through inoculation with rhizobacteria containing ACC deaminase activity

Twenty rhizobacterial strains containing 1-aminocyclopropane-1-carboxylate deaminase were isolated from the rhizosphere of salt-affected maize fields. They were screened for their growth-promoting activities under axenic conditions at 1, 4, 8, and 12 dS x m-1 salinity levels. Based upon the data of the axenic study, the 6 most effective strains were selected to conduct pot trials in the wire house. Besides one original salinity level (1.6 dS x m-1), 3 other salinity levels (4, 8, and 12 dS x m-1) were maintained in pots and maize seeds inoculated with selected strains of plant growth-promoting rhizobacteria, as well as uninoculated controls were sown. Results showed that the increase in salinity level decreased the growth of maize seedlings. However, inoculation with rhizobacterial strains reduced this depression effect and improved the growth and yield at all the salinity levels tested. Selected strains significantly increased plant height, root length, total biomass, cob mass, and grain yield up to 82%, 93%, 51%, 40%, and 50%, respectively, over respective uninoculated controls at the electrical conductivity of 12 dS x m-1. Among various plant growth-promoting rhizobacterial strains, S5 (Pseudomonas syringae), S14 (Enterobacter aerogenes), and S20 (Pseudomonas fluorescens) were the most effective strains for promoting the growth and yield of maize, even at high salt stress. The relatively better salt tolerance of inoculated plants was associated with a high K+/Na+ ratio as well as high relative water and chlorophyll and low proline contents.