Rhizobacteria producing ACC deaminase mitigate water-stress response in finger millet (Eleusine coracana (L.) Gaertn.)

The aim of the study was to examine the influence of single and consortia treatments of drought tolerant rhizobacteria producing ACC deaminase together with additional plant growth promoting (PGP) characteristics on finger millet growth, antioxidant and nutrient concentration under water-stressed and irrigated (no stress) conditions. These rhizobacteria belong to the Variovorax sp. Achromobacter spp. Pseudomonas spp. and Ochrobactrum sp. The single inoculant of RAA3 (Variovorax paradoxus) and a consortium inoculant of four bacteria, i.e., DPC9 (Ochrobactrum anthropi), DPB13 (Pseudomonas palleroniana), DPB15 (Pseudomonas fluorescens) and DPB16 (Pseudomonas palleroniana), significantly boosted the overall growth parameters and nutrient concentrations in leaves of finger millet. Moreover, elevated levels of the reactive oxygen species scavenging enzymes–superoxide dismutase (17.3%, 11.6%), guaiacol peroxidase (38.7%, 22.2%), catalase (33.7%, 21.3%) and ascorbate peroxidase (18.2%, 10.0%); cellular osmolytes–proline (41.5%, 25.0%), phenol (44.5%, 37.5%); higher leaf chlorophyll (64.4%, 30.8%) and a reduced level of hydrogen peroxide (50.7%, 59.5%) and malondialdehyde (48.4%,72.5%) were noted, respectively, after single inoculation of RAA3 and a consortium treatment by strains DPC9 + DPB13 + DPB15 + DPB16, in contrast with non-treated plants mainly under water-stressed conditions. This finding clearly illustrates that PGPB that express ACC deaminase along with additional PGP traits could be an efficient approach for improving plant health in environments, where agricultural practices are reliant on rain for water.