Scrutinizing Rhizobia to Rescue Maize Growth under Reduced Water Conditions

Availability of fresh water for crop production is a major concern these days. Therefore inoculation biotechnology has been tried as a tool to support crop growth and yield under water deficit conditions. Thirty rhizobia were isolated from the nodules of three legumes (Lens culinaris, Vigna radiata, and Cicer arietinum) cultivated in arid and semiarid regions of Punjab (Pakistan). Nine fast growing isolates were evaluated for drought tolerance capability with PEG-6000-induced water stress. These nine isolates were assessed for plantgrowth-promoting-activity on maize under drought in gnotobiotic conditions by planting inoculated seeds between filter sheets soaked with each respective inoculum. Drought was imposed by applying PEG solutions of -0.61 and -1.2 MPa osmotic potential and isolates rhizobial strain (RS)-1, RS-3, RS-8, and RS-12 were selected as prominent growth promoters. Selected isolates were evaluated in a pot trial under natural conditions where irrigation was delayed at the vegetative and reproductive growth stages of the maize crop to develop water deficit stress. Improvement in fresh cob yield, root/ shoot length, shoot fresh weight and drought tolerance index was observed. The isolates displayed P-solubilization (RS-1 and RS-12), siderophores (RS-3 and RS-8), oxidase (RS-1), indole acetic acid, catalases, and exopolysaccharides production ability (RS-1, RS-3, RS-8, and RS-12). Isolates RS-1 and RS-3 were identified as Rhizobium phaseoli whereas RS-8 and RS-12 were Mesorhizobium ciceri. Results suggested rhizobia as potential inoculants to maize for improving growth and productivity under drought. However, evaluation in field conditions is required to confirm their capability.