Effects of PGPR Co-inoculation on Growth, Phosphorus Nutrition and Phosphatase/Phytase Activities of Faba Bean under Different Phosphorus Availability Conditions

Plant growth promoting rhizobacteria (PGPR) may improve crop yield and reduce or optimize the use of chemical fertilizers. We investigated the effect of co-inoculation on growth, phosphorus nutrition, and phosphatase-phytase activities of Vicia faba under different phosphorus availability conditions. The studied strains possess several PGPR traits such as nitrogen fixation ability, solubilization of phosphate and potassium, and production of exopolysaccharides, auxins, and siderophores. Based on their 16S rDNA sequences, the strains were identified as Rahnella aquatilis (PGP30), Pseudomonas brassicacearum (PGP291) and Rhizobium sp. (RhOF57A). In a greenhouse experiment, plants were inoculated with an individual strain or co-inoculated with two strains in addition to uninoculated controls. Each setup was supplemented either with tricalcium phosphate Ca-3(PO4)(2) (TCP treatment) or irrigated with potassium phosphate KH2PO4 (PO4 treatment). Regardless of the applied phosphorus source, co-inoculation significantly increased biomass and phosphorus concentrations in plants as well as in bean pods. Moreover, especially co-inoculation increased phosphatase-phytase activities in roots supplemented with tricalcium phosphate. This study suggests that co-inoculation of plants is a means to prevent phosphorus limitation and for judicious use of chemical fertilizers.