Plant growth-promoting rhizobacteria differently influence crops growth and physiology depending on cultivar and rhizobacteria consortium's composition.

Recent studies have highlighted several advantages in using well-formulated blends of plant growth-promoting rhizobacteria (PGPR) that promote synergistic interactions over single PGPR strains. However, developing PGPR consortia (i.e., blends) that are effective in multiple crop cultivars is challenging. Five PGPR blends were evaluated for broad-spectrum growth promotion efficacy. Rhizosphere bacteria were isolated from crops grown in Texas to identify indigenous PGPR strains, and those with biological activity against fungal pathogens were used to formulate three PGPR blends, hereafter called TX1, TX2 and TX3. Using two corn and two cotton cultivars of contrasting resistance levels to fungal pathogens, the efficacy of these three PGPR blends was compared to two previously reported blends (AU9 and AU8). In addition, effects of the PGPR blends on the crops' transpiration rate and stomatal conductance were evaluated. The newly identified PGPR strains belong to five bacterial taxonomic groups: Bacillus, Paenibacillus, Pantoea, Peribacillus and Priestia. All PGPR blends increased the length and weight of root and shoot of the susceptible cultivars. For the resistant cultivars, blends AU8, TX1, TX2 and TX3 enhanced at least one of the corn growth parameters, while only TX2 and TX3 increased growth of the cotton plants. Resistant corn plants treated with AU8, TX1, TX2 or TX3 blend, and resistant cotton plants treated with AU8 or TX3 blend showed increased transpiration rate and stomatal conductance compared with untreated plants, but no significant differences were observed for the susceptible cultivars. The findings indicate that the PGPR blends showed better growth promotion efficacy in susceptible cultivars than in resistant cultivars. Only blends TX2 and TX3 made of PGPR strains from across four and three bacterial taxonomic groups, respectively, significantly increased growth of all four cultivars, regardless of resistance levels, suggesting that these blends have a great potential to enhance growth of a broad range of corn and cotton cultivars. [ABSTRACT FROM AUTHOR]