Plant growth-promoting rhizobacteria differently influence the germination, growth and physiology of crops depending on cultivar and rhizobacteria consortium

The use of plant growth-promoting rhizobacteria (PGPR) is a key component in sustainable agriculture. Recent studies have highlighted several advantages in using well-formulated PGPR consortium (blend) that promotes synergistic interactions over single strains. Here, we isolated bacteria from corn and wheat grown in Texas, USA, to investigate locally available PGPR strains which were used to formulate three blends, hereafter called TX1, TX2 and TX3. Using maize and cotton cultivars of contrasting resistance levels to fungal pathogens, we compared the effectiveness of these PGPR blends to two other blends (AU8 and AU9 previously reported in Alabama, USA) in promoting growth of several crop cultivars. We further evaluated the PGPRs’ effects on the crops’ transpiration and stomatal conductance. Bacteria identified belong to five genera: Bacillus, Peribacillus, Paenibacillus, Pantoea and Priestia. Seeds inoculated with PGPR (AU8, TX1 and TX3) germinated earlier and changed physiological growth stages faster compared with control, except for the resistant cotton cultivar. All PGPR blends increased the length and weight of root and shoot of the susceptible maize and cotton seedlings. For the resistant cultivars, blends AU9, TX1, TX2 and TX3 enhanced at least one of the maize growth parameters, while only TX3 increased the growth of cotton seedlings. Transpiration and stomatal conductance varied between untreated and PGPR-treated plants depending on cultivar and blend. The findings indicate that the TX3 blend has a great potential to enhance growth of a broad range of maize and cotton cultivars.