Effect of plant growth promoting rhizobacteria (PGPR) inoculation on microbial community structure in rhizosphere of forage corn cultivated in Thailand

Plant Growth Promoting Rhizobacteria (PGPR) play an important role in agricultural systems, especially as biofertilizer. The objectives of this study were to select effective PGPR for forage corn (Zea mays L.) cultivation and to investigate the effect of their inoculation on indigenous microbial community structure. The putative genera Pseudomonas sp. SUT 19 and Brevibacillus sp. SUT 47 were selected for determining their efficiency in forage corn growth promotion in both pot and field experiments. In field experiment, PGPR amended with compost gave the highest results in comparison to all treatments. Denaturing Gradient Gel Electrophoresis (DGGE) fingerprints of 16S rDNA amplified from total community DNA from rhizosphere confirmed that our isolates existed in rhizosphere throughout this study. The microbial community structures were slightly different among all treatments whereas major changes depended on stages of plant growth. In order to evaluate whether PGPR have effect on species diversity in rhizosphere, DNA sequencing of excised DGGE bands was done. The results demonstrated that dominant species in microbial community structure were not interfered by PGPR, but strongly influenced by plant development.

Research highlights
► Pseudomonas sp. and Brevibacillus sp. performed satisfactory results on forage corn.
► The mode of action may be derived from ACC-deaminase, P-solubilization etc.
► In addition, no effects from PGPR on microbial community structure were observed.
► Indeed, plant age is a major factor controlling microbial community structure.