Inoculation of Burkholderia cepacia, Pseudomonas fluorescens and Enterobacter sp. on Sorghum bicolor: Root colonization and plant growth promotion of dual strain inocula

Burkholderia cepacia strain PHP7 was tested for its ability to colonize roots and to promote the growth of Sorghum bicolor alone or in combination with Enterobacter sp. strain BB23T4d or Pseudomonas fluorescnes strain A23T3c. All three strains were able to colonize the root system of sorghum but only B. cepacia and P. fluorescens promoted plant growth in single strain inoculation tests. Dual strain inocula were no more effective than single ones. Moreover, in one case, the dual strain inoculum (B. cepacia and P. fluorescens) did not have any significant effect on plant growth in contrast to the separate inoculation of both strains. In dual strain tests, the B. cepacia population was significantly reduced in the presence of Enterobacter sp. but not of P. fluorescens. Establishment of large populations of bacterial inoculants on roots did not appear to be essential for plant growth promotion.