A method for screening phosphate solubilizing bacteria based on the rhizosphere colonization ability of strains.

In this study, phosphate solubilizing bacteria(PSB)were screened from rhizosphere soil and root of maize and elephantgrass using modified Pikovskaya(PVK)plate method, and phosphate-solubilizing activity of these strains was determined by measuring the soluble P concentration in National Botanical Research Institute's Phosphate(NBRIP)broth. In addition,3 strains designated as X14, X32,and Y21 were tested in the laboratory for their ability to colonize the rhizosphere of maize seedlings in sterile quartz sand. Finally, a pot trial was carried out in greenhouse to evaluate whether the laboratory test can predict beneficial effects of PSB on maize. The results showed that soluble P concentration in NBRIP broth of strain X14 was significantly lower than that of strain X32 and Y21,which was 22.80% and 19.99% of strain X32 and Y21,respectively. However, strain X14 was found to be a better rhizosphere colonizer than that of strain X32 and Y21,whose final population in the rhizosphere of maize seedlings expressed as CFU.g-1 was an order of magnitude higher than that of strain X32 in equal inoculum size. Under greenhouse conditions, application of PSB remarkably improved plant diameter,shoot height,fresh and dry weight,and P uptake of maize as compared to the control,but there was no significant difference between treatments inoculated with PSB. The strains X14, X32, and Y21 were identified under the genera Bacillus, Acinetobacter, and Pseudomonas using 16S rDNA sequences in comparison with GenBank database. This study showed that the phosphate-solubilizing activity of strain X14 was significantly lower than that of strain X32 and Y21 in the laboratory test, but its beneficial effect on P uptake of maize was equal to that of strain X32 and Y21 in the pot trail because of its better colonization in the rhizosphere of maize. So screening of PSB should be based on the colonization ability of strain in the rhizosphere of plant. [ABSTRACT FROM AUTHOR]