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Efficient colonization of plant growth-promoting rhizobacteria (PGPR) on plant roots is crucial for the exertion of the growth promotion and bio-control effects. This study was performed to investigate the colonization patterns of Bacillus amyloliquefaciens SQR9 on banana roots to understand its application prospect on plant growth and biological control. The colonization patterns of B. amyloliquefaciens SQR9 tagged by green fluorescence protein(GFP)on banana roots was investigated in hydroponic and natural soil system by confocal laser scanning microscopy(CLSM)and scanning electron microscopy(SEM). The results showed that SQR9 carrying gfp(SQR9-gfp)could effectively colonize on banana roots and formed micro-colonies at 2 to 4 days of inoculation. The colonization of bacterial cells mainly occurred on the differentiation and elongation zones of the main roots, the lateral roots, junctions between roots and the root hairs, while few labeled bacterial cells were detected to attach along the root tips. In addition, similar colonization patterns of SQR9-gfp were obtained under both systems suggested that the hydroponic system could represent the natural soil system in a short time. The quantitative analysis revealed that at 4 days after inoculation, the population of SQR9-gfp was maintained at about 105-106 CFU·g-1 roots, and 106-107 CFU·g-1 soil, respectively; While the abundance of SQR9 slightly decreased at 15 days post inoculation. Conclusions:SQR9 could effectively colonize on banana roots and reach the appropriate population, which could provide the theoretical basis for the practical application of SQR9 for suppression of banana wilt. [ABSTRACT FROM AUTHOR]

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]