Investigation of the colonization patterns of plant growth-promoting rhizobacteria Bacillus amyloliquefaciens SQR9 on banana roots.

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]