Community analysis of plant growth promoting rhizobacteria for apple trees

• Alterations of PGPR from apple trees of continuous cropping were analyzed.
• The community structure of PGPR changed greatly due to continuous cropping.
• The microbial community structure of apple trees varied with districts.

Plant growth promoting rhizobacteria (PGPR) for perennial apple trees (PAT) and apple tree saplings under continuous cropping (ATS) from two places in China were isolated and analyzed, and cluster analysis of BOX-PCR data was performed. The results showed that the quantities of both total rhizobacteria and the four kinds of PGPR (nitrogen-fixing bacteria, phosphate-solubilizing bacteria, silicate bacteria and antagonistic bacteria) from PAT were higher than those of ATS at different sampling points. The largest dissimilitude of BOX-PCR patterns for the PGPR indicated the genetic evolutionary distance of bacteria isolates was closer for the same sampling point. The shared cluster groups of the same variety of PGPR from two kinds of apple rhizosphere or different sampling points were very few. The diversity index, richness index and evenness index of PGPR from PAT were higher than those of ATS at both sampling points, while the dominance index was lower. The amounts and varieties of PGPR significantly changed between the PAT and ATS from different areas, which indicated the PGPR of the same plant varied from place to place due to the different environmental conditions. These results indicate that PGPR from PAT have the advantage of species diversity compared with ATS.