Screening and Identification of Harmful and Beneficial Microorganisms Associated with Replanting Disease in Rhizosphere Soil of Pseudostellariae heterophylla.

Pseudostellariae heterophylla, an important medicinal plant, has been shown to suffer from serious replanting disease that causes significant declines in both yield and quality. The objective of this study was to isolate the soil-born pathogen and antagonistic microorganism for investigation of the relationship between these microorganism and consecutive monoculture problems of P heterophylla. In this study, we isolated the bacteria with different morphology from P heterophylla rhizosphere soil, detected the pathogenicity of these bacteria to P heterophylla plantlet and antagonistic ability to Fusarium of P heterophylla biotype, identified their species and analyzed their abundance with qRT-PCR in rhizosphere soil of different planting years. We isolated Enterobacter sp1 and Burkholderia sp1 from P heterophylla rhizosphere soil, and found Enterobacter sp1 possessed the pathogenicity to P heterophylla plantlet and Burkholderia sp1 was antagonistic for Fusarium of P heterophylla biotype. However, Burkholderia sp1 was not the antagonistic microorganism to Enterobacter sp1. The growth of Enterobacter sp1 was stimulated by phenolic acids at a certain concentration nearly closed to that in P heterophylla rhizosphere soil, which increased as planting years of P heterophylla increased. On the contrary, the phenolic acids had no promoting effect on the growth of Burkholderia sp1. And with the increase of planting years, the abundance of Burkholderia sp1 decreased and abundance of Enterobacter sp1 increased in the P heterophylla rhizosphere soil. The results indicated that harmful microorganisms increase and beneficial microorganisms decrease, which were mediated by the accumulated autotoxins in rhizosphere soil of consecutively monocultured P heterophylla, and hence leads to the imbalance of microbial community structure and the degradation of soil ecological function. So several abatement methods, such as crop rotation, specific microbial fertilizer and organic matter, could be used to improve the structure and functional diversity of microbial community, and overcome the obstacles of continuous cropping. © 2015 Friends Science Publishers [ABSTRACT FROM AUTHOR]