Successive soybean-monoculture cropping assembles rhizosphere microbial communities for the soil suppression of soybean cyst nematode

One of the mechanisms of disease suppressiveness in soils is long-term monoculture (LTM) cropping to dissuade pathogen infestation. However, the linkage between monoculturing and microbial community assemblage in the rhizosphere for disease suppression remains unclear. To decipher this potential relationship, soil samples were collected from seven locations in northeastern China, where LTM (6-38 yr) and short-term monoculture (STM <= 5 yr) cropping of soybean showed varying degrees of soil suppressiveness to the soybean cyst nematode (SCN; Heterodera glycines). Using high-throughput pyrosequencing to examine bacterial 16S rRNA and fungal ITS1 genes, we observed substantial variation in the species richness and relative abundance of taxa in the rhizosphere across different sampling sites. At the genus level, the genera Pseudomonas, Purpureocillium and Pochonia, which have been documented to suppress SCN in earlier studies, were much more abundant in LTM soils than in STM soils. Moreover, the relative abundance of several bacterial and fungal genera with metabolic, biocidal and parasitic activities was also monitored in the rhizosphere. In this study, we provide additional evidence that plants shift the structural and functional composition of the rhizosphere microbiota to suppress pathogen infection in LTM cropping soils.