Bacterial Community Profiling in Rhizoctonia Soils

We report findings from three bacterial community profiling studies of agricultural soils exhibiting Rhizoctonia root rot and bare patch. In the Pacific Northwest, USA and Australia, these diseases are associated with sandy soils in regions of low annual precipitation and high temperatures. One Pacific Northwest location under continuous no-till cropping to wheat and broadleaf crops underwent disease suppression. In the studies, we hypothesized that 1) the composition of bacterial communities in soils from inside bare patches differ from those outside the patch; 2) disease suppression is associated with a shift in bacterial community composition; 3) bacterial community composition is affected by tillage; and 4) it also is impacted by host cultivar. Analysis of 16S rDNA frequencies indicated that members of the genera Chitinophaga, Pedobacter, Oxalobacteriaceae and Chyseobacterium were more prevalent in soils within bare patches, whereas Acidobacteria and Gemmatimonas were more prevalent in adjacent soils just outside the patches. In contrast, soils showing suppression of bare patch were enriched for Dyella and AcidobacteriaGp7. Bacterial community composition varied significantly for soils from the rhizosphere vs. bulk soil. However, tillage had less impact on composition than expected. Analysis of bacterial communities from soils planted to different cultivars is in progress; an update on the findings will be reported. Taken together, our data indicate that bacteria are responsive to the rhizosphere and to rhizosphere community members, with implications for the dynamics of soil health.