Rhizoctonia communities in soybean fields and their relation with other microbes and nematode communities

Abstract

Soybean root rot, caused by Rhizoctonia solani, is one of the most serious soybean diseases in the North Central Region of the United States. There is no report of the relationship between Rhizoctonia root rot and soil physical and chemical properties, or microbial and nematode communities. A commercial soybean field with a long history of Rhizoctonia root rot was examined to explore this relationship. Results demonstrated that high disease incidence in sampled areas was positively correlated with high levels of nitrogen, phosphorus, manganese, populations of soil Rhizoctonia, thermophiles and fungi, root Rhizoctonia colonies, populations of lesion and stunt nematodes, and negatively correlated with high levels of calcium, magnesium, sodium, base saturation, and populations of Pseudomonas based on correlation analysis and canonical correspondence analysis (CCA). Cluster analysis showed that the communities of both Rhizoctonia and bacteria in sampled areas were separated based on healthy and diseased plants using denaturing gradient gel electrophoresis (DGGE); however, there was no clear separation for Fusarium, Pythium and Trichoderma communities in sampled areas based on healthy and diseased plants, indicating these species might not be directly associated with Rhizoctonia root rot. Moreover, the disease suppression seems to be more related to the quantity of soil beneficial microorganisms rather than specific species. In addition, DGGE is a reliable technique to characterize microbial communities and identify fungal and bacterial species in complex soil systems.