Submitted to: APS Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2004
Publication Date: 7/20/2004
Citation: Paulitz, T.C., Schroeder, K.L. 2004. A method for the quantification of rhizoctonia solani and rhizoctonia oryzae from soil using toothpicks. APS Annual Meeting. Phytopathology 94:S82.
Technical Abstract: Rhizoctonia solani AG-8 and R. oryzae are important root pathogens on wheat and barley in the dryland production areas of the inland Pacific Northwest. R. solani AG-8 is difficult to isolate from root systems and quantify in soil because of slow growth and low population densities. However, both pathogens form extensive hyphal networks in the soil and can grow a considerable distance from a food base. We developed a quantitative assay using toothpicks as baits inserted into sample soils. After 2 days in soil, toothpicks were placed on a selective medium, and the numbers of colonies that grew after 24 h were counted under a dissecting microscope. R. solani and R. oryzae could be distinguished from other fungi based on hyphal morphology. This method was tested in natural soils amended with known densities of R. solani AG-8 and R. oryzae. Regressions were used to compare the inoculum density/toothpick colonization curves to a predicted curve based on the volume of the toothpicks. The slopes and Y-intercept of log-log transformed regressions did not differ from the predicted curve in most cases. This technique was used to assess the hyphal activity of R. solani AG-8 and R. oryzae from soil cores taken from various positions in and around Rhizoctonia bare patches at two locations. Activity of R. solani was highest in the center and inside edge of the patch, but there was no effect of patch position on R. oryzae. This simple and inexpensive technique can be used for detection and diagnosis in grower fields and to study the ecology and epidemiology of Rhizoctonia.