Sequence-tagged site markers to identify Rhizoctonia solani AG 4 or 8 infecting wheat in South Australia

Polymerase chain reaction with random amplified polymorphic DNA primers was used to generate polymorphisms from Rhizoctonia solani isolates of anastomosis groups (AG) 4 and 8. Products specific to AG 4 and 8 were selected, cloned, sequenced, and used in conjunction with a published AG 8 sequence to obtain four sequence-tagged site (STS) markers that produced different sized products from AG 4 and 8 isolates. A positive control primer (for ribosomal DNA [rDNA]) was mixed with the STS markers, but to obtain products from both the rDNA and the R. solani DNA, the magnesium concentration had to be increased. At the higher magnesium concentration, the specificity of one AG 8 primer changed to encompass all R. solani tested. Wheat root DNA reduced the sensitivity of the STS primers. Wheat plants were inoculated with R. solani AG 4 or 8 isolates, and DNA extracted from tissue samples was tested with mixtures of the ribosomal and AG-specific STS primers. The results yielded both ribosomal and AG-specific markers, illustrating that this technique can be used to identify R. solani within wheat roots