SEQUENCE-TAGGED SITE MARKERS TO IDENTIFY RHIZOCTONIA-SOLANI AG-4 OR AG-8 INFECTING WHEAT IN SOUTH AUSTRALIA

Polymerase chain reaction with random amplified polymorphic DNA primer s was used to generate polymorphisms from Rhizoctonia solani isolates of anastomosis groups (AG) 4 and 8. Products specific to AG 4 and 8 we re selected, cloned, sequenced, and used in conjunction with a publish ed AG 8 sequence to obtain four sequence-tagged site (STS) markers tha t produced different sized products from AG 4 and 8 isolates. A positi ve control primer (for ribosomal DNA [rDNA]) was mixed with the marker s, but to obtain products from both the rDNA and the R. solani DNA, th e magnesium concentration had to be increased. At the higher magnesium concentration, the specificity of one AG 8 primer changed to encompas s 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 iso lates, 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 c an be used to identify R. solani within wheat roots.