DETECTION OF RHIZOCTONIA-SOLANI AG-8 IN SOIL USING A SPECIFIC DNA-PROBE

A reliable method of detecting low levels of AG-8 isolates of Rhizoctonia solani in soil samples using the specific DNA probe, pRAG12, has been developed. The procedure involves separation of particulate organic matter from soil by flotation and sieving followed by extraction of DNA from a minimum of 0.1 g of the air dried material. Further purification through a Sepharose CL-6B column is required to remove the humic substances before AG-8 DNA can be measured in a slot blot assay. The procedure gives yields of DNA in excess of 80%. in addition, the DNA is pure enough to be used, without dilution, for RFLP analysis as well as DNA amplification using the PCR. The specificity and high copy number of the AG-8 probe and the rapid DNA purification procedure provide the means for a sensitive diagnostic test for X. solani in the soil and for fundamental studies on the biology of the fungus.