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 Rhizocto nia solani in soil samples using the specific DNA probe, pRAG12, has b een developed. The procedure involves separation of particulate organi c 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 purific ation 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 i s pure enough to be used, without dilution, for RFLP analysis as well as DNA amplification using the PCR. The specificity and high copy numb er 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 an d for fundamental studies on the biology of the fungus.