Conventional and real-time PCR assays for detection and identification of Rhizoctonia solani AG-2-2, the causal agent of root rot of sugar beet

Soil-borne fungi belonging to the genus Rhizoctonia are considered to be among the most destructive sugar beet pathogens. Although multinucleate R. solani AG-2-2 is frequently detected as the main causal agent of root rot of sugar beet worldwide, several binucleate (AG-A, AG-E and AG-K) and multinucleate Rhizoctonia (R. solani AG-4, AG-5 and AG-8) have also been included in the disease complex. Due to their soil-borne nature and wide host range, the management of Rhizoctonia root rot of sugar beet is highly demanding. Identification of Rhizoctonia AG associated with root rot of sugar beet is the essential first step in determining a successful disease management strategy. In this paper we report a highly specific and sensitive real-time PCR protocol for detection of R. solani AG-2-2 which showed a high level of specificity after testing against 10 different anastomosis groups and subgroups, including AG-2-1 as the most closely related. Moreover, a similar conventional PCR assay showed the same specificity but proved to be at least a 100 times less sensitive. Future research will include further testing and adaptation of this protocol for direct detection and quantification of R. solani AG-2-2 in different substrates, including plant tissue and soil samples.