Molecular methods for the detection of Ralstonia solanacearum (race3/biovar2) and for biovar differentiation.

Ralstonia solanacearum can be separated into 4 races and 5 biovars. R. solanacearum race3/biovar2 infects primarily potato, causing brown rot disease, and has never been reported to infect potato in the US. Brown rot disease is spread by latently infected seed potatoes; therefore a highly sensitive diagnostic method is required for quarantine purposes. In the present study, primer pairs designed from a novel repetitive insertion sequence were developed for PCR detection of R. solanacearum race3/biovar2. This PCR method provided a reliable and sensitive tool for the specific detection of all the R. solanacearum race3/biovar2 strains tested, including strains isolated from geranium in the US. Southern hybridization and rep-PCR analyses showed that the geranium strains are very closely related to the potato strains. A PCR/RFLP method based on the ribosomal protein operon was also developed for the molecular differentiation of 5 biovars, which are currently distinguished according to different biochemical properties .