Introduction to Europe of Ralstonia solanacearum biovar 2, race 3 in Pelargonium zonale cuttings.
In December 1999, a sample of imported Pelargonium zonale cuttings was found to be infected by Ralstonia solanacearum in the UK. From September to December 2000, bacterial wilt was diagnosed in several Pelargonium nurseries in Belgium, Germany and the Netherlands. R. solanacearum biovar 2, race 3 was consistently isolated and identified. Surveys traced the origin of infections to cuttings produced in Kenya for the European market. Quarantine measures were imposed to prevent spread and persistence of the organism. Infections of R. solanacearum have not been found on imported cuttings or nurseries in European countries since then. The introduction of the pathogen in Pelargonium raised concern of spread to potato. In Kenya, it was found that the contamination most probably occurred through contaminated surface (river) water used for irrigation in the nurseries. Infection was found in different cultivars. The nurseries in Kenya have taken strict hygiene and water disinfection measures and eliminated all infected and probable infected plant material. Since than no further infections have been found. The R. solanacearum isolates from Pelargonium were characterized as R. solanacearum biovar 2, race 3 on the basis of host range, morphology, serology, PCR (also using biovar-specific primers, REP-PCR, AFLP) and fatty acid patterns. Symptoms in Pelargonium, results of strain characterization and a proposed testing method for latent infections are presented.