Detection of Pseudomonas savastanoi pv. savastanoi in Asymptomatic Olive Plants

Pseudomonas savastanoi pv. savastanoi (ex Smith) Young is the causal agent of olive (Olea europaea L.) knot disease. In countries where P. savastanoi pv. savastanoi has not been observed, it is mandatory to use P. savastanoi pv. savastanoi–free plant materials. A certification scheme for pathogen-tested olive trees and rootstocks is available through the European Plant Protection Organisation (EPPO). According to EPPO, every 7 years, each olive mother plant must be inspected visually for P. savastanoi pv. savastanoi olive knot symptoms, as well as for Verticillium dahliae, Spilocaea oleagina, and several viruses. Propagation materials should be produced and screened according to this scheme, and symptomatic plants should be eliminated. However, these procedures do not address the spread of P. savastanoi pv. savastanoi by asymptomatic olive plant materials. Traditional microbiological methods and PCR-based assays are available for the detection and identification of P. savastanoi pv. savastanoi. However, they do not differentiate between P. savastanoi pv. savastanoi, P. savastanoi pv. nerii, and P. savastanoi pv. fraxini strains. Here, several reliable PCR-based assays are reported, recently developed for the specific discrimination and quantification of these three P. savastanoi pathovars.