Isolation, Characterization and PCR Tests of the Causal Agent of the Olive Knot Disease (Pseudomonas savastanoi pv. savastanoi) in North Jordan

Forty olive twigs showing symptoms of the olive knot disease were collected from randomly chosen olive orchards located from different locations in north Jordan, including: Irbid, North Mazar, Taibeh, and Korah. The causal agent of the disease (Pseudomonas savastanoi pv. savastanoi) was isolated and then characterized from all samples on the basis of biochemical and physiological tests (LOPAT and pathogenicity tests). The identity of the pathogen was confirmed by PCR tests. The primers used in these tests were specific to the iaaL gene of the bacterium and directed the amplification of a 454 bp fragment from all samples. Moreover, PCR detected P. savastanoi in symptomless olive samples as nine out of 13 of apparently healthy olive samples yielded the 454 bp fragment. This was made after enrichment of the bacteria in the sap of symptomless samples in the semiselective liquid medium PVF-1. The bacterial preenrichment step improved the PCR sensitivity level, allowing the detection of 10 CFU/ml of plant extract. In general, PCR assay proved to be specific, sensitive and faster than the routine methods for the detection and identification of this pathogen. It may also provide a useful tool for the early detection of low levels of P. savastanoi in olive plants during plant material propagation for certification purposes or epidemiological studies