Relationships between populations of Pseudomonas syringae pv. persicae from different origins
It is recalled that Pseudomonas syringae pv. persicae (EPPO A2 quarantine pest) was first recorded in 1967 from the Rhone valley in France, and almost simultaneously from Hauwke's Bay in New Zealand. In France, the pathogen is confined to peach (Prunus persica) and nectarine (P. persica subsp. nucipersica). In New Zealand, it is found on peach, nectarine and Japanese plum (P. salicina). In 1966, a related pathogen was observed in England (in Kent) on myrobalan plum (P. cerasifera). Comparison studies of DNA restriction endonuclease fragment patterns were carried out in New Zealand on the relationships between populations of P syringae pv. persicae. In these studies, it was also attempted to explain the origin of the pathogen. One could wonder whether the pathogen had been present as independent populations in New Zealand and Europe or has been transported between the two hemispheres. Results showed first that the comparison of 31 strains from the three countries formed a single cluster. The authors felt that strains from England should be classified in P. syringae pv. persicae*. It was also found that fragment patterns produced by strains from France and England formed homogeneous but separate groups, while those from New Zealand were relatively heterogeneous. The data suggests that the populations from New Zealand are older than the European populations, and this could therefore indicate that the origin of P. syringae pv. persicae is in New Zealand (provided an ancestral population is not found elsewhere in the world). As populations from England and France are distinct, this could imply that separate introductions took place. However, many questions remains unanswered: e.g. the absence of likely ancestral hosts of P. syringae pv. persicae in New Zealand (Prunus spp. were introduced to southern New Zealand at the end of last century); the pathway to other countries, as there is no large-scale dissemination of stone-fruit planting material from New Zealand to the northern hemisphere.
* EPPO note: P. syringae pv. persicae was previously not considered as present in United Kingdom.
Young, J.M.; Jones, D.S.; Gillings, M. (1996) Relationships between populations of Pseudomonas syringae pv. persicae determined by restriction fragment analysis.
Plant Pathology, 45(2), 350-357.