An unknown trees die back caused by Pseudomonas species in Switzerland

A model for tree pathogen diagnosis – Prunus domestica L. has been studied against pathogenic bacteria. An orchard of 110 trees of P. domestica showed dying back symptoms in May 2009 and nineteen of these trees were eradicated and burnt for prophylaxis. No symptoms correlated with those caused by pathogens previously observed in stone fruit die back in Europe or elsewhere (Pseudomonas syringae pv syringae van Hall, Pseudomonas syringae pv morsprunorum Lazarowtz, Phytophthora sp., Diaporthe perniciosa Marchal., phytoplasma or viruses) were not found. Interestingly, cutting the trunk in transversal sections allowed the observation of stem heart necrosis which was mostly important at the grafting point. Isolations from necrotic stem heart allowed to identify anot yet described Pseudomonas species not related to P. syringae. The method described in the paper for isolation of pathogenic bacteria and their quick an reliable identification can be also applied for detection of pathogens in forest tree plantations.Przemysław Szmi