Fast molecular detection of Pseudomonas syringae pv. aesculi in diseased horse chestnut trees

A molecular technique was used to detect the bacterium Pseudomonas syringae pv. aesculi in horse chestnut trees (Aesculus hippocastanum), affected by the recently recognized European ‘Pseudomonas horse chestnut bark disease’. The technique helped identify the pathogen within 6 h of sample preparation including DNA extraction, polymerase chain reaction (PCR) and electrophoresis until gel documentation. PCR primer pairs derived from the gyrase B gene sequence were used. Because of the great similarity in the gyrase B gene sequences of the numerous closely related P. syringae pathovars, the primers were not only totally specific to the pathovar aesculi, but also detected a few other pathovars. The assumption that other bacteria should not occur at least near to a necrotic lesion of a horse chestnut tree was corroborated by sequence identity of the PCR products obtained with the gyrase B gene sequence of P. syringae pv. aesculi. Koch’s postulates were fulfilled for an isolate of P. syringae pv. aesculi obtained from a diseased horse chestnut tree sampled in Hamburg in 2007.