Screening of ornamental plants from the Botanic Gardens of Melbourne and Adelaide for the occurrence of Erwinia amylovora

Host plants of Erwinia amylovora in the Royal Botanic Gardens of Melbourne (RBGM) and the Adelaide Botanic Gardens (ABG) were inspected for symptoms of fire blight including dieback, and shoot and stem cankers. Forty five symptomatic plants were sampled and concurrently tested for the presence of E, amylovora at the Institute for Horticultural Development, Victoria; Macquarie University, New South Wales; and the Max Planck Institute, Germany. At Max Planck, E. amylovora was isolated from wood samples from a Cotoneaster (Ag0002) and a Sorbus sorbus (Ag0034) from RBGM, and from a soft agar culture of bacteria isolated in Australia from Ag0002 and forwarded to Germany. Wood samples from ABG tested negative. Identification was confirmed by tests on selective media, by polymerase chain reaction assays, and by reactions on tobacco, pear slices and juvenile apple plants. The patterns obtained by pulsed field gel electrophoresis of the strains isolated from Australian samples in Germany and New Zealand were identical with each other and with strains of E. amylovora from Central Europe, New Zealand and with the English standard strain Ea595. However, the German and New Zealand strains of E. amylovora isolated from Australian wood samples differed in the size of the short DNA sequence repeat within the amplified plasmid pEA29 fragment. Exhaustive attempts in both Australian laboratories to isolate E, amylovora by similar test protocols from wood samples from RBGM and ABG were unsuccessful. Extensive surveys since the original outbreak have not detected the disease or the pathogen.