Occurrence of "Candidatus Phytoplasma ulmi" in native elm trees in Germany
A countrywide survey has been performed to examine the occurrence of the elm yellows phytoplasma in three elm species native to Germany. The DNA of more than 5,000 trees was extracted and the presence of phytoplasmas verified by universal and pathogen-specific quantitative PCR assays. In total, 33% of all plants resulted phytoplasma-positive. The highest presence was found in the European white elm, followed by the wych elm and the field elm. Regional clusters of high incidence were found in east and in south-west Germany, while in the western states the phytoplasma presence was low or absent. Disease symptoms were only occasionally visible as witches’ broom for wych elm and yellowing and small leaves for field elm. The survey revealed that ‘Candidatus Phytoplasma ulmi’ is widespread in Germany questioning the current quarantine status of this pathogen.