Pest survey card on Melampsora medusae f. sp. tremuloidis

This pest survey card was prepared in the context of the EFSA mandate on plant pest surveillance (M-2020-0114), at the request of the European Commission. Its purpose is to guide the Member States in preparing data and information for Melampsora medusae f. sp. tremuloidis surveys. These are required to design statistically sound and risk-based pest surveys, in line with current international standards. Melampsora medusae f. sp tremuloidis is one of the causal agents of leaf rust of poplar and is one of two formae speciales of M. medusae which has been recognised as a distinct phylogenetic species. The fungus native to North America, is a Union quarantine pest, not known to occur in the EU. The pathogen requires two hosts (aecial and telial hosts) to complete its life cycle through five stages and five types of fructifications and spores. The main aecial hosts belong to the family Pineaceae and the only known natural telial host is Populus tremuloides, with uncertainty about other Populus species. Detection surveys in the EU should target P. tremuloides, while delimiting surveys should target poplar species from the Populus section. The pathogen spreads naturally via wind-borne aeciospores and urediniospores and via human-assisted means, such as importing infected host plants. Climatic conditions are not to be considered a limiting factor for the establishment of the pathogen in the EU. However, the scarce presence of telial hosts may limit the pathogen’s establishment, unless it becomes able to jump onto a new host. Melampsora medusae f. sp. tremuloidis can be detected in the field through telial host specificity and observation of symptoms on poplar leaves in late summer, however these symptoms can be confused with those of European native rust fungi. Observation of morphological characteristics in the laboratory allows M. medusae to be distinguished from other Melampsora species, but not to distinguish the two formae speciales. Once the pathogen is identified at the species level, DNA-based methods must be used for identification at the formae speciales level. A molecular assay developed for M. medusae f. sp. deltoidis can serve as a negative control for identifying M. medusae f. sp. tremuloidis.