First detection of 'Candidatus Phytoplasma ulmi' in Switzerland and in Orientus ishidae Matsumura, 1902

'Candidatus Phytoplasma ulmi' (Ca. P. ulmi) belongs to the ribosomal subgroup 16SrV-A and is associated with dieback, shoot proliferation and yellows disease on various Ulmus spp. Other plant species, such as Carpinus betulus and Prunus spp. have also been reported infected by the same pathogen. In 2021, in the frame of research activities focused on grapevine's Flavescence doree (FD), one specimen of Orientus ishidae - an East Palearctic leafhopper that was identified as an alternative vector of FD phytoplasmas was found harboring Ca. P. ulmi in southern Switzerland. No phytoplasmas were detected in plant samples taken in the same location. Orientus ishidae has already been reported to be able to acquire diverse phytoplasmas associated with other plant diseases, such as Peach X-disease. This is the first report of Ca. P. ulmi in Switzerland, as well as in O. ishidae. Ca. P. ulmi may potentially be present in the wild compartment of the Swiss Pre-alpine and Alpine range, but no dedicated survey has so far been conducted. In the case of O. ishidae, this finding highlights the broad affinity of such a species for the acquisition of several phytoplasmas. This calls for a further investigation regarding its potential role as a vector on various pathosystems of agronomic importance.