A regional-scale survey to define the known and potential vectors of grapevine yellow phytoplasmas in vineyards South of Swiss Alps

The most important Grapevine Yellows (GY) phytoplasma diseases in Europe are Flavescence dorée (FD) and Bois noir (BN); they are spread in vineyard by two proven vectors, Scaphoideus titanus Ball and Hyalesthes obsoletus Signoret, respectively. Other potential vectors of GY have been identified, which are thought to play a secondary role. The GY control strategies are not always effective and an in-depth study on the ecological cycle of the pathogens at regional scale would be of paramount importance. This study was carried out in 48 representative sites of wine-growing area South of Swiss Alps, with the aim to identify known and potential vectors and to characterize the FD and BN phytoplasmas isolates. Out of 167 Auchenorrhyncha species recorded, 27 were known or potential vectors of phytoplasmas and five of those tested positive for phytoplasmas. S. titanus was infected by 16SrV-D subgroup phytoplasma and no clear relationship between its population density and disease outbreaks was observed. Orientus ishidae harboured 16SrV-C and 16SrV-D subgroups suggesting its potential role in spreading 16SrV-C phytoplasma isolates from arboreal plants to grapevine and FD-D from grapevine to grapevine. H. obsoletus was infected by BN phytoplasmas, tuf-types a and b, however it was collected with relatively low abundance. Reptalus panzeri and R. cuspidatus tested positive to tuf-type b, but only R. cuspidatus was common and abundant in the investigated vineyards. To define the range of alternative vectors using a detailed approach on regional scale provides background information to get a more clear vision on the spreading of phytoplasmas in the vineyards.