The role of reservoir plants and alternative vectors for the spread of Flavescence dorée (FD) phytoplasmas in FD-free regions: Lamprotettix nitidulus identified as a new vector

Abstract The vineyards of Palatinate (Germany) and Alsace (France) in the Upper Rhine valley are still free from Flavescence dorée (FD) disease, but the main vector in grapevine, the leafhopper Scaphoideus titanus , has recently been detected. Knowledge of reservoir plants and alternative vectors of FD phytoplasmas (FDp) is crucial for management strategies. An interregional survey showed that among 12 main wild woody plants and liana species sampled in the environments of vineyards, only alders were infected by FDp, with high prevalence of MAP-FD2 genotypes. Yellow sticky traps were used to record the abundance and analyze the natural infection rate of potential leafhopper vectors on alders, clematis and cultivated grapevine. Live specimens were collected for inoculation trials. High infection rates and transmission capacities of resident Allygus spp. and the invasive Orientus ishidae were confirmed. In addition, five other Deltocephalinae species were identified as potential vectors of FDp. Lamprotettix nitidulus showed a high abundance and high infection rates with FDp in both regions. Its transmission competence of FDp to alder and broad bean could be demonstrated through repeated trials and high FDp titers were measured in infective individuals. Similar titers were measured in Synophropsis lauri, suggesting it could also transmit FDp. Fieberiella florii , Euscelidius variegatus and Japananus hyalinus may also play a role for the spread of 16SrV group phytoplasmas. Six new MAP-FD1 and FD2 genotypes were detected in leafhoppers. The prevalent and only transmitted genotype was M38: a vectotype II compatible with S. titanus transmission. The results show that the natural spread of FDp among alders is more complex than previously thought, and thus, the risk of transmissions to grapevine is more difficult to evaluate.