Investigations on the transmission pathway of 16SrV-C phytoplasma from Clematis vitalba to Vitis vinifera by Phlogotettix cyclops

Abstract: Flavescence dorée (FD) is a serious grapevine yellows disease in Europe caused by
phytoplasmas belonging to the 16SrV taxonomic group. The main FD phytoplasma (FDp) vector from grapevine to grapevine is the leafhopper Scaphoideus titanus (Ball, 1932). In addition to the grapevine-FD-S. titanus pathosystem, some wild plants play an important role in the epidemiology of FD. One of the reservoir host plants is Clematis vitalba L., for which it was shown that the planthopper Dictyophara europeae L. can occasionally transmit the subgroup 16SrV-C to grapevine. Previous studies in Austria indicated that the leafhopper species Phlogotettix cyclops (Mulsant & Rey, 1855) may act as a potential vector, as it occurred on clematis and grapevine, and both were also infected by 16SrV-C phytoplasmas.
In 2021, acquisition and transmission trials were carried out with Vicia faba and Vitis vinifera (cv. Chardonnay, potted plants and seedlings) to investigate, whether S. titanus could acquire 16SrV-C from test plants previously infected by P. cyclops and then infect healthy test plants in this way. Results of these trials showed for the first time that both, transmission from 16SrV-C phytoplasma positive clematis to V. faba (trial 1) and grapevine (trial 3) by P. cyclops, is possible and that further transmission by S. titanus to V. faba occurred. Thus, the transmission of 16SrVC phytoplasma from infected clematis to grapevine by P. cyclops in natural conditions seems possible but further investigations would be necessary to determine their ability to cause a FD infection in grapevines.