Are grapevine plants recovered from Flavescence dorée susceptible to new infections by this phytoplasma?

Abstract: Grapevine can be affected by several phytoplasma diseases and, among them, Flavescence dorée is probably the most epidemic and dangerous in Europe, where it affects many viticultural areas in several countries. Recovery from phytoplasma infection is known for woody plants; this phenomenon is interesting because it can be exploited for the management of phytoplasma diseases in fruit growing and viticulture. Recently, in apricot trees, plants recovered from ESFY phytoplasmas, have shown a remarkable resistance to re-infections of this pathogen. The aim of this work was to ascertain if grapevine plants obtained from propagative material derived from FD-recovered plants show resistance/tolerance to new FD infections. To this purpose, potted cuttings of the cv. Barbera and Glera (from FD-recovered or from healthy, never infected plants) were exposed to FD-infected Scaphoideus titanus leafhoppers and then transplanted in the field. Their infection status was confirmed the following year by molecular detection and symptom observation. No difference in susceptibility to FD inoculation was recorded between plants derived from recovered and healthy vines of the same variety. More than 90 % of Barbera plants exposed to vector inoculation, compared to 30 % of Glera ones, became infected, confirming a very high susceptibility of Barbera cv to FD. Recovery can be exploited to manage FD in heavily infected areas on grapevine varieties that are prone to recover, but it does not provide immunity or tolerance to further re-infections.