Recent spread of the “flavescence dorée” disease in north-eastern Italy

Recently, in the northern grapevine-growing area of Udine province (Friuli Venezia Giulia region) an epidemic of “flavescence dorée” (FD) disease is spreading. With the aim to investigate the genetic variability of the FD phytoplasma, 72 and 5 strains identified respectively in grapevine and Scaphoideus titanus samples, collected in the years 2016–2018 both in the epidemic area and in previous infected areas of Friuli Venezia Giulia, were typed by nested-PCR/RFLP analyses based on 16S rRNA and map genes. Both analyses produced two restriction profiles among FD phytoplasmas: map-FD2 (16SrV-D) and map-FD3 (16SrV-C). Only the map-FD2 was identified in the insects. In grapevines, map-FD2 type was the prevalent (73.6%) and according to the province of origin, it was predominantly present in Udine province (95%); whereas in Pordenone province the two map-FD types were almost equally distributed: map-FD2 in 45% of grapevine samples and map-FD3 in 55%. Map gene sequence analysis performed on 20 FD phytoplasma selected strains, confirmed their assignment to map-FD types and showed 100% sequence identity within each map-type. Based on the preliminary data obtained from the investigation on the wild plants there are no elements that suggest their potential involvement as FD-phytoplasma source for the infected vineyards in the new epidemic area studied.