Phytoplasmas associated with Flavescence dorée (FDp) grapevine disease are
quarantine pathogens controlled through mandatory measures including the
prompt eradication and destruction of diseased plants, and the insecticide
treatments against the insect vector, the ampelophagous leafhopper Scaphoideus
titanus. In the present study, a multidisciplinary approach has been applied to
investigate the FDp ecological cycle in a test vineyard agro-ecosystem in Canton
Ticino, south Switzerland. Despite the scarce population density of S. titanus, a
regular trend of new infections (3.4% of the total vines) through the years
was observed. The leafhopper Orientus ishidae was found as the most abundant
among the captured insect species known as phytoplasma vectors (245 out
of 315 specimens). The population of O. ishidae was evidenced prevalently
(167 specimens) in the south-western side of the vineyard and within the
neighbouring forest constituted mainly by hazel (Corylus avellana) and willow
(Salix spp.). These plant specieswere found infected by FDp related strains (30%
of analysed trees) for the first time in this study. Interestingly, O. ishidae was
found to harbour FDp related strains in high percentage (26% of the analysed
pools). In addition, 16SrV phytoplasma group was detected for the first time
in the insect Hyalesthes obsoletus and a FDp related strain in Thamnotettix dilutior,
present in low populations within the test vineyard. Molecular characterisation
and phylogenetic analyses of methionine aminopeptidase (map) gene sequences
of FDp and related strains, here identified, revealed the great prevalence
of the map-type FD2 in grapevines (97%) and in O. ishidae pools (72%).
Such a map-type was found also in hazel and in T. dilutior, but not in S.
titanus. Moreover, map-types FD1 and FD3 were identified for the first time
in Switzerland in several host plants and phytoplasma vectors, including
grapevine (FD1), S. titanus (FD1) and O. ishidae (FD1 and FD3). Based on the
data obtained in this study, it is reasonable to hypothesise that the ecological
cycle of FDp could be related not exclusively to the grapevine-specific feeding
diet of S. titanus, but it could include other insect vector(s) and/or plant host(s).
Further studies will be needed to prove the role of O. ishidae as vector able to
transmit FDp from wild plants (e.g. hazel) to grapevine.