Attilio Rizzoli

Flavescence dorée (FD) is a grapevine disease caused by 'Candidatus Phytoplasma vitis' (FDp), which is epidemically transmitted by the Nearctic leafhopper Scaphoideus titanus. In this study, we applied dendrochronological techniques to analyse the response to FDp infections in terms of wood ring widths and anatomical structures of the xylem and phloem tissues of the trunk of the susceptible grapevine cultivar 'Chardonnay.' As a rule, grapevines are susceptible to water shortage and reduce their growth in diameter in case of summer drought. In the season of the external expression of FD symptoms, however, the ring width reductions are extreme and supersede any drought-induced effects. In addition, the anatomy of the phloem tissue in the year of the FD symptom expression appears heavily disarranged. Moreover, in the most suffering individuals, the xylem formation remains incomplete and mostly limited to the early wood tissue. In conclusion, even though the FD phytoplasma does not inhabit and replicate inside the xylem tissue, our results confirm existing indirect inhibiting effects on the ring growth and the xylem tissue formation in FDp-infected grapevines.

Phytoplasma strains were sporadically found in specimens of Hishimonus hamatus, Japananus hyalinus and Graphocephala fennahi caught during an entomological survey conducted in Southern Switzerland on the edges and woods surrounding cultivated vineyards in 2017. The subsequent molecular characterization of the pathogens allowed to identify them as strains strictly associated to Flavescence dorée, a serious European grapevine disease, transmitted from vine to vine by the leafhopper Scaphoideus titanus. In particular, M12 and M50 genotypes were found in H. hamatus and J. hyalinus, respectively, while G. fennahi harboured mixed phytoplasma genotypes with at least two different Flavescence dorée isolates. The potential importance of these findings in the frame of the Flavescence dorée epidemics in Europe is discussed.

Anatomical modifications of xylem and phloem tissues of grapevine (Vitis vinifera) stems of shoots infected by the flavescence dorée phytoplasma (FDp) were first observed and described in the 1960s, but never quantified in detail. In this paper, we describe and quantify the impact of FDp on grapevine stem tissues, and relate it to the level of expression of symptoms and to cultivar‐specific FDp susceptibility. For this purpose, we measured and quantified the anatomical parameters of xylem and phloem tissues of a tolerant (Merlot) and a susceptible (Chardonnay) cultivar. For each cultivar, thin sections of eight shoots with symptoms from FDp‐infected grapevines, eight symptomless shoots from the same FDp‐infected grapevines, and eight symptomless shoots from symptomless grapevines (control) were compared. Results showed general inhibition of xylem growth and proliferation of phloem tissues (hyperplasia) with lack or irregular arrangement of the fibre‐sclereids in the axial phloem of the stems from shoots with symptoms, irrespective of the cultivar. Xylem vessels of infected Merlot shoots were partly occluded by tyloses and a higher number of smaller vessels were produced than in control plants. Thus, the anatomical responses confirmed the detrimental effect of FDp on stems of infected grapevine shoots, including impaired stem development and lack of periderm formation. Statistically significant differences were found between the two cultivars with different levels of susceptibility to FDp infection.

Flavescence dorée (FD) is a grapevine disease caused by associated phytoplasmas (FDp) which are epidemically spread by their main vector Scaphoideus titanus. The possible roles of alternative and secondary FDp plant hosts and vectors have gained interest in terms of better understanding of the FDp ecology and epidemiology. The findings of a survey conducted in the surroundings of three vineyards in the southern Swiss Alps aimed at studying the possible epidemiological role of the FDp secondary vector Orientus ishidae and the FDp host plant Alnus glutinosa are reported. This work demonstrates that O. ishidae is able to complete its biological cycle on A. glutinosa and to acquire FDp and 16SrV phytoplasmas very efficiently with an infection rate of 69% for the nymphal instars and 85% for the imagoes. A high prevalence of the map genotype M50 (map type FD1), which is included in the S. titanus - grapevine epidemiological cycle, was found in O. ishidae and A. glutinosa. Additionally, M12 (map type FD3), M44 and M47 were also sporadically detected. Surprisingly, the grapevines tested during this work were all infected by M54 (map type FD2) only, while the few S. titanus caught in the vineyard canopy were all FDp free. In conclusion, the occurrence of infected common alder stands and O. ishidae nearby vineyards do not seem to play a prominent role in FD epidemics in southern Switzerland. Nevertheless, wild vegetation acts as a reservoir of the FDp inoculum, which may locally trigger a FD emergence if S. titanus populations are established inside vineyards.

Nella diffusione della Flavescenza dorata (FD) giocano un ruolo anche piante come l'ontano nero, l'acero, il rododendro e l'azalea. Le misure di contenimento funzionano, ma una maggiore conoscenza del ruolo del bosco nella sua diffusione potrebbe migliorarne la gestione futura.

The first record of Erasmoneura vulnerata Fitch, 1851 in Switzerland is reported. Specimens were collected in 2019 using yellow sticky traps during a Scaphoideus titanus monitoring campaign in vineyards in Ticino (Southern Switzerland). E. vulnerata is a grapevine pest that has recently been introduced to Europe, whose phytophagy causes detrimental damage to grapevine leaves. Its occurrence in this area has likely been favored by the ongoing suspension of insecticide treatments for the control of the S. titanus population, the vector agent of the "Flavescence dorée" phytoplasma in grapevines.

The constant, even if low, presence of grapevine "flavescence dorée" (FD) in the vineyards of Ticino, Switzerland, challenged the stakeholders to investigate for other players involved in the FD dynamics. This study was aimed to explore the impact that the exotic leafhopper Orientus ishidae may have on FD epidemics in Ticino by monitoring its population density and level of infection with 16SrV group phytoplasmas. In 2018, 283 leafhoppers were collected from three FD infected areas, both from the vineyards and the surrounding landscape. Spatial density maps showed that the captures occurred mostly in the landscape, with a clear clustered distribution among the traps. Molecular analyses revealed a high infection percentage of O. ishidae samples in the three investigated plots, both inside and outside the vineyards.