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 species were 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.

Bois noir is an important grapevine yellows disease in Europe that can cause serious economic losses in grapevine production. It is caused by stolbur phytoplasma strains of the taxonomic group 16Sr‐XII‐A. Hyalesthes obsoletus Signoret (Hemiptera: Cixiidae) is the most important vector of bois noir in Europe. This polyphagous planthopper is assumed to mainly use stinging nettle [Urtica dioica L. (Urticaceae)] and field bindweed [Convolvulus arvensis L. (Convolvulaceae)] as its host plants. For a better understanding of the epidemiology of bois noir in Switzerland, host plant preferences of H. obsoletus were studied in the field and in the laboratory. In vineyards of Western Switzerland, adults of H. obsoletus were primarily captured on U. dioica, but a few specimens were also caught on C. arvensis, hedge bindweed [Calystegia sepium (L.) R. Brown (Convolvulaceae)], and five other dicotyledons [i.e., Clematis vitalba L. (Ranunculaceae), Lepidium draba L. (Brassicaceae), Plantago lanceolata L. (Plantaginaceae), Polygonum aviculare L. (Polygonaceae), and Taraxacum officinale Weber (Asteraceae)]. The preference of the vector for U. dioica compared to C. arvensis was confirmed by a second, more targeted field study and by the positioning of emergence traps above the two plant species. Two‐choice experiments in the laboratory showed that H. obsoletus adults originating from U. dioica preferred to feed and to oviposit on U. dioica compared to C. arvensis. However, H. obsoletus nymphs showed no host plant preference, even though they developed much better on U. dioica than on C. arvensis. Similarly, adults survived significantly longer on U. dioica than on C. arvensis or any other plant species tested [i.e., L. draba and Lavandula angustifolia Mill. (Lamiaceae)]. In conclusion, although nymphs of H. obsoletus had no inherent host plant preference, adults tested preferred to feed and oviposit on U. dioica, which is in agreement with the observed superior performance of both nymphal and adult stages on this plant species. Urtica dioica appears to be the principal host plant of H. obsoletus in Switzerland and plays therefore an important role in the epidemiology of the bois noir disease in Swiss vineyards.

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Grapevine red blotch virus (GRBV) is a recently described virus that infects grapevine. Little information is available on the possible occurrence and distribution outside North America. Therefore, we surveyed commercial vineyards from the three major grape-growing regions in Switzerland to determine the presence or absence of GRBV. In total, 3,062 vines were analyzed by polymerase chain reaction. None of the vines tested positive for GRBV, suggesting the absence of GRBV from Swiss vineyards. We also investigated whether GRBV was present in 653 grapevine accessions in the Agroscope grapevine virus collection at Nyon, including dominantly Swiss (457) but also international accessions. Only six referential accessions were infected by GRBV, all originating from the United States, whereas all others from 10 European and 8 non-European origins tested negative. High-throughput sequencing analysis of Zinfandel A2V13, in the collection since 1985, confirmed close similarity of GRBV isolate Z_A2V13 to American isolates according to genomes deposited in GenBank. Because the Zinfandel A2V13 reference was also maintained grafted on the leafroll virus indicator Vitis vinifera ‘Gamay’, we evaluated the effect of GRBV on viticultural performance over a 3-year period. Our results showed clear detrimental effects of GRBV on grapevine physiology (vine vigor, leaf chlorophyll content, and gas exchange) and fruit quality. These findings underscore the importance of implementation of GRBV testing worldwide in certification and quarantine programs to prevent the dissemination of this virus.

The complete genome sequence of a highly divergent strain of Grapevine leafroll-associated virus 4 (GLRaV-4) was determined using 454 pyrosequencing technology. This virus, designated GLRaV-4 Ob, was detected in Vitis vinifera 'Otcha bala' from our grapevine virus collection at Agroscope. The GLRaV-4 Ob genome length and organization share similarities with members of subgroup II in the genus Ampelovirus (family Closteroviridae). Otcha bala was graft-inoculated onto indicator plants of cultivar Gamay to evaluate the biological properties of this new strain, and typical leafroll symptoms were induced. A monoclonal antibody for the rapid detection of GLRaV-4 Ob by enzyme-linked immunosorbent assay is available, thus facilitating large-scale diagnostics of this virus. Based on the relatively small size of the coat protein, the reduced amino acid identity and the distinct serological properties, our study clearly shows that GLRaV-4 Ob is a divergent strain of GLRaV-4. Furthermore, molecular and serological data revealed that the AA42 accession from which GLRaV-7 was originally reported is in fact co-infected with GLRaV-4 Ob and GLRaV-7. This finding challenges the idea that GLRaV-7 is a leafroll-causing agent.