Integrated field and laboratory assessment of Swiss grapevine cultivar susceptibility to flavescence dorée reveals a central role for plant-vector interactions
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Cultivar susceptibility strongly influences the epidemiology of vector-borne plant diseases, and understanding cultivar-specific variation can inform management strategies. This is particularly relevant for flavescence dorée, an incurable grapevine disease associated with a phytoplasma and transmitted by the leafhopper Scaphoideus titanus . In this study, we investigated the susceptibility of the main Swiss varieties, by combining controlled insect-mediated inoculation experiments with complementary field analyses conducted at progressively finer spatial scales. Together, these approaches allowed us to compare both infection probability and phytoplasma relative titre under standardised transmission conditions with disease incidence and relative titre under natural epidemiological conditions. For most cultivars, laboratory results were broadly consistent with field observations. However, a marked discrepancy emerged in the relative infection pattern between the two main grapevine cultivars grown in Switzerland: Chasselas and Pinot Noir. Under controlled conditions, they did not differ significantly in either their probability of infection or the phytoplasma relative titre, indicating no detectable difference in susceptibility to phytoplasma infection. In contrast, Pinot Noir consistently showed higher disease incidence than Chasselas under natural conditions. This pattern was observed across all spatial scales examined, from regional surveys to neighbouring vineyard plots, and was mirrored by higher phytoplasma relative titres. Importantly, under controlled conditions, S. titanus mortality during the one-week inoculation period was significantly higher on Chasselas than on Pinot Noir, indicating that Chasselas may provide a less favourable host for S. titanus . Together, these findings support the hypothesis that differences in field disease incidence between these cultivars may arise from differences in vector performance rather than intrinsic susceptibility to phytoplasma infection. This highlights the importance of considering plant-vector interactions, alongside susceptibility to infection, when assessing cultivar-specific vulnerability to vector-borne plant diseases.
Author summary
Grapevines are threatened by many diseases, including flavescence dorée, a serious disease associated with a phytoplasma, a wall-less bacterium that is transmitted between grapevines by the leafhopper Scaphoideus titanus . Because infected grapevines cannot be cured, disease management relies on removing infected plants, repeated insecticide applications against the vector, and annual surveillance. Here, we compared the susceptibility of the main grapevine cultivars grown in Switzerland by combining controlled transmission experiments with complementary field analyses based on ten years of disease surveillance data. Although the two main Swiss cultivars, Pinot Noir and Chasselas, were equally likely to become infected under controlled laboratory conditions, Chasselas showed a much lower disease incidence in vineyards. During the transmission experiments, we also found that insect mortality during the one-week inoculation period was substantially higher on Chasselas than on Pinot Noir. These findings suggest that Chasselas may be a lower-quality host for S. titanus , potentially contributing to the differences in disease incidence observed in the field. Further research is needed to test this hypothesis, which could help identify grapevine cultivars that are less suitable hosts for the insect vector and therefore less susceptible to flavescence dorée, ultimately informing breeding programmes and more sustainable disease management strategies.
