Towards an understanding of the impact of drought and elevated CO₂ on the plant-vector-virus interactions of grapevine leafroll disease

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In times of climate change, plant health in natural and agricultural ecosystems is affected by abiotic climate change-related stressors in combination with the biotic stress of pests and pathogens. This project aims to evaluate the effects of abiotic climate change-related stressors, such as elevated CO₂ and drought stress, on the interaction between grapevine plants, Grapevine leafroll-associated virus (GLRaV), and its vector, the mealybug Planoccus ficus. GLRaV, specifically the type GLRaV-3, alters the plant's CO₂ assimilation, water use efficiency, and primary and secondary metabolites which eventually leads to reduced yield, delayed fruit maturity, and poor grape quality. The virus spreads through the use of infected propagation material and phloem-sucking insect vectors, such as mealybugs. Elevated CO₂ and water stress can have a significant impact on plant physiology and insect pests. On the other hand, plant viruses cause biotic stress to plants and alter vector behavior, but they are also exposed to the same climate-change-related abiotic stressors as any other member of the ecosystem. There are very few studies on climate change impacts on viral infections in grapevine, and none on mealybugs as virus vectors. Deriving conclusions from other pathosystems is difficult since the effects of abiotic climate-change-related stress usually are species-specific. So far, research has experimented mostly on pairwise interactions of single climate change parameters with plants, insects, or pathogens. Now, broader research approaches are needed to understand the interactions among multiple stressors and the complex relationships among plants, pathogens, and vectors. In this way, research can facilitate the development of effective management and adaptation strategies that are needed to maintain plant health and productivity in the face of climate change. The project proposes a series of experiments exposing grapevines to two climate change parameters (water stress + CO₂) in combination with biotic stress from GLRaV-3 infection. Starting with classic transmission experiments, I will evaluate the susceptibility, infectiousness, and virus titers of grapevines under different climatic conditions. The next step will assess the mechanisms (gene expression) and the effects on plants (amino acids, phenols, C/N, sugars, Chlorophyll). In addition, the influence of GLRaV, water stress, and eCO₂ on the food preference and fitness of mealybugs is also investigated. The call for multifactorial stress experiments has been made for decades. These experiments are ambitious and complex, but they are the necessary next step to gain insight into the evolution of leafroll disease in the future.