Grapevines under drought do not express esca leaf symptoms.

In the context of climate change, plant mortality is increasing worldwide in both natural and agroecosystems. However, our understanding of the underlying causes is limited by the complex interactions between abiotic and biotic factors and the technical challenges that limit investigations of these interactions. Here, we studied the interaction between two main drivers of mortality, drought and vascular disease (esca), in one of the world's most economically valuable fruit crops, grapevine. We found that drought totally inhibited esca leaf symptom expression. We disentangled the plant physiological response to the two stresses by quantifying whole-plant water relations (i.e., water potential and stomatal conductance) and carbon balance (i.e., CO2 assimilation, chlorophyll, and nonstructural carbohydrates). Our results highlight the distinct physiology behind these two stress responses, indicating that esca (and subsequent stomatal conductance decline) does not result from decreases in water potential and generates different gas exchange and nonstructural carbohydrate seasonal dynamics compared to drought.