The reduced canopy area in esca-symptomatic grapevine plants leads to lower canopy transpiration and mitigates water stress

In perennial plants, abiotic and biotic stresses may occur in combination and/or in sequence over many years, making understanding and predicting the combined effects of drought and pathogens on plant health and productivity a considerable challenge. In this study, we investigated the susceptibility of esca-symptomatic grapevines (Vitis vinifera L.) to drought. Esca is a grapevine vascular disease leading to decreased vineyard longevity worldwide. Using transplanted, naturally infected 20-yr-old "Sauvignon blanc" vines with known esca histories, we subjected esca-symptomatic and asymptomatic control vines to different drought periods. Whole-plant and leaf physiology, radial growth, anatomical traits, and long-term recovery were compared among treatments. Esca leaf symptoms were associated with stem xylem vessel occlusion, leaf drop, and decreased symptomatic leaf gas exchange, resulting in reduced canopy area and thus, lower whole canopy transpiration. When esca-symptomatic plants were subjected to drought, declines in water potential, CO2 assimilation and stomatal conductance measured on green leaves, as well as canopy maximum transpiration, were delayed. Water stress did not cause a significant increase in stem xylem occlusion. The esca-symptomatic stems showed greater radial stem diameter recovery that coincided with faster regrowth of healthy new shoots at the top of the plant associated with a recovery of whole plant gas exchange. Esca mitigates the effects of drought through reduced canopy area, confirming an antagonistic interaction between these stresses. These results demonstrate the importance of combining abiotic and biotic stresses and understanding their interactions when studying dieback in the climate change context.