Seasonal and long-term consequences of esca on grapevine stem xylem integrity

Hydraulic failure has been extensively studied during drought-induced plant dieback, but its role in plant-pathogen interactions is under debate. During esca, a grapevine (Vitis vinifera) disease, symptomatic leaves are prone to irreversible hydraulic dysfunctions but little is known about the hydraulic integrity of perennial organs over the short- and long-term. We investigated the effects of esca on stem hydraulic integrity in naturally infected plants within a single season and across season(s). We coupled in vivo X-ray microtomography visualizations with direct (ks) and indirect (kth) hydraulic conductivity measurements, and tylose and vascular pathogen detection. Although no loss of hydraulic conductivity (PLC) was observed in asymptomatic stems, 60% of symptomatic stems presented xylem occlusions with subsequent PLC, which could reach critical levels (over 50% PLC). A loss of stem ks was observed simultaneously, or after, the occurrence of leaf symptoms in the presence of tyloses. The impact of esca on xylem integrity was only seasonal and no long-term impact of disease history was recorded. Our study demonstrated how and to what extent a vascular disease such as esca, affecting xylem integrity, could amplify plant mortality by hydraulic failure.