Global warming raises concerns about temporal and spatial water availability in grape growing regions in many wine countries. In Europe, at present, irrigation in many areas is not a sustainable way to counteract low water availability, since legal limits, infra-structural problems (access to water, technological challenges (i.e. steep slopes)) and a growing competition for the resource water hampers the successful implementation of irrigation systems on a larger scale. Consequently, other practices potentially improving water management of vineyards and water acquisition by grapevines have to be considered. Aside of canopy systems and their management, plant material is a key issue. However, in many regions, such as Reingau (Hesse region, Germany) or Bordeaux (Aquitaine region, France), the reputation of wines is based on the use of specific grape varieties, such as Riesling or Cabernet Sauvignon and thus the potential for improving water use efficiency is limited. In this sense significant progress with respect to plant water relations may be achievable primarily through the adaptation of rootstocks, an important adaptive parameter to environmental stresses.

Studies on the underlying mechanisms of water stress adaptation in grapevines dealt mainly with eco-physiological, physiological and molecular responses of Vitis vinifera varieties and largely excluded rootstocks as a factor in acclimation. Even the large number of studies devoted to the subject of root to shoot signalling and resulting strategies in water management, such as partial root zone drying (PRD), have not included rootstock variations and to date there have been very few publications of molecular analyses on roots.
 
The main objectives of the study which should be conducted in the frame of the proposed PhD project, are to determine the underlying adaptive mechanisms to water stress of grapevine rootstocks. The study will largely focus on the root system. Several rootstocks (both established ones and new selections) will be compared under controlled conditions of limited water supply. Morphological (root anatomy parameters, vessels size and distribution) and physiological (e.g. hydraulic conductivity, cavitation susceptibility, gas exchange, abscisic acid content in xylem sap, water use efficiency, root and shoot growth) data will be collected in order to evaluate differences between genotypes. The final choice of these eco-physiological parameters will be based on the stage of plant development and root functioning. On several genotypes, roots will be collected at different stages of water limitation treatments to establish transcriptomic and metabolomic profiles. This will also be applied to several clones of a transgenic rootstock presumed to differ in root characteristics. The study should provide insight into the underlying mechanisms of root system responses to water limitation.

Most of the eco-physiological analysis will be conducted at the Geisenheim Research Centre (GRC), whereas metabolic and transcriptomic profiling would be performed at the Institut de Sciences de la Vigne et du Vin (ISVV) in Bordeaux. The experimental set up will be organised to allow the successful candidate to follow the experiments in the two locations.