Grapevine is a crop of global economic importance which is often cultivated in dry Mediterranean climates. In the context of climatic change, periods of drought could increase and become more intense. Growers will face increasing pressure to increase irrigation efficiently and/or adopt new grapevine varieties with increased drought resistance and water use efficiency. Adapting viticulture to these challenges requires an improved understanding of how grapevines behave under drought to enable sustainable management strategies and develop new varieties and rootstocks. This chapter summarizes our current understanding of the changes in physiology, signaling, metabolism, and gene expression that mediate grapevine's response and adaptation to drought.

Some grapevine rootstocks perform better than others during and after drought events, yet it is not clear how inherent and stress-induced differences in root morphology and anatomy along the length of fine roots are involved in these responses. Using a variety of growing conditions and plant materials, we observed significant differences in root diameter, specific root length (SRL) and root diameter distribution between two commonly used commercial grapevine rootstocks: Richter 110 (110R; drought resistant) and Millardet et de Grasset 101-14 (101-14Mgt; drought sensitive). The 110R consistently showed greater root diameters with smaller SRL and proportion of root length comprised of fine lateral roots. The 110R also exhibited significantly greater distance from tip to nearest lateral, longer white root length, and larger proportion of root length that is white under drought stress. Mapping of fine root cortical lacunae showed similar patterns between the rootstocks; mechanical failure of cortical cells was common in the maturation zone, limited near the root tip, and increased with drought stress for both genotypes; however, lacuna formed under wetter soil conditions in 110R. Results suggest that drought resistance in grapevine rootstocks is associated with thick, limitedly branched roots with a larger proportion of white-functional roots that tend to form lacuna under more mild water deficit, all of which likely favor continued resource acquisition at depth.