Grapevine rootstock affects xylem vessel anatomy of the scion Pinot Blanc in response to water stress

• Rootstock significantly affected xylem anatomy of cv. Pinot Blanc under drought. • Two tolerant rootstocks induced contrasting strategies in water stress response. • 1103P induced a reduction of xylem vessel size and an increment of vessel number. • M4 showed stable xylem anatomy and water flow throughout the entire experiment. • A faster recovery after rehydration was performed by M4 grafting combination. Grafting is a common practice in modern viticulture for enhancing adaptation to environmental stresses. The new challenges related to climate change require innovation in rootstock genotypes for facing drought conditions, becoming increasingly frequent in many wine-growing regions. Understanding the influence of rootstock on scion response to water deficit is relevant for the success of future breeding programs. The aim of this study is to investigate the effect of two drought-tolerant rootstocks (i.e. M4 and 1103P) on physiological and morphological adaptation of Pinot Blanc to fast and severe water stress and recovery. The two grafting combinations were compared in pots under semi-controlled conditions. Progressive water deficit was applied for 12 days, followed by rewatering. Physiological response of vines was monitored, and morphological traits of leaves, petioles and stems grown under water stress were recorded. Xylem vessel density and size were also measured in stems and petioles and used to assess the theoretical hydraulic conductance (Kh). Results of the study highlighted a faster physiological response of Pinot Blanc to water stress when grafted onto M4 respect to 1103P, in both water deprivation and rewatering dynamics. The faster physiological recovery of M4 is also confirmed by Kh, which rapidly recovered to the well-watered levels in both stems and petioles. No significant modifications were induced by M4 in scion xylem vessel anatomy, whereas 1103P reduced vessel diameter and increased vessel density in response to water stress. This study emphasized the role of rootstock in short-term drought adaptation of grapevines, providing in-depth insights into the stress response mechanisms of drought-tolerant genotypes.