UC Davis

Context and purpose of the study:Crossings of three wild Vitis species are commonly used worldwide as rootstocks in grape production. Disease resistance and vigor are among the most important factors for their selection. With climate change resulting in increasing water limitations, finding rootstocks conferring increased tolerance to drought will be of great importance as well. Therefore, identifying Vitis species with improved drought tolerance, and incorporating them into breeding programs could contribute to more resilient rootstocks under water-limiting conditions. Furthermore, these species will serve as valuable resources for increasing the genetic variation of the current rootstocks available. Investigating the leaf physiology of these species is pivotal, potentially offering valuable insights into their adaptive mechanisms under drought stress. We hypothesized that species native to drier habitats would exhibit a superior physiological performance under drought stress. Materials and methods: The root and canopy physiological characteristics, and the anatomical and biochemical bases of photosynthetic capacity of nine North American wild Vitis species across a wide latitudinal range (New England through Mexico) under two soil moisture treatments (controlled dry down (20–40% w/w ‘drought’) and maintained irrigated (70–90% w/w ‘control’)), were evaluated using a whole-plant experimental approach. We investigated the links between leaf structural diversity and physiological features that enhance photosynthetic capacity under controlled, non-stressed conditions and whether these relationships are upheld under prolonged water stress. Experiments were performed in a greenhouse under ambient atmospheric conditions using clonal and non-grafted saplings. Physiological parameters measured throughout the experiment included midday and predawn leaf water potentials, leaf gas exchange, root and leaf biomass, and spectral measurements. Additionally, X-ray imaging of plant tissues was performed at a single time point mid-experiment, and manual segmentation was used to prepare images for auto-segmentation using machine learning algorithms. Linear regression models were used to describe the relationships between anatomical and physiological variables, and their associations with biogeoclimatic variables. Results and discussion: Our data shows the impact of drought treatment and indicated differential responses to drought stress across species. Furthermore, structural differences that drive photosynthetic responses were observed. Elucidating canopy traits associated with improved performance under drought conditions could facilitate the rapid screening of germplasms to develop drought- tolerant rootstocks in the future. Keywords: Vitis, grapevines, water-use efficiency, water stress, drought tolerance