Genotypic variation in xylem vessel anatomy in a replicated F₂ grapevine (Vitis spp.) population under field conditions in California

Abstract

Breeding for complex quantitative traits remains a major challenge in perennial crop systems, particularly for traits related to water use efficiency (WUE), which are strongly influenced by environmental variation and difficult to phenotype at scale. As water limitation intensifies in major grape-growing regions, identifying genetically controlled components of hydraulic architecture may provide new avenues for improving WUE in grapevine. We evaluated xylem vessel anatomy in a replicated VRS-F2 grapevine population produced from a selfed F1 (Vitis. sp. ‘19-9-2’) derived from a cross between Vitis riparia ‘Manitoba 37’ and Vitis sp. ‘Seyval blanc’. The resulting population consisted of 183 genotypes, each with three clonal replicates, which were planted in Greenfield, California and commercially managed. This population was expected to segregate for hydraulic traits, providing an opportunity to evaluate genetically driven differences in xylem structure under field conditions. Cane samples were collected in 2024 and 2025 during winter pruning, cross-sectioned, and imaged using UV light microscopy. ABiodock AI model was trained to annotate images and extract vessel size (area) and density. Leaf-level physiological measurements were collected at two time points in 2024 and 2025 growing season, and petioles of same leaf collected, cross-sectioned and imaged. Pruning weight and cane diameter? were collected to monitor vine vigor. Analyses indicate consistent genotypic differences in vessel size and density across years, suggesting xylem architecture is under partial genetic control. Variation in xylem traits is associated with differences in leaf physiological performance, indicating functional consequences for water transport and use. QTL mapping for xylem traits has been completed, and ongoing analyses will identify genomic regions associated with vessel size and density. These results lay the groundwork for integrating hydraulic traits into grapevine breeding programs aimed at improving water use efficiency under increasingly water-limited conditions.