Technical Abstract: Grapevine genotypes differ in their susceptibility/tolerance to Pierce’s disease (PD). This may be related to the concentration and presence or absence of chemical compounds in the xylem sap and/or due to anatomical features of the xylem. Here we report on a three-pronged comparative approach investigating various grapevine species ranging in PD tolerance. Results from in vitro xylem sap assays indicate a broad range of Xf growth responses in both planktonic growth and biofilm formation. Investigations into Xf population dynamics in the stem tissues of greenhouse grown plants, confirm large differences in the size of Xf populations between susceptible and tolerant genotypes. Microscopic investigations into xylem vessel occlusions document the differences in occlusion percentages as well as the kinds of occlusions prevalent among four different Vitis genotypes.