1a.Objectives (from AD-416):
1. Identification of PD resistance genes in Vitis species.
2. Molecular determination PD resistance mechanisms.
1b.Approach (from AD-416):
1. Identify candidate R genes from microarray global gene expression analyses.
2. Cloning and molecular characterization of target genes using in vitro expression system.
3. Develop R gene molecular markers for marker-assisted selection.
Results from this study are in support of Objective 2.D. of the in-house project, the goal of which is to identify genetic resistance mechanisms in Pierce's disease (PD) resistant grape species. Since the causal agent of PD (Xylella fastidiosa [Xf]) is limited to xylem vessels, the chemical composition of host xylem sap could play an important role in Xf pathogenesis. Vinifera-based grape cultivars are susceptible to Xf infection. However, some grape species such as V. arizonica, V. shuttleworthii, V. simpsonii, V. smalliana and Muscadinia rotundifolia are resistant. A laboratory assay was developed to evaluate bacterial growth and biofilm formation in media supplemented with xylem sap from PD-resistant or PD-susceptible grapevines. In addition, a microfluidic chamber was employed to assess motility of Xf treated with PD-resistant or PD-susceptible xylem sap. The results showed that growth and biofilm formation of Xf cells cultured in PD-resistant xylem sap were significantly less than that of PD-susceptible xylem sap. However, no significant differences in Xf motility were observed between resistant and susceptible xylem sap treatments. This study confirms that differences in xylem sap composition in PD-resistant and PD-susceptible grapes may affect Xf pathogenesis.