Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract only
Publication Acceptance Date: 11/28/2012
Publication Date: 12/12/2012
Citation: Wallis, C.M., Wallingford, A.K., Chen, J. 2012. Induction of phenolic compounds in response to Xylella fastidiosa infection in five different grapevine cultivars. In: Esser, T., Randhawa, R. [eds.], Proceedings, 2012 Pierce's Disease Research Symposium. California Department of Food and Agriculture, Sacramento, CA pp. 253. Interpretive Summary:
Technical Abstract: Previously, Thompson seedless grapevines infected with Xylella fastidiosa (Xf), the causal agent of Pierce’s disease (PD), were observed to possess greater phenolic levels in xylem sap and tissues than non-infected plants shortly after inoculation. Plants often produce greater levels of phenolic compounds in response to pathogen infections, and commercially-available phenolic compounds were observed to inhibit Xf growth in vitro. Therefore, an improved understanding of induced phenolic production is needed to optimize efforts to breed PD-tolerant cultivars. Phenolic compounds in xylem sap were examined by high-performance liquid chromatography at two-, four- and six-months after mock- or Xf-inoculation for five different cultivars (Chardonnay, Flame seedless, Grenache noir, Merlot, and Rubired). No differences overall were observed at two months post-inoculation between mock- and Xf-inoculated grapevines, but Flame seedless and Grenache noir grapevines possessed greater levels of sap phenolics than Cardonnay, Merlot, or Rubired grapevines. Four months after mock- or Xf-inoculation, levels of catechins (catechin and epicatechin), procyanidins (various catechin dimers and trimers), and hydroxycinnamoyltartaric acids (coutaric acid and fetaric acid) were greater in xylem sap from Xf-infected versus control grapevines. Merlot grapevines had greater sap phenolic levels than the other cultivars four months after inoculation. Six months post-inoculation, levels of coutaric acid, hydroxyphenylpropionic acid, patulein, and a procyanidin B isomer were greater in Xf-inoculated versus mock-inoculated grapevines. Also six months after inoculation, Grenache noir grapevines had lower phenolic levels than the four other cultivars. Caftaric acid, fetaric acid, epicatechin, and four procyanidins were negatively associated with Xf titer suggesting antibiotic activity. Disease symptoms did not appear until six months after inoculation, at which time Merlot grapevines had greater symptom severity than Rubired. Disease severity did not otherwise differ between cultivars. Sap levels of procyanidins were positively correlated with disease severity measurements. It was possible that increased phenolic levels in xylem sap resulted in Xf aggregation and biofilm formation, which in turn resulted in greater PD symptom progression. This could explain why Merlot had significantly greater symptom expression than Rubired even though Merlot possessed more putatively antibiotic phenolic compounds than the other cultivars at four months post-inoculation.