Xylella fastidiosa infection effects on xylem sap and tissue phenolics in different grapevine cultivars

Authors: Wallis, Christopher; Wallingford, Anna; Chen, Jianchi

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2013
Publication Date: 7/24/2013
Citation: Wallis, C.M., Wallingford, A.K., Chen, J. 2013. Xylella fastidiosa infection effects on xylem sap and tissue phenolics in different grapevine cultivars. Physiological and Molecular Plant Pathology. 84:28-35.

Interpretive Summary: Pierce’s disease (PD) of grapevines, caused by the bacteria Xylella fastidiosa (Xf), is a major threat to the billion-dollar grape industry in California. Improvements in our knowledge of how different grape cultivars respond to Xf infection would contribute to optimizing breeding of tolerant varieties. Phenolic compounds, which have putative antibiotic activity against a variety of pathogens, were examined two-, four-, and six-months post-Xf inoculation in five different grapevine cultivars (Chardonnay, Flame seedless, Grenache noir, Merlot, and Rubired). For all five cultivars, phenolic levels in infected plants were greater than levels in non-infected plants four- and six-months after inoculation. Phenolic levels were negatively correlated with Xf titer, which suggests antibiotic roles for these compounds. However, phenolics also were positively correlated with disease severity. A possible explanation is that systemic acquired resistance responses against infection resulted in Xf becoming more virulent, causing it to aggregate more readily which resulted in increased PD symptoms. This occurred despite increased phenolic production which would putatively reduce Xf growth within the host.

Technical Abstract: The bacterium Xylella fastidiosa (Xf) causes Pierce’s disease (PD), a serious disease that threatens the billion-dollar California grape industry. Previous studies observed that Xf-infected grapevines, as part of a defense response, produced greater xylem levels of phenolics, which are compounds that inhibited Xf growth in vitro. Improved understanding of differences in host responses, including induced phenolic production, between cultivars exhibiting different rates of PD symptom development could contribute in optimizing breeding of PD tolerant grapevines. This study examined phenolic levels in xylem sap and tissues for five different cultivars (Chardonnay, Flame seedless, Grenache noir, Merlot, and Rubired) at two-, four- and six-months after Xf inoculation. Many phenolic compounds, including catechins, procyanidins, hydroxycinnamoyltartaric acds, and stilbenoids, were present at greater concentrations in xylem sap and tissues of infected plants versus controls four months post-inoculation. Fewer phenolics remained at elevated levels at six months. Various phenolics, especially catechins and procyanidins, were negatively associated with Xf titer implying antibiotic activity. However, many phenolics also were positively associated with PD disease severity. A possible explanation for this observation is that as a response to grapevine systemic acquired resistance responses, including increased phenolic production, aggregation of Xf increased, which resulted in increased PD symptom development.