Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/25/2012
Publication Date: 8/1/2012
Citation: Wallis, C.M., Chen, J. 2012. Grapevine phenolics in xylem sap and tissues are significantly altered during infection by Xylella fastidiosa. Phytopathology. 102:816-826. Interpretive Summary: Pierce’s disease (PD), caused by Xylella fastidiosa (X.f.), is a serious disease of grapes in California with the potential to kill up to 30% of vines in areas where vector and pathogen presence is great. Long-term solutions for PD management lie in development of resistant cultivars. Key for developing resistant cultivars is knowledge of the interactions that occur between grapevines and X.f. This study examined accumulation of phenolic compounds in response to X.f. infection. Phenolic compounds were monitored from early stages of X.f. infection (before symptoms were observed) to late stages of infection (when plants where fully symptomatic). Before symptoms were observed, many phenolics were present in greater levels in xylem sap, tissues, and cell walls in X.f. infected plants compared to non-infected controls. However, by the time grapevines exhibited systemic PD symptoms, many phenolics where found at lower levels in X.f. infected plants than non-infected controls. It was hypothesized that severely diseased plants (greater than half of the foliage dead) were no longer capable of supporting phenolic production.
Technical Abstract: Pierce’s disease of grapevine (PD), caused by the bacterial pathogen Xylella fastidiosa (X.f.), remains a serious problem for grape production in California and elsewhere. This research examined induction of phenolic compounds in grapevines (cv. Thompson Seedless) infected with X.f. over a six month period. Two months post-inoculation with X.f., catechin, digalloylquinic acid, and astringin were found at greater levels in xylem sap; multiple catechins, procyanidins, and stilbenoids were found at greater levels in xylem tissues; and precursors to lignin and condensed tannins were found at greater levels in xylem cell walls. However, such large-scale induction of phenolic compounds were not observed four months after inoculation. Six months after inoculation, infected plants had significantly reduced phenolic levels in xylem sap and tissues when compared to control plants, including lowered levels of lignin and condensed tannins. At six months, PD symptoms were severe in infected plants and most photosynthetic tissue was abscised. These results suggest that even though grapevine may initially respond to X.f. infection with increased production of phenolic compounds, ultimately Pierce’s disease causes grapevines to enter a state of decline whereby diseased hosts no longer support secondary metabolite production, including defense-associated phenolic compounds.