Submitted to: Frontiers in Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/22/2013
Publication Date: 12/12/2013
Citation: Wallis, C.M., Wallingford, A.K., Chen, J. 2013. Grapevine rootstock effects on scion sap phenolic levels, resistance to Xylella fastidiosa infection, and progression of Pierce’s disease. Frontiers in Plant Physiology. 4:502. http://dx.doi.org/10.3389/fpls.2013.00502. Interpretive Summary: Pierce’s disease (PD) causes substantial losses each year for the ~$8 billion Californian grape industry. One component of an effective PD management program could be using rootstocks that impart increased tolerance to commercially-valuable grapevine scions. Grapevines that consisted of Cabernet Sauvignon or Chardonnay grafted to 13 different rootstocks were infected with Xylella fastidiosa (the pathogen causing PD) and evaluated for symptoms after six months. Grapevines grafted to ‘Freedom’, ‘Salt Creek’, ‘101-14 MG’, and ‘420A’ exhibited the mildest PD symptoms. To assess why these rootstocks imparted greater tolerance, levels of defense-associated phenolic compounds were assessed from grapevine xylem sap. However, only caftaric acid was present in significantly greater amounts in rootstocks that reduced scion PD severity. Grape growers who are concerned about PD could use grapevines grafted to ‘Freedom’, ‘Salt Creek’, ‘101-14’, or ‘420A’. Knowledge gained from this study also improves understanding about how rootstocks affect xylem sap phenolic levels and xylem-limited pathogens.
Technical Abstract: The xylem-limited bacterium Xylella fastidiosa (Xf) causes Pierce’s disease (PD), an important disease of grapevine, Vitis vinifera L. Grapevine rootstocks were developed to provide increased resistance to root disease, but rootstock effects on cane and vine diseases remain unclear. Grapevines that consisted of Cabernet Sauvignon or Chardonnay grafted to 13 different rootstocks were inoculated with Xf and evaluated for PD severity and Xf titer after six months. A subset of six rootstock/scion combinations had xylem sap phenolic levels assessed in non-infected and Xf-infected grapevines. Vigor also was analyzed by measuring root lengths and masses. Cabernet Sauvignon grafted to ‘101-14MG’, ‘1103P’, ‘420A’, or ‘Schwarzmann’ had reduced PD severity compared to Cabernet Sauvignon grafted to ‘110R’, ‘5BB’, or ‘SO4’. Chardonnay grafted to ‘Salt Creek’ or ‘Freedom’ had reduced PD severity compared to Chardonnay grafted to ‘RS3’ or ‘Schwarzmann’. Chardonnay grafted to ‘RS3’ had greater Xf titer than Chardonnay grafted to ‘101-14MG’, ‘Freedom’, or ‘Salt Creek’. No other differences in Xf titer among rootstocks were observed. Of the six scion/rootstock combinations which had xylem sap phenolics analyzed, Chardonnay/ ‘RS3’ had the highest levels of most phenolics whereas Cabernet Sauvignon/ ‘110R’ had the lowest phenolic levels. However, Chardonnay/ ‘101-14MG’, which had mild PD symptoms, had greater sap levels of caftaric acid than other scion/rootstock combinations. Sap levels of caftaric acid, methyl salicylate, a procyanidin trimer, and quinic acid were greater in Xf-infected versus non-infected grapevines. Chardonnay on ‘101-14MG’ or ‘Salt Creek’ had greater root mass than Chardonnay on ‘RS3’. Cabernet Sauvignon on ‘101-14MG’ had greater root mass than Cabernet Sauvignon on ‘110R’. These results identified rootstocks with the capacity for reducing PD symptom progression. Rootstocks also were shown to affect Xf titer, xylem sap phenolic levels, and plant vigor.