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 6 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/101-14MG 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 vs. 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.
Highlights
Grapevine cultivars are generally grown for specific fruit qualities and are predominately selections of Vitis vinifera L., which is propagated throughout the world
Pierce’s disease (PD) is caused by a strain of the xylem-limited bacterium Xylella fastidiosa Hopkins (Xf), which is thought to have originated in Northern Mexico and the Southeastern United States (Wells et al, 1987)
ROOTSTOCK EFFECTS ON PD SYMPTOMS Disease severity was significantly different due to rootstock for Cabernet Sauvignon (H = 18.423; P = 0.031; N = 67), with plants on 110R rootstock having greater PD severity than those on Schwarzmann, 101-14, 420A, 1103P, and O39-16 (Figure 1A)
Summary
Grapevine cultivars are generally grown for specific fruit qualities and are predominately selections of Vitis vinifera L., which is propagated throughout the world. PD is caused by a strain of the xylem-limited bacterium Xylella fastidiosa Hopkins (Xf), which is thought to have originated in Northern Mexico and the Southeastern United States (Wells et al, 1987). In these places, wild grape species are tolerant of the disease and do not exhibit symptoms when infected with Xf (Keller, 2010). V. solonis × V. riparia V. riparia × V. rupestris V. vinifera × V. rotundifolia V. berlandieri × V. riparia. 110 Richter (110R)* 101-14 Millardet et de Grasset (101-14)* 1616 Couderc 3309 Couderc O39-16 (3916) 420A Millardet et de Grasset (420A) 5BB [Kober] Schwarzmann SO4
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