|WALKER, ANDREW - University Of California, Davis|
Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2017
Publication Date: 12/1/2017
Citation: Backus, E.A., Cervantes, F.A., Walker, A.M. 2017. Preliminary findings suggest that vector feeding behaviors controlling inoculation of Xylella fastidiosa are performed less on Vitis arizonica than on V. vinifera ‘Chardonnay’. CDFA Pierce's Disease Control Program Research Symposium. p. 171.
Technical Abstract: The most successful example of classical grapevine breeding for resistance to Xylella fastidiosa (Xf) is the PdR1 gene, which mediates resistance to Xf multiplication and spread in the host, once Xf has been inoculated. No effort has been made to determine whether resistance of PdR1 or its parent wild Vitis species affects inoculation of Xf during vector feeding. Use of electropenetrography (EPG) to study vector feeding in relation to Xf transmission has recently shown that the EPG X wave represents the Xf inoculation behavior. With this knowledge, it is now possible to determine whether V. arizonica or its PdR1-containing offspring might be additionally resistant to vector behaviors that control Xf inoculation. A quantitative EPG study was performed to test this hypothesis. Stylet probing behaviors of 80 blue-green sharpshooters, Graphocepha atropunctata, were EPG-recorded for about 10 h each; 20 insects on each of four treatments in a 2x2 factorial experimental design. Host plants were either V. arizonica or V. vinifera ‘Chardonnay.’ Sharpshooters either had not acquired Xf or putatively had acquired Xf (via a 4-day acquisition access period on symptomatic leaves of mechanically inoculated grapevines). Of the 20 insects per treatment, waveforms from six each have now been completely measured and analyzed using mixed model ANOVA and LSD pairwise comparisons via SAS. Preliminary conclusions are based on statistically significant differences (a=0.05) among treatments for these 24 insects. One X wave component, C1, is the most important for Xf inoculation, because it represents direct expulsion of fluid (potentially containing saliva-loosened bacteria) into xylem from the entire mouth cavity. C1 was performed two to seven times more often by inoculative insects on V. arizonica, compared with all other insects. However, each C1 event was four to 13 times shorter, causing the overall duration of C1 to be shorter. These preliminary findings suggest that, despite unusually frequent attempts to spit up bacteria, inoculative sharpshooters on V. arizonica are prevented from doing so for the typical long durations seen on Chardonnay. Some feature of V. arizonica xylem cells may present an impediment to fluid injection. Such a novel resistance trait could be pyramided with the PdR1 trait, for more durable field resistance to Xf.