Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 9/28/2018
Publication Date: 11/24/2018
Citation: Backus, E.A., Ledbetter, C.A. 2018. Preliminary findings support that vector feeding behaviors controlling inoculation of Xylella fastidiosa are performed less on three backcross siblings of PdR1 parents than on Chardonnay. CDFA Pierce's Disease Control Program Research Symposium. p. 167.
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 grapevine. PdR1 originated from from wild grape species such as Vitis arizonica and was introgressed into V. vinifera cultivated genotypes. Electropenetrography (EPG) makes it possible to study whether vector feeding behaviors that control Xf transmission (acquisition, retention, and inoculation) could be affected by wild grapes or their PdR1-containing offspring. If so, then PdR1 might confer resistance to Xf transmission, in additon to bacterial multiplication and spread. The sharpshooter EPG X wave should be diagnostic for such a behavioral resistance mechanism because it is thought to represent Xf inoculation. Last year, it was reported that X waves of blue-green sharpshooters, Graphocephala atropunctata, were different for inoculative versus clean insects, and those on resistant versus susceptible grape. This year, preliminary findings from a second study of blue-green sharpshooter feeding continue to support a behavioral component to PdR1 resistance. Stylet probing behaviors of 80 sharpshooters were EPG-recorded; 20 each on four, non-factorial treatments. All sharpshooters had putatively acquired Xf Stags Leap (were inoculative). Host plants were either Chardonnay or one of three PdR1 accessions (8909-8, 8909-17, and A81-139) resulting from offspring of V. arizonica b43-17 X V. vinifera, then backcrossed to V. vinifera. Preliminary results from six out of 20 insects per host plant were statistically tested (a=0.05). Sharpshooters on Chardonnay made more frequent but shorter probes containing more X waves than did insects on all three PdR1 siblings. In addition, xylem sap ingestion was significantly longer on all three PdR1 siblings than on Chardonnay. It is possible that, while sharpshooters might acquire more bacteria during xylem sap ingestion (if Xf were present) on the PdR1 siblings, they would be less likely to inoculate it to clean PdR1 plants than to susceptible Chardonnay. EPG could be used to identify novel resistance traits to pyramid with the PdR1 traits, for more durable field resistance to Xf in the future.