|SHUGART, HOLLY - University Of Florida|
Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/25/2017
Publication Date: 12/12/2017
Citation: Backus, E.A., Shugart, H., Cervantes, F.A. 2017. Association of the sharpshooter X wave with xylem inoculation of Xylella fastidiosa leading to systemic, symptomatic Pierce’s diesease infection in grape. CDFA Pierce's Disease Control Program Research Symposium. p. 237.
Technical Abstract: Despite several decades of study, the mechanism of inoculation of X. fastidiosa (Xf) to grapevines by its sharpshooter vectors still is not fully understood. Recent research showed that Xf is inoculated into or onto artificial diets by a combination of egestion and salivation. However, the salivation-egestion mechanism has not been: 1) demonstrated in plants, 2) associated with the sharpshooter X wave (the proposed electropenetrography [EPG] waveform thought to represent salivation and egestion), nor 3) associated with systemic Pierce’s disease (PD) symptoms. Herein is reported results of a preliminary experiment consistent with all three associations for the salivation-egestion hypothesis. Non-inoculative blue green sharpshooters were wired for EPG recordings, then were individually allowed 1–3 h of access to diets containing Xf ‘Temecula.’ One at a time, a wired insect was removed from a diet and immediately placed on a petiole of a small (8 – 10 cm tall) ‘Chardonnay’ grapevine for EPG. Each sharpshooter was allowed to make a single, marked probe until the stylets had reached a xylem cell and produced three, consecutive X waves in that cell, whereupon the insect was immediately removed from the plant; two control insects were not permitted to reach xylem before their probes were terminated. Probed grapevines were transferred to a greenhouse and held for 5 mo. for symptom development. Of the 26 insect-probed grapevines, 16 developed apparent PD symptoms, and 12 of those plants were found to be PCR-positive for Xf. Therefore, about half of the insects that fed on Xf-laden diets and then produced X waves on grape successfully inoculated Xf into xylem. Each of those single inoculation probes later led to a systemic, symptomatic PD infection that was confirmed by PCR. Neither of the two plants from control insects became infected. The experiment will be replicated two more times, including many more controls where insects are not permitted to reach xylem. If future tests continue to be successful, there will be conclusive evidence that the sharpshooter X wave represents Xf inoculation. Ultimately, this research aims to improve host plant resistance to Xf by using EPG of X waves to select grapevines resistant to Xf inoculation by the vector.