SHARPSHOOTER FEEDING BEHAVIOR IN RELATION TO TRANSMISSION OF THE PIERCES DISEASE BACTERIUM

• Author(s): Backus, Elaine; Bennett, William; Blua, Matthew; Civerolo, Ed; Habibi, Javad; Purcell, Alexander; Yan, Fengming;
• Abstract: Backus is studying the stylet penetration (probing) behaviors of the glassy-winged sharpshooter (GWSS), and how they interact with populations of Xylella fastidiosa (Xf) to facilitate transmission to grape. Electropenetration graph (EPG) monitoring is combined with videotaping of stylet movements in artificial diet and histology of fed-upon plant tissues. For Objective 1, AC EPG waveforms have been identified, characterized, and correlated with salivary sheath formation, stylet advancement, ingestion, and sheath terminations in various cell types in grape. Results show that most probes are very long (8 hrs), and sustained ingestion events longer than 2 min generally occur in xylem. For Objective 2, a 2 x 4 factorial test was performed, using 2 probing treatments (short probe [pathway + 1 min ingestion] or long probe [pathway + 1 hr sustained ingestion]) and 4 bacterial detection methods (PCR, culturing, immunocytochemistry and symptoms). Results show that Xf inoculation can be PCR-detected from both short and long probes, and thus it occurs during pathway or the first minute of ingestion. Durations for waveforms B1, C and N were significantly different between PCR-positive and PCR-negative plants, for long probes only. This suggests that inoculation occurs when B1 is coupled with stylet tips in xylem. The bacterial detection methods compared have differential sensitivities; immunocytochemistry is the most sensitive, PCR is intermediate and culturing is the least sensitive. The more sensitive the test, the earlier and more frequently the bacteria were detected. Present results support the following inoculation hypothesis. Xf bacteria exit the stylets during brief stylet activities represented by the B1 waveform, probably within seconds of the first puncture of a penetrated cell, either along the path or in the xylem. Proper placement of the bacteria appears to be crucial; placement in xylem leads to growth of the bacteria sufficient for detection by less sensitive methods. Further analysis will test this hypothesis, and also associate this behavior with appearance of bacteria in the head. This research provides crucial baseline data for future development of a Stylet Penetration Index for inoculation behavior.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium