Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 11/14/2005
Publication Date: 12/7/2004
Citation: Freeman, T.P., Leopold, R.A., Nelson, D.R., Buckner, J.S., Henneberry, T.J. 2004. Ultrastructural contributions to the study of the glassy-winged sharpshooter and Pierce's Disease. Proceedings of CDFA Pierce's Disease Control Program Research Symposium. p. 100-102.
Technical Abstract: The objectives of this research were to ascertain the path of glassy-winged sharpshooter (GWSS) mouthparts from the epidermal layer to the vascular tissue of the host plant, to ascertain if the sharpshooter had fed in parenchymatous or phloem tissue en route to xylem tissue, and to determine the ultrastructure of the salivary sheath and its association with all plant tissues encountered from the epidermal layer to the xylem tissue. Using a variety of microscopic techniques including light microscopy, confocal scanning light microscopy, transmission electron microscopy, and scanning electron microscopy, results showed that many un-branched salivary sheaths and branches of very complex sheaths, formed by nymph and adult sharpshooters, did not always extend directly from the host-plant epidermis to the xylem tissue. We observed that both nymph and adult sharpshooters produce salivary exudates during probes that do not reach the xylem, suggesting that they may be feeding in host cells located between the epidermal layer and the xylem. It was observed that vessel elements penetrated by the GWSS stylet became partially or completely occluded with salivary sheath material, a situation that could disrupt water translocation. In our greenhouse and laboratory studies, host plants fed on by sharpshooters for several days to weeks began to show symptoms similar to those of plants shown by others to be infected with the GWSS-specific bacterium, Xylella fastidiosa. These symptoms occurred in our host plants even though the sharpshooters we study are free of Xylella. Our research is ongoing to determine the correlation of mechanical damage and occlusion of vessel elements to the onset of symptoms in non-Xylella-infected host plants.