Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/8/2015
Publication Date: 11/1/2015
Citation: Backus, E.A., Shugart, H.J., Rogers, E.E., Morgan, J.K., Shatters, R.G. 2015. Sharpshooters may be “flying syringes:” First direct evidence of mixed egestion and salivation in inoculation of Xylella fastidiosa. American Phytopathological Society Annual Meeting. 105:S4.10. Interpretive Summary:
Technical Abstract: Despite nearly 70 years of research, the inoculation mechanism of Xylella fastidiosa by its sharpshooter vectors remains unproven. X. fastidiosa is unique among insect-transmitted plant pathogens because it is propagative but non-circulative, adhering to and multiplying on the cuticular lining of the anterior foregut. Thus X. fastidiosa is termed “foregut-borne.” A non-circulative mechanism for inoculation of X. fastidiosa must explain how bacterial cells exit the vector’s stylets via the food canal and directly enter the plant. A combined egestion-salivation mechanism has been proposed to explain these unique features. Egestion is the putative outward flow of fluid from the foregut via hypothesized bidirectional pumping of the cibarium (part of the foregut). The present study traced green fluorescent protein-expressing X. fastidiosa or fluorescent nanoparticles acquired from artificial diets by glassy-winged sharpshooters, Homalodisca vitripennis, as they were egested into simultaneously secreted saliva. X. fastidiosa or nanoparticles were shown to mix with gelling saliva to form fluorescent deposits and salivary sheaths on artificial diets, providing the first direct, conclusive evidence of egestion by any hemipteran insect. Therefore, the present results strongly support an egestion-salivation mechanism of X. fastidiosa inoculation. Evidence also suggests an additional model for inoculation: a column of fluid, potentially containing suspended bacteria, may be held in the foregut during the vector’s transit from plant to plant. Thus, sharpshooters could be true “flying syringes,” a new paradigm for X. fastidiosa inoculation.