Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2014
Publication Date: 12/1/2014
Citation: Backus, E.A., Rogers, E.E. 2014. Multiple, stochastic factors can determine acquisition success of the foregut-borne bacterium, Xylella fastidiosa, by a sharpshooter vector. In: Proceedings of the 2014 Pierce's Disease Symposium. p. 6.
Technical Abstract: Xylella fastidiosa is a phytopathogenic foregut-borne bacterium whose vectors are sharpshooter leafhoppers. Despite several decades of study, the mechanisms of transmission (acquisition and inoculation) of X. fastidiosa still are not fully understood. Studies of the inoculation mechanism depend upon reliable and consistent acquisition of the bacteria by test sharpshooters. Reliability of acquisition was recently improved by development of an in vitro method, using artificial diets in parafilm feeding sachets to deliver bacteria to sharpshooters. However, while in vitro acquisition is more controlled than acquisition from plants, the number of bacteria acquired from diets by individual sharpshooters is still highly variable. The effects of several underlying factors were assessed in an attempt to improve the consistency of in vitro acquisition methods. Blue green sharpshooters, Graphocephala atropunctata, were allowed a 3-4 h acquisition access period on diets housing X. fastidiosa ‘Temecula’ or control, plain diets. Insects then were removed from the diets and caged for a 10-day multiplication period, in groups of 20 on small (8-10 cm tall) Chardonnay grapevines. Sharpshooter heads were dissected and tested using qPCR to determine the number of bacterial genomes in each head. Experimental factors such as: 1) duration of bacterial culture, 2) age and 3) gender of sharpshooters were correlated with the number of bacterial cells detected in the sharpshooter heads. Results suggest that acquisition of X. fastidiosa from diets can be made more reliable and consistent by standardizing the three factors listed above. Improving the reliability and consistency of X. fastidiosa acquisition will facilitate future experiments using electropenetrography (EPG) to determine whether insects with and without acquired bacteria feed differently on resistant and susceptible grapevines. Ultimately, this research aims to improve host plant resistance to X. fastidiosa by selecting grapevines resistant to inoculation of the bacterium by the vector.