Targeted mutations in Xylella fastidiosa affect acquisition and retention by the glassy-winged sharpshooter, Homalodisca vitripennis

Authors: Sengoda-Gounder, Venkatesan; Shi, Xiangyang; Krugner, Rodrigo; Backus, Elaine; Lin, Hong

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2019
Publication Date: 1/6/2020
Citation: Sengoda-Gounder, V., Shi, X., Krugner, R., Backus, E.A., Lin, H. 2020. Targeted mutations in Xylella fastidiosa affect acquisition and retention by the glassy-winged sharpshooter, Homalodisca vitripennis. Journal of Economic Entomology. 113(2):612-621. https://doi.org/10.1093/jee/toz352.
DOI: https://doi.org/10.1093/jee/toz352

Interpretive Summary: Xylella fastidiosa (Xf) causes Pierce’s Disease (PD) of grapevines. The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is one of the vectors that transmit this phytopathogenic bacterium to plants. To assess the role of four Xf virulence genes on transmission by GWSS, mutant strains of the bacteria were constructed and evaluated for adherence and retention to the insect foregut, and for efficiency of transmission to grapevines. While some mutants exhibited reduced colonization and an altered bacterial population density in GWSS foreguts relative to wild type, all mutants remained capable of being transmitted by GWSS. These results indicate that strategies aimed at disrupting the transmission process likely must completely eliminate colonization of the insect foregut to be effective as a practical means of controlling PD.

Technical Abstract: Xylella fastidiosa is a xylem limited bacterium that causes Pierce’s Disease of grapevines. The bacterium is transmitted between plants by insect vectors such as the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis. In this study, greenhouse experiments were conducted to compare the role of selected X. fastidiosa genes on 1) bacterial acquisition and retention in insect foreguts, and 2) transmission to grapevines by GWSS. Mutant bacterium genotype treatments used were Xf-'pilG, Xf-'pilH, Xf-'gacA, and Xf-'popP; and X. fastidiosa wild type (WT) as control. After feeding on artificial insect diet treated with each bacterial genotype, the proportion of X. fastidiosa-positive insects within treatments did not change over incubation periods ranging from 12h to 30 days post bacterial acquisition but did vary among treatments. A larger proportion of X. fastidiosa-positive insects was observed for treatments Xf-'pilG (0.52), Xf-'gacA (0.45), and WT (0.45) compared to Xf-'popP (0.25) and Xf-'pilH (0.03). Overall, the number of X. fastidiosa genome copies detected per insect over time was consistently high and low in Xf-'pilG- and Xf-'pilH-fed insects, respectively. The glassy-winged sharpshooter transmitted all bacterial genotypes to grapevines. There were no differences in the proportion of infected grapevines among treatments (range = 0.07 to 0.2) despite large differences in bacterial population sizes in insects among treatments. Results indicate that in order to stop spread of X. fastidiosa by vectors using gene-level targets, complete disruption of bacterial colonization mechanisms is required.