Virulence comparison of a comprehensive panel of Xylella fastidiosa Pierce’s disease isolates from California

Authors: Burbank, Lindsey; GOMEZ, LAURA - Auburn University; SHANTHARAJ, DEEPAK - Auburn State University; Abdelsamad, Noor; Vasquez, Karen; Burhans, Alanna; Ortega, Brandon; Helm Rodriguez, Sydney; Strickland, Jaime; Krugner, Rodrigo; Naegele, Rachel

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2023
Publication Date: 5/16/2024
Citation: Burbank, L.P., Gomez, L., Shantharaj, D., Abdelsamad, N.A., Vasquez, K., Burhans, A.N., Ortega, B.C., Helm-Rodriguez, S.D., Strickland, J.A., Krugner, R., Naegele, R.P. 2024. Virulence comparison of a comprehensive panel of Xylella fastidiosa Pierce’s disease isolates from California. Plant Disease. 108(6):1555-1564. https://doi.org/10.1094/PDIS-09-23-1923-RE.
DOI: https://doi.org/10.1094/PDIS-09-23-1923-RE

Interpretive Summary: The pathogen Xylella fastidiosa is found in all grape growing regions in California. Many different strains of Xylella fastidiosa have been collected from grapevines in California to compare for regional differences in the pathogen based on genetics and disease properties. In this study, a wide range of different strains of Xylella fastidiosa from all California grape growing regions were tested in susceptible grapevines and in the model plant tobacco to evaluate whether some strains cause more severe disease than others. Twenty nine strains were tested in both grapevine and tobacco, and 71 strains total were tested in at least one plant species. Grapevines were tested both in a screenhouse using potted plants, and in the field. The results of this study show that there are not significant differences in disease severity caused by the different Xylella fastidiosa strains from California. This information is important for disease management and future testing of control options for Xylella fastidiosa in grapevines.

Technical Abstract: Xylella fastidiosa, the causal agent of Pierce’s disease in grapevine has been found in all grape growing regions in California, USA. Large collections of X. fastidiosa isolates are available from these areas which enable comparative studies of pathogen genetic traits and virulence. Due to the significant space and time requirements for experimental inoculation of X. fastidiosa in grapevine however, most studies use only a single isolate to evaluate disease under the test conditions and it is not clear how much variability between isolates impacts disease development in experimental or natural settings. In this study, a comprehensive panel of X. fastidiosa isolates from all California grape growing regions were tested for virulence in susceptible Vitis vinifera Cabernet Sauvignon and in the model host plant tobacco using mechanical inoculation. A total of 71 isolates were tested, with 29 isolates tested in both grapevine and tobacco. Grapevines were tested in a screenhouse and in the field, and virulence of isolates was compared across all the experimental conditions. The results of this study highlight the inherent variability of inoculation experiments with X. fastidiosa, including variation in disease severity in plants inoculated with a single isolate, and variability between experimental replicates. There were limited differences in virulence between isolates that were consistent across experimental replicates, or across different host plants. This suggests that choice of isolate within the Xylella fastidiosa subspecies fastidiosa Pierce’s disease group may not make any practical difference when testing in susceptible grape varieties, and that pathogen evolution has not significantly changed virulence of Pierce’s disease isolates within California.