Metabolomic changes in xylem tissue of susceptible and resistant olive cultivars to Xylella fastidiosa infection

Xylella fastidiosa subsp. pauca ST53 (Xfp) is a pathogenic bacterium causing one of the most severe plant diseases currently threatening the olive-growing areas of the Mediterranean, the “Olive Quick Decline Syndrome” (OQDS). The majority of the olive cultivars upon infections develop severe desiccation phenomena, while few are resistant, being less impacted by the infections. Currently, there are no curative solutions to rehabilitate Xfp-infected plants, and control is based on reducing the vector population and removing infected sources. The success of this depends on the timely application of the interventions.1 In this context, one strategy proposed to mitigate losses is to replant susceptible crops with resistant or tolerant varieties. Several genetic, biochemical, and biophysical traits are associated with Xfp disease resistance or tolerance. Resistance refers to the ability of a plant to prevent or limit the establishment and spread of pathogens, effectively reducing the severity of disease symptoms. On the other hand, tolerance is defined as the capacity of a plant to sustain damage caused by pathogens without a significant loss in fitness or reproductive success.2 Recently, our lab has been involved in a number of projects based on the application of spectroscopy-based metabolomics to the study of Xfp infections in olive crops.3,4 Some important clues on the resistance phenomenon against Xfp were obtained by investigating the composition of plant tissues collected from cultivars with different phenotypes towards Xfp.5 The main focus of the present study is to unveil changes in the metabolic composition due to the Xfp infection by investigating the xylem samples extracted from two different olive cultivars, namely FS17 and Arbequina. FS17 exhibits significant resistance and tolerance traits, while Arbequina shows a susceptible phenotype.6 A non-targeted approach based on a combination of NMR and LC-HRMS data was applied to analyze aqueous xylem extracts to identify possible biomarkers correlated to the resistance or tolerance mechanism against Xfp infection in olive trees.