Measuring the threat from a distance: a sentinel plantation in Palma de Mallorca to test the susceptibility of Belgian trees to several subspecies of Xylella fastidiosa

Sentinel plantations are a promising tool to collect valuable information on plant-pathogen interactions. While it has proven its efficiency to discover new significant threatening organisms (Kenis et al., 2018; Vettraino et al., 2017), this technique has also the potential to identify new host plants for known pathogens. The objective of this study was to investigate the susceptibility of selected Belgian potential host plant species to Xylella fastidiosa by establishing and monitoring ex-patria plantings (EPPO 2020) in a Xylella-contaminated area, the campus of the University of the Balearic Islands (UIB) situated in Palma de Mallorca. First, official approval was obtained from the local government and from the UIB Authorities. Then, selected plant species (Prunus domestica cv. opal, Salix alba, Quercus petraea), were acquired from Belgian producers. Although they were provided with phytosanitary certificates, they were also checked for X. fastidiosa before 27 plants of each species were brought to Spain and planted in March 2018. Later on, they were regularly submitted to regular symptom observations and molecular analyses. Simultaneously, within a 100 meters radius area around the plantation, the abundance and the infectivity of the potential insect vectors, as well as the sanitary state of the local vegetation, were monitored. The survey is still ongoing. So far, no infection by X. fastidiosa has been observed, possibly due to the young age of the trees and the recent establishment of the assay, as well as to the scarcity of the ground herbaceous vegetation and vectors during the first year. This study underlines the hurdles that may be encountered with sentinel plants. Yet it provides a methodology highlighting key features to address X. fastidiosa studies through sentinel plantations.

Reference : 
European and Mediterranean Plant Protection Organization (EPPO) (2020). PM 3/91(1) Sentinel woody plants: concepts and application. Bulletin OEPP/EPPO Bulletin, 50(3), 429–436.
Kenis, M., Li, H., Fan, J. T., Courtial, B., Auger-Rozenberg, M. A., Yart, A., ... & Roques, A. (2018). Sentinel nurseries to assess the phytosanitary risks from insect pests on importations of live plants. Scientific reports, 8(1), 1-8.
Vettraino, A. M., Li, H. M., Eschen, R., Morales-Rodriguez, C., & Vannini, A. (2017). The sentinel tree nursery as an early warning system for pathway risk assessment: Fungal pathogens associated with Chinese woody plants commonly shipped to Europe. PLoS One, 12(11), e0188800.