Measuring the threat from a distance: insight into the complexity and perspectives for implementing sentinel plantation to test the host range of Xylella fastidiosa

Casarin, Noemi [UCL] Hasbroucq, Séverine [Spatial Epidemiology lab (SpELL), Université Libre de Bruxelles (ULB), CP 160/12, 50 av. F.D. Roosevelt, 1050 Bruxelles, Belgium ] López-Mercadal, Júlia [Zoologia Aplicada i de la Conservació (ZAP), Universitat de les Illes Balears (UIB), Cra. De Valldemossa, km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain] Miranda, Miguel Ángel [Zoologia Aplicada i de la Conservació (ZAP), Universitat de les Illes Balears (UIB), Cra. De Valldemossa, km 7.5, 07122 Palma de Mallorca, Illes Balears, Spain] Bragard, Claude [UCL] Grégoire, Jean-Claude [Spatial Epidemiology lab (SpELL), Université Libre de Bruxelles (ULB), CP 160/12, 50 av. F.D. Roosevelt, 1050 Bruxelles, Belgium ]

The sentinel plantation concept consists of assessing the impact of exotic factors, such as pests and patho- gens, on plants of interest by planting them out of their native range. This tool is a way to enhance knowl- edge for pest risk analysis (PRA) by guiding decisions on how quarantine organisms should be regulated and where to focus prevention and surveillance efforts for an early detection. In this study, the sentinel method was used in the case of research on Xylella fastidiosa, a plant pathogenic bacterium that has re- cently been found established in southern Europe, but whose potential impact and possible host range are still poorly documented in northern areas where the bacterium is not known to occur. To improve knowl- edge on the susceptibility of potential hosts of X. fastidiosa in northern Europe, a sentinel plantation of Prunus domestica cv. Opal, Quercus petraea and Salix alba was established in the X. fastidiosa-infected area of Majorca. In order to assess the circulation of the bacterium in the sentinel plot and around it, surveys of the local flora and insect vectors were carried out, as well as the planting of a network of rosemary “spy plants”. Symptomatic monitoring and molecular analyses were performed on the sentinel plants for four years. During these years, X. fastidiosa was never detected in our sentinel plants most likely because of the low infectivity pressure recorded in the surroundings. This study underlines the complexity of conducting sentinel plantation assays combined with X. fastidiosa research, highlighting the need for long-term inves- tigation and questioning the efficiency of the sentinel tool. However, this study is placed in perspective with other valuable sentinel plantations. It also highlights the complementarity of the tool and proposes elements to improve or re-orientate the implementation of future sentinel projects.