Use of indicator plants for the early detection of X. fastidiosa

Xylella fastidiosa (Xf) is considered to be one of the most serious threats to plant health globally (1, 2, 3). Movement of plants for planting has been estimated as the most important pathway for entry of Xf into Europe, especially when present without symptoms (3). The significance of this pathway is enhanced by the enormous host range of Xf and the high volumes of plants for planting imported from countries where Xf was known to occur. To control further the spread of Xf, it is crucial that newly infected sites are quickly detected (3). 

Experimental host plants have been previously used for studying the plant-Xylella fastidiosa interactions (4), as being good indicators of pathogen infection, allowing systemic colonization and the expression of disease symptoms. Seven indicator plants were selected for experiments, namely: Nicotiana tabacum cv. SR1 (Petite Havana), Catharanthus roseus cv. Cooler Peppermint, Polygala myrtifolia cv. Bibi Pink, Prunus avium, Prunus domestica, Nerium oleander cv. Rojo Red, Coffea arabica cv. Nana. These indicator plants were artificially inoculated (in repeated rounds of inoculation) with two Xf subsp pauca and one Xf subsp multiplex isolate. Two independent experiments have been performed. Experiments have been completed in 20-22 months after the first artificial inoculations. Final sampling was performed from each individual plant in a destructive way, and tested by the real time PCRs (Harper et al., 2010; erratum 2013 and Quyang et al., 2013) to check for the presence of Xf. 

Our results demonstrated that mainly P. myrtifolia and alternatively, N. oleander are two very efficient indicator plants, under the restriction that the initial infection occurs during the spring and summer period. However, when the initial infection occurs during the autumn and winter period, Xf could not be confirmed in the majority of the individual plants included in this experiment, regardless of the plant species and the Xf isolate used for the inoculation. 

This study was financially supported by H2020 programme – SFS-09-2016, XF-ACTORS, grant agreement 727987.

1.    Sicard, A., Zeilinger, A.R., Vanhove, M., Schartel, T.E., Beal, D.J., Daugherty, M.P., and Almeida, R.P.P. 2018. Xylella fastidiosa: Insights into an emerging plant pathogen. Annu. Rev. Phytopathol. 56:181-202.
2.    Almeida R.P.P., De La Fuente L., Koebnik R., Lopes J.R.S., Parnell S. and Scherm H., 2019. Addressing the New Global Threat of Xylella fastidiosa. Phytopathology 109:172-174, https://doi.org/10.1094/PHYTO-12-18-0488-FI
3.    EFSA Panel on Plant Health (PLH), Bragard, C., Dehnen‐Schmutz, K., Di Serio, F., Gonthier, P., Jacques, M.‐A., Jaques Miret, J. A., Justesen, A. F., MacLeod, A., Magnusson, C. S., Milonas, P., Navas‐Cort´es, J. A., Potting, R, Reignault, P. L., Thulke, H.‐H., van der Werf, W., Vicent Civera, A., Yuen, J., Zappal`a, L., Boscia, D., Chapman, D., Gilioli, G., Krugner, R., Mastin, A., Simonetto, A., Spotti Lopes, J. R., White, S., Abrahantes, J. C., Delbianco, A, Maiorano, A., Mosbach‐Schulz, O., Stancanelli, G., Guzzo, M., and Parnell, S. 2019. Update of the scientific opinion on the risks to plant health posed by Xylella fastidiosa in the EU territory. EFSA J. 17: 5665.
4.    Lopes, S. A., Ribeiro, D. M., Roberto, P. G., & França, S. C. (2000). Nicotiana tabacum as an experimental host for the study of plant-Xylella fastidiosa interactions. Plant Disease, 84, 827–830.