Evaluation of molecular tests for the determination of Xylella fastidiosa subspecies: results from an European test performance study and a proficiency test

Xylella fastidiosa (Xf) is an European priority pest with a broad host range. Plants can be infected with Xf for prolonged periods before symptoms appear. Symptomless plants are a source for introduction and spread of the bacteria in the European Union. 
    Five Xf subspecies can be identified: fastidiosa, multiplex, pauca, sandyi, and morus. Identification of the subspecies supports the disease control by deciding which host plants need to be destroyed or surveyed.
    Based on the Implementing Regulation (EU) 2020/1201 subspecies determination after a positive detection test is currently performed by Multi Locus Sequence Typing (MLST; Yuan et al. (2010)). Two real-time PCRs have been published that can identify different subspecies of Xf: Dupas et al. (2019) and Hodgetts et al. (2021). 
    A Test Performance Study (TPS) was organized by the NIVIP to assess the performance of the two real-time PCRs. Subsequently, we organized a proficiency test (PT) for determination of Xf. This PT was mandatory for EU national reference laboratories (NRLs). Most NRLs made use of one or both of the tests assessed in the TPS.