Presence of non-regulated Elsinoë species on citrus species
Elsinoë fawcettii, E. australis, and E. citricola are EU Quarantine pests according to EU Commission Implementing Regulation 2019/2072 Annex II A. It is currently considered that they are the only Elsinoë species associated with Citrus fruits and that Elsinoë species are very highly host specific.
As a consequence, the detection of regulated Elsinoë species on imported citrus in the Netherlands was based on a genus-level real-time PCR test.
However, during routine testing of citrus fruits during import inspections in the Netherlands, citrus samples from countries where no regulated Elsinoë species are known to occur tested positive for Elsinoë sp., with high Ct values, raising questions regarding the presumed host specificity of Elsinoë species.
To determine the presence of Elsinoë species, a metabarcoding test was conducted on symptomatic fruits of five citrus host (Citrus hystrix, Citrus limon, Citrus maxima, Citrus sinensis, Citrus x latifolia) found during phytosanitary inspections at import between September 2022 and July 2024. These fruits were imported from nine countries (Brazil, Colombia, Indonesia, Peru, South Africa, Spain, Thailand, Vietnam, and Zimbabwe). Using the ITS1 metabarcoding technique, DNA sequences of regulated and non-regulated Elsinoë species were identified on the citrus samples and clustered into five distinct clades representing a broad range of Elsinoë species. It should be noted that this technique cannot provide species-level resolution.
In samples that represented clades where no regulated Elsinoë species were present, citrus fruits still displayed symptoms including irregular, thick, warty and fissured lesions, associated with E. fawcettii, and large, flat and smooth lesions associated with E. australis. van de Vossenberg et al. (2025) suggests that the current practice of genus-level molecular testing, combined with symptom analysis, host plant species and origin of the fruits used during phytosanitary inspections may be insufficient, as these tests may detect non-regulated species.
However, further research is needed; to determine whether these non-regulated Elsinoë species act as opportunistic or primary pathogens, to study spread mechanisms of these non-regulated species, and to validate existing and new diagnostic tests covering all relevant Elsinoë species.
Sources
van de Vossenberg BT, van Ingen-Buijs VA, Elliott AJ, van den Bosch TJ, Wildhagen MM, van Duijnhoven AA, van der Linde S (2025) Presence of non-regulated Elsinoë species on citrus fruits and their impact on regulatory plant health diagnostics. European Journal of Plant Pathology 18, 1-3 https://doi.org/10.1007/s10658-025-03168-0