Section outline

  • Ringspot disease of oak

    Collapse all Expand all

    Susanne von Bargen, Kira Köpke, Artemis Rumbou, Carmen Büttner

    Humboldt-Universität zu Berlin, Albrecht Daniel Thaer-Institute, Division Phytomedicine, Berlin, Germany

    Logo der Humboldt-Universität zu Berlin

      • Symptoms

        Chlorotic ringspots, chlorotic spots and mottle of leaves, which are sometimes accompanied by foliar deformations such as twisting and underdevelopment of the lamina. Diseased trees sometimes, also suffer from a distinct loss of vigor. Examples of symptoms in common oak (Quercus robur) see below.

        Deformed leaves of CORaV-infected oak (Quercus robur) exhibiting chlorotic ringspots, spots and mottle (left), virus transmission, virus transmission by grafting (right).

      • Biology

        CORaV has been confirmed in ringspot-diseased oaks in various locations in Germany, Southern Sweden and Southern Norway. Typical leaf symptoms of chlorotic ringspots, chlorotic spots and mottling have also been reported to occur in Quercus sp. in further European countries, for instance the UK, Hungary and the Czech Republic (Biddle 1968, Cooper 1979). The ringspot disease has been shown to be graft transmissible (Büttner & Führling, 1996), while it is neither mechanically transmissible nor by seeds. The natural vector, which is most likely an eriophyid mite species is so far unknown.

        Diverse chlorotic spots and ringspots in leaves of CORaV-infected common oak (Quercus robur), in some cases chlorosis turns into necrosis (left).

      • Hosts

        Common oak (Quercus robur) is so far the only known natural host species, which has been confirmed to be infected by CORaV.

      • Actions/ Management Recommendations

        The use of virus-tested plant material is highly recommended. CORaV-induced leaf symptoms can easily be confused with leaf chloroses induced by other causes in oak, which become dominant in the later vegetation period between July and September (Büttner & Führling 1993, Hahn et al. 2003). Therefore, reliable diagnosis of CORaV should be done for instance by molecular tools such as virus-specific RT-PCR or RT-PCR using genus-specific primers in combination with Sanger-sequencing (Rehanek et al. 2022, Bandte et al. 2020). Also, commercial serological tests (DAS-ELISA) are available for instance from Loewe Biochemica GmbH to confirm the CORaV infection of oaks.

      • Geography

        Wide distribution in European countries has to be assumed. So far confirmed in Germany, Southern Norway, southern parts of Sweden.

      • Research & Science

        CORaV (genus Emaravirus, family Fimoviridae) is a single stranded RNA virus with a negative orientation (Rehanek et al. 2022). It´s genome consists of five RNAs (Rehanek et al. 2021) and phylogenetic analyses of RNA1-RNA4 confirm that the virus is a member of the genus Emaravirus (Rehanek et al. 2021). Studies on morphology of the virus are missing, although it is likely that CORaV forms spherical particles of varying size (80-100 nm) in the cytoplasm of infected mesophyll cells as described for other emaraviruses (Rehanek et al. 2022). Also, many epidemiological questions regarding the disease are still open, because the virus has only recently been identified as putative causal agent. For instance, investigations on the natural gall mite vector species of CORaV could not associate any mite species inducing galls on Quercus spp. with the ringspot disease, so far (Büttner et al. 2023). However, we could detect CORaV by RT-PCR in single free-living eriophyid mites of an unknown species collected from the underside of leaves showing typical leaf symptoms of the ringspot disease. The leaves were also confirmed to be CORaV-infected by virus-specific RT-PCR targeting the viral RNA3. Also the natural host range of the virus requires further research as similar symptoms have been described to occur for instance in Q. marilandica and Q. velutina, respectively in the USA (Cooper 1979), however, the virus is not yet confirmed as causal agent.

      • References

        1.    Bandte, M., Rehanek, M., Leder, B., von Bargen, S., Büttner, C., 2020. Identification of an Emaravirus in a Common Oak (Quercus robur L.) Conservation Seed Orchard in Germany: Implications for Oak Health. Forests 11, e1174 [doi: 10.3390/F11111174]

        2.    Biddle, P.G., 1968. A study of virus diseases of forest trees. D.Phil. Thesis, University of Oxford.

        3.    Büttner C., Führling M., 1993: Beobachtungen zu virusbedingten Symptomen an Stieleichen (Quercus robur L.) - eine Abgrenzung zu ähnlichen nicht virusbedingten Krankheitsbildern - Nachrichtenblatt Deutscher Pflanzenschutzdienst 45, 110-115.

        4.    Büttner C, Führling M, 1996. Studies on virus infection of diseased Quercus robur (L) from forest stands in northern Germany. Annales des sciences forestières, 53, 383-388.

        5.    Büttner C, Landgraf M, Fernandez Colino HL, von Bargen S, Bandte M, 2023. Virus diseases of forest and urban trees. Chapter 3. In: Asiegbu F & Kovalchuk A (Eds.): Forest Microbiology. Tree diseases and pests, Volume 3. Elsevier 2023, London, United Kingdom, 61-97.

        6.    Cooper JI, 1979. Virus diseases of trees and shrubs. Institute of Terrestrial Ecology/National Environment Research Council: London, 74 pages.

        7.    Hahn S, Bandte M, Obermeier C, Büttner C, 2003. Viruserkrankungen an Stieleichen – eine kurze Übersicht. In: Jahrbuch der Baumpflege 2003, Dujesiefken D, Kockerbeck P (eds.) Thalacker Medien, Braunschweig, Germany, 213-218.

        8.    Mielke-Ehret, N., Mühlbach, H.P., 2012. Emaravirus: A novel Genus of Multipartite, Negative Strand RNA Plant Viruses. Viruses, 4, 1515–1536, doi:10.3390/v4091515.

        9.    Rehanek M, von Bargen S, Bandte M, Karlin DG, Büttner C, 2021. A novel emaravirus comprising five RNA segments is associated with ringspot disease in oak. Archives of Virology 166, 987-990. https://doi.org/10.1007/s00705-021-04955-w

        10. Rehanek M, Karlin DG, Bandte M, Al Kubrusli R, Nourinejhad Zarghani S, Candresse T, Büttner C, von Bargen S, 2022. The Complex World of Emaraviruses—Challenges, Insights and Prospects. Forests 13, 1868. https://doi.org/10.3390/f13111868

        11. Rumbou, A.; Vainio, E.J.; Büttner, C., 2021. Towards the Forest Virome: High-Throughput Sequencing Drastically Expands Our Understanding on Virosphere in Temperate Forest Ecosystems. Microorganisms, 9, 1730. https://doi.org/10.3390/microorganisms9081730

        12. Vainio, E.J., Rumbou, A., Diez, J.J., Büttner, C., 2024. Forest Tree Virome as a Source of Tree Diseases and Biological Control Agents. Curr. For. Rep. 10, 153–174. https://doi.org/10.1007/s40725-024-00214-8