Chlorotic spots on small-leaved lime

Urban pest & disease

Chlorotic spots on small-leaved lime (Tilia cordata)

Pathogen

Cytorhabdovirus tiliae

Chlorotic spots on leaves; Studies on the association of symptoms need to be confirmed

Leaf of a lime tree infected by the novel cytorhabdovirus tiliae showing chlorotic lesions.

Cytorhabdovirus tiliae has been confirmed in lime trees in a tree nursery in Germany, as well as in buds from from a street tree in Berlin. Currently, there are no findings regarding the vectors or transmission means for Chytorhabdovirus tiliae because there has been no research conducted on the transmission of this virus. However, in general, Cytorhabdoviruses can be transmitted by aphids (Cytorhabdovirus lactucanecante, Cytorhabdovirus medicagonis), planthoppers (Cytorhabdovirus gramineae, Cytorhabdovirus hordei), leafhoppers (Cytorhabdovirus oryzae) or whiteflies (Cytorhabdovirus caricae). Some viruses are also transmitted by vegetative propagation and some can be transmitted mechanically from infected sap. Seed transmission has not been reported.

Small-leaved lime (Tilia cordata) is the only known natural host species, which has been confirmed to be infected by cytorhabdovirus tiliae. To our knowledge, no screening or bioassay has been performed to determine the host range of this virus.

The use of tested virus-free plant material is highly recommended. Therefore, reliable diagnosis of cytorhabdovirus tiliae should be performed, using molecular tools, such as virus-specific RT-PCR as described by Köpke et al. 2023. No commercial serological tests (DAS-ELISA) are available to confirm the infection of lime trees with cytorhabdovirus tiliae.

Not regulated within the EU

unknown

Chytorhabdovirus tiliae (genus Chytorhabdovirus, family Rhabdoviridae) is a single-stranded, unsegmented RNA virus with a a negative-sense orientation and 14,152 nucleotides [nt] in the coding region. The assumed genome organization is 3'-N-P-P3-M-G-p6-p6’-L-5'. The N gene encodes the putative nucleoprotein (59.1 kDa), P encodes the phosphoprotein (34.7 kDa), P3 encodes the movement protein (23.1 kDa), M encodes the matrix protein (23.1 kDa), G encodes a glycoprotein (64.4 kDa), and L encodes the viral RNA polymerase (247 kDa). P6 and P6’ are overlapping open reading frames (ORFs), which may encode gene products of 7.9 and 9.5 kDa, respectively, of unknown functions. The phylogenetic analyses of open reading frames of viral RNA-polymerase, glycoprotein, and nucleoprotein confirm that the virus is a member of the genus Cytorhabdovirus (Köpke et al. 2023). Studies on the morphology of the virus are lacking, but Chytorhabdovirus tiliae is likely to form enveloped bacilliform particles (60-75 nm) in the cytoplasm of infected mesophyll cells. Many epidemiological questions regarding the disease remain unanswered, as the virus was only recently identified as the putative causal agent.

1.    Köpke, K., Rumbou, A., von Bargen, S., Büttner, C., 2023. Identification of the Coding-Complete Genome Sequence of a Novel Cytorhabdovirus in Tilia cordata Showing Extensive Leaf Chloroses. Microbiology Resource Announcements 0, e00052-23. https://doi.org/10.1128/mra.00052-23

2.    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

3.    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