engleski

The first finding of Coleus vein necrosis virus in Europe

Coleus (Plectranthus scutellarioides, syn. Coleus blumei) is a globally distributed and economically important ornamental plant. So far, six Coleus blumei viroid (CBVd) species and two viruses, namely Coleus vein necrosis virus (CVNV) and Cucumber mosaic virus are known to infect this plant. Unlike viruses, most of the CBVd variants result in asymptomatic infections. In the scope of CBVd study, one of the coleus plants displaying symptoms of witches broom, fasciation and vein necroses was found to host CbVd-3 and stolbur phytoplasma (‘Candidatus Phytoplasma solani’ ; ribosomal subgroup 16SrXII-A). Its offspring plants produced by cuttings were selected for the high throughput sequencing (HTS). The aim of this work was to confirm previous findings of CBVd-3 and ‘Ca. P. solani’ by HTS and to test for the possible presence of viruses. Total nucleic acids were isolated from two symptomatic plants by CTAB method and pooled. After the DNase treatment, the extract was checked for quality and quantity by NanoDrop spectrophotometer and Bioanalyzer. The HTS was performed on Illumina Nextseq 500 platform yielding a total number of 4.2 million reads (2×150 nt). Contigs resulting from de novo assembly performed by Geneious software (Biomatters Ltd., Auckland, New Zealand) were used for BLAST searches against NCBI viral database. The sequences were also mapped to the reference CBVd-3 and CVNV genomes confirming the existence of CBVd-3 in the sample and unexpectedly revealing the presence of a full CVNV genome. CVNV is a filamentous virus from the genus Carlavirus (Betaflexiviridae) with a +RNA genome about 8.7 kb long. It has been recorded so far only in the USA independently from coleus and Verbena x hybrida plants with respective strains named CVNV-C and CVNV-V. Although they have typical carlavirus genome organization, their biological properties differ in terms of the host range and transmissibility by aphid vector Myzus persicae. Biological tests (host range, symptomatology) and RT-PCR experiments with specific CVNV coat protein primers confirmed the presence of this virus in our samples. The presence of ‘Ca. P. solani’ was confirmed by real-time PCR. More precise biological and molecular characterization of this new CVNV isolate from coleus is en route. Nevertheless, this represents the first record of CVNV out of the North America and the third in the world. This work was supported by the University of Zagreb grant no. 20282308 and COST Action FA1407 (COST DIVAS).

Coleus blumei syn. Plectranthus scutellarioides, Carlavirus, CVNV, Coleus blumei viroid 3, 'Candidatus Phytoplasma solani', high throughput sequencing, biological tests, RT-PCR, phylogeny

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