The transmission of the apscaviroid tentatively named apple chlorotic fruit spot viroid (ACFSVd) was investigated using a one-step reverse-transcription (RT) droplet digital PCR assay for absolute quantification of the viroid, followed by quantification of relative standard curves by RT-qPCR. Our results indicate that ACFSVd is effectively transmitted by grafting, budding and seeds. No transmission has yet been observed to the viroid-inoculated pome fruit species Pyrus sp. and Cydonia sp. ACFSVd was detected in viruliferous aphids (Myzus persicae, Dysaphis plantaginea) and in codling moths (Cydia pomonella). The viroid was also detected systemically in the infected hemiparasitic plant Viscum album subsp. album (mistletoe).

Viroid-like symptoms were observed in 2016 on apple fruits of the cultivar “Ilzer Rose” in southern Burgenland, Austria. Preliminary molecular biological investigations indicated that the symptoms were caused by a new unknown viroid. Therefore, new primers were designed, and the whole genome sequence of the viroid (354 nt) was determined by next-generation amplicon sequencing using the Illumina MiSeq® platform (San Diego, California, USA). The viroid secondary structure has a rod-like conformation and contains conserved regions (the TCR, CCR upper strand, and CCR lower strand) that are characteristic of members of the genus Apscaviroid. Based on our results and the demarcation criteria for viroids, the tentatively named “apple chlorotic fruit spot viroid” should be considered a putative new member of the genus Apscaviroid.Electronic supplementary materialThe online version of this article (10.1007/s00705-019-04420-9) contains supplementary material, which is available to authorized users.

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The availability and accessibility of suitably characterized plant virus and viroid isolates for reference is vital for research and diagnostic laboratories. To ensure the long‐term availability of isolates and reference materials, there is a need for international collaboration. The Euphresco (European Plant Health Research Coordination) project VirusCollect aimed to establish a platform to link collections of viruses and viroids maintained by individual institutions via Q‐bank (http://www.q-bank.eu/), a database on plant pests and diseases. Within the VirusCollect project, standard operating procedures were developed and implemented by the participating laboratories to guarantee the quality of isolates and data. In addition, over 135 virus and viroid isolates of phytosanitary and/or economic importance were added to Q‐bank, which now provides links to over 500 virus isolates of almost 100 species, in addition to basic information on many more plant viruses. VirusCollect has enabled the first step in collaboration between curators and standardization of maintenance of virus collections. The project established the basis for improving the quality of individual collections and the layout of Q‐bank as a platform to share data and information. The follow‐up project, VirusCollect II, enables further international collaboration to ensure future access to reliable collections of plant viruses and viroids.

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