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International audience; Members of the genus Luteovirus are responsible for economically destructive plant diseases worldwide. Over the past few years, three luteoviruses infecting Prunus trees have been characterized. However, the biological properties, prevalence, and genetic diversity of those viruses have not yet been studied. High throughput sequencing of samples of various wild, cultivated, and ornamental Prunus species enabled the identification of four novel species in the genus Luteovirus for which we obtained complete or nearly complete genomes. Besides, we identified another new putative species recovered from Sequence Read Archive data. Furthermore, we conducted a survey on peach-infecting luteoviruses in eight European countries. Analyses of 350 leaf samples collected from germplasm, production orchards, and private gardens showed that peach-associated luteovirus (PaLV), nectarine stem pitting-associated virus (NSPaV), and a novel luteovirus, peach-associated luteovirus 2 (PaLV2), are present in all countries, while the most prevalent virus was NSPaV, followed by PaLV. An analysis of the genetic diversity of these viruses was also conducted. Moreover, the biological indexing on GF305 peach indicator plants demonstrated that PaLV and PaLV2, like NSPaV, are transmitted by graft at relatively low rates. No clear viral symptoms have been observed either in graft-inoculated GF305 indicators, or in different peach tree varieties observed in an orchard. The data generated during this study provide a broader overview of the genetic diversity, geographical distribution and prevalence of peach-infecting luteoviruses, and suggest these viruses are likely asymptomatic in peach under most circumstances.

Plants can be infected with multiple viruses. High-throughput sequencing tools have enabled numerous discoveries of multi-strain infections, when more than one viral strain or divergent genomic variant infects a single plant. Here, we investigated small interfering RNAs (siRNAs) in a single strawberry plant co-infected with several strains of strawberry mottle virus (SMoV), strawberry crinkle virus (SCV) and strawberry virus 1 (StrV-1). A range of plants infected with subsets of the initial viral species and strains that were obtained by aphid-mediated transmission were also evaluated. Using high-throughput sequencing, we characterized the small RNA fractions associated with different genotypes of these three viruses and determined small RNA hotspot regions in viral genomes. A comparison of virus-specific siRNA (vsiRNA) abundance with relative viral concentrations did not reveal any consistent agreement. Strawberry mottle virus strains exhibiting considerable variations in concentrations were found to be associated with comparable quantities of vsiRNAs. Additionally, by estimating the specificity of siRNAs to different viral strains, we observed that a substantial pool of vsiRNAs could target all SMoV strains, while strain-specific vsiRNAs predominantly targeted rhabdoviruses, SCV and StrV-1. This highlights the intricate nature and potential interference of the antiviral response within a single infected plant when multiple viruses are present.

Raspberries (Rubus idaeus L.), occurring in the temperate zone of the northern hemisphere and blackberries (R. fruticosus L.), cultivated and growing all over the world, are plant species of the family Rosaceae. These species are susceptible to phytoplasma infections, which cause Rubus stunt disease. It spreads uncontrolled by vegetative propagation of plants (Linck and Reineke 2019a) and by phloem-sucking insect vectors, especially Macropsis fuscula (Hemiptera: Cicadellidae) (de Fluiter and van der Meer, 1953; Linck and Reineke 2019b). During a survey in commercial field in June 2021, over 200 raspberry bushes cv Enrosadira exhibiting typical symptoms of Rubus stunt were observed in Central Bohemia. Symptoms included dieback, leaf yellowing/reddening, stunted growth, severe phyllody and fruit malformations. Most diseased plants were growing in the edge rows of the field (about 80%). No symptomatic plants were observed in the middle of the field. Similar symptoms were observed in private gardens in South Bohemia on raspberry cv Rutrago and blackberry (unknown cultivar) in June 2018 and August 2022, respectively. DNA was extracted using the DNeasy Plant Mini Kit (Qiagen GmbH, Hilden, Germany) from flower stems and parts affected by phyllody of seven symptomatic plants as well as flower stems, leaf midribs, and petioles of five asymptomatic field plants. The DNA extracts were analyzed by a nested polymerase chain reaction assay using universal phytoplasma P1A/P7A primers followed by R16F2m/R1m and the group-specific R16(V)F1/R1 primers (Bertaccini et al. 2019). All samples from the symptomatic plants yielded an amplicon of expected size, while no product was amplified in asymptomatic plants. The P1A/P7A amplicons from three selected plants (two raspberries and one blackberry, each from different location) were cloned and bi-directionally Sanger sequenced (GenBank Accession Nos.OQ520100-2). The sequences spanned nearly full-length of 16S rRNA gene, 16S-23S rRNA intergenic spacer, tRNA-Ile gene, and a partial 23S rRNA gene. BLASTn search revealed the highest sequence identity (99.8-99.9%, query coverage 100%) to ‘Candidatus Phytoplasma rubi’ strain RS (GenBank Accession No. CP114006). To further characterize the ‘Ca. P. rubi’ strains, all these three samples were subjected to multigene sequence analysis. Sequences from a major portion of the tuf, rplV-rpsC, rpsH-rplR, uvrB-degV, and rplO-SecY-map genes (Acc. Nos. OQ506112-26) were obtained as described previously (Fránová et al. 2016). Comparison to GenBank sequences confirmed their highest identity (99.6-100%, query coverage 100%) with ‘Ca. P. rubi’ RS strain, regardless of their geographic location and host (raspberry or blackberry). Recently, Bertaccini et al. (2022) suggested the 98,65 % ‘Ca. Phytoplasma’ strain identity threshold within 16Sr RNA sequences. In this survey, all three strains sequenced shared ≥99.73% sequence identity of the analysed 16S rRNA gene sequences and the high identity in the other genes with the reference ‘Ca. P. rubi’ RS strain. To our knowledge, this is the first report of Rubus stunt disease in the Czech Republic as well as the first molecular identification and characterization of ‘Ca. P. rubi’ from raspberry and blackberry in our country. As Rubus stunt disease is of great economic importance (Linck and Reineke 2019a), the pathogen detection and prompt removal of the diseased shrubs are essential to mitigating the spread and impact of the disease.

Seven novel tailed lytic viruses (Ds3CZ, Ds5CZ, Ds9CZ, Ds16CZ, Ds20CZ, Ds23CZ, Ds25CZ) infecting the bacterium Dickeya solani were isolated in the Czech Republic. Genomes of these viruses are dsDNA, 149,364 to 155,285 bp in length, and the genome arrangement is very similar to that of the type virus Dickeya virus LIMEstone 1. All but the Ds25CZ virus should be regarded as strains of a single species. Most of the sequence differences are due to the presence or absence of homing endonuclease (HE) genes, with 23 HEs found in Ds3CZ, Ds5CZ, and Ds20CZ, 22 in Ds9CZ, 19 in Ds16CZ, 18 in Ds25CZ, and 15 in Ds23CZ.

This article provides an up-to-date review of disease-causing viruses and phytoplasmas of currants including symptoms, transmission, detection, economic impact, and control measures. Currants are widely cultivated in more than 30 countries in the temperate zones of Europe, Asia, South America, Australia, and New Zealand. Ribes spp. can be infected by more than 20 virus species and four Candidatus Phytoplasma species, with more to be described in the future. High-throughput sequencing opened a new era of deciphering virus variants and mixed infections, leading to the characterization of several new species. The use of clean propagation material is the basis for control of Ribes graft-transmissible diseases, but this has become a challenging task given the ever-growing number of newly discovered pathogens.

Widely distributed in water environments and in soil, cyanobacteria are hosts of lysogenic or lytic bacterioviruses. A novel, probably lysogenic virus (phage) for which the name Arthronema africanum virus TR020 (Aa-TR020) is proposed, has been isolated from filamentous freshwater cyanobacterium Arthronema africanum. The virus formed turbid plaques on plate culture of A. africanum strain 1980/01 but not on other Arthronema strain and other bacterial species. The genome of Aa-TR020 is linear molecule of dsDNA, 44,805 bp in length with 216 bp long terminal repeats and with G + C content of 46%. Fifty-five genes organized on plus and minus strands were predicted there. The genome size, gene arrangement, and selected protein sequences showed relatedness to Phormidium virus Pf-WMP3 and other viruses known to infect cyanobacteria and classified in the family Podoviridae.

We provide the complete sequence of a virus tentatively named "Tetranychus urticae-associated picorna-like virus 1PK13" (TuaPV1-PK13) obtained from the high-throughput sequencing of a symptomless apple leaf sample. Although the virus sequence was originally derived from apple leaves, the data suggest that the virus is associated with the two-spotted mite Tetranychus urticae.

Screening of apple samples using a high-throughput sequencing (HTS) approach led to the discovery of a novel virus, tentatively named "Malus domestica virus A" (MdoVA). Its genomic organisation and phylogenetic relationship showed relatedness to viruses of the genus Velarivirus in the family Closteroviridae. It is not clear whether MdoVA has any impact on its host, as the analysed apple tree contained other viruses and a viroid.

Unfortunately, the inclusion of original names (in non-Latin script) of the following authors caused problems with author name indexing in PubMed. Therefore, these original names were removed from XML data to correct the PubMed record. Mengji Cao, Yuya Chiaki, Hideki Ebihara, Jingjing Fu, George Fú Gāo, Tong Han, Jiang Hong, Ni Hong, Seiji Hongo, Masayuki Horie, Dàohóng Jiāng, Fujio Kadono, Hideki Kondō, Kenji Kubota, Shaorong Li, Longhui Li, Jiànróng Lǐ, Huazhen Liu, Tomohide Natsuaki, Sergey V. Netesov, Anna Papa, Sofia Paraskevopoulou, Liying Qi, Takahide Sasaya, Mang Shi, Xiǎohóng Shí, Zhènglì Shí, Yoshifumi Shimomoto, Jin‑Won Song, Ayato Takada, Shigeharu Takeuchi, Yasuhiro Tomitaka, Keizō Tomonaga, Shinya Tsuda, Changchun Tu, Tomio Usugi, Nikos Vasilakis, Jiro Wada, Lin‑Fa Wang, Guoping Wang, Yanxiang Wang, Yaqin Wang, Tàiyún Wèi, Shaohua Wen, Jiangxiang Wu, Lei Xu, Hironobu Yanagisawa, Caixia Yang, Zuokun Yang, Lifeng Zhai, Yong‑Zhen Zhang, Song Zhang, Jinguo Zhang, Zhe Zhang, Xueping Zhou. In addition, the publication call-out in the supplementary material was updated from issue 11 to issue 12. The original article has been corrected.

Phomopsis. longicolla is a hemibiotrophic fungus causing significant soybean yield loss worldwide. To reveal the role of zinc in plant-pathogen interactions, soybean seedlings were grown hydroponically with a range of Zn concentrations, 0.06 µM (deficient, Zn0), 0.4 µM (optimal growth), 1.5 µM, 4 µM, 12 µM, and toxic 38 μM, and were subsequently inoculated with P. longicolla via the roots. In vivo analysis of metal distribution in tissues by micro-X-ray fluorescence showed local Zn mobilization in the root maturation zone in all treatments. Decreased root and pod biomass, and photosynthetic performance in infected plants treated with 0.4 µM Zn were accompanied with accumulation of Zn, jasmonoyl-L-isoleucine (JA-Ile), jasmonic acid, and cell wall-bound syringic acid (cwSyA) in roots. Zn concentration in roots of infected plants treated with 1.5 µM Zn was seven-fold higher than in the 0.4 µM Zn treatment, which together with accumulation of JA-Ile, cwSyA, cell wall-bound vanilic acid and leaf jasmonates contributed to maintaining photosynthesis and pod biomass. Host-pathogen nutrient competition and phenolics accumulation limited the infection in Zn-deficient plants. The low infection rate in Zn 4 µM-treated roots correlated with salicylic and 4-hydroxybenzoic acid, and cell wall-bound p-coumaric acid accumulation. Zn toxicity promoted pathogen invasion and depleted cell wall-bound phenolics. The results show that manipulation of Zn availability improves soybean resistance to P. longicolla by stimulating phenolics biosynthesis and stress-inducible phytohormones.

This article provides an up-to-date review of disease-causing viruses and phytoplasmas of currants including symptoms, transmission, detection, economic impact, and control measures. Currants are widely cultivated in more than 30 countries in the temperate zones of Europe, Asia, South America, Australia, and New Zealand.

In this study, the complete genomic sequence of a novel virus was determined by next-generation sequencing of a sample from a symptomatic strawberry plant with severe yellow spots and mosaic on its leaves. Its genomic organization and sequence showed that this virus is related to members of the proposed insect-specific genus "Negevirus". The sample also contained sequences from the geranium aphid Acyrthosiphon malvae. Although the virus was detected repeatedly in the same plant during the three following years, no other positive samples were obtained from the surroundings or more-distant locations. Reverse transcription qPCR analysis revealed the presence of both genomic positive and complementary negative strands of the viral genome in the sample, with a 3- to 30-fold excess of the positive strand, indicating active viral replication. As the virus was not detected in any insect species collected at this location, the virus was provisionally named "Fragaria vesca-associated virus 1" (FVaV-1).

The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), is a major global pest of cereal grains. Infestations are difficult to control as larvae feed inside grain kernels, and many populations are resistant to both contact insecticides and fumigants. We sequenced the genome of R. dominica to identify genes responsible for important biological functions and develop more targeted and efficacious management strategies. The genome was assembled from long read sequencing and long-range scaffolding technologies. The genome assembly is 479.1 Mb, close to the predicted genome size of 480.4 Mb by flow cytometry. This assembly is among the most contiguous beetle assemblies published to date, with 139 scaffolds, an N50 of 53.6 Mb, and L50 of 4, indicating chromosome-scale scaffolds. Predicted genes from biologically relevant groups were manually annotated using transcriptome data from adults and different larval tissues to guide annotation. The expansion of carbohydrase and serine peptidase genes suggest that they combine to enable efficient digestion of cereal proteins. A reduction in the copy number of several detoxification gene families relative to other coleopterans may reflect the low selective pressure on these genes in an insect that spends most of its life feeding internally. Chemoreceptor genes contain elevated numbers of pseudogenes for odorant receptors that also may be related to the recent ontogenetic shift of R. dominica to a diet consisting primarily of stored grains. Analysis of repetitive sequences will further define the evolution of bostrichid beetles compared to other species. The data overall contribute significantly to coleopteran genetic research.

A quarantine organism, "Candidatus Phytoplasma mali," is the causal agent of apple proliferation, one of the most important apple diseases in Europe. The genetic diversity of this pathogen in Central and Southern Europe has already been reported; however, almost no data exists from Eastern Europe. In this study, "Ca. P. mali" strains, which were identified in 14 apple trees from the Bulgarian germplasm collection, were characterized by restriction fragment length polymorphism (RFLP) and sequence analysis of four genomic loci. In total, nine distinct genetic lineages were recognized based on the combination of the following detected RFLP profiles: two profiles for the 16S-23S rDNA region (16SrX-A2, -A3), four profiles for the secY gene (one previously known: secY(X)-A, and three new: secY-C, secY-D, secY-E), three profiles for the rpl22-rps3 genes (rpX-A, rpX-B, rpX-F), and one profile for the nitroreductase- and rhodanese-like gene (AT-1). Phylogenetic analysis of the Bulgarian and other European "Ca. P. mali" strains based on 16S-23S rRNA gene sequences confirmed RFLP grouping, regardless of the phytoplasma origin. In a phylogenetic tree based on the secY data, only German strains formed separate clade from the other strains. The tree based on rp genes did not correspond to RFLP profiles. Unexpectedly, when using nitroreductase and rhodanese-like gene sequences, the Bulgarian strains clustered separately from the other European strains. Apart from the identification of different "Ca. P. mali" strains, the paper also recommends the unification of the rpX-subgroup nomenclature to avoid future confusions. Both aims of this paper provide valuable tools to understand the epidemiology of this quarantine pathogen.

A lichen body is formed most often from green alga cells trapped in a net of ascomycetous fungi and accompanied by endolichenic or parasitic fungi, other algae, and symbiotic or free-living bacteria. The lichen&rsquo, s microcosmos is inhabited by mites, insects, and other animals for which the lichen is a source of food or a place to live. Novel, four-segmented dsRNA viruses were detected in saxicolous Chrysothrix chlorina and Lepraria incana lichens. Comparison of encoded genome proteins revealed classification of the viruses to the genus Alphachrysovirus and a relationship to chrysoviruses from filamentous ascomycetous fungi. We propose the names Chrysothrix chrysovirus 1 (CcCV1) and Lepraria chrysovirus 1 (LiCV1) as acronyms for these viruses. Surprisingly, observation of Chrysothrix chlorina hybridization with fluorescent-labelled virus probe by confocal microscope revealed that the CcCV1 virus is not present in the lichen body-forming fungus but in accompanying endolichenic Penicillium citreosulfuratum fungus. These are the first descriptions of mycoviruses from a lichen environment.

This study reports the complete genomic sequence of a novel virus isolated from red clover. According to its genomic organization, its similarity to luteoviruses, and a greater than 10% difference in all genes, this virus isolate likely represents a new luteovirus species. As seen in nectarine stem pitting-associated virus (NSPaV) and NSPaV-South Korea (SK) luteoviruses, it differs from typical luteoviruses through the absence of ORF3a and ORF4 encoding movement proteins. Furthermore, its P5 protein (responsible for aphid transmission) is more similar to the P5 of enamoviruses than that of luteoviruses. The virus isolate has been named red clover-associated luteovirus (RCaV).

During aetiological study of diseased red clover (Trifolium pratense L.) using high throughput sequencing, a novel virus with a 10 kb genome divided into two segments was discovered. The virus, tentatively named red clover associated varicosavirus (RCaVV), is phylogenetically related to classifiable members of the genus Varicosavirus (family Rhabdoviridae, order Mononegavirales). Analysis of mRNA levels from the individual RCaVV genes suggested possible differences in transcription regulation between rhabdoviruses with divided and undivided genomes.

A survey for phytoplasma diseases was conducted in a sweet and sour cherry germplasm collection and in cherry orchards within the Czech Republic during 2014–2015. Phytoplasmas were detected in 21 symptomatic trees. Multiple infections of cherry trees by diverse phytoplasmas of 16SrI and 16SrX groups and 16SrI-A, 16SrI-B, 16SrI-L, 16SrX-A subgroups were detected by restriction fragment length polymorphism (RFLP). Nevertheless, phylogenetic analysis placed subgroups 16SrI-B and 16SrI-L inseparable together onto one branch of phylogenetic tree. This is the first report of subgroups 16SrI-A and 16SrI-L in Prunus spp., and subgroup 16SrX-A in sour cherry trees. Additionally, novel RFLP profiles for 16SrI-A and 16SrI-B-related phytoplasmas were found in cherry samples. Phytoplasmas with these novel profiles belong, however, to their respective 16SrI-A or 16SrI-B phylogenetic clades.

Using high-throughput sequencing, a novel waikavirus was identified in a mixed virus infection of red clover (Trifolium pratense L.). Its complete genomic sequence was determined and characterized. The virus, tentatively named red clover associated virus 1 (RCaV1), is phylogenetically related to members of the genus Waikavirus (family Secoviridae, order Picornavirales).

During high throughput sequencing (HTS) of leaves from a symptomatic red clover plant, a new RNA virus, tentatively named red clover nepovirus A (RCNVA), was discovered. The complete genomic sequence was determined and characterized. Particularly noteworthy was that RCNVA shares high sequence identities in RNA1 with a group of phylogenetically related nepoviruses while homologies in the RNA2 segments are markedly lower. Based on the genomic organization and phylogenetic attributes, RCNVA should be classified as a novel virus of the genus Nepovirus (subfamily Comovirinae, family Secoviridae, order Picornavirales).

Recent studies have shown that insects harbor numerous viruses of various taxa and that viral infections are often latent without noticeable symptoms. The red firebug Pyrrhocoris apterus, a true flightless bug from the family Pyrrhocoridae, is widely used for physiological studies on insect metabolism, endocrinology, and digestion. While exploring the transcriptome of P. apterus salivary glands, a nearly complete genomic sequence of a novel RNA virus was reconstructed. The virus, provisionally named Pyrrhocoris apterus virus 1 (PaV1), possesses eight potential open reading frames (ORFs) encoding for an array of proteins, some of which are involved in virus replication while others ensure success of the virus in multiple ways, including evasion of the host immune response. In addition to the information obtained from sequence analyses, we documented virus transmission, virus-induced mortality, host response upon persistent PaV1 infection, virion morphology, and putative virus-induced structures in salivary gland cells in a laboratory culture of red firebug. We propose that PaV1 belongs to a novel viral species of a new, yet-to-be established family.

A new phytoplasma was identified in naturally infected blackberry plants exhibiting witches’ broom symptoms in Portugal. The 16S rRNA gene sequence revealed that it is related to ‘Candidatus Phytoplasma rubi’ (16SrV-E ribosomal subgroup) and RFLP analysis revealed a unique profile following Mse I endonuclease digestion of R16F2n/R2 amplicons that distinguished it from the strains belonging to previously established 16SrV phytoplasma subgroups. The in silico restriction analyses confirmed that the phytoplasma strain from blackberry is different from all the other strains reported in group 16SrV. Phylogeny of the 16S rRNA gene sequences, sequence analyses of 16S–23S, tuf, rplV-rpsC, rplF-rplR, rplO-SecY-map and uvrB-degV genetic loci, as well as the variability of unique oligonucleotide sequences defined for ‘Candidatus Phytoplasma rubi’ confirmed the uniqueness of this phytoplasma strain from Portugal for which a novel ribosomal subgroup, 16SrV-I, is proposed. The representative of this new subgroup was named blackPort phytoplasma (Portuguese blackberry phytoplasma).

A novel dsRNA virus was identified in the mycorrhizal fungus Thelephora terrestris (Ehrh.) and sequenced. This virus, named Thelephora terrestris virus 1 (TtV1), contains two reading frames in different frames but with the possibility that ORF2 could be translated as a fusion polyprotein after ribosomal -1 frameshifting. Picornavirus 2A-like motif, nudix hydrolase, phytoreovirus S7, and RdRp domains were found in a unique arrangement on the polyprotein. A new genus named Phlegivirus and containing TtV1, PgLV1, RfV1 and LeV is therefore proposed. Twenty species of oribatid mites were identified in soil material in the vicinity of T. terrestris. TtV1 was detected in large amounts in Steganacarus (Tropacarus) carinatus (C.L. Koch, 1841) and in much smaller amounts in Nothrus silvestris (Nicolet). This is the first description of mycovirus presence in oribatid mites.

The complete nucleotide sequence of a novel virus from red currant, provisionally named currant virus A (CuVA), was determined. The genome is 7925 nucleotides long and has a 3'-poly(A) tail. The genome organization with two overlapping open reading frames is similar to that of capilloviruses, but the CuVA genome is about 600 nucleotides longer than that of the longest known capillovirus, cherry virus A. The RNA is predicted to encode a polyprotein with domains of methyltransferase, 2OG-Fe(II) oxygenase, papain-like protease, RNA helicase, RdRp, and capsid protein. Phylogenetic analysis confirms that CuVA is a new and distinct member of the genus Capillovirus.

We recently completed the Special Issue on 'Plant Virus Epidemiology and Control'. As editors, we decided not to offer vouchers to scientists that submit to this issue. This action had an effect on the number of papers received and accepted. We received a total of 19 papers and we accepted four [...].

Five isolates of a new member of the family Closteroviridae, tentatively named blackcurrant leafroll-associated virus 1 (BcLRaV-1), were identified in the currant. The 17-kb-long genome codes for 10 putative proteins. The replication-associated polyprotein has several functional domains, including papain-like proteases, methyltransferase, Zemlya, helicase, and RNA-dependent RNA polymerase. Additional open reading frames code for a small protein predicted to integrate into the host cell wall, a heat-shock protein 70 homolog, a heat-shock protein 90 homolog, two coat proteins, and three proteins of unknown functions. Phylogenetic analysis showed that BcLRaV-1 is related to members of the genus Closterovirus, whereas recombination analysis provided evidence of intraspecies recombination.

Strawberry crinkle disease is one of the major diseases that threatens strawberry production. Although the biological properties of the agent, strawberry crinkle virus (SCV), have been thoroughly investigated, its complete genome sequence has never been published. Existing RT-PCR-based detection relies on a partial sequence of the L protein gene, presumably the least expressed viral gene. Here, we present complete sequences of two divergent SCV isolates co-infecting a single plant, Fragaria x ananassa cv. Cacanska rana.

During their lifetime, perennial woody plants are expected to face multiple infection events. Furthermore, multiple genotypes of individual virus species may co-infect the same host. This may eventually lead to a situation where plants harbor complex communities of viral species/strains. Using high-throughput sequencing, we describe co-infection of sweet and sour cherry trees with diverse genomic variants of two closely related viruses, namely prunus virus F (PrVF) and cherry virus F (CVF). Both viruses are most homologous to members of theFabavirusgenus (Secoviridaefamily). The comparison of CVF and PrVF RNA2 genomic sequences suggests that the two viruses may significantly differ in their expression strategy. Indeed, similar to comoviruses, the smaller genomic segment of PrVF, RNA2, may be translated in two collinear proteins while CVF likely expresses only the shorter of these two proteins. Linked with the observation that identity levels between the coat proteins of these two viruses are significantly below the family species demarcation cut-off, these findings support the idea that CVF and PrVF represent two separateFabavirusspecies.

Primula acaulis (L.) Hill. plants showing stunting, leaf-yellowing and virescence were first discovered in the Czech Republic. Polymerase chain reactions with subsequent restriction fragment length polymorphism analyses and sequencing enabled classification of the detected phytoplasmas into the aster yellows group, ribosomal subgroup 16SrI-B, tufI-B, rpI-B, groELIB-III and SecY-IB subgroups. Phylogeny of the 16S rRNA gene sequences as well as sequence analysis of several chromosomal regions, such as the 16S-23S ribosomal operon, ribosomal proteins, spc ribosomal protein operon, genes for elongation factor EF-Tu, molecular chaperonin large subunit GroEL, immunodominant membrane protein, ribosome recycling factor, urydilate kinase, ATP- and Zn2+-dependent proteases not only confirmed its affiliation with the ‘Candidatus Phytoplasma asteris’ species but also enabled its detailed molecular characterization. The less researched regions of phytoplasma genome (amp, adk, hflB, pyrH-frr genes) could be valuable as additional markers for phytoplasma through differentiation especially within the 16SrI-B ribosomal subgroup.