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Abstract The Panel on Plant Health performed a pest categorisation of Longidorus diadecturus (Nematoda: Longidoridae) for the EU. The nematode is a well‐defined taxon and was described from Ontario, Canada and later reported from some states in the USA. The nematode is not present in the EU. It is regulated by Council Directive 2000/29/EC, listed in Annex I A I as L. diadecturus Eveleigh and Allen. It is a migratory ectoparasitic nematode species puncturing cells of plant roots thereby able to transmit the nepovirus Peach rosette mosaic virus (PRMV). The pest is found in soil associated with plant species belonging to different families. L. diadecturus is able to cause direct damage to plants, but its main damage is caused by vectoring PRMV. Soil is a potential pathway for this nematode for entry into the EU. The nematode is able to survive adverse conditions, but the virus may not persist inside the nematode for extended periods. Climatic conditions in the EU are similar to those found in the countries where the pest is currently present. Hosts of the nematode (and the associated virus) are, e.g. peaches and grapes; those crops are also widely cultivated in the EU. The nematode only moves short distances (around 1 m) but may be spread with soil moving activities. Measures are available to inhibit entry via soil as such. Entry of the nematode with soil attached to plants for planting that are not regulated is possible. L. diadecturus does satisfy all the criteria that are within the remit of EFSA to assess to be regarded as a potential Union quarantine pest.

Rosette caused by rose rosette virus (RRV) is a devastating disease of rose in the United States. The virus was discovered in 2011 and Koch's postulates completed in 2015. Because of these recent discoveries, assumptions about the disease including movement, transmission and resistance are based on visual observations of material that may or may not have been infected by the virus. This study addresses several aspects of virus and disease dynamics. Twenty rose genotypes were screened for mite and/or virus resistance. Phyllocoptes fructiphilus, the only known vector of RRV, was able to establish, lay eggs and develop nymphs and adults in all rose genotypes. Cultivar ‘Stormy Weather’ showed resistance to the virus as assessed in both mite and cleft‐grafting transmission experiments. Mites showed a long acquisition/latent period but a rapid inoculation time for RRV. Knowledge of resistance as well as transmission attributes will assist in better management of vector and disease. The identified resistant genotype would be used in areas with high disease pressure to minimize spread, for identification of the mechanisms behind resistance or as a breeding parent to incorporate virus resistance to new cultivars. The short inoculation access period suggests that chemical control for this vector may be challenging to undertake. [ABSTRACT FROM AUTHOR]

The Panel on Plant Health performed a pest categorisation of Longidorus diadecturus (Nematoda: Longidoridae) for the EU. The nematode is a well-defined taxon and was described from Ontario, Canada and later reported from some states in the USA. The nematode is not present in the EU. It is regulated by Council Directive 2000/29/EC, listed in Annex I A I as L. diadecturus Eveleigh and Allen. It is a migratory ectoparasitic nematode species puncturing cells of plant roots thereby able to transmit the nepovirus Peach rosette mosaic virus (PRMV). The pest is found in soil associated with plant species belonging to different families. L. diadecturus is able to cause direct damage to plants, but its main damage is caused by vectoring PRMV. Soil is a potential pathway for this nematode for entry into the EU. The nematode is able to survive adverse conditions, but the virus may not persist inside the nematode for extended periods. Climatic conditions in the EU are similar to those found in the countries where the pest is currently present. Hosts of the nematode (and the associated virus) are, e.g. peaches and grapes; those crops are also widely cultivated in the EU. The nematode only moves short distances (around 1 m) but may be spread with soil moving activities. Measures are available to inhibit entry via soil as such. Entry of the nematode with soil attached to plants for planting that are not regulated is possible. L. diadecturus does satisfy all the criteria that are within the remit of EFSA to assess to be regarded as a potential Union quarantine pest. [ABSTRACT FROM AUTHOR]

There is limited information on the distribution of blueberry viruses in the U.S. or around the world other than where the viruses were first discovered and characterized. A survey for blueberry viruses was carried out in the U.S. in 2015–2017. Most blueberry viruses have been characterized to the point that sensitive diagnostic assays have been developed. These assays are based on ELISA or variations of PCR, which were employed here to determine the presence of blueberry viruses in major blueberry production and nursery areas of the U.S. The viruses included in this study were: blueberry fruit drop (BFDaV), blueberry latent (BlLV), blueberry leaf mottle (BLMoV), blueberry mosaic (BlMaV), blueberry red ringspot (BRRV), blueberry scorch (BlScV), blueberry shock (BlShV), blueberry shoestring (BlSSV), blueberry virus A (BVA), peach rosette mosaic (PRMV), tobacco ringspot (TRSV), and tomato ringspot (ToRSV). In the Pacific Northwest BlShV was the most widespread virus, with BlScV and ToRSV detected in a limited number of fields in Oregon and Washington, but BlScV was widespread in British Columbia. In the upper midwest, the nematode-borne (ToRSV, TRSV), aphid-transmitted (BlSSV and BVA) and pollen-borne (BLMoV) viruses were most widespread. In the northeast, TRSV, ToRSV, and BlScV, were detected most frequently. In the southeast, BRRV and BNRBV were the most widespread viruses. BlLV, a cryptic virus with no known symptoms or effect on plant growth or yield was present in all regions. There are other viruses present at low levels in each of the areas, but with the lower incidence they pose minimal threat to nursery systems or fruit production. These results indicate that there are hotspots for individual virus groups that normally coincide with the presence of the vectors. The information presented highlights the high risk viruses for nursery and fruit production each pose a different challenge for control.

The Peach rosette mosaic virus (PRMV) is a plant pathogen of the genus Nepovirus, and has been designated as a controlled quarantine virus in Korea. In this study, a specific reverse transcription (RT)-PCR marker set, nested PCR marker set, and modified-plasmid positive control were developed to promptly and accurately diagnose PRMV at plant-quarantine sites. The final selected PRMV-specific RT-PCR marker was PRMV-N10/C70 (967 bp), and the nested PCR product of 419 bp was finally amplified. The modified-plasmid positive control, in which the SalI restriction-enzyme region (GTCGAC) was inserted, verified PRMV contamination in a comparison with the control, enabling a more accurate diagnosis. It is expected that the developed method will continuously contribute to the plant-quarantine process in Korea. [ABSTRACT FROM AUTHOR]

The article offers information on several American nepoviruses that can cause degeneration and decline on grapevines. The nepoviruses include the Blueberry leaf mottle virus (BLMoV), the Peach rosette mosaic virus (PRMV), and the Tobacco ringspot virus (TRSV). Information on the main symptoms, transmission, and detection of the nepoviruses is provided.

Viroids are plant pathogens infecting a broad range of herbaceous and tree crops. Among them, the Peach latent mosaic viroid (PLMVd) infects mainly peach trees, causing a loss of production with no curative options. Detecting this viroid is thus important for certification procedures aiming to avoid the release of infected material into orchards. Presented here is a complete detection method based on reverse transcription (RT) followed by a quantitative real-time polymerase chain reaction (PCR). New primers were selected and optimal reaction conditions determined for routine application of the method. The technique is 105 times more sensitive than the endpoint RT-PCR used for PLMVd detection, and permits earlier detection of PLMVd in infected plants. The quick, low-cost extraction procedure used and the quality of the results obtained make this method suitable for routine testing. [ABSTRACT FROM AUTHOR]

The presence of Peach latent mosaic viroid (PLMVd) was monitored during 2 years in peach orchards located in the North of Tunisia. PLMVd population was surveyed using a specific RT-PCR test adapted to crude sap extract. During the first year (2004), 228 samples were randomly selected in 22 peach orchards (eight cultivars) and tested for the presence of PLMVd. Results showed that PLMVd is highly and equally present in four regions of the North of Tunisia. Analyses of some key factors in relation to PLMVd incidence revealed that the tree age did not influence the infection rate. The eight studied cultivars were clustered in three groups according to their PLMVd incidence. Furthermore, the early and season cultivars were statistically more infected than the late cultivars. Prospections in May and October 2005 were performed in four selected orchards. Each two orchards contained Early May Crest (early cultivar) and Carnival (late cultivar) cultivars, respectively. The difference in PLMVd incidence observed in 2004 was confirmed. Furthermore, no correlation between the tree physiological state and the viroid detection was observed. Further investigations on the origin of the differences in PLMVd incidence between Early May Crest and Carnival cultivars would be of interest. [ABSTRACT FROM AUTHOR]

Peach mosaic virus (PcMV) and Cherry mottle leaf virus (CMLV) are serologically related viruses that cause distinct diseases, have a different host range, and are vectored by different eriophyid mites. Sequence analysis of the genome of PcMV indicates that it is closely related genetically to CMLV but distinct, with similar genome organization and a member of the genus Trichovirus. The genome of PcMV consists of 7,988 nucleotides, excluding a poly(A) tail at the 3′ end of the genome. Four putative open reading flames (ORF1 to 4) were identified coding for proteins of 216.3, 47.2, 21.7, and 15.7 kDa, respectively. Also, three noncoding regions were identified, including an intergenic region separating ORF3 and ORF4. The complete nucleotide sequence of PcMV shares 73% identity with CMLV. The CP amino acid sequence identity between isolates of PcMV ranged from 97 to 99% versus 83% identity when compared with the CP of CMLV. In vitro expression and subsequent western blot analysis confirmed ORF3 as encoding the CP gene of PcMV. Phylogenetic analysis supports classification of PcMV and CMLV as members of the genus Trichovirus. They are unique members of this genus with an extra ORF (ORF4). PcMV ORF4 appears to code for a putative nucleic acid-binding (NB) protein which has identity with the NB protein of CMLV and members of the genera Allexivirus, Carlavirus, and Vitivirus. PcMV and CMLV appear to be the products of recombination between members of the genus Trichovirus and a virus group containing the putative NB protein. Alternatively, PcMV and CMLV may represent the intact genome, with a deletion event producing members that lack ORF4. A reverse transcription-polymerase chain reaction procedure was developed for reliable and specific detection of PcMV. This will be an asset for stone fruit virus certification. [ABSTRACT FROM AUTHOR]

Provides information on the peach mosaic virus. Common names; Taxonomic position; Notes on taxonomy and nomenclature; Host plants; Geographical distribution.

The coat protein cistron of tobacco mosaic virus has been located on the viral RNA starting between 975 and 1050 nucleotides from the 3'-hydroxyl end. This locates its 5' end close to the origin for virus assembly, where the first protein disk interacts with the RNA. It also means that the coat protein mRNA must have a short 5'-untranslated tail and a long (over 500 nucleotides) 3' one. The recovery of characteristic oligonucleotides in nuclease-protected rods during the growth from RNA and a protein disk preparation shows that elongation of the nucleated rods proceeds independently in both directions though, on average, much more rapidly along the longer 5' tail than the shorter 3' tail. Protected RNA of length equal to that in the complete virion is first seen within 6 min, showing that the most rapidly elongated particles are substantially complete by this time. [ABSTRACT FROM AUTHOR]

A novel nepovirus was identified and characterised from caraway, and tentatively named caraway yellows virus (CawYV). Tubular structures with isomeric virus particles typical for nepoviruses were observed in infected tissues by electron microscopy. The whole genome of CawYV was identified by high throughput sequencing (HTS). It consists of two segments with 8026 nt for RNA1 and 6405 nt for RNA2, excluding the poly(A) tails. CawYV-RNA1 shared closest nt identity to peach rosette mosaic virus (PRMV) with 63%, while RNA2 shared 41.5% with blueberry latent spherical virus (BLSV). The amino acid sequences of the CawYV protease-polymerase (Pro-Pol) and capsid protein (CP) regions share the highest identities with those of the subgroup C nepoviruses. The Pro-Pol region shared highest aa identity with PRMV (80.1%), while the CP region shared 39.6% to soybean latent spherical virus. Phylogenetic analysis of the CawYV-Pro-Pol and -CP aa sequences provided additional evidence of their association with nepoviruses subgroup C. Based on particle morphology, genomic organization and phylogenetic analyses, we propose CawYV as a novel species within the genus Nepovirus subgroup C. [ABSTRACT FROM AUTHOR]

There is limited information on the distribution of blueberry viruses in the U.S. or around the world other than where the viruses were first discovered and characterized. A survey for blueberry viruses was carried out in the U.S. in 2015–2017. Most blueberry viruses have been characterized to the point that sensitive diagnostic assays have been developed. These assays are based on ELISA or variations of PCR, which were employed here to determine the presence of blueberry viruses in major blueberry production and nursery areas of the U.S. The viruses included in this study were: blueberry fruit drop (BFDaV), blueberry latent (BlLV), blueberry leaf mottle (BLMoV), blueberry mosaic (BlMaV), blueberry red ringspot (BRRV), blueberry scorch (BlScV), blueberry shock (BlShV), blueberry shoestring (BlSSV), blueberry virus A (BVA), peach rosette mosaic (PRMV), tobacco ringspot (TRSV), and tomato ringspot (ToRSV). In the Pacific Northwest BlShV was the most widespread virus, with BlScV and ToRSV detected in a limited number of fields in Oregon and Washington, but BlScV was widespread in British Columbia. In the upper midwest, the nematode-borne (ToRSV, TRSV), aphid-transmitted (BlSSV and BVA) and pollen-borne (BLMoV) viruses were most widespread. In the northeast, TRSV, ToRSV, and BlScV, were detected most frequently. In the southeast, BRRV and BNRBV were the most widespread viruses. BlLV, a cryptic virus with no known symptoms or effect on plant growth or yield was present in all regions. There are other viruses present at low levels in each of the areas, but with the lower incidence they pose minimal threat to nursery systems or fruit production. These results indicate that there are hotspots for individual virus groups that normally coincide with the presence of the vectors. The information presented highlights the high risk viruses for nursery and fruit production each pose a different challenge for control. [ABSTRACT FROM AUTHOR]

The continuing threat of dengue fever necessitates a comprehensive characterisation of its epidemiological trends. Phylogenetic and recombination events were reconstructed based on 100 worldwide dengue virus (DENV) type 1 genome sequences with an outgroup (prototypes of DENV2-4). The phylodynamic characteristics and site-specific variation were then analysed using data without the outgroup. Five genotypes (GI-GV) and a ladder-like structure with short terminal branch topology were observed in this study. Apparently, the transmission of DENV1 was geographically random before gradual localising with human activity as GI-GIII in South Asia, GIV in the South Pacific, and GV in the Americas. Genotypes IV and V have recently shown higher population densities compared to older genotypes. All codon regions and all tree branches were skewed toward a negative selection, which indicated that their variation was restricted by protein function. Notably, multi-epistatic interaction sites were found in both PrM 221 and NS3 1730. Recombination events accumulated in regions E, NS3-NS4A, and particularly in region NS5. The estimated coevolution pattern also highlights the need for further study of the biological role of protein PrM 221 and NS3 1730. The recent transmission of emergent GV sublineages into Central America and Europe mandates closely monitoring of genotype interaction and succession. [ABSTRACT FROM AUTHOR]

The transmission of North American nepoviruses by putative species belonging to the Xiphinema americanum-group is reviewed. Xiphinema americanum sensu stricto, X. californicum, and X. rivesi each transmit cherry rasp leaf (CRLV), tobacco ringspot (TobRSV), and tomato ringspot nepovirus (TomRSV), and X. bricolensis is a vector of TomRSV. The apparent lack of specificity in the transmission of North American nepoviruses by X. americanum-group species markedly contrasts with the specific associations between European nepoviruses and their vector nematode species. Two complementary projects are described examining the taxonomic identity of putative species in the X. americanum-group, their morphological and genetic relationships, their ontogeny, and their ability to transmit viruses.

Nematode population trends and vertical distribution were monitored in a southwest Michigan vineyard (Vitis labrusca cv. Concord) from 1976 through 1983. Shallow (20 cm) and deep (90 cm) applications of 1,3-dichloropropene applied at 281 (shallow) plus 658 or 1,122 (deep) liters/ ha provided excellent control of Xiphinema americanum, Criconemella xenoplax, and Meloidogyne hapla. Populations of X. americanum remained below detectable levels for the entire 8-year experimental period where the fumigant was applied. X. americanum and C. xenoplax populations exhibited multiyear cycling in nonfumigated plots. M. hapla was first detected in 1978 and increased in prominence from 1980 through 1982. Criconemella spp. were commonly parasitized by an endoparasitic fungus. Parasitism was monitored and reported as an indication of nematode population quality.