Identification of Rubus yellow net virus as a distinct badnavirus and its detection by PCR in Rubus species and in aphids

Rubus yellow net virus (RYNV) infects Rubus species and cultivars worldwide and is an essential component of raspberry veinbanding mosaic (RVBMD), a virus disease complex that causes serious decline in plant vigour and productivity. The virus is transmitted, probably in a semi‐persistent manner, by the large raspberry aphid, Amphorophora idaei in Europe, and A. agathonica in North America. The particles of RYNV are bacilliform in shape and measure 80–150 × 25–30 nm, similar to those of badnaviruses. A1.7 kb fragment of the viral DNA was amplified by PCR and then directly sequenced. Analysis of this sequence suggests that RYNV is possibly a distinct species in the genus Badnavirus and is most closely related to Gooseberry vein banding associated virus (GVBAV) and Spiraea yellow leaf spot virus, two other badnaviruses described recently. Using the sequence derived from the PCR‐amplified viral DNA fragment, RYNV‐specific primers were designed and used in PCR to assay for RYNV in a range of Rubus germplasm infected with RYNV, with other unrelated viruses and virus‐like diseases found in Rubus, and in healthy plants. RYNV was detected in all glasshouse cultures of RYNV‐infected plants, whether alone or in complex infections with other viruses, but not from healthy Rubus plants, nor from plants infected with other viruses. It was also detected in field‐grown raspberry plants with and without symptoms of RVBMD and in raspberry plants infected with RYNV by viruliferous A. idaei. RYNV was also detected by PCR in A. idaei following access feeds on RYNV‐infected plants of 1 h or more. PCR failed to amplify DNA from gooseberry infected with GVBAV confirming the specificity of the RYNV analysis. PCR detection of RYNV in dormant raspberry buds allows assays to be made outside the natural growing season, providing a useful application for plant introduction and quarantine programmes.     

Molecular evidence for association of Cotton leaf curl Alabad virus with yellow vein mosaic disease of okra in North India

Two virus isolates (OY77 and OY81B) from okra plants showing yellow vein mosaic, downward curling and vein twisting symptoms were collected from different farmer's fields in Karnal, Haryana state, India. The genomes of the two isolates were amplified, cloned, sequenced and analysed. The analysis indicated that the isolates are similar with 89.2% nucleotide sequence identity. Based on the current threshold cut-off value for taxonomy distinguishing the genus begomoviruses species from strains, the two isolates are designated as strains of Cotton leaf curl Alabad virus (CLCuAV) which shared nucleotide sequence identity of >90% with CLCuAV infecting cotton in Pakistan. Phylogenetic and recombination analyses of the major genome component of OY77 and OY81B is derived from different begomviruses (CLCuAV, BYVMV, CLCuMuV) as the foremost parents for evolution of these new recombinant strains.     

Serological detection and antigenic variation of two whitefly-transmitted geminiviruses: tobacco leaf curl and croton yellow vein mosaic viruses

A panel of 25 monoclonal antibodies (MAbs) raised against particles of two heterologous whitefly-transmitted geminiviruses (begomoviruses) was used in triple antibody-sandwich ELISA (TAS-ELISA) to determine the detectability and epitope profiles of 26 Indian isolates of tobacco leaf curl virus (TLCV) and 13 of croton yellow vein mosaic virus (CYVMV). Stock cultures of the two viruses had indistinguishable epitope profiles although they differ in symptomatology and particle stability. Their epitope profiles also strongly resembled those of Indian isolates of bhendi (okra) yellow vein mosaic and Indian cassava mosaic (ICMV) viruses. TLCV isolates from Andhra Pradesh, Gujarat and Karnataka States differed slightly in epitope profile: they reacted with at least eight out of 10 MAbs raised to ICMV but only one to four out of 15 MAbs raised to African cassava mosaic virus (ACMV). Virus isolates serologically indistinguishable from TLCV were detected in symptom-bearing weeds (Acanthospermum hispidum, Ageratum conyzoides, Euphorbia geniculata, Parthenium hysterophorus) found in leaf curl-affected tobacco fields and shown previously to be experimental hosts of TLCV. Indian TLCV isolates had small, consistent differences in epitope profile from Pakistani isolates but large differences from isolates from Burkina Faso, Malawi or Uganda. Isolates from the three African countries reacted with four or five of the ACMV MAbs but only one or two of the ICMV MAbs, and there were small but consistent inter-country differences. CYVMV isolates from three Indian States showed less epitope variation than did Indian isolates of TLCV. TAS-ELISA with MAb SCR 18 was a more sensitive test for detecting Indian TLCV isolates than was double antibody-sandwich ELISA with polyclonal antibodies.     

A damaging outbreak of arabis mosaic nepovirus in blackcurrant, the occurrence of other nepoviruses in Ribes species, and the demonstration that alfalfa mosaic virus is the cause of interveinal white mosaic in blackcurrant

In a crop of blackcurrant (Ribes nigrum), cv. Baldwin in Eire, chlorotic mottling and ringspot symptoms in leaves on plants and severe crop loss was associated with infection with arabis mosaic nepovirus (ArMV) and the presence in the soil of its nematode vector, Xiphinema diversicaudatum. This is only the second report of ArMV damaging a crop of blackcurrant. Tomato black ring (TBRV) and raspberry ringspot nepoviruses were detected in single plants of redcurrant (R. rubrum) in England and flowering currant (R. sanguineum) in Scotland respectively; each of these infected plants showed foliar chlorotic line-pattern symptoms. This is the first record of TBRV in redcurrant. A single blackcurrant plant in New Zealand showing symptoms typical of those described for interveinal white mosaic disease, contained alfalfa mosaic virus (AMV). When AMV particles were purified and concentrated from herbaceous test plants and mechanically inoculated to young blackcurrant plants, several became infected with AMV and most infected plants developed systemic symptoms typical of the original disease. This provides the strongest evidence to date that AMV is the causal agent of interveinal white mosaic disease.     

Association of tomato leaf curl Palampur virus with yellow mosaic disease of Armenian cucumber (Cucumis melo var. flexuoses) and wild melon (C. callosus var. agrestis) in India

Natural occurrence of yellow mosaic disease was observed on Armenian cucumber (Cucumis melo var. flexuoses) and wild melon (C. callosus var. agrestis) with disease incidences of ~36 and ~27%, respectively. Association of tomato leaf curl Palampur virus (ToLCPV) with the disease was investigated by Polymersae chain reaction (PCR) using begomovirus-specific primers. Full-length genome was amplified by rolling circle amplification (RCA) method from representative samples of C. melo and C. callosus. RCA products obtained were cloned and sequenced. Analyses of sequence data revealed the presence of full-length begomoviral genome of 2756 nucleotides with the gene arrangement of a typical begomovirus: HQ848383 (C. melo) and GU253914 (C. callosus). Both the isolates shared 99% sequence identity together and high 97–99% identities and the closest phylogenetic relationships with ToLCPV strains reported worldwide, hence identified as two new members of ToLCPV. Natural occurrence of ToLCPV on C. melo and C. callosus is the first report.     

Transmission of Zucchini yellow mosaic virus by Colonizing and Non-colonizing Aphids in Greece and New Aphid Species Vectors of the Virus

Nineteen aphid species were tested for their ability to transmit Zucchini yellow mosaic virus (ZYMV) from and to zucchini under laboratory conditions. Sixteen species were found to be new vectors of ZYMV (i.e. Aphis craccae, Aphis fabae, Aphis nerii, Aulacorthum solani, Brachycaudus cardui, Brevicoryne brassicae, Hyalopterus pruni complex, Hyperomyzus lactucae, Macrosiphoniella sanborni, Macrosiphum rosae, Metopolophium dirhodum, Myzus cerasi, Rhopalosiphum maidis, R. padi, Semiaphis dauci and Sipha maydis). Their transmission efficiency by a single aphid was low (0.1–4.2%). Myzus persicae was used as a control and was the most efficient vector (41.1%, one aphid per plant). Hayhurstia atriplicis, Myzus ascalonicus and Sitobion avenae did not transmit the virus. In four out of six new vectors assayed in arena tests for propensity estimation, propensity was higher than efficiency. Data from an experimental zucchini field in northern Greece revealed a high correlation between ZYMV spread and alatae of the vector species. The most abundant aphid vectors during 2 years experimentation were M. persicae, Aphis gossypii and Aphis spiraecola. The possible role of the 16 new and the previously known aphid vectors in the epidemiology of ZYMV was investigated using data of transmission efficiency combined with the captures of their alatae in the Greek net of a Rothamsted type suction trap.     

Incidences and progression of tomato chlorosis virus disease and tomato yellow leaf curl virus disease in tomato under different greenhouse covers in southeast Spain

Epidemics of whitefly‐transmitted Tomato chlorosis virus, Tomato yellow leaf curl Sardinia virus and Tomato yellow leaf curl virus have been present in the south east of Spain since the 1990s. A survey was performed in 40 greenhouses and nethouses during 2003 to establish the relationship between the disease incidence and the quality of greenhouse or nethouse coverings, providing a physical protection of crops against whiteflies. For tomato chlorosis virus disease (ToCD), the incidence correlated with the type of greenhouse cover and was most reduced under higher quality covers. Control of tomato yellow leaf curl disease (TYLCD) was achieved only for crops grown in the highest quality greenhouses. TYLCD incidence in tolerant tomatoes remained below 100% within the 5 months of sampling, despite the disease progress rate at the initial stage of the cultivation being higher than that of ToCD, which did reach 100% incidence in many greenhouses. Linear regression analysis showed that the development of ToCD and TYLCD in most of the greenhouses was best described by the monomolecular model and the Gompertz model, respectively. Tomato infectious chlorosis virus was not detected in parallel surveys carried out during this study, although it has been described previously in the area studied.