Interveinal Yellowing Caused by Tomato infectious chlorosis virus in Lettuce and Escarole in Southern Italy

In 2005 and 2006, a severe disease of lettuce and escarole, characterized by interveinal yellowing of the leaves, was observed in the Calabria region (Southern Italy). Samples collected were positive in RT‐PCR assay when specific primers for Crinivirus were used. The identity of the virus was determined by using Tomato infectious chlorosis virus (TICV)‐specific primers and probe. An amplicon of the same size (501 bp) as that from TICV‐infected tomato controls, corresponding to the partial Hsp70 viral gene, was obtained from 36 of 40 lettuce samples and from 19 of 24 escarole samples tested in 2005. The sequences obtained had 99–100% nucleotide sequence identity with other TICV sequences. In an extensive survey carried out in 2006 with TICV‐specific probe, 92% of symptomatic lettuce and 89% of escarole samples were infected with TICV. Adults of Trialeurodes vaporariorum, harvested from symptomatic lettuce and escarole plants, transmitted the virus to healthy plants of the same species. This is the first evidence of a disease caused by TICV in lettuce in Italy and the first record of TICV infection in escarole.     

Evolutionary relationship of alfalfa mosaic virus with cucumber mosaic virus and brome mosaic virus

The amino acid sequences of the non-structural protein (molecular weight 35,000; 3a protein) from three plant viruses — cucumber mosaic, brome mosaic and alfalfa mosaic have been systematically compared using the partial genomic sequences for these three viruses already available. The 3a protein of cucumber mosaic virus has an amino acid sequence homology of 33.7% with the corresponding protein of brome mosaic virus. A similar protein from alfalfa mosaic virus has a homology of 18.2% and 14.2% with the protein from brome mosaic virus and cucumber mosaic virus, respectively. These results suggest that the three plant viruses are evolutionarily related, although, the evolutionary distance between alfalfa mosaic virus and cucumber mosaic virus or brome mosaic virus is much larger than the corresponding distance between the latter two viruses.     

山东烟台小麦土传病毒病由小麦黄花叶病毒和土传小麦花叶病毒相关病毒复合侵染所致

在山东省烟台地区的小麦上发生一种由土壤中禾谷多粘菌Polymyxa graminis传播的病毒病,感病小麦植株表现矮化褪绿和花叶症状.我们于1997年4月从病区采集感病小麦植株,进行了病毒种类鉴定.直接电镜观察发现有二种病毒粒子,一种粒子呈棒状,占大多数,其长度约为300nm和150nm; 另一种粒子呈线状,数量较少,长度为500nm～700nm.免疫电镜结果表明,棒状病毒粒子仅与土传小麦花叶病毒(soil-borne wheat mosaic virus, SBWMV)抗血清反应,而不与小麦黄花叶病毒(wheat yellow mosaic virus,WYMV)抗血清和小麦梭条斑花叶病毒(wheat spindle streat mosaic virus,WSSMV)抗血清反应;反之,线状病毒仅与WYMV、WSSMV抗血清反应,而不与SBWMV抗血清反应.用WYMV和SBWMV两种抗血清同时进行修饰时,线状病毒粒子和棒状病毒粒子均发生反应.     

Occurrence of fungally transmitted wheat mosaic viruses in China

A soil-borne mosaic disease of winter wheat in Sichuan, Shaanxi, Hubei and Henan provinces was associated with infection by a virus with filamentous particles and that in Shandong, Anhui, Jiangsu and Zhejiang provinces by co-infection with this virus and soil-borne wheat mosaic virus. The virus with filamentous particles was identified serologically, by particle sizes, cytopathology and the molecular weights of the coat protein and the two RNA species to be either wheat spindle streak mosaic virus (WSSMV) or wheat yellow mosaic virus. These viruses are probably isolates of the same virus and the name WSSMV is preferred. In baiting tests using infested soil, the dilution endpoints for detecting WSSMV were 1/625-1/15625, and for the fungus vector, Polymyxa graminis, 1/3125-1/15625.     

Application of a Simplified Molecular Protocol to Reveal Mixed Infections with Begomoviruses in Cassava

Samples of cassava leaves exhibiting severe symptoms of cassava mosaic disease (CMD) were collected with the PhytoPASS kit in fields surrounding the city of Bujumbura (Burundi). These materials were then sent to Belgium for polymerase chain reaction determination of the CMD begomoviruses inducing the observed symptoms. Different pairs of specific primers were used to amplify DNA sequences specific to African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), East African cassava mosaic Cameroon virus (EACMCV), East African cassava mosaic Malawi virus (EACMMV), East African cassava mosaic Zanzibar virus (EACMZV), the Uganda variant of East African cassava mosaic virus (EACMV-UG) and South African cassava mosaic virus (SACMV). It was revealed that mixed infections were prevailing in the analyzed materials. Most of the samples submitted to this analysis were found to be co-infected by three different begomoviruses (ACMV + EACMV + EACMV-UG). The so revealed mixed infections could explain the high severity of CMD symptoms noticed on cassava in the region of Bujumbura while the diversity within the CMD causal agents illustrates the importance to take this parameter into consideration for a successful use of plant genetic resistance to control the disease.     

Evidence for plant viruses in the region of Argentina Islands, Antarctica

This work focused on the assessment of plant virus occurrence among primitive and higher plants in the Antarctic region. Sampling occurred during two seasons (2004/5 and 2005/6) at the Ukrainian Antarctic Station 'Academician Vernadskiy' positioned on Argentina Islands. Collected plant samples of four moss genera (Polytrichum, Plagiatecium, Sanionia and Barbilophozia) and one higher monocot plant species, Deschampsia antarctica, were further subjected to enzyme-linked immunosorbent assay to test for the presence of common plant viruses. Surprisingly, samples of Barbilophozia and Polytrichum mosses were found to contain antigens of viruses from the genus Tobamovirus, Tobacco mosaic virus and Cucumber green mottle mosaic virus, which normally parasitize angiosperms. By contrast, samples of the monocot Deschampsia antarctica were positive for viruses typically infecting dicots: Cucumber green mottle mosaic virus, Cucumber mosaic virus and Tomato spotted wilt virus. Serological data for Deschampsia antarctica were supported in part by transmission electron microscopy observations and bioassay results. The results demonstrate comparatively high diversity of plant viruses detected in Antarctica; the results also raise questions of virus specificity and host susceptibility, as the detected viruses normally infect dicotyledonous plants. However, the means of plant virus emergence in the region remain elusive and are discussed.     

Isolation, characterisation and identification of a potyvirus from Dioscorea alata L. (water yam) in Nigeria

A yam potyvirus was isolated from Dioscorea alata samples collected in Nigeria. The virus was not transmissible mechanically but was transmitted by Aphis craccivora to four cowpea cultivars (Ife Brown, IT84S-2114, IT82E-10 and TVu2657), and from which it could be mechanically transmitted between the cowpea cultivars. In infectivity- tests using cowpea extracts, the virus had a dilution end point of 10^-4, a thermal inactivation point of 60–65°C and longevity in vitro of 2 days at room temperature. The virus coat protein had an estimated molecular weight of 32 100 daltons. The virus was identified as an isolate of Dioscorea alata virus (DAV; syn. yam virus 1) due to its biological characteristics and its serological reaction with antiserum raised against DAV. The virus is not related to yam mosaic virus, but distantly related to blackeye cowpea mosaic virus and cowpea aphid-borne mosaic virus.     

Detection of three whitefly-transmitted geminiviruses occurring in Europe by tests with heterologous monoclonal antibodies

Selected monoclonal antibodies (MAbs), prepared to particles of African cassava mosaic or Indian cassava mosaic geminiviruses, detected three geminiviruses that occur in Europe: abutilon mosaic virus in Abutilon pictum ‘Thompsonii’, tobacco leaf curl virus in Lonicera japonica var. aureo-reticulata and tomato yellow leaf curl virus in Lycopersicon esculentum. All three viruses were detected in indirect ELISA by MAbs SCR 17 and SCR 20 but they were differentiated by their reactions with SCR 18 and SCR 23. Tobacco leaf curl virus was detected only when reducing agents were included in the leaf extraction medium. Inclusion of sodium sulphite slightly improved detection of tomato yellow leaf curl virus but reducing agents were not needed for detection of abutilon mosaic virus.     

Homology between the proteins encoded by tobacco mosaic virus and two tricornaviruses

Summary A comparison was made of the amino acid sequences of the proteins encoded by RNAs 1 and 2 of alfalfa mosaic virus (A1MV) and brome mosaic virus (BMV), and the 126K and 183K proteins encoded by tobacco mosaic virus (TMV). Three blocks of extensive homology of about 200 to 350 amino acids each were observed. Two of these blocks are located in the A1MV and BMV RNA 1 encoded proteins and the TMV encoded 126K protein; they are situated at the N-terminus and C-terminus, respectively. The third block is located in the A1MV and BMV RNA 2 encoded proteins and the C-terminal part of the TMV encoded 183K protein. These homologies are discussed with respect to the functional equivalence of these putative replicase proteins and a possible evolutionary connection between A1MV, BMV and TMV.     

Particle purification and properties of cassava Ivorian bacilliform virus

A virus found in cassava from the north-west of the Ivory Coast was transmitted by inoculation with sap extracts to herbaceous species in six plant families. Chenopodium quinoa was used as a propagation host and C. murale was used for local lesion assays. The virus particles are bacilliform, c. 18 nm in diameter, with predominant lengths of 42,49 and 76 nm and a structure apparently similar to that found in alfalfa mosaic virus. Purified preparations of virus particles had A₂₆₀/A₂₈₀ of 1.7 ±0.05, contained one protein of M_rc. 22 000, and yielded three species of RNA with M_r (× 10^-6) of c. 0.7, 0.8 and 1.2. Although the virus particles were poorly immunogenic, an antiserum was produced and the virus was detected by enzyme-linked immunosorbent assay (DAS-ELISA) in leaf extracts at concentrations down to c. 6 ng/ml. Four other field isolates were also detected, including a strain which caused only mild systemic symptoms in C. quinoa instead of necrosis. The naturally infected cassava source plants were also infected with African cassava mosaic virus (ACMV) but when the new virus was cultured in Nicotiana benthamiana, either separately or together with ACMV, its concentration was the same. The new virus did not react with antisera to several plant viruses with small bacilliform or quasi-bacilliform particles, and alfalfa mosaic virus reacted only weakly and inconsistently with antiserum to the cassava virus. The new virus, for which the name cassava Ivorian bacilliform virus is proposed, is tentatively classified as the second member of the alfalfa mosaic virus group.     

Similarity in structure and function of the 3′-terminal region of the four brome mosaic viral RNAs

A 3′-terminal fragment, about 160 nucleotides long, was cleaved by limited nuclease digestion from each of the four RNA components of brome mosaic virus, and purified by two cycles of gel electrophoresis. These fragments accepted tyrosine in reactions catalyzed by wheat germ aminoacyl-tRNA synthetase. Analyses of nuclease digests suggested that the sequences of the fragments from brome mosaic virus RNA 3 and 4 were identical and that the fragments from RNA 1 and 2 differed from that of RNA 4 only in the positions of two and one nucleotides, respectively. A fragment isolated in a similar way from cowpea chlorotic mottle virus was similar in size to the brome mosaic virus RNA fragments, accepted tyrosine in the presence of wheat germ aminoacyl-tRNA synthetase, but had a substantially different nucleotide sequence.     

Comparative Analysis of Tissue Tropism of Bipartite Geminiviruses

Abutilon mosaic virus (AbMV), a bipartite geminivirus of the genus Begomovirus, has been vegetatively propagated for many years in Abutilon sellovianum in which it is strictly phloem-restricted. Using in situ hybridization and immunological analyses, the tissue tropism of AbMV in the laboratory host Nicotiana benthamiana was compared with that of two other bipartite begomoviruses, African cassava mosaic virus (ACMV) and tomato golden mosaic virus (TGMV). Analysis of the first systemically infected leaves and longitudinal sections of axillary and flower buds revealed that all three viruses are initially confined to the vascular traces, although both ACMV and TGMV are later detectable in nearly all tissue types. In contrast, AbMV remained strictly phloem-limited in this host throughout the course of infection. The ability of ACMV and TGMV to move out of N. benthamiana phloem tissues is correlated with the development of severe symptoms in comparison with the mild symptoms associated with AbMV infection. It was also demonstrated that Sida micrantha mosaic virus, a virus that is closely related to AbMV, is phloem-limited in Malva parviflora even though it induces severe leaf curl, stunting and necrosis in this host. The present data demonstrate that bipartite begomoviruses can exhibit strikingly different patterns of tissue tropism.     

我国真菌传线状小麦花叶病毒病病原初步鉴定为小麦黄花叶病毒(WYMV)

由禾谷多粘菌（Ｐｏｌｙｍｙｘａｇｒａｍｉｎｉｓ）传播的线状小麦花叶病毒有两种,一种是加拿大首先报道的小麦梭条斑花叶病毒（ＷＳＳＭＶ）,另一种是日本报道的小麦黄花叶病毒（ＷＹＭＶ）。这两种病毒粒子形态以及血清学性质非常相似,但核酸序列存在一定差异。经反转录聚合酶链反应（ＲＴＰＣＲ）和单链构象多态性分析（ＳＳＣＰ）,明确我国广泛发生的禾谷多粘菌传线状小麦花叶病毒都是小麦黄花叶病毒,但供试的８个分离物ＲＮＡ１和ＲＮＡ２序列存在差异,无一彼此完全相同     

Translation of the RNAs of brome mosaic virus: The monocistronic nature of RNA1 and RNA2

Each of the two largest brome mosaic virus RNAs, RNA1 and RNA2, directs the synthesis of a large protein in cell-free extracts derived from wheat embryo. The size of each protein represents the translation of almost the entire length of the corresponding RNA. It was shown previously that brome mosaic virus RNA4 directs the synthesis of the coat protein and that brome mosaic virus RNA3, although it also contains the coat protein cistron, is translated mostly into a single product unrelated to the coat protein (Shih & Kaesberg, 1973). Thus, the brome mosaic virus genome encodes a total of four proteins.     

Role of a novel type of double infection in the geminivirus-induced epidemic of severe cassava mosaic in Uganda

To study the cause of the current epidemic of severe mosaic in Ugandan cassava, PCR analysis was used to detect and identify African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV) and the recently reported recombinant geminivirus (UgV), which is derived from ACMV and EACMV, in leaf extracts from cassava plants grown from cuttings in the glasshouse at Dundee. The cuttings were collected from plants showing symptoms of different severities and growing at different sites in Uganda inside, at the periphery of, and outside, the area affected by the epidemic. ACMV occurred throughout the nine districts sampled but UgV was detected only in the area affected by the epidemic. EACMV was not found in Uganda. Most plants containing ACMV alone expressed mild or moderate mosaic, whereas very severe mosaic developed in most plants containing UgV plus ACMV and a few of those containing UgV only. Very severe mosaic in cassava from southern Sudan was likewise associated with co-infection by UgV and ACMV. The very severe disease was reproduced by graft-inoculating geminivirus-free cassava with UgV plus ACMV; plants inoculated with either UgV or ACMV developed severe or moderate symptoms, respectively. Unlike ACMV, Malawian EACMV did not enhance the severity of symptoms induced by UgV. However, a very severely affected plant from Ukerewe Island, Tanzania, contained ACMV and EACMV but not UgV. UgV attained a much greater concentration in cassava than did ACMV but the opposite occurred in Nicotiana benthamiana. In neither host was total virus antigen concentration affected by co-infection. Factors affecting the genesis, selection and spread of UgV are discussed. The evidence indicates that UgV is probably of relatively recent origin, that such variants do not appear often, and that the current epidemic has resulted from the rapid spread of UgV to infect plants and to invade regions in which ACMV already occurred. The novel type of virus complex so produced, consisting of an interspecific recombinant virus (UgV) and one of its parents (ACMV), typically has even more severe effects than UgV alone.     

The prevalence and spatial distribution of viruses in natural populations of Brassica oleracea

We report a survey of four viruses (beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV), turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV)) in five natural populations of Brassica oleracea in Dorset (UK). All four viruses were common; 43% of plants were infected with BWYV, 60% with CaMV, 43% with TuMV and 18% with TYMV. For each virus there were significant differences in the proportion of infected plants among populations, which were not completely explained by differences in the age of plants. Multiple virus infections were prevalent, with 54% of plants having two or more virus types. There were statistically significant associations between pairs of viruses. The CaMV was positively associated with the other three viruses, and BWYV was also positively associated with TuMV. There was no detectable association between BWYV and TYMV, whereas TuMV and TYMV were negatively associated. We suggest these associations result from BWYV, CaMV and TuMV having aphid vectors in common, as aphids are attracted to plants that already have a virus infection. Infected plants were distributed randomly or were very weakly aggregated within populations. The implications of widespread multiple virus infections in natural plant populations are discussed with respect to the release of transgenic plants expressing virus-derived genes.     

Use of Monoclonal Antibodies for the Serological Differentiation of Wheat and Oat Furoviruses

Twenty monoclonal antibodies (MAbs) to Chinese wheat mosaic virus (CWMV) were produced by immunizing BALB/c mice with purified CWMV. These MAbs and polyclonal antisera against CWMV and soil-borne wheat mosaic virus Oklahoma isolate (SBWMV-Okl) were used to differentiate the wheat and oat furoviruses, CWMV, SBWMV, oat golden stripe virus (OGSV) and European wheat mosaic virus (EWMV). Enzyme-linked immunosorbent assays and Western blotting showed that the dominant epitope(s) of CWMV was shared partially with OGSV whereas those of SBWMV were shared with CWMV, OGSV and EWMV in varying degrees. When CWMV virions were briefly digested with trypsin, coat protein fragments of about 12, 10 and 8 kDa were produced and these reacted with the polyclonal antisera and some MAbs, indicating that they contained dominant epitopes of CWMV and SBWMV. Computer analysis of the coat protein sequences suggested that the epitope shared between CWMV and OGSV was located at amino acids 35–40, whereas the dominant epitopes of SBWMV, which were shared with CWMV, EWMV and OGSV, were in the C terminal half of the coat protein     

Structure of hibiscus latent singapore virus by fiber diffraction: a nonconserved his122 contributes to coat protein stability

Hibiscus latent Singapore virus (HLSV) is a rigid rod-shaped plant virus and a new member of the Tobamovirus family. Unlike all other Tobamoviruses, the HLSV genome contains a unique poly(A) tract in its 3′ untranslated region. The virion is composed of a monomeric coat protein (CP) unit of 18 kDa, arranged as a right-handed helix around the virus axis. We have determined the structure of HLSV at 3.5 Å by X-ray fiber diffraction and refined it to an R-factor of 0.096. While the overall structure of the HLSV CP resembles that of other Tobamoviruses, there are a few unique differences. There is a kink in the LR helix due to the presence of His122. Also, the adjacent Lys123 may further destabilize the helix by positive charge repulsion, making the kink more pronounced. The His122-Asp88 salt bridge provides significant stability to the loop adjacent to the RR helix. Carboxyl-carboxylate interactions that drive viral disassembly are also different in HLSV. The nucleotide recognition mechanisms for virus assembly between HLSV and ribgrass mosaic virus are similar, but different between tobacco mosaic virus and cucumber green mottle mosaic virus.     

Patchouli virus X, a new potexvirus from Pogostemon clabin

This work describes a potexvirus obtained from patchouli, Pogostemon clabin, collected in São Paulo, Brazil in 1992. The plants showed mosaic and were infected by a potyvirus and a potexvirus. The potexvirus had a host range limited to Amaranthaceae, Solanaceae and Labiatae and was named Patchouli virus X (PatVX). PatVX was not transmitted by scissors pruning, in tobacco seeds or by Myzus nicotinae. The virus was purified and a specific antiserum with a titre great than 1:512 000 in dot‐ELISA was produced. The virus was serologically related to Papaya mosaic virus, Potato virus X, Viola mottle virus, White clover mosaic virus and Lily virus X. It had a coat protein of 21 071 ± 1 010 Mr. as determined by SDS‐PAGE. Immunolabelling tests demonstrated that fibrillar masses in the cytoplasm contain the coat protein. The presence of a dsRNA was detected in PatVX infected plants.