Molecular identification of a new begomovirus associated with yellow mosaic disease of Jatropha gossypifolia in India

Yellow mosaic disease was observed on Jatropha gossypifolia plants growing in Kathaupahadi, Madhya Pradesh, India, and whiteflies (Bemisia tabaci) were found in the vicinity. Association of a new begomovirus with yellow mosaic disease of J. gossypifolia has been detected by PCR using begomovirus DNA-A-specific primers. The complete DNA-A genome (~2.7 kb) of this virus isolate was amplified by rolling-circle amplification (RCA) followed by digestion with Bam HI. The ~2.7-kb amplicons was cloned and sequenced, and the data obtained were submitted to GenBank under accession numbers FJ177030. The genome of the virus isolate consisted of six open reading frames (ORFs): V2 (pre-coat protein) and V1 (coat protein) in the virion sense and C3 (REn protein), C2 (TrAP protein), C1 (replication-associated protein) and C4 (C4 protein) in the complementary sense. BLASTn analysis of the nucleotide sequence (2757 nt) of the viral genome (FJ177030) showed 84–85% identity and a distinct phylogenetic relationship with DNA-A of tomato leaf curl virus-Bangalore II (U38239) and tomato leaf curl Karnataka virus (AY754812). Based on its 85% sequence identity to all other begomoviruses known to date and ICTV species demarcating criteria (< 88% identity), the name Jatropha yellow mosaic India virus (JYMIV) is proposed. JYMIV is considered to be monopartite, as neither DNA-B nor DNA-β components associated with begomoviruses were detected.     

Complete nucleotide sequence of <Emphasis Type="Italic">Croton yellow vein mosaic virus</Emphasis> and DNA-β associated with yellow vein mosaic disease of <Emphasis Type="Italic">Jatropha gossypifolia</Emphasis> in India

A severe yellow vein mosaic disease was noticed on several Jatropha gossypifolia plants growing nearby agriculture fields at Lucknow, India. Diseased plants exhibited yellow vein mosaic, leaf deformation, vein swelling and stunting. A population of whiteflies (Bemisia tabaci) was also noticed in the vicinities; therefore, begomovirus infection was suspected. To confirm begomovirus association, total DNA was isolated from symptomatic leaf samples and subjected to PCR using DNA-A, DNA-B and DNA-β-specific primers. DNA-A and DNA-β was successfully amplified but several attempts failed to amplify DNA-B indicating monopartite nature of the begomovirus. The sequence analysis of amplicons revealed the presence of 2757 nucleotides of DNA-A genome (EU727086) and 1315 nt of DNA-β molecule (EU604296). The sequence analysis of DNA-A (EU727086) revealed the highest 96% identities and closest relationship with Croton yellow vein mosaic virus (CYVMV, AJ507777) infecting Croton bonplandianum in India. The DNA-β (EU604296) showed the highest 96% sequence identity and closest phylogenetic relationship with CYVMV-associated DNA-β (AM410551) isolated from Croton sp. in Pakistan. Based on the highest sequence identities and closest phylogenetic relationships of the DNA-A genome and DNA-β molecule with respective sequences of various isolates of Croton yellow vein mosaic virus, the begomovirus associated with yellow vein mosaic disease of J. gossypifolia was identified as an isolate of Croton yellow vein mosaic virus.     

Application of Phi29 DNA polymerase in identification and full-length clone inoculation of tomato yellow leaf curl Thailand virus and tobacco leaf curl Thailand virus

Summary. Tomato plants grown in greenhouses in Thailand developed typical symptoms of a tomato yellow leaf curl Thailand virus (TYLCTHV) infection. After confirmation by ELISA, a Phi29 DNA polymerase approach was chosen for further molecular analysis of TYLCTHV. Total DNA purified from infected tomato leaves was subjected to rolling-circle amplification (RCA) of DNA-A and DNA-B of TYLCVTHV. In addition, a new monopartite geminivirus with a putative recombinant background was identified by RCA and tentatively named tobacco leaf curl Thailand virus (TbLCTHV). To confirm the composition of both geminiviruses, full-length clones were established and used for inoculation of Nicotiana benthamiana by particle bombardment or agroinfection. When TYLCTHV DNA-A and DNA-B were applied together by particle bombardment or agroinfection, severe stunting, yellowing, and leaf curling were observed. Whereas TYLCTHV DNA-A and TbLCTHV revealed no infection after'particle bombardment, similar symptoms in N. benthamiana, like leaf upward curling and yellowing were observed following agroinfection. DNA components of TYLCTHV DNA-A and DNA-B were excised from their respective plasmids, ligated, and amplified by Phi29 DNA polymerase. The ability of viral concatamere inoculation was evaluated in particle co-bombardment experiments on N. benthamiana. Thus, particle bombardment of RCA-derived multimeric products proved to be at least as effective as inoculation with a partial repeat construct and tenfold as effective as inoculation with excised unit-lengths of DNA-A and DNA-B of TYLCVTHV when using each DNA component in an amount of 5 ng.     

Molecular characterization of a distinct bipartite begomovirus species infecting tomato in India

A distinct bipartite begomovirus was found associated with tomato plants showing yellowing, curling, and crumpling of the leaves, in a sub-temperate region in India. The complete DNA-A and DNA-B components were amplified through rolling circle amplification (RCA) using Φ-29 DNA polymerase and characterized. The DNA-A of the isolate was comprised of 2,756 nucleotides, encoding six open reading frames (ORFs) and DNA-B that of 2,725 nucleotides, encoding two ORFs. Genome organization of the isolate was typical of an old world bipartite begomovirus. Comparisons showed that DNA-A and its intergenic region (IR) have the highest sequence identity (86% and 84%, respectively) with the Tomato leaf curl New Delhi virus (ToLCNDV; DQ116885) and some other begomoviruses (>84%) reported from cucurbits and tomato. This data suggested that the isolate is a distinct begomovirus species for which a name Tomato leaf curl Palampur virus (ToLCPMV) is proposed. DNA-B showed the maximum sequence identity (73%) with Tomato leaf curl New Delhi virus-India-[Pakistan:Dargai:T5/6:2001] (AY150305). The common region (CR) of DNA-A and DNA-B showed 94% sequence similarity with each other. In the present study, phylogenetic relationship of this new species was also established with different begomoviruses reported from tomato and other begomoviruses showing highest homologies with complete DNA-A and DNA-B sequences. ToLCPMV is being reported from a sub-temperate region in India which was previously unaffected by begomoviruses and its whitefly vector. An erratum to this article can be found at     

Host range and genetic diversity of croton yellow vein mosaic virus, a weed-infecting monopartite begomovirus causing leaf curl disease in tomato

Croton yellow vein mosaic virus (CYVMV) is a widely occurring begomovirus in Croton bonplandianum, a common weed in the Indian subcontinent. In this study, CYVMV (genus Begomovirus, family Geminiviridae) was transmitted by whiteflies (Bemisia tabaci) to as many as 35 plant species belonging to 11 families, including many vegetables, tobacco varieties, ornamentals and weeds. CYVMV produced bright yellow vein symptoms in croton, whereas in all the other host species, the virus produced leaf curl symptoms. CYVMV produced leaf curl in 13 tobacco species and 22 cultivars of Nicotiana tabacum and resembled tobacco leaf curl virus (TobLCV) in host reactions. However, CYVMV was distinguished from TobLCV in four differential hosts, Ageratum conyzoides, C. bonplandianum, Euphorbia geniculata and Sonchus bracyotis. The complete genome sequences of four isolates originating from northern, eastern and southern India revealed that a single species of DNA-A and a betasatellite, croton yellow vein mosaic betasatellite (CroYVMB) were associated with the yellow vein mosaic disease of croton. The sequence identity among the isolates of CYVMV DNA-A and CroYVMB occurring in diverse plant species was 91.8-97.9 % and 83.3-100 %, respectively. The CYVMV DNA-A and CroYVMB generated through rolling-circle amplification of the cloned DNAs produced typical symptoms of yellow vein mosaic and leaf curling in croton and tomato, respectively. The progeny virus from both the croton and tomato plants was transmitted successfully by B. tabaci. The present study establishes the etiology of yellow vein mosaic disease of C. bonplandianum and provides molecular evidence that a weed-infecting monopartite begomovirus causes leaf curl in tomato.     

Tomato yellow leaf curl China virus: monopartite genome organization and agroinfection of plants.

The complete DNA sequence (2734 nucleotides) of the monopartite genome of tomato yellow leaf curl China virus (TYLCCNV), a begomovirus transmitted by the whitefly Bemisia tabaci, was determined. The circular genomic DNA contains six open reading frames (ORFs) encoding proteins of molecular weights >10 kDa, of which two (V1 and V2) are located on the virion-sense strand and four (C1, C2, C3 and C4) on the complementary-sense strand. The ORFs are comparable to those of other whitefly-transmitted begomoviruses with a monopartite genome and to those encoded by DNA-A of bipartite begomoviruses. Sequence comparisons with other geminiviruses showed that TYLCCNV belongs to Begomovirus from the Old World. No putative DNA-B genome was found. Nicotiana species and tomato plants agroinoculated with the TYLCCNV monopartite genome developed typical yellowing and leaf-curling symptoms. The cloned molecule carried all the information needed for virus replication and systemic infection of plants.     

East African cassava mosaic Zanzibar virus – a recombinant begomovirus species with a mild phenotype

Summary. Cassava plants exhibiting mild symptoms of cassava mosaic disease (CMD) were collected from Unguja island, Zanzibar. Cuttings grown from these plants in the glasshouse produced similar symptoms, which were milder than those caused by other known cassava mosaic geminiviruses (CMGs). The whitefly vector, Bemisia tabaci (Gennadius), transmitted the putative virus to 27.7% (n=18) of target plants. Total DNA extracted from diseased leaves did not yield diagnostic PCR-bands using virus-specific primers to known CMGs. Degenerate primers, however, produced a diagnostic band indicating the presence of a begomovirus. Full-length DNA-A (2785 nucleotides) and DNA-B (2763 nucleotides) components were subsequently PCR-amplified, cloned and sequenced. Phylogenetic analyses of DNA-A and -B sequences showed that they were most similar to strains of East African cassava mosaic virus from Tanzania and Uganda at 83% and 86% nucleotide identities, respectively. The number and arrangement of open reading frames were similar to those of bipartite begomoviruses from the Old World. DNA-A was predicted to have recombined in the intergenic region (IR), AC1 and AC4 genes, and DNA-B in the IR. A maximum nucleotide identity of 83% in the DNA-A component with other sequenced begomoviruses, together with different biological properties allows this virus to be recognised as belonging to a new species named East African cassava mosaic Zanzibar virus (EACMZV).     

A novel recombinant tomato-infecting begomovirus capable of transcomplementing heterologous DNA-B components

The genome of a tomato-infecting begomovirus from Ranchi, India, was cloned, sequenced and analysed. The viral genome shared 88.3% sequence identity with an isolate belonging to the species Tobacco curly shoot virus (TbCSV), and this virus should therefore be considered a member of a new species, tentatively named Tomato leaf curl Ranchi virus (ToLCRnV). The DNA-?? molecule, which had 74.5% sequence identity with tomato leaf curl Bangladesh betasatellite (ToLCBDB), is named tomato leaf curl Ranchi betasatellite (ToLCRnB). Phylogenetic analysis revealed that ToLCRnV is related to tomato leaf curl Bangladesh virus (ToLCBDV), tobacco curly shoot virus (TbCSV) and tomato leaf curl Gujarat virus (ToLCGV). An infectivity study with ToLCRnV established the monopartite nature of the viral genome, whereas inoculation with ToLCRnB resulted in increased symptom severity. ToLCRnV could transreplicate DNA-B of tomato leaf curl Gujarat virus (ToLCGV) and tomato leaf curl New Delhi virus (ToLCNDV), both in N. benthamiana and tomato, although DNA-B accumulation of was less than with the wild-type combinations. ToLCRnB could be efficiently replicated by DNA-A of both ToLCNDV and ToLCGV. A leaf disk assay suggests that DNA-A could transreplicate the homologous DNA-B and DNA-?? more efficiently than the heterologous one.     

Evidence for recombination among the tomato leaf curl virus strains/species from Bangalore,India

Summary.  Tomato leaf curl virus (ToLCV) belongs to the Begomovirus genus of the family Geminiviridae. These viruses have circular single stranded DNA molecules as their genome encapsidated in icosahedral geminate particles. Generally the Begomoviruses are bipartite with respect to their genomic composition. ToLCV from South India is unique in that only DNA A component has been isolated and sequenced thus far and there is no evidence for the presence of DNA B component. In this communication we report the genomic sequences of DNA A component of two strains of Tomato leaf curl Bangalore virus (ToLCBV), one from Bangalore, ToLCBV [Ban 5] and the other from Kolar (70 kms from Bangalore), ToLCBV [Kolar]. We have examined the possibility of recombination between strains/species that co-exist within the same geographical location. A novel method has been used to analyze the variation of ToLCV sequences reported from Bangalore and to assess the frequency and importance of recombinational events among the strains/species existing in Bangalore. The results indicate that there are potential sites of recombination in AV1, AV2, AC1 and intergenic regions of the viral genome and this accounts for the observed variability in these strains/species. Received May 7, 2001 Accepted October 18, 2001     

Tomato chlorotic leaf distortion virus,a new bipartite begomovirus infecting <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> and <Emphasis Type="Italic">Capsicum chinense</Emphasis> in Venezuela

Virus isolate T217L was obtained from a diseased tomato (Solanum lycopersicum) plant showing leaf deformation and chlorotic mottle symptoms near Maracaibo in the state of Zulia, Venezuela. Full-length DNA-A and DNA-B molecules of T217L were cloned and sequenced. The genome organization of T217L was identical to the bipartite genomes of other begomoviruses described from the Americas. Characteristic disease symptoms were reproduced in S. lycopersicum and Capsicum annum plants inoculated using the cloned viral DNA-A and DNA-B components, confirming disease aetiology. A sequence analysis of DNA-A showed that the T217L isolate has the highest sequence identity (84%) with sida yellow mosaic Yucatan virus (SiYMYuV), sida golden mosaic Honduras virus (SiGMHV) and bean dwarf mosaic virus (BDMV) isolates. This is less than the 89% identity in the DNA-A component that has been defined as the threshold value for the demarcation of species in the genus Begomovirus. The molecular data show that isolate T217L belongs to a novel tentative begomovirus species, for which the name tomato chlorotic leaf distortion virus is proposed. TCLDV was also detected in symptomatic C. chinense plants growing near the T217L-infected plant.     

Phylogenetic Analysis and Homologies of the Replicase of Tomato Leaf Curl Geminiviruses: Implications for Obtaining Pathogen Derived Resistance

Geminiviruses encode a replication initiator protein, Rep, which binds to iterated DNA motifs functioning as essential elements for virus specific replication. Rep protein gene of three isolates of whitefly transmitted geminivirus causing leaf curl disease of tomato in India were amplified, cloned and sequenced. Nucleotide sequence and the derived amino acid sequence for the replicase gene of these isolates was determined and included in an analysis with the published sequences. Phylogenetic relationship clearly indicates two subsets, one belonging to Tomato leaf curl virus (ToLCV) having bipartite genome and the other having the monopartite genome. Comparisons of various functional domains and motifs involved in specificity determinants, DNA-binding and catalysis were discussed. The implications of the sequence analysis were discussed with respect to the strategy for the generation of engineered resistance having wide spectrum applications.     

Transreplication of a Tomato yellow leaf curl Thailand virus DNA-B and replication of a DNAbeta component by Tomato leaf curl Vietnam virus and Tomato yellow leaf curl Vietnam virus

The genomes of two tomato-infecting begomoviruses from Vietnam were cloned and sequenced. A new variant of Tomato leaf curl Vietnam virus (ToLCVV) consisting of a DNA-A component and associated with a DNAbeta molecule as well as an additional begomovirus tentatively named Tomato yellow leaf curl Vietnam virus (TYLCVV) consisting also of a DNA-A component were identified. To verify if monopartite viruses occurring in Vietnam and Thailand are able to transreplicate the DNA-B component of Tomato yellow leaf curl Thailand virus-[Asian Institute of Technology] (TYLCTHV-[AIT]) infectivity assays were performed via agroinoculation and mechanically. As result, the DNA-B component of TYLCTHV-[AIT] was transreplicated by different DNA-A components of viruses from Vietnam and Thailand in Nicotiana benthamiana and Solanum lycopersicum. Moreover, the TYLCTHV-[AIT] DNA-B component facilitated the mechanical transmission of monopartite viruses by rub-inoculation as well as by particle bombardment in N. benthamiana and tomato plants. Finally, defective DNAs ranging from 735 to 1457 nucleotides were generated in N. benthamiana from those combinations containing TYLCTHV-[AIT] DNA-B component.     

A novel cassava-infecting begomovirus from Madagascar: cassava mosaic Madagascar virus

Cassava mosaic geminiviruses (CMGs) are implicated in cassava mosaic disease (CMD), the main constraint to cassava production in Africa. Here, we report the complete nucleotide sequences of the DNA-A and DNA-B of a newly characterized CMG found infecting cassava in Madagascar, for which we propose the tentative name cassava mosaic Madagascar virus. With the exception of two recombinant regions that resembled a CMG, we determined that the non-recombinant part of the DNA-A component is distantly related to the other CMGs. Whereas the DNA-B component possesses one recombinant region originating from an unidentified virus, the rest of the genome was seen to be closely related to members of the species East African cassava mosaic Zanzibar virus (EACMZV). Phylogenetic analysis based on complete genome sequences demonstrated that DNA-A and DNA-B components are outliers related to the clade of EACMV-like viruses and that DNA-A is related to the monopartite tomato leaf curl begomoviruses described in islands in the south-west Indian Ocean.     

Velvet bean severe mosaic virus: a distinct begomovirus species causing severe mosaic in <Emphasis Type="Italic">Mucuna pruriens</Emphasis> (L.) DC

Velvet bean [Mucuna pruriens (L.) DC] is one of the most important medicinal plants. It is used to treat many ailments, but is widely used for the treatment especially for Parkinson’s disease because of the presence of 3,4-dihydroxyphenylalanine (l-dopa) in it. It was noticed in last 5 years that the plants in the field showed severe mosaic, downward curling of the leaves, stunting, etc. This is consistently observed over the years in India. The disease was transmitted by whiteflies and by grafting and the causal agent was found to be a bipartite begomovirus. The whole genome was amplified by rolling circle amplification (RCA) using ϕ-29 DNA polymerase and characterized. DNA-A and DNA-B shared a 124-nucleotide (nt) long highly conserved (98%) common region (CR). Comparisons with other begomovirus showed that DNA-A sequence has highest identity (76%) with an isolate of Mungbean yellow mosaic India virus (MYMIV; AY937195) reported from India. This data suggested that the present isolate is a new species of genus Begomovirus for which the name “Velvet bean severe mosaic virus” (VbSMV) is proposed. DNA-B has a maximum sequence identity of 49% with an isolate of Horsegram yellow mosaic virus (HgYMV; AM932426) reported from India. Infectious clones consisting of a 1.7 mer partial tandem repeat of DNA-A and a dimer of DNB-B were constructed and agro-inoculated to Macuna pruriens (L.) DC plants, which showed field observed symptoms 24 days post-infiltration (dpi). In phylogenetic analysis, DNA-A and DNA-B of the present isolate grouped with DNA-A of different begomoviruses reported from fabaceous crops. The study presents first ever molecular evidence of any disease in velvet bean and whole genome analysis of the causative virus which is a distinct bipartite species of Begomovirus.     

A divergent isolate of <Emphasis Type="Italic">Tomato yellow leaf curl virus</Emphasis> from Oman with an associated DNAβ satellite: an evolutionary link between Asian and the Middle Eastern virus–satellite complexes

Tomato is cultivated in the coastal region of Al-Batinah, in the Sultanate of Oman, during the winter season, to meet the high demand for fresh produce in the domestic market. In order to identify the causal agent of a widespread disease associated with infestations of the whitefly Bemisia tabaci (Genn.) leaves were collected from tomato plants showing symptoms characteristic of the disease in Al-Batinah during 2004 and 2005. Total nucleic acids were isolated from the tomato leaves and used as the template for Φ29 DNA polymerase amplification of begomoviral circular DNA. Putative full unit length begomoviral DNA multimers were digested with Nco I and cloned into the plasmid vector pGEM7Zf+. The complete nucleotide (nt) sequence was determined as 2,765 bases, indicative of a monopartite begomoviral genome. A comparison of the genome sequence for the seven field isolates examined, indicated that they shared 99% nt identity. The virus from Oman was most closely related to TYLCV-IR at 91% nt identity, a monopartite begomoviral species described previously from Iran. Based on the guidelines of the ICTV the Oman isolate has been designated TYLCV-Om and is considered an isolate of TYLCV-IR. A satellite DNA (satDNA β), was amplified by polymerase chain reaction using degenerate primers and cloned, and the DNA sequence was determined. Analysis of the complete nt sequence of 1,371 bases indicated that the satDNA shared 88.5% similarity with its closest relatives, which are DNAβ molecules from tomato in Pakistan. This is the first report of a satDNA β associated with the TYLCV species. The TYLCV-Om and associated satDNA, thus represent a begomovirus-complex at the Asian-Middle East crossroads that quiet uniquely share geographical and genetic hallmarks of both.     

Genetic variability of begomoviruses associated with cotton leaf curl disease originating from India

Summary. Cotton leaf curl disease (CLCuD) causing viruses belong to the Begomovirus genus of the family Geminiviridae. Most begomoviruses are bipartite with two molecules of circular single stranded DNA (A and B) encapsidated in icosahedral geminate particles. However, the begomoviruses associated with CLCuD have DNA- instead of DNA-B. In this communication we report the complete genomic sequence of DNA-A component of two CLCuD-causing begomoviruses, cotton leaf curl Kokhran virus-Dabawali (CLCuKV-Dab), tomato leaf curl Bangalore virus-Cotton [Fatehabad] (ToLCBV-Cotton [Fat]) and partial sequences of two other isolates cotton leaf curl Rajasthan virus-Bangalore (CLCuRV-Ban) and cotton leaf curl Kokhran virus-Ganganagar (CLCuKV-Gang). A phylogenetic analysis of these isolates along with other related begomoviruses showed that ToLCBV-Cotton [Fat] isolate was closest to the tomato leaf curl Bangalore virus-5 (ToLCBV-Ban5) where as CLCuKV-Dab isolate was close to the cotton leaf curl Kokhran virus-Faisalabad1 (CLCuKV-Fai1), cotton leaf curl Kokhran virus-72b (CLCuKV-72b) and cotton leaf curl Kokhran virus-806b (CLCuKV-806b) isolates from Pakistan. The phylogenetic analysis further showed that the ToLCBV-Cotton [Fat] and CLCuKV-Dab isolates along with CLCuKV-Fai1, CLCuKV-72b and CLCuKV-806b are closer to the ToLCBV, tomato leaf curl Gujarat virus (ToLCGV), tomato leaf curl Gujarat virus-Varanasi (ToLCGV-Var) and tomato leaf curl Sri Lanka virus (ToLCSLV) isolates, where as cotton leaf curl Alabad virus-804a (CLCuAV-804a), cotton leaf curl Multhan virus (CLCuMV) cluster with the isolates from cotton leaf curl Rajasthan virus (CLCuRV) and okra yellow vein mosaic virus (OYVMV). These results demonstrate the extensive variability observed in this group of viruses. The AC4 ORF is the least conserved among these viruses. In order to further asses the variability in the CLCuD-causing begomoviruses, the region showing minimum similarity in the DNA-A sequence was first determined by a comparison of segments of different lengths of the aligned sequences. The results indicated that region 2411–424 (771nt) was the least conserved. A phylogenetic tree constructed using the sequences of all the CLCuD causing begomoviruses, corresponding to the least conserved region showed that they form two distinct clusters.     

Molecular characterization and phylogenetic relationships of two new bipartite begomovirus infecting malvaceous plants in Yucatan,Mexico

Sida acuta and Corchorus siliquosus plants showing yellow mosaic and yellow vein symptoms, respectively, were collected in the Yucatan Peninsula, Mexico. Total DNA was isolated from both plant species and used for the amplification, cloning, and sequencing of the Begomovirus genome. Nucleotide comparison of the complete DNA-A component isolated from S. acuta and C. siliquosus confirmed the presence of two distinct begomoviruses species. Based on phenotypic symptoms observed in infected field plants, the names Sida yellow mosaic Yucatan virus (SiYMYuV) and Corchorus yellow vein Yucatan virus (CoYVYuV) were proposed. The SiYMYuV DNA-A shared the highest nucleotide identity (86%) with the Okra yellow mosaic Mexico virus (OkYMMV). The complete DNA-B component shared the highest nucleotide identity (80%) with CoYVYuV. The CoYVYuV DNA-A shared the highest nucleotide identity (84%) with SiYMYuV. The 166-nt common region (CR) sequence for the DNA-A and DNA-B components of SiYMYuV shared a high nucleotide identity of 99%, and the 151 nt of CoYVYuV CR shared 95% of nucleotide identity. The organization and the iterated sequence of the putative AC1 binding site (located within the common region) of both isolates, were similar to that of the begomoviruses of the Western Hemisphere. Phylogenetic analyses placed the DNA-A and DNA-B of SiYMYuV and CoYVYuV in the clade containing the Abutilon mosaic virus (AbMV).     

PCR-based detection and partial genome sequencing indicate high genetic diversity in Bangladeshi begomoviruses and their whitefly vector, <Emphasis Type="Italic">Bemisia tabaci</Emphasis>

The population diversity of Bangladeshi begomoviruses and their vector, Bemisia tabaci was analysed by PCR-based detection and partial genome sequencing. B. tabaci adults and plants expressing symptoms of virus infection were collected from locations representing diverse agro-ecological regions of the country. Universal and species-specific primers were used to detect begomoviruses in seven crops (chilli, okra, papaya, pumpkin, sponge gourd, tomato and yardlong bean) and two common weeds (Ageratum conyzoides and Croton bonplandianum). At least five distinct species of tomato leaf curl viruses infected tomato and other host-plants. Phylogenetic analyses of their nucleotide sequences (∼530 bases) from the intergenic region and capsid protein of DNA-A indicated the existence of five distinct clusters of begomoviruses. Begomoviruses infecting tomato, chilli and dolichos have been reported previously, and those infecting Ageratum, Croton, okra, papaya, pumpkin and yardlong bean are described for the first time. Phylogenetic analyses based on mitochondrial cytochrome oxidase I gene sequences of 21 B. tabaci from Bangladesh and other reference sequences grouped them into at least two independent clusters. Some sequences from different countries, e.g., Bangladesh, China, India, Nepal, Pakistan and Thailand were almost identical while others collected from plants within the same field diverged by as much as 15%, indicating high diversity even at the local level. None of the B. tabaci from Bangladesh grouped with the reference B- and Q-biotype sequences, thus these two aggressive biotypes were apparently absent from Bangladesh.     

Strains of a new bipartite begomovirus, pepper yellow leaf curl Indonesia virus, in leaf-curl-diseased tomato and yellow-vein-diseased ageratum in Indonesia

The complete nucleotide sequences of begomoviruses from pepper with leaf curl and yellowing symptoms, tomato with leaf curl symptoms, and ageratum with yellow vein in Indonesia were determined. On the basis of genome organization and sequence homology, they were proposed to belong to a new species, Pepper yellow leaf curl Indonesia virus (PepYLCIV), which includes the new strains PepYLCIV-Tomato and PepYLCIV-Ageratum. These viruses had bipartite genomes. Pepper virus DNAs from Indonesia (PepYLCIV, PepYLCIV-Tomato and PepYLCIV-Ageratum DNA-As) were noticeably distinct, forming a separate branch from the viruses infecting pepper. Considerable divergence was observed in the common region (CR) of the genomic components of PepYLCIV (77%), PepYLCIV-Tomato (82%) and PeYLCIV-Ageratum (75%). A stem-loop-forming region and a Rep-binding motif were identical in the CR of the three viruses. The CRs of PepYLCIV-Ageratum DNA-A was approximately 10 nucleotides longer than that of PepYLCIV DNA-A and PepYLCIV-Tomato DNA-A. A similar insertion was also found in the CR of PepYLCIV-Ageratum DNA-B. PepYLCIV DNA-A alone was infectious in pepper and Nicotiana benthamiana plants, and association with DNA-B increased symptom severity.     

Evidence for Transovarial Transmission of Tomato Yellow Leaf Curl Virus by Its Vector, the WhiteflyBemisia tabaci

The whiteflyBemisia tabaciis the only vector of the tomato yellow leaf curl geminivirus (TYLCV). The insect transmits the virus in a persistent-circulative manner. TYLCV DNA was detected by polymerase chain reaction and by Southern blot hybridization in progeny (eggs, first and second instars, adults) of single viruliferous whiteflies that developed on eggplant or on cotton (two TYLCV nonhost plants). Furthermore, TYLCV DNA was present in the progeny of insects that had acquired the virus through the egg. The adult progeny of the viruliferous insects and their own progeny were able to infect tomato test plants, producing typical disease symptoms. Ovaries and maturing eggs of viruliferous insects contained viral DNA, as did eggs laid by viruliferous insects maintained on an artificial diet. Eggs laid by nonviruliferous whiteflies on cotton plants previously caged with viruliferous insects did not acquire viral DNA from the plant. Hence, TYLCV can be transmitted through the egg for at least two generations. In the absence of an available plant host, the whitefly may serve as a reservoir of the virus between growing seasons.