Sweet Potato Leaf Curl Virus Research Articles

Detection of Sweet potato virus 2 in Sweet Potato in New Zealand.

In New Zealand, sweet potato (Ipomoea batatas) is a crop of cultural importance and an important food source; it is grown mainly in the districts of Kaipara, Auckland, and the Bay of Plenty in the North Island. In January of 2008, virus symptoms that included chlorotic spots, ring spots, and mottling were observed on the leaves of commercial sweet potato crops (cvs. Beauregard, Owairaka Red, and Toka Toka Gold) growing in the three main production areas. A survey was done to determine the extent of virus infection in these crops. Fifty to one hundred leaves were collected randomly from each of 26 different fields. Leaves from each field were bulked into groups of 10, giving a total of 173 composite samples. All samples tested negative for Cucumber mosaic virus, C-6 virus, Sweet potato caulimo-like virus, Sweet potato chlorotic fleck virus, Sweet potato chlorotic stunt virus (SPCSV), Sweet potato latent virus, and Sweet potato mild specking virus by nitrocellulose membrane enzyme-linked immunosorbent assays (International Potato Center-CIP, Lima, Peru). Total nucleic acid was extracted from all 173 composite samples and used in real-time PCR assays specific for Sweet potato leaf curl virus (SPLCV) and real-time reverse transcription (RT)-PCR specific for SPCSV, Sweet potato feathery mottle virus (SPFMV), Sweet potato virus G (SPVG), and Sweet potato virus 2 (SPV2; synonym Sweet potato virus Y) (1). No samples were positive for SPLCV or SPCSV, but 107 and 138 samples tested positive for SPFMV and SPVG, respectively. SPFMV and SPVG have been reported previously in New Zealand (2,3). Sixty four samples from 16 different fields tested positive for SPV2. Of the 64 samples, 52 were also infected with SPVG and SPFMV, and 10 were co-infected with SPVG but not SPFMV; no samples were co-infected with SPV2 and SPFMV when SPVG was absent. From a representative SPV2 positive sample, the 70-bp amplicon obtained by the real-time RT-PCR primers was cloned and sequenced A BLAST search showed 100% nucleotide sequence identity with SPV2 (GenBank Accession Nos. AM050887 and AY178992). Subsequently, primers (V2-F1c: 5'-AGAACAGGACAAACTCAACC-3'; V2-R1: 5'-TAATCACCCTTCACACCTTC-3') were designed to amplify an approximately 434-bp fragment within the SPV2 coat protein gene. One-step RT-PCR was done on four of the SPV2 positive samples and amplicons of the expected size were sequenced directly (GenBank Accession No. FJ461774). Sequence comparison showed 99% nucleotide sequence identity with SPV2 (GenBank Accession Nos. AM050886, AM050887, AY178992, and EF577437). SPV2 is a member of the genus Potyvirus but the virus has not been fully characterized. It is known that single-potyvirus infections cause mild or no symptoms in sweet potato, and consequently, no significant yield reduction is observed generally. However, co-infection with other viruses such as SPCSV produces a synergistic effect and more severe disease symptoms (4). To our knowledge, this is the first report of SPV2 infecting sweet potato in New Zealand.

Occurrence of Sweet potato feathery mottle virus and Sweet potato leaf curl Georgia virus on Sweet Potato in India

Viruses are a major biotic constraint on sweet potato (Ipomoea batatas (L.) Lam) production worldwide. In 2005, 10 to 60% viral disease incidence was observed in sweet potato fields. Symptoms include ring and chlorotic spots, puckering, feathering, vein clearing, and leaf curl with chlorotic specks and pink spots. Cuttings from symptomatic plants were collected from Kerala (two clones), Orrisa (eight clones), and Adrapradesh (three clones) and maintained in an insect-proof glasshouse. Leaves from symptomatic plants were mechanically inoculated to I setosa, I. nil, Nicotiana tabacum, N. benthamiana, Datura stramonium, and Chenapodium quinoa (12 seedlings each). Vein clearing, netting, and leaf distortion were observed in I. setosa and N tabacum 7 days postinoculation, chlorotic spots observed in N. benthamiana, and violet spots and violet margins on leaves observed on I. Nil. No symptoms were observed on D. stramonium and C. quinoa. When scions from the symptomatic sweet potato plants were graft inoculated onto I. setosa, vein clearing, leaf curl, and puckering-like symptoms were observed within 5 days. Mosaic and leaf curling symptoms were also observed on mechanically inoculated N. tabacum. Total nucleic acids isolated from the 33 field-collected sweet potato samples, graft inoculated I. setosa plants, and mechanically inoculated N. tabacum and I. nil plants were used for PCR and reverse transcription (RT)-PCR with geminivirus group specific (2) and potyvirus group specific primers (1). The expected 530-bp and 1.3-kb fragment were generated from the geminivirus and potyvirus primer sets, respectively. Potyvirus alone was detected in 7 of the 33 field-collected plants; geminivirus alone was detected in 7 other plants, while 19 plants contained detectible levels of potyvirus and geminivirus. To further identify the viruses, nested primers specific for the coat protein gene of Sweet potato feathery mottle virus (SPFMV) (CP1S 5'AGT GGG AAG GCA CCA TAC ATA GC 3', CP1A5' GCA GAG GAT GTC CTA TTG CAC ACC 3') (CP2S 5'TCT AGT GAA CGT ACT GAA TTC AAA GA 3', CP2A 5'ATT GCA CAC CCC TGA TTC CTA AGA 3') and Sweet potato leaf curl virus (SPLCV) (CP1- 5'ATG ACA GGG CGA ATT CGC GTT TC 3', CP2- 5'TTA ATT TTT GTG CGA ATC ATA 3') were designed. I. setosa and N. tabacum were amplified with SPFMV and SPLCV primers and the amplicons of 960 and 764 bp, respectively, obtained were subsequently cloned into pGEM-T Easy vector and sequenced. Nucleotide BLAST analysis revealed that the 960-bp fragment (GenBank Accession No. EF015398.) was 98% identical to two Egyptian isolates of SPFMV (Nos. AJ 515379 and AJ 515378). The nucleotide sequence of the 764-bp products (Nos. EF 151926 and EF15483) from the samples collected from Kerala and Orisa was 95% identical to each other. The sequence identity of EF 15483 with Sweet potato leaf curl Georgia virus (SPLCGV) isolate AF326775. was 91% and identity with China isolate DQ 512731 was 90% The isolate EF 151926 also was 91% identical to the SPLCGV with a high query and alignment score whereas identity with the China isolate was 91% with a low query coverage and alignment score. Phylogenic analysis with MEGA software program also showed the highest sequence similarity with SPLCGV, hence it is concluded that the geminivirus isolate under study is SPLCGV. To our knowledge, this is the first report of identification of SPFMV and SPLCGV occurring on sweet potato in India. Further study is required to understand the consequences of occurrence of these two viruses in India.

Molecular characterization of sweet potato leaf curl virus isolate from China (SPLCV-CN) and its phylogenetic relationship with other members of the Geminiviridae

A Sweet potato-infecting sweet potato leaf curl virus (SPLCV) isolated in China was detected by Polymerase Chain Reaction (PCR). PCR products amplified from DNA-A were cloned and sequenced. The isolates of SPLCV from China(SPLCV-CN)has a genome organization similar to that of monopartite begomoviruses. The DNA-A had two ORFs (AV1 and AV2) in the virion sense and four ORFs (AC1, AC2, AC3, and AC4) in the complementary sense, separated by an intergenic region (IR) containing a conserved stem-loop motif. Three incomplete direct repeat iterons were also found within the IR. The presence of AV2 ORF supports the relationship of SPLCV-CN to the Old World gemimiviruses. Sequence comparisons showed that the DNA-A sequence of SPLCV-CN were closely related to those of sweet potato leaf curl Georgia virus-[16] (SPLCGV-[16]), Ipomoea yellow vein virus (IYVV-SI), and sweet potato leaf curl virus (SPLCV) with nucleotide sequence identity ranging from 88% to 91%. Comparison of individual encoded proteins between SPLCV-CN and that of three other SPLCV isolates showed the coat protein (AV1) shared the highest amino acid sequence identity (93%-96%), suggesting the coat protein of these viruses may have identical ancestor. The relationships between SPLCV-CN and other whitefly-transmitted geminiviruses were investigated by using phylogeny of derived AV1, AC1, and AV2 amino acid sequences. In all phylogenetic trees, SPLCV-CN clustered with three other isolates of SPLCV. The analyses revealed that the four isolates of SPLCV have coat proteins which are unique from its counterparts from both the Old World and New World. The present of AV2 and phylogenic analysis of AC1 suggest that SPLCV is more close to begomoviruses from the Old World but isolates of this virus seems to form a separate subset.

First Report of Sweet potato leaf curl virus in China.

During the 2004 growing season in the Liaoning Province in China, where there was large population of whiteflies, several sweet potato (Ipomoea batatas) breeding lines showed leaf curl symptoms. A survey was conducted to determine the incidence of Sweet potato leaf curl virus (SPLCV) in China. Sixteen plants were collected and stem scions from those plants were graft inoculated to Ipomoea nil. Three weeks later, the indicator developed symptoms of leaf curling, interveinal chlorosis, and stunting. Total nucleic acid was extracted from young leaves of sweet potato and then evaluated using polymerase chain reaction (PCR). Primers, developed by Briddon and Markham (1) and used as universal primers for amplification of the geminivirus DNA fragment, were BM-V (5'-KSG GGT CGA CGT CAT CAA TGA CGT TRT AC-3') and BM-C (5'-AAR GAA TTC ATK GGG GCC CAR ARR GAC TGG C-3'). Amplified fragments with BM primers theoretically should have sizes almost equal to the full length of the DNA A component of the bipartite genome (2). Expected DNA fragments of 2.8 kb that contained the AV1, AV2, AC1, AC2, AC3, and AC4 open reading frames were obtained from symptomatic, but not from symptomless (uninfected) plants. The 2.8-kb fragments obtained by amplification were purified and cloned into the PMD18-T vector. Recombinant plasmids were then transformed into competent cells of Escherichia coli strain DH5(. The fragment was sequenced (GenBank Accession No. DQ512731), and nucleotide sequence of corresponding regions were compared with a published sequence of SPLCV available in GenBank (Accession No. AF104036). The AC4 and AC2 genes showed the highest (92%) and the lowest (83%) identity, respectively. This virus has been reported in the United States, Taiwan, Japan, and Peru. To our knowledge, this is the first report of the natural occurrence of SPLCV in China.

First Report of a Begomovirus Infecting Sweetpotato in Kenya

Previous surveys for viruses in sweetpotatoes (Ipomoea batatas) in Africa did not assay for the presence of begomoviruses such as Sweet potato leaf curl virus (SPLCV), which have been found recently in the Americas and Asia. Symptomatic sweetpotato plants, including some with leaf curling symptoms similar to those observed in SPLCV-infected sweet-potato plants (2), were collected from a germplasm collection plot at Kakamega Research Station in Western Kenya during February 2005. Whiteflies, the vectors for begomoviruses, were observed in the same plots. Ipomoea setosa plants graft-inoculated with scions from the symptomatic sweetpotato developed leaf curl, leaf roll, interveinal chlorosis, and stunting symptoms similar to those caused by infection with SPLCV alone or in combination with Sweet potato feathery mottle virus. Total DNA was isolated from 10 I. setosa plants using the GenElute Plant Genomic DNA Kit (Sigma-Aldrich Inc., St. Louis, MO). Sweetpotato cuttings from 39 clones, selected from the Kenyan germplasm collection for their resistance or susceptibility to sweetpotato virus disease (SPVD), were sent to the Plant Germplasm Quarantine Office of USDA-ARS. The cuttings were planted in a greenhouse. Total DNA was extracted from sweetpotato leaves 1 month later using a cetyltrimethylammoniumbromide (CTAB) extraction method (1). Degenerate primers SPG1/SPG2, developed for PCR detection of begomoviruses (1), amplified a 912-bp DNA fragment from 3 of 10 DNA extracts from I. setosa and 5 of 39 sweetpotato plants held in quarantine. The primers anneal to regions of open reading frame (ORF) AC2 and ORF AC1 that are highly conserved in begomoviruses infecting sweetpotato. SPLCV-specific primers PW285-1/PW285-2 (2) amplified a 512-bp DNA fragment of ORF AC1 from seven samples (two from I. setosa and five from I. batatas). Amplicons from three independent PCR assays of two samples and single PCR assays of four additional samples were cloned into the pGEM-T Easy vector. Clone inserts were sequenced, and compared with sequences deposited in GenBank using the basic local alignment search tool (BLAST). Sequences were closely related to SPLCV (GenBank Accession No. AF104036) with nucleotide sequence identities varying from 93% (GenBank Accession No. DQ361004) to 97% (GenBank Accession No. DQ361005). The presence of the virus poses a challenge to the dissemination of planting materials in the region because begomovirus-infected plants often do not show symptoms. To our knowledge, this is the first report of a begomovirus infecting sweetpotato in Kenya or the East African Region.

AN UPDATE ON EVALUATION OF VIRUS STATUS IN THE HEIRLOOM SWEETPOTATO GERMPLASM MATERIALS WITH REAL-TIME PCR TECHNOLOGY

Sweet potato virus disease (SPVD) is the most devastating virus disease on sweetpotato [Ipomoea batatas (L.) Lam] world wide, especially in East Africa. However, weather it is present in the U.S. is unknown. SPVD is caused by co-infection of sweetpotato feathery mottle virus (SPFMV) and sweetpotato chlorotic stunt virus (SPCSV). Presence of two other potyviruses, sweetpotato virus G (SPVG) and Ipomoea vein mosaic virus (IVMV) has also been confirmed in the U.S. Sweet potato leaf curl virus (SPLCV), a whitefly (Bemisia tabaci) transmitted Begomovirus, also has the potential to spread to commercial sweetpotato fields and poses a great threat to the sweetpotato industry. The U.S. collection of sweetpotato germplasm contains about 700 genotypes or breeding lines introduced from over 20 different countries. Newly introduced sweetpotato germplasm from foreign sources are routinely screened for major viruses with serology and graft-transmission onto indicator plants (Ipomoea setosa). However, a large portion of this collection including heirloom cultivars or old breeding materials has not been systemically screened for these major sweetpotato viruses. In this study, a total of 69 so-called heirloom sweetpotato PI accessions were evaluated for their virus status. We used Real-time PCR to detect five sweetpotato viruses, including four RNA viruses (SPCSV, SPFMV, SPVG, and IVMV) and one DNA virus (SPLCV). A multiplex Real-time RT-PCR system was developed to detect three RNA viruses (SPFMV, SPVG, and IVMV). Preliminary data indicated that about 15% of these heirloom sweetpotato germplasm carried at least one of these viruses tested. Details on virus infection status will be presented.

Real-Time PCR Assays for Detection and Quantification of Sweetpotato Viruses.

Viral diseases, especially those caused by mixed infections, are among the economically most important diseases of sweetpotato. The difficulties inherent in detecting, quantifying, and isolating viruses directly from sweetpotato have impeded progress in sweetpotato virus research. Real-time polymerase chain reaction (PCR) assays were developed for the detection and relative quantification in singleplex reactions of the potyviruses Sweet potato feathery mottle virus (SPFMV), Sweet potato virus G (SPVG), and Ipomoea vein mosaic virus (IVMV); the crinivirus Sweet potato chlorotic stunt virus (SPCSV); and the begomovirus Sweet potato leaf curl virus(SPLCV) directly from infected sweetpotato plants. There was no significant effect from potential inhibitors in total nucleic acid extracts from sweetpotato leaves on the performance of the real-time PCR assays. Virus titers of SPFMV, IVMV, and SPVG were quantified using real-time PCR and found to be lower in singly infected sweetpotato plants compared with singly infected Brazilian morning-glory (Ipomoea setosa Ker.) and I. nil cv. Scarlet O'Hara plants. Real-time PCR was a more efficient detection method for SPLCV than conventional PCR assay.

Occurrence of Sweet potato leaf curl virus in Sicily

The Ipomoea -infecting begomoviruses are an evolutionary curiosity. Two such viruses have been identified: Sweet potato leaf curl virus (SPLCV; Lotrakul & Valverde, 1999) and Sweet potato leaf curl Georgia virus (SPLCGV), originating from the USA (SPLCV and SPLCGV) and Spain [SPLCV-Ipo, previously known as Ipomoea yellow vein virus (Banks et al ., 1999) but now recognized as a distinct strain of SPLCV]. These viruses are monopartite (no DNA B or DNA β component has been identified for any of the viruses), have a genome organization typical of Old World begomoviruses, and are distinct from all other begomoviruses. Cuttings of Ipomoea indica (Convolvulaceae) showing yellow vein symptoms were collected in the vicinity of Catania, Sicily in 1999. A full-length clone of the begomovirus associated with the disease was produced by PCR-mediated amplification with a pair of primers abutting at their 5 ′ ends and spanning (for SPLCV-Ipo) nucleotides 697–758 (virion-sense primer 5 ′ -GGATCCGCTGAACTTTGGCCAGATCTTCACTATG-3 ′ ; complementary-sense primer 5 ′ -GGATCCTTATTGGGCCTTGTATCACGAATCAACC-3 ′ ). These were designed to the sequence of SPLCV-Ipo (EMBL accession number AJ132548) and span a unique Bam HI restriction endonuclease site. The full-length PCR product was cloned into the T-Easy vector (Promega) and the sequence of a single clone was determined. This sequence (accession no. AJ586885) is 2830 nucleotides long and shows the arrangement of genes typical of the genomes (or DNA A components) of Old World begomoviruses. The virus is closely related to other begomoviruses isolated from Ipomoea spp., including SPLCGV (84·2% nucleotide sequence identity), SPLCV (89·9%) and SPLCV-Ipo (90·9%), with which it clusters in phylogenetic analyses. We conclude that the isolate originating from Sicily is a strain of SPLCV which is provisionally designated SPLCV-[Sicily]. The occurrence of this begomovirus species in Sicily indicates that its geographical range extends further across the Mediterranean basin than previously identified.

Effects of Common Viruses on Yield and Quality of Beauregard Sweetpotato in Louisiana.

During cycles of vegetative propagation, sweetpotato accumulates viruses that are thought to contribute to decline in yield and quality of cultivars, but the effects of specific viruses, many of which have been described only recently, are unknown. Field plots planted with graft-inoculated plants of a virus-tested (VT) mericlone of cv. Beauregard were used to assess the effects of three common potyviruses, Sweet potato feathery mottle virus (SPFMV), Sweet potato virus G (SPVG), and Ipomoea vein mosaic virus (IVMV); and a begomovirus, Sweet potato leaf curlvirus (SPLCV), compared with natural inoculum introduced by grafting plants from farmers' stock. Single infections with SPFMV, SPVG, or IVMV did not significantly affect yield, whereas mixed infections with SPFMV + SPVG or SPFMV + SPVG + IVMV resulted in mean yields 14% less than the VT controls. Infection with SPLCV resulted in mean yields 26% less than the VT controls, despite not causing symptoms on the foliage. However, grafting with farmers' plants infected with an unknown mixture of pathogens resulted in mean yields 31 to 44% less than the VT controls. Infection with potyviruses resulted in storage roots with tan periderm and infection with SPLCV induced darker periderm than the rosy VT controls. Infection with the viruses known to occur commonly in the United States did not reproduce the magnitude of yield reduction that has been observed with naturally infected plants.

Detection of Geminiviruses in Sweetpotato by Polymerase Chain Reaction.

Geminivirus infection of sweetpotato (Ipomoea spp.) germplasm acquired from foreign regions is common. Graft inoculation of the indicator host, Ipomoea setosa, is the accepted detection method for these viruses, but the assay is laborious and requires up to 8 weeks. When infected sweetpotato is subjected to meristem tip culture to eliminate these viruses, the eradication rate is low. In this study, a polymerase chain reaction (PCR) detection assay was developed for the detection of geminiviruses in a variety of sweetpotato cultivars. Different methods were evaluated to extract nucleic acids suitable for PCR from Ipomoea spp., and a reliable and simple extraction method was developed for large-scale sample preparation. PCR products of the expected sizes were amplified from infected plants using degenerate and virus-specific primers, but not from noninoculated indicator plants. PCR assays using three primer pairs detected nine uncharacterized isolates of the geminiviruses in sweetpotato from Asia and America. However, the best PCR result was obtained with degenerate primers SPG1/SPG2, which detected a Taiwan isolate of Sweet potato leaf curl virus (SPLCV-Taiwan) in a sample diluted to 10-9. Viral identities of three amplicons from SPLCV-Taiwan were confirmed by sequencing. The degenerate primers had a broader detection range than virus-specific primers; therefore, they were used to detect geminiviruses in in vitro plantlets and greenhouse-grown sweetpotato plants, and in several Ipomoea hosts. PCR was shown to be as reliable for virus detection as grafting.

Whitefly transmission of sweet potato viruses

Three genera of plant viruses, Begomovirus (Geminiviridae), Crinivirus (Closteroviridae) and Ipomovirus (Potyviridae), contain members that infect sweet potato ( Ipomoea batatas) and are transmitted by whiteflies. The begomoviruses, Sweet potato leaf curl virus (SPLCV) and Ipomoea leaf curl virus (ILCV), and the ipomovirus Sweet potato mild mottle virus are transmitted by Bemisia tabaci, the sweet potato whitefly. The crinivirus, Sweet potato chlorotic stunt virus (SPCSV), is transmitted by B. tabaci and Trialeurodes abutilonea, the bandedwinged whitefly. Transmission experiments were done with three of these viruses using laboratory-reared whiteflies and 2-day acquisition and transmission feeding periods. SPLCV and ILCV were transmitted from single and double infections by B. tabaci at rates of 5–10%. Transmission rates for SPLCV by B. tabaci were 15–20%. T. abutilonea transmitted SPCSV at a rate of ca. 3% but did not transmit ILCV or SPLCV.

First Report of Sweet potato leaf curl virus in Peru.

Leaf curling symptoms have been reported in sweet potato (Ipomoea batatas) plants infected with a geminivirus (1). Leaf curl disease appeared in Peru after the 1997 to 1998 El Niño, when the population and activity of whiteflies (Bemisia tabaci, B. argentifolii, and B. afer) increased. Approximately 6% of plants in farmers' commercial fields in San Ramón, Junín (September 2000) and Cañete, Lima (February 2001) showed typical leaf curling symptoms. Seventeen plants in total were collected from both places, and stem scions from those plants were graft-inoculated to I. setosa, which developed symptoms of leaf curling, interveinal chlorosis, and stunting. Total nucleic acid was obtained from infected sweet potato and I. setosa plants using cetyltrimethylammoniumbromide (CTAB) extraction, and primers PW285-3 (5'-CGT CGT TAG CAG TCT GCA GGC CTC CTC TAG-3') and PW285-4 (5' -AAC TGT AAA TAC GGA ACT GCA GTT CGA ATT-3') for Sweet potato leaf curl virus (SPLCV), developed and provided by R. Valverde and C. Clark of Louisiana State University (2), were used to amplify SPLCV by polymerase chain reaction (PCR). Expected DNA fragments of ca. 900 bp (in all samples) and 2.4 kp (in some samples), characteristic of the subgenomic and genomic DNAs of SPLCV respectively, were obtained from symptomatic but not from symptomless (uninfected) plants. This 2.4-kb fragment was amplified in relatively small amounts compared to the 900-bp fragment. Presence of SPLCV was also confirmed by nucleic acid spot hybridization using a full-length clone of SPLCV-US. Fourteen of 17 plants infected with SPLCV were also infected with Sweet potato chlorotic stunt virus (determined by nitrocellulose membrane enzyme-linked immunosorbent assay serological test), which is also transmitted by whiteflies. These viruses now seem to be common in farmers' fields in San Ramón and Cañete. To our knowledge, this is the first report of SPLCV in Peru.

SWEETPOTATO LEAF CURL VIRUS AND RELATED GEMINIVIRUSES IN SWEETPOTATO

Sweetpotato leaf curl diseases have been reported in Taiwan, Japan, and the United States. The causal agent is the whitefly transmitted geminivirus, Sweetpotato leaf curl virus (SPLCV). Viral DNA can be detected in plant samples using polymerase chain reaction (PCR) with SPLCV-specific primers. Of 152 samples of sweetpotato and other Ipomoea species collected from various locations in the USA, only 14 were infected with SPLCV. The virus also was detected in total DNA extracted from I. setosa grafted with sweetpotato genotypes from Brazil, China, Mexico, Puerto Rico, and Taiwan. Selected PCR-amplified viral DNA fragments were cloned and sequenced. Based on the partial AC1 ORF sequences, the phylogenetic relationships among SPLCV-like isolates was determined. The results indicated that SPLCV-like isolates clustered into three groups, and all of them might have evolved from the same common ancestor possibly from the Old World. This study suggests that there might be several other geminiviruses of sweet potato yet to be described.

Geminate Particle Morphology of Sweet Potato Leaf Curl Virus in Partially Purified Preparation and Its Serological Relationship to Two Begomoviruses by Western Blotting

Sweet potato leaf curl virus (SPLCV) is a possible member of the genus Begomovirus; however, the presence of typical geminate particles in sap has not been confirmed. We attempted to observe SPLCV virions by partially purifying the virus using an enzyme-assisted procedure. The observed virions in the partially purified preparations were typical geminate particles with a size of ca. 18×30nm. This virus preparation was subjected to western blot analysis using antisera against Bean golden mosaic virus (BGMV) and Mungbean yellow mosaic virus (MYMV). SPLCV reacted with both antisera. Specific bands appeared to be slightly larger than the 30-kDa marker protein and were considered to be SPLCV coat protein. This western blot analysis revealed for the first time a serelogical relationship between SPLCV and the two well-characterized begomoviruses.

Detection of a Geminivirus Infecting Sweet Potato in the United States

In 1994, a sweet potato sample showing leaf curl symptoms was collected from the field in Louisiana. When graft-inoculated, Ipomoea nil cv. Scarlett O'Hara reacted with severe leaf distortion and chlorosis symptoms. I. aquatica reacted with a bright yellow mottle. The virus isolated was designated the United States isolate of sweet potato leaf curl virus (SPLCV-US). It was transmitted to I. nil by the sweet potato whitefly, Bemisia tabaci biotype B. DNA probes prepared with component A of pepper Huasteco geminivirus, with an isolate of bean golden mosaic geminivirus from Guatemala, with an isolate of tomato mottle geminivirus from Florida, and with an isolate of tomato yellow leaf curl geminivirus from the Dominican Republic (TYLCV-DR) hybridized with a 2.6-kb DNA band present in DNA extracts from plants infected with SPLCV-US. Probes prepared with the B component of these geminiviruses did not hybridize with these DNA extracts. We were unable to amplify SPLCV-US DNA products by polymerase chain reaction (PCR) in quantities that could be visualized by ethidium bromide staining. However, Southern blots from amplifications with primers AV494/AC1048 revealed PCR products of approximately 600 bp and 550 bp when hybridized with the TYLCV-DR probe. These results were consistently obtained from infected I. cordatotriloba and less consistently from I. aquatica or I. setosa. Fibrillar inclusions were occasionally seen, and granular aggregates of viruslike particles were observed in the nucleus of infected I. cordatotriloba. These results suggest that the virus isolated from sweet potato with leaf curl symptoms belongs to the geminivirus group.

Ipomoea crinkle leaf curl caused by a whitefly‐transmitted gemini‐like virus

SummaryA whitefly‐transmitted infectious agent, associated with geminate particles, induced distinct symptoms on several Ipomoea species, but not on I. batatas cv. Georgia Jet. The virus was transmitted by Bemisia argentifolii in a persistent manner and by grafting, but not mechanically. No transmission to species outside Ipomoea was obtained. Extracts from infected Ipomoea plants hybridised with a bean yellow mosaic virus riboprobe and a tomato yellow leaf curl virus riboprobe, although not so strongly as hybridisation of these riboprobes with extracts from plants infected with the homologous viruses. Based on host range, we consider this virus to be distinct from sweet potato leaf curl virus reported from the Far East, and propose it be named “Ipomoea crinkle leaf curl virus” (ICLCV).