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Differential response of hosta cultivars to infection by hosta virus X potexvirus - A basis for practical disease management
Abstract
Hosta virus X potexvirus is the most commonly occurring virus of hostas (Hosta spp.) in the USA, and can produce very damaging symptoms in some hosta cultivars. Fifty-seven hosta cultivars were evaluated for response to natural or experimental infection by HVX, and fell into three distinct categories. Susceptible cultivars developed pronounced symptoms, frequently resulting in complete leaf desiccation. Tolerant cultivars became infected but developed no visual symptoms. Immune cultivars were not infected by HVX. Management of HVX infection in hostas can be achieved by elimination of HVX-infected susceptible cultivars, ELISA indexing of tolerant cultivars, and using planting distances that minimize the possibility of me chanical spread of HVX between tolerant and susceptible cultivars.
... Sinds Hosta Virus X (HVX) in 1996 voor het eerst beschreven werd (Currier and Lockhart, 1996), is het in relatief korte tijd een bedreiging gaan vormen voor de Hosta-teelt. Al in 2000 toonde B. Lockhart aan dat minimaal 2/3 van het door hem geteste sortiment gevoelig bleek te zijn voor het virus (Lockhart, 2002). Sinds voorjaar 2004 komen er vanuit de VS signalen dat Hosta's besmet zijn met HVX, en de druk vanuit de VS (Amerikaanse PD) om gezond plantmateriaal te leveren, is steeds groter geworden. ...
... In nature, the virus has been isolated only from hostas, where the transmission occurs through seed, mechanical contact or vegetative propagation [6]. Symptoms of HVX infection in hostas varies and includes mosaic, necrosis and leaf deformation as well as reduction in plant growth [16,21]. ...
Triple gene block 1 (TGB1) and coat protein (CP) sequences of 30 hosta virus X (HVX) isolates from Tennessee (TN), USA, were determined and compared with available sequences in GenBank. The CPs of all known HVX isolates, including those from TN, shared 98.3-100% and 98.2-100% nucleotide and amino acid sequence identity, respectively, whereas TGB1 shared 97.4-100% nucleotide and 97-100% amino acid sequence identity. TGB1 of TN isolates were all longer by one codon from that of a Korean isolate, which is the only sequence publicly available. Phylogenetic analysis of nucleotide and amino acid sequences of TGB1 and CP of all known HVX isolates, separately or combined, revealed a close relationship, suggesting that all of them are derived from a common ancestor. Phylogenetic analysis with the type member of each genus of the family Flexiviridae confirmed that HVX is a member of a distinct species of the genus Potexvirus.
The one-step real-time turbidity loop-mediated isothermal amplification assay (RealAmp) was developed to detect Hosta virus X (HVX), the most devastating threat to hosta industry. The reaction was performed in a single tube at 63°C for 15 min, and real-time turbidimetry was used to monitor the amplification results. Specificity and sensitivity analyses demonstrated that this RealAmp method was sensitive as real-time TaqMan RT-PCR and about 100-fold higher than conventional RT-PCR with no cross-reaction with other viral pathogens. Field samples detection showed that HVX could be identified effectively with this method. Overall, this RealAmp assay for HVX detection was simple, specific, sensitive, convenient and time-saving and could assist in the quarantine measures for prevention and control of the disease caused by HVX.
Hosta virus X (HVX) is the most damaging virus of hosta (Hosta spp.). By taking advantage of the conserved coat protein (CP) sequences of characterised isolates of HVX, a reliable and sensitive diagnostic assay, based on RT-PCR, was developed. The conserved, single Hind II recognition site within the CP sequences was also exploited for restriction fragment length polymorphism (RFLP)-based verification of the amplicons.The reliability of the assay was demonstrated by successful amplification of 30 HVX isolates from 20 cultivars of hosta.The effectiveness of the assay was demonstrated by detecting several distinct isolates of HVX in a mechanically-inoculated hosta cultivar containing a low virus titre. The assay was capable of detecting HVX in composite samples consisting of a single HVX-infected leaf disc, approx. 1 cm in diameter, combined with up to 200 virus-free leaf discs of similar size, which demonstrated its potential for large-scale screening. The sensitivity of the assay was not affected by genetic variation in the hosta cultivars or in the virus isolates.We conclude that RT-PCR/RFLP is reliable, sensitive, and efficient for large-scale screening of hosta for HVX infection.
A virus (isolate 10306) was isolated from bait plants (Nicotiana sp.) grown in a soil sample collected from an old orchard in the eastern part of Norway. Preliminary results from electron microscopy identified isolate 10306 as a putative member of the genus Potexvirus based on particle morphology. Molecular and biological methods were further used to determine the coat protein (CP) sequence and the host range of isolate 10306, respectively. Potexvirus-specific degenerate primers were designed and used to amplify a ~300 nucleotide fragment belonging to the RNA-dependent RNApolymerase region of the viral genome by reverse-transcription PCR (RT-PCR). Based on the results from the sequence analysis, new specific primers were designed to amplify a fragment encompassing the CP gene. Furthermore, isolate 10306 was mechanically inoculated to different test plants and found to systemically infect eight plant species belonging to five families. CP sequence comparisons, at amino acid and nucleotide level, as well as phylogenetic analysis identified isolate 10306 as Tulip virus X (TVX). However, results from the host range studies differed from the ones previously published for this virus, suggesting that isolate 10306 could be considered a different strain of TVX. Moreover this is the first report of TVX in Norway.
A potexvirus was isolated from diseased hosta (Host a longipes) plants causing mosaic, mottle interveinal chlorosis symptoms between secondary veins, and leaf desiccation, identified as Hosta virus X (HYX-Kr) based on its biological, serological and molecular properties in this study. Infection rate of HVX in cultivated hostas was 48.4%, 21 out of 43 collected samples contained HVX. The virus was detected from seeds, and sprouts and seedlings. HVX was ascertained seed transmission of the virus from infected parent plant to progeny ones for breeding program of hosta plants. HVX was seed-transmitted on Hosta 'Blue Cadet'. Over 7.5% of seeds from HVX-infected hosta were HVX-contaminated surveyed in this study. The CP gene of HVX-U was amplified by RT-PCR and its nucleotide sequence was determined. The CPs of HVX-Kr and HVX-U had 100% and 98.9% identical amino acids and nucleotides, respectively. Variability of HVX was confirmed by sequences of CP gene of individual isolates from different hostas. Total nucleic acids extracted from leaf of virus-infected Hostas were used for detection of HVX by RT-PCR using the HVX-specific primers (HV UP:5722-5742 bp region of HVX-Kr strain /HV DN: 6428-6448 bp region of HVX-Kr strain). Overall similarities for the coat proteins are from 98.3% to 99.7% and from 98.2% to 100.0% identity with those of other HVX isolates at nucleotide and amino acid levels, respectively. This is the first report of molecular evidence supporting HVX as a distinct species of the genus Potexvirus and seed transmission of HVX.
The purpose of the study was to evidence occurrence of Canna yellow mottle virus (CaYMV) and Canna yellow streak virus (CaYSV) in Canna spp. and Hosta virus X in Hosta spp. in the Czech Republic. Canna plants showing symptoms such as mottling and veinal streaking and Hosta plants showing symptoms such as mosaic, mottling and chlorosis were analyzed by PCR in the year 2010.
The complete genome of Hosta Virus X (HVX), which is thought to be a distinct species of Potexvirus, was sequenced. Nucleotide sequences of HVX were compared with those of other members of the genus Potexvirus and phylogenetic tree was constructed. The range of identities of viral replicase open reading frame 1 (ORF1) between HVX and other potexviruses were 43.1%-55.1% and 35.9%-46.6% at the nucleotide and amino acid levels, respectively. Phylogenetic analysis was performed according to the amino acid sequence of the replicase to determine the position of HVX in the genus Potexvirus. Results from the phylogenetic analysis demonstrated that HVX was in the same group as Cassava common mosaic virus (CsCMV), Plantago asiatica mosaic virus (PlAMV), Tulip virus X (TVX), and Hydrangea ring spot virus (HdRSV). In particular, coat protein (CP) sequences among viruses from different Hosta cultivars were revealed to be less variable than those from different isolates of Potato virus X (PVX), a Potexvirus type species. In the present study, HVX was transmissible by seeds of the Hosta "Blue Cadet" cultivar. Moreover, HVX was detected in the embryo but not in the seed coat or endosperm of the seed.
Four viruses, hosta virus X potexvirus, tomato ringspot nepovirus, impatiens necrotic spot tospovirus and a tobravirus were identified in hostas (Hosta spp.) in the USA. Three unidentified isometric viruses were also found in hostas. Hosta virus X, a previously undescribed potexvirus, was the most frequently occurring virus in hostas, whose response to infection by this virus varied from immunity to severe mosaic and leaf desiccation. Tomato ringspot virus infection in hostas was associated with leaf mottling and chlorosis. Impatiens necrotic spot virus caused primary foliar lesions followed by latent infection. The tobravirus occurring in hosta was related serologically to both pea early-browning and tobacco rattle viruses, but was unusual in not being transmitted by mechanical inoculation to Nicotiana benthamiana or to N. clevelandii. Three unidentified isometric viruses, detected by electron microscopy and ds RNA analysis, were found in hostas with chlorotic ringspots, veinal necrosis and interveinal chlorosis. This is the first report identifying viruses in hostas in the USA.
A previously undescribed potexvirus, named Hosta virus X (HVX), was found in 17 naturally infected hosta (Hosta spp.) cultivars from Minnesota, Indiana, Illinois, Iowa, and Michigan. HVX was readily transmitted mechanically but infected only Nicotiana benthamiana and Hosta spp., in which symptoms ranged from severe mosaic and leaf necrosis to latency. Particles of HVX averaged 530 nm in length, had a buoyant density in cesium chloride of 1.28 gm/cm3, and contained a single genomic species of ssRNA approximately 3 kb in size. The capsid protein of HVX had a molecular mass of approximately 27 kDa. In indirect enzyme immunoassays, HVX reacted with an antiserum to clover yellow mosaic virus (ClYMV), and less strongly with antiserum to hydrangea ringspot virus (HRSV), but not with antisera to any of 14 other potexviruses tested. However, in reciprocal tests, ClYMV reacted only very weakly with HVX antiserum. HVX did not infect any of three cultivars of pea that were susceptible to infection by ClYMV, and ClYMV did not infect any of three hosta cultivars susceptible to infection by HVX. Spread of HVX infection in hosta appears to occur by vegetative propagation and accidental mechanical transmission, and management of the disease can be achieved by virus indexing and cultural practices that minimize the risk of virus spread to susceptible cultivars.