Evidence for Lettuce big‐vein associated virus as the causal agent of a syndrome of necrotic rings and spots in lettuce

Lettuce big‐vein associated virus (LBVaV, genus Varicosavirus) was shown to be responsible for characteristic necrotic symptoms observed in combination with big‐vein symptoms in lettuce breeding lines when tested for their susceptibility to lettuce big‐vein disease (BVD) using viruliferous Olpidium virulentus spores in a nutrient film technique (NFT) system. Lettuce plants showing BVD are generally infected by two viruses: Mirafiori lettuce big‐vein virus (MiLBVV, genus Ophiovirus) and LBVaV. New mechanical inoculation methods were developed to separate the two viruses from each other and to transfer both viruses to indicator plants and lettuce. After mechanical inoculation onto lettuce plants MiLBVV induced vein‐band chlorosis, which is the characteristic symptom of BVD. LBVaV caused a syndrome of necrotic spots and rings which was also observed earlier in lettuce plants inoculated in the NFT system, resembling symptoms described for lettuce ring necrosis disease (RND). This observation is in contrast with the idea that LBVaV only causes latent infections in lettuce. De novo next‐generation sequencing demonstrated that LBVaV was the only pathogen present in a mechanically inoculated lettuce plant with symptoms, providing evidence that LBVaV was the causal agent of the observed necrotic syndrome and thus fulfilling Koch’s postulates for this virus. The necrotic syndrome caused by LBVaV in lettuce is referred to as LBVaV‐associated necrosis (LAN).     

The Natural Occurrence of Two Distinct Begomoviruses Associated with DNAbeta and a Recombinant DNA in a Tomato Plant from Indonesia

ABSTRACT Two begomoviruses (Java virus-1 and Java virus-2), two satellite DNAs (DNAbeta01 and DNAbeta02), and a recombinant DNA (recDNA) were cloned from a single tomato plant from Indonesia with leaf curl symptoms, and the role of these satellite DNAs in the etiology of begomovirus disease was investigated. The genome organizations of the two viruses were similar to those of other Old World monopartite begomoviruses. Comparison of the sequences with other begomoviruses revealed that Java virus-1 was a newly described virus for which the name Tomato leaf curl Java virus (ToLCJAV) is proposed. Java virus-2 was a strain of Ageratum yellow vein virus (AYVV) (AYVV-[Java]). ToLCJAV or AYVV-[Java] alone did not induce leaf curl symptoms in tomato plants. However, in the presence of DNAbeta02, both ToLCJAV and AYVV-[Java] induced leaf curl symptoms in tomato plants. In the presence of DNAbeta01, these viruses induced mild leaf curl symptoms in tomato plants. The recDNA had a chimeric sequence, which arose from recombination among ToLCJAV, AYVV-[Java], DNAbeta01, and DNAbeta02; it was replicated only in the presence of AYVV-[Java] in tomato plants.     

在中国广东侵染胜红蓟的中国胜红蓟黄脉病毒的鉴定和全基因组分析

2022年9月在广东省罗定市发现了叶片表现为黄色网状症状的胜红蓟病株。为了明确胜红蓟叶片的黄脉症状是否由双生病毒感染引起, 本研究使用检测双生病毒的简并引物PA/PB进行PCR扩增, 获得约500 bp的片段。根据该序列设计特异性引物扩增并且克隆得到了病毒DNA-A的全基因组序列。通过BLAST比对发现, 获得的DNA-A与中国胜红蓟黄脉病毒(ageratum yellow vein China virus, AYVCNV)海南分离物(OQ421190)的DNA-A的相似性最高, 相似度为98.11%。系统进化树分析显示, 获得的病毒DNA-A与海南分离物(OQ421190)在同一分支, 说明具有较近的亲缘关系。以上研究结果表明侵染胜红蓟的病毒是AYVCNV的分离物。这是关于AYVCNV在广东地区侵染胜红蓟的首次报道, 可为当地病毒病的防控提供参考。     

Identification and characterization of a novel whitefly-transmitted member of the family potyviridae isolated from cucurbits in Florida

ABSTRACT A novel whitefly-transmitted member of the family Potyviridae was isolated from a squash plant (Cucurbita pepo) with vein yellowing symptoms in Florida. The virus, for which the name Squash vein yellowing virus (SqVYV) is proposed, has flexuous rod-shaped particles of approximately 840 nm in length. The experimental host range was limited to species in the family Cucurbitaceae, with the most dramatic symptoms observed in squash and watermelon, but excluded all tested species in the families Amaranthaceae, Apocynaceae, Asteraceae, Chenopodiaceae, Fabaceae, Malvaceae, and Solanaceae. The virus was transmitted by whiteflies (Bemisia tabaci) but was not transmitted by aphids (Myzus persicae). Infection by SqVYV induced inclusion bodies visible by electron and light microscopy that were characteristic of members of the family Potyviridae. Comparison of the SqVYV coat protein gene and protein sequences with those of recognized members of the family Potyviridae indicate that it is a novel member of the genus Ipomovirus. A limited survey revealed that SqVYV also was present in watermelon plants suffering from a vine decline and fruit rot recently observed in Florida and was sufficient to induce these symptoms in greenhouse-grown watermelon, suggesting that SqVYV is the likely cause of this disease.     

Ageratum yellow vein China virus Is a Distinct Begomovirus Species Associated with a DNAbeta Molecule

ABSTRACT Ageratum conyzoides plants exhibiting yellow vein symptoms, collected near Haikou, Hainan Province, China, contained begomoviral DNA-A-like molecules. The complete sequences of the molecules from two samples, Hn2 and Hn2-19, were shown to consist of 2,768 and 2,748 nucelotides (nt), respectively. These sequences have more than 97% nucleotide sequence identity, but less than 86% identity with other reported begomovirus sequences. In line with the taxonomic convention for begomoviruses, Hn2 and Hn2-19 are therefore considered to represent isolates of a distinct begomovirus species, for which the name Ageratum yellow vein China virus (AYVCNV) is proposed. Sequence alignment shows AYVCNV has arisen by recombination among viruses related to Ageratum yellow vein virus, Papaya leaf curl China virus, and an unidentified begomovirus. Southern blot analyses revealed that all plants sampled contained molecules resembling DNAbeta. DNAbeta molecules from three samples were 1,323 or 1,324 nt long and had >98% sequence identity but <81% identity with previously reported DNAbeta sequences. Infectious clones of Hn2 and its associated DNAbeta were constructed and agroinoculated to plants. Hn2 alone caused sporadic asymptomatic systemic infection of Nicotiana benthamiana, N. glutinosa, Lycopersicon esculentum, Petunia hybrida, and A. conyzoides but its accumulation was much enhanced in plants co-inoculated with DNAbeta. The co-inoculated N. benthamiana, N. glutinosa, P. hybrida, and L. esculentum plants developed leaf curling or leaf crinkling symptom; those in A. conyzoides were typical of ageratum yellow vein disease. When the DNAbeta molecules associated with four other Chinese begomoviruses were coinoculated with Hn2 to N. benthamiana and N. glutinosa, the DNAbeta molecules were replicated, and the plants developed systemic symptoms of types that were specific for each DNAbeta. This illustrates that there is less specific interaction between monopartite begomovirus and DNAbeta than between the DNA-A and DNA-B of begomoviruses with bipartite genomes.     

Description of symptoms and assessment of loss caused by some viruses in the carnation cultivar ‘william sim’

A study was made of the influence of carnation mottle, ring spot and vein mottle viruses on carnations of the ‘William Sim’ variety by artificial infection of virus-free plants of one single clone. No clear leaf symptoms were obtained by artificial infection with the mottle virus, but leaf symptoms appeared on plants infected with the ring spot virus and the growth of these plants was markedly reduced. The carnation vein mottle virus caused a definite leaf flecking. A depressing effect on yield was demonstrated with all three viruses. Vein mottle was serious, particularly because it caused flower colour breaking. The ring spot virus, also, had a depressing effect on the quality of the flowers, causing a high percentage of split calices. The carnation mottle virus also caused a reduction in the quality of the produce, though not so intense as that caused by the ring spot virus. A combination of the two last-mentioned viruses proved slightly more serious than the ring spot virus alone.     

Population structure,evolution and detection of blackberry leaf mottle-associated virus,an emerging emaravirus

Blackberry leaf mottle-associated virus (BLMaV) is a recently described emaravirus associated with yellow vein disease, the main constraint of blackberry production in the southern USA. The population structure and genetic variation of BLMaV, based on the nucleocapsid and movement protein genes was resolved. BLMaV diversity is low when compared to other emaraviruses, with the genes studied being under strong negative selection. Phylogenetic analyses suggest long distance migration of the virus whereas incongruent phylogenetic relatedness and predicted reassortment events suggest that genetic exchange could play an important role in BLMaV evolution. A quantitative PCR (qPCR) protocol was developed based on the knowledge obtained through the population structure of the virus; this is a sensitive test able to detect all the isolates studied. The assay was optimized and applied successfully on multiple samples collected from several regions in the United States. Comparison between a previously developed test and the new protocol illustrated that the latter is at least 1000 times more sensitive.     

Successful Back-inoculation Confirms the Role of Black Currant Reversion Associated Virus as the Causal Agent of Reversion Disease

Reversion is the most wide-spread and serious virus-like disease infecting black currant but the causal agent of the disease has not been described. Recently, we have isolated a new nepovirus from reversion-infected black currant and by using immunocapture-RT-PCR detection, we have shown that the virus is consistently associated with reversion disease (Lemmetty et al., Phytopathology 87: 404–413, 1997). These data suggested that the virus, tentatively called black currant reversion associated virus (BRAV), could be the causal agent of reversion disease. Here we report that the isolated virus was successfully inoculated back to healthy black currant plants by slash inoculation of in vitro propagated young recipient plants. Vein pattern symptoms identical or very similar to the reported early symptoms of reversion disease were produced in the virus-infected plants. Using immunocapture-RT-PCR, the virus was again detected from symptomatic but not from inoculated symptomless plants or from the mock-inoculated or uninoculated controls. Production of the acute reversion symptoms demonstrates that BRAV is the causal agent of reversion disease, and we therefore propose that the virus be named black currant reversion virus, abbreviated BRV.     

Downy mildew of boysenberry and tummelberry in the UK

Peronospora rubi was observed in the UK on boysenberry, a blackberry x red raspberry hybrid, and on tummelberry, a cross between tayberry (blackberry cv. Aurora x tetraploid red raspberry) and another tayberry seedling from the same cross. These findings were new UK and world records respectively. The principal disease symptoms were leaf spots and blotches. The source of infection could not be identified.     

Tomato leaf curl Guangxi virus is a distinct monopartite begomovirus species

Three begomovirus isolates were obtained from tomato plants showing leaf curl symptoms in Guangxi province of China. Typical begomovirus DNA components representing the three isolates (GX-1, GX-2 and GX-3) were cloned and their full-length sequences were determined to be 2752 nucleotides. Nucleotide identities among the three viral sequences were 98.9–99.7%, but all shared <86.7% nucleotide sequence identity with other reported begomoviruses. The sequence data indicated that GX-1, GX-2 and GX-3 are isolates of a distinct begomovirus species for which the name Tomato leaf curl Guangxi virus (ToLCGXV) is proposed. Further analysis indicated that ToLCGXV probably originated through recombination among viruses related to Ageratum yellow vein virus, Tomato leaf curl China virus and Euphorbia leaf curl virus. PCR and Southern blot analyses demonstrated that isolates GX-1 and GX-2 were associated with DNAβ components, but not isolate GX-3. Sequence comparisons revealed that GX-1 and GX-2 DNAβ components shared the highest sequence identity (86.2%) with that of Tomato yellow leaf curl China virus (TYLCCNV). An infectious construct of ToLCGXV isolate GX-1 (ToLCGXV-GX) was produced and determined to be highly infectious in Nicotiana benthamiana, N. glutinosa, tobacco cvs. Samsun and Xanthi, tomato and Petunia hybrida plants inducing leaf curl and stunting symptoms. Co-inoculation of tomato plants with ToLCGXV-GX and TYLCCNV DNAβ resulted in disease symptoms similar to that caused by ToLCGXV-GX alone or that observed in infected field tomato plants.     

Tospoviruses infecting vegetable crops in Israel

Symptoms of vein clearing, stem necrosis, curling, necrotic spots and rings on the leaves associated with infection by tomato spotted wilt tospovirus (TSWV) were documented among vegetable crops growing in commercial glasshouses and open fields in Israel. Plants exhibiting symptoms were collected, from 1994-01 to 1998-12. Among cultivated vegetable crops analysed for TSWV by ELISA, the following plants were found to be infected: tomato, capsicum, aubergine, lettuce, cabbage and cucumber. These incidences of the virus were all correlated with the occurrence in high population of Frankliniella occidentalis. Transmission of the virus from infected Datura stramonium to Petunia leaf discs, by F. occidentalis , was up to 26%. TSWV antigens were readily detected by ELISA in seeds harvested from naturally infected vegetable crops. However, we failed to show virus transmission to the progeny plants. Iris yellow spot tospovirus (IYSV) was detected in onion. High incidence of the disease was associated with large populations of Thrips tabaci.     

海南红麻曲叶病的病原检测与鉴定

 红麻曲叶病是2012年在海南省海口市发现的一种新病害,病株表现为叶片向上卷曲、叶脉肿大、叶脉变深绿色等症状。PCR检测结果显示,该病样中均存在菜豆金色花叶病毒属病毒。基因克隆及序列分析结果表明,该病毒分离物(HN08)基因组仅含A组分(DNA-A),其全长为2 738 nt,与木尔坦棉花曲叶病毒(CLCuMuV)各分离物的相似性均大于89.0 %,其中与中国各分离物的相似性均大于99.0 %。该病毒分离物也伴随有β卫星分子,其全长为1 346 nt,与CLCuMuV各分离物伴随的β卫星分子(CLCuMuB)序列相似性大于83.0 %,其中与分离物Fz1的序列相似性最高,为99.7 %。构建了HN08 DNA-A及其β卫星分子侵染性克隆,通过农杆菌注射接种红麻,接种后30 d,HN08 DNA-A及其β卫星分子混合接种的红麻植株新出叶片开始产生曲叶症状;接种后60 d,二者混合接种的植株大部分叶片表现为严重的曲叶症状,且与田间自然病株症状相同,而二者各自单独接种的红麻植株没有产生明显的症状。PCR及Southern blot检测进一步证实这些症状是由HN08 DNA-A及其β卫星分子的共同侵染引起的。因此,海南红麻曲叶病是由CLCuMuV及其伴随的β卫星分子(CLCuMuB)共同侵染引起的。本文首次报道了红麻是CLCuMuV自然新寄主。     

Drought as a modulator of plant–virus–vector interactions: Effects on symptom expression,plant immunity and vector behaviour

Plant–virus interactions are affected by environmental conditions that determine plant vulnerability to pathogens and the population dynamics of insect vectors. We hypothesize that drought enhances horizontal transmission by dampening the basal immunity of plants, which triggers symptom expression and vector manipulation. The potato yellow vein virus (PYVV) causes potato yellow vein disease (PYVD), a re-emerging epidemic of potato crops in South America, and is transmitted horizontally by the greenhouse whitefly (GWF), Trialeurodes vaporariorum (Hemiptera: Aleyrodidae), or vertically through infected seed tubers. We investigated the role of drought and temperature as modulators of PYVD symptom expression, plant immune response, and vector survival, development and host preference. We found that drought induced symptom expression, suppressed the salicylic acid pathway and increased PYVV replication. GWF survival was reduced on PYVV-infected hosts and development was slowest when they fed on plants with PYVD symptoms, which also triggered adults’ attraction to PYVV-infected plants. However, adults previously fed on infected plants showed the opposite effect, being more attracted to PYVV-free plants. We propose a theoretical model that explains the role of drought in modulating potato–PYVV–GWF interactions and provides new insights into plant–virus–vector coevolution.     

Characterization of a Novel Member of the Family Closteroviridae from Mentha spp

ABSTRACT While characterizing the agents involved in symptomatology of a variegated mint, Mentha x gracilis 'Variegata', a nursery plant with atypical symptoms was examined. This plant, unlike 'Variegata', did not exhibit yellow vein banding symptoms but instead had distorted and crinkled leaves. Molecular tests for the three viruses found in 'Variegata' clones failed to detect any of these viruses in the plant. Double-stranded RNA was extracted and cloned, disclosing the presence of two unknown viruses. One of the viruses was a novel member of the family Closteroviridae. The complete nucleotide sequence of the virus, designated as Mint virus 1, has been obtained. A detection test was developed, and revealed the presence of the virus in several other mint clones and species. Genomic regions from three additional isolates were examined to investigate the genetic diversity of the virus. Genome and phylogenetic analysis placed Mint virus 1 in the genus Closterovirus and transmission studies have identified the mint aphid, Ovatus crataegarius, as a vector for this new member of the genus Closterovirus.     

Identities and pathogenicities of phytophthora spp. causing root rot of red raspberry

Phytophthora syringae, P. drechsleri, P. cactarutn, P. cambiuora and P. megasperma were isolated from the roots of red raspberry plants affected by severe root and crown rot with associated cane death. Phytophthora megasperma occurred most frequently and consisted of two types of isolates which differed in colony morphology, growth rates, and oogonial, oospore, sporangial and zoospore size, and pathogenicity to a range of plants. One type with large oospores was typical of P. megasperma var. megasperma , and was non-pathogenic to red raspberries, while the other with smaller oospores and which grew more slowly in culture than the first, was highly pathogenic, producing symptoms similar to those observed in the field. Highly pathogenic isolates from Germany and the USA were of this type.
All red and black raspberry cultivars tested were susceptible to the pathogenic type, although North American cultivars were generally less affected than British ones. Inoculated plants had reduced shoot and root weights, stem lesions and wilted and yellowed leaves. The blackberry × raspberry hybrid Tayberry and its blackberry parent were immune.
Phytophthora drechsleri, P. cactorum and P. cambivora produced small to moderate amounts of root rot on red raspberry, and P. cambivora also caused slight symptoms on shoots.     

引起哈密瓜坏死的两种病毒的分离及鉴定

 从哈密瓜上分离到两种引起坏死症状的病毒,称为哈密瓜坏死病毒(HmNV)和哈密瓜叶脉坏死病毒(H-mVNV).两者都能系统感染哈密瓜,响影植株滞长.     

Further evidence of Mirafiori lettuce big-vein virus but not of Lettuce big-vein associated virus with big-vein disease in lettuce

Mirafiori lettuce big-vein virus (MLBVV) and Lettuce big-vein associated virus (LBVaV) are found in association with big-vein disease of lettuce. Discrimination between the two viruses is critical for elucidating the etiology of big-vein disease. Using specific antibodies to MLBVV and LBVaV for western blotting and exploiting differences between MLBVV and LBVaV in host reaction of cucumber and temperature dependence in lettuce, we separated the two viruses by transfering each virus from doubly infected lettuce plants to cucumber or lettuce plants. A virus-free fungal isolate was allowed to acquire the two viruses individually or together. To confirm the separation, zoospores from MLBVV-, LBVaV-, and dually infected lettuce plants were used for serial inoculations of lettuce seedlings 12 successive times. Lettuce seedlings were infected at each transfer either with MLBVV alone, LBVaV alone, or both viruses together, depending on the virus carried by the vector. Lettuce seedlings infected with MLBVV alone developed the big-vein symptoms, while those infected with LBVaV alone developed no symptoms. In field surveys, MLBVV was consistently detected in lettuce plants from big-vein-affected fields, whereas LBVaV was detected in lettuce plants not only from big-vein-affected fields but also from big-vein-free fields. LBVaV occurred widely at high rates in winter-spring lettuce-growing regions irrespective of the presence of MLBVV and, hence, of the presence of the big-vein disease.     

Yellowing disease in zucchini squash produced by mixed infections of Cucurbit yellow stunting disorder virus and Cucumber vein yellowing virus

Zucchini squash is host to Cucurbit yellow stunting disorder virus (CYSDV), a member of the genus Crinivirus, and Cucumber vein yellowing virus (CVYV), a member of the genus Ipomovirus, both transmitted by the whitefly Bemisia tabaci. Field observations suggest the appearance of new symptoms observed on leaves of zucchini squash crops when both viruses were present. When infected during controlled experiments with CYSDV only, zucchini plants showed no obvious symptoms and the virus titer decreased between 15 and 45 days postinoculation (dpi), after which it was no longer detected. CVYV caused inconspicuous symptoms restricted to vein clearing on some of the apical leaves and the virus accumulated progressively between 15 and 60 dpi. Similar accumulations of virus followed single inoculations with the potyvirus Zucchini yellow mosaic virus (ZYMV) and plants showed severe stunting, leaf deformation, and mosaic yellowing. However, in mixed infections with CYSDV and CVYV, intermediate leaves showed chlorotic mottling which evolved later to rolling, brittleness, and complete yellowing of the leaf lamina, with exception of the veins. No consistent alteration of CVYV accumulation was detected but the amounts of CYSDV increased ≈100-fold and remained detectable at 60 dpi. Such synergistic effects on the titer of the crinivirus and symptom expression were not observed when co-infected with ZYMV.     

RNA 3 deletion mutants of beet necrotic yellow vein virus do not cause rhizomania disease in sugar beets

ABSTRACT Two mutant strains of beet necrotic yellow vein virus (BNYVV) containing deletions in RNA 3 were obtained by single lesion transfers in Tetragonia expansa. The deleted regions encode either 94 or 121 amino acids toward the C-terminal part of the 25-kDa protein (P25). Wild-type and mutant virus strains were inoculated by Polymyxa betae to sugar beet seedlings of susceptible and partially resistant cultivars. No differences were found in virus content in rootlets between mutant and wild-type viruses or between susceptible and resistant cultivars after culture for 4 weeks in a growth cabinet. However, when virus-inoculated seedlings were grown in the field for 5 months, the wild-type virus caused typical rhizomania root symptoms (69 to 96% yield loss) in susceptible cultivars, but no symptoms (23% loss) developed in most plants of the resistant cultivar, and BNYVV concentrations in the roots were 10 to 20x lower in these plants than in susceptible plants. In contrast, the mutant strains caused no symptoms in susceptible or resistant cultivars, and the virus content of roots was much lower in both cultivars than in wild-type virus infections. Wild-type RNA 3 was not detectable in most of the taproots of a resistant cultivar without any symptoms, suggesting that replication of undeleted RNA 3 was inhibited. These results indicate that the P25 of BNYVV RNA 3 is essential for the development of rhizomania symptoms in susceptible cultivars and suggest that it may fail to facilitate virus translocation from rootlets to taproots in the partially resistant cultivar.     

Accumulation of short interfering RNAs characteristic of RNA silencing precedes recovery of tomato plants from severe symptoms of <Emphasis Type="Italic">Potato spindle tuber viroid</Emphasis> infection

Tomato plants infected with Potato spindle tuber viroid (PSTVd) had severe leaf curling and vein necrosis. The disease symptoms began to diminish during the late stages of infection, however, and almost healthy-looking leaves began to appear on the upper portion of the plants. PSTVd concentrations reached their highest levels in leaves with severe symptoms and decreased in upper leaves recovering from severe symptoms. PSTVd-specific short interfering RNAs (siRNAs), characteristic of RNA silencing, accumulated in all leaves in which PSTVd reached a detectable level, suggesting that recovery from severe disease was induced by RNA silencing via sequence-specific degradation of PSTVd.