Transmission attributes and resistance to rose rosette virus

Rosette caused by rose rosette virus (RRV) is a devastating disease of rose in the United States. The virus was discovered in 2011 and Koch's postulates completed in 2015. Because of these recent discoveries, assumptions about the disease including movement, transmission and resistance are based on visual observations of material that may or may not have been infected by the virus. This study addresses several aspects of virus and disease dynamics. Twenty rose genotypes were screened for mite and/or virus resistance. Phyllocoptes fructiphilus, the only known vector of RRV, was able to establish, lay eggs and develop nymphs and adults in all rose genotypes. Cultivar ‘Stormy Weather’ showed resistance to the virus as assessed in both mite and cleft‐grafting transmission experiments. Mites showed a long acquisition/latent period but a rapid inoculation time for RRV. Knowledge of resistance as well as transmission attributes will assist in better management of vector and disease. The identified resistant genotype would be used in areas with high disease pressure to minimize spread, for identification of the mechanisms behind resistance or as a breeding parent to incorporate virus resistance to new cultivars. The short inoculation access period suggests that chemical control for this vector may be challenging to undertake.     

Viruses transmitted by nematodes1

The transmission of plant viruses by nematodes is remarkable in involving only two distinct groups of viruses, nepo viruses and tobraviruses, and being limited to longidorid, Paratrichodorus and Trichodorus nematodes respectively. Tobraviruses and their associated vector nematodes are not discussed here. Only 11 of the 36 described nepoviruses are transmitted by nematodes, and 6 of these 11 viruses are present in Europe naturally associated with 8 virus-vector longidorids. Specific relationships exist between the serologically distinct viruses and their vector nematode species. Specificity is largely determined by the virus coat protein and by an inherited ability of the nematode to retain virus particles at specific sites within its oesophagus. This specific relationship can be quite subtle, extending to populations of vector nematodes and also to virus isolates which apparently are serologically indistinguishable. Several serological and/or symptomatological variants of nepoviruses may be present at a field site in association with one or more vector nematode species. The exposure of different crops and new cultivars to these virus and vector combinations will probably result in the occurrence of further nematode-transmitted virus diseases. New methods for suppressing damage to crops caused by these diseases are required including the likely use of transgenic resistant cultivars.     

The Use of Molecular Beacons Combined with NASBA for the Sensitive Detection of Sugarcane Yellow Leaf Virus

Sugarcane yellow leaf virus (ScYLV) is widely distributed in Brazil and other sugarcane producing countries causing significant yield losses. Due to the high incidence of the aphid vector, the virus is widespread in the field and in parental clones used in sugarcane breeding programmes. Aiming to present a sensitive and reliable detection of ScYLV, we have adapted an AmpliDet RNA system, compared it with the currently available detection methods and discussed its applicability for routine diagnosis. AmpliDet RNA consists of nucleic acid sequence-based amplification (NASBA) of the target RNA with specific primers and simultaneous real-time detection of the amplification products with molecular beacons. The results showed that the system produced a detection level of at least 100fg of purified virus. Virus was readily detected in plant tissues with low levels of infection (without the need of previous RNA extraction) and in the hemolymph of aphids. The method showed to be virus-specific, testing negative for other species of the Luteoviridae. In conclusion, the system has potential to become a diagnostic method for the detection of sugarcane viruses.     

Virus transmission by aphids in potato crops

This paper reviews the contribution of vector activity and plant age to virus spread in potato crops. Determining which aphid species are vectors is particularly important for timing haulm destruction to minimize tuber infection by potato virus Y (PVY). Alate aphids of more than 30 species transmit PVY, and aphids such asRhopalosiphum padi, that migrate in large numbers before flights of the more efficient vector,Myzus persicae, appear to be important vectors. Differences in methodology, aphid biotypes and virus strains prevent direct comparisons between estimates of vector efficiencies obtained for aphids in different countries in north western Europe. M. persicae is also the most efficient vector of potato leafroll virus (PLRV), but some clones ofMacrosiphum euphorbiae transmit PLRV efficiently toNicotiana clevelandii and potato test plants. The removal of infected plants early in the season prevents the spread of PLRV in cool regions with limited vector activity. The proportion of aphids acquiring PLRV from infected potato plants decreases with plant age, and healthy potato plants are more resistant to infection later in the season. Severe symptoms of secondary leafroll developed on progeny plants of cv. Maris Piper derived from mother plants inoculated with PLRV in June or July of the previous year. Progeny plants derived from mother plants inoculated in August showed only mild symptoms, but the concentration of PLRV in these plants was as high as that in the plants with severe symptoms.     

Seasonal dynamics and virus translocation of Grapevine leafroll‐associated virus 3 in grapevine cultivars

Grapevine leafroll‐associated virus 3 (GLRaV‐3) is associated with grapevine leafroll disease, one of the most economically important viral diseases of grapevines. This disease impacts on both vine health and grape quality; reduction in yield, brix and wine colour are among its detrimental effects. Many methods, including serological and molecular procedures, have been developed for the detection of GLRaV‐3; however, there is no PCR‐based assay available to quantify virus populations within plant tissues. A real‐time RT‐PCR assay with TaqMan probe was developed for specific and reliable quantitative detection of GLRaV‐3 in infected tissues. The designed primers and probes target the conserved sequence in the RNA‐dependent RNA polymerase (RdRp) domain of the viral genome to prevent amplification of most subgenomic and defective RNAs. This protocol was used to examine the seasonal dynamics and translocation of GLRaV‐3 in field‐grown grapevines. The results showed that the virus spread quickly from trunks to new growing shoots and leaves early in the growing season, and most samples still harboured detectable virus during late summer and autumn. The seasonal progress of one GLRaV‐3 isolate was compared in four grapevine cultivars (Chardonnay, Cabernet Sauvignon, Italia and Thompson Seedless). Within cultivars there was little variability in the distribution and translocation of GLRaV‐3, except for in Thompson Seedless. This quantitative detection assay will be a valuable tool for GLRaV‐3 diagnosis, disease monitoring and population ecology studies.     

A Cucumber mosaic virus isolated from Momordica charantia L.

Momordica charantia L. plants systemically infected with Cucumber mosaic virus (CMV) were found in Oita Prefecture. The virus isolated from the host plant was characterized by biological, serological, and molecular biological methods. The purified virus was used to mechanically inoculate the host and produced green mottle, green mosaic, and/or chlorotic spots in the noninoculated upper leaves of the host. The virus was identified as an isolate of CMV containing genomic RNA3 derived from subgroup IA by several lines of evidence based on electron microscopy, serological detection, host range, symptoms, and the entire nucleotide sequence of RNA3.     

New insights into virus yellows distribution in Europe and effects of beet yellows virus,beet mild yellowing virus,and beet chlorosis virus on sugar beet yield following field inoculation

Beet yellows virus (BYV), beet mild yellowing virus (BMYV), beet chlorosis virus (BChV), and beet mosaic virus (BtMV) cause virus yellows (VY) disease in sugar beet. The main virus vector is the aphid Myzus persicae. Due to efficient vector control by neonicotinoid seed treatment over the last decades, there is no current knowledge regarding virus species distribution. Therefore, Europe-wide virus monitoring was carried out from 2017 to 2019, where neonicotinoids were banned in 2019. The monitoring showed that closterovirus BYV is currently widely spread in northern Europe. The poleroviruses BMYV and BChV were most frequently detected in the northern and western regions. The potyvirus BtMV was only sporadically detected. To study virus infestation and influence on yield, viruses were transmitted to sugar beet plants using viruliferous M. persicae in quadruplicate field plots with 10% inoculation density simulating natural infection. A plant-to-plant virus spread was observed within 4 weeks. A nearly complete infection of all plants was observed in all treatments at harvest. In accordance with these findings, a significant yield reduction was caused by BMYV and BChV (−23% and −24%) and only a moderate reduction in yield was observed for BYV (−10%). This study showed that inoculation at low densities mimics natural infection, and quick spreading induced representative yield effects. Within the background of a post-neonicotinoid era, this provides the basis to screen sugar beet genotypes for the selection of virus tolerance/resistance and to test the effectiveness of insecticides for the control of M. persicae with a manageable workload.     

Diversity of European begomoviruses: identification of a new disease complex*

The diversity of whitefly‐transmitted begomoviruses in Europe is low, most being exotic, introduced species. The only agriculturally important viruses are two species causing tomato yellow leaf curl. These viruses are believed to have originated in the Middle East but have since spread right across the Mediterranean region. Two ornamentals (Abutilon and Lonicera japonica) were introduced into Europe from the New World and the Far East, respectively, for the striking symptoms induced by the viruses which infect them. The virus infecting honeysuckle (Honeysuckle yellow vein mosaic virus) has been shown to be part of newly identified cluster of begomoviruses which require an additional component, a satellite molecule termed DNA β, to induce symptoms in their host plants. A further begomovirus, Ipomoea yellow vein virus, which infects the weed Ipomoea indica, is present in the Mediterranean region. The precise origin and relationship of this virus to other begomoviruses is unclear.     

Serological differences between red currant spoon leaf virus,virus isolates from Eckelrade-diseased cherry trees and the Scottish raspberry ringspot virus

Antisera were made to red currant spoon leaf virus (SLV), an isolate of the Scottish raspberry ringspot virus (RRV), and two virus isolates from Eckelrade-diseased cherry trees (EV). Different virus isolates, including one from Belgium, were tested against these antisera. The results indicate that we are dealing with a group of virus isolates with different antigenic properties. SLV is very closely related to RRV, being undoubtedly a strain of this virus. Dutch EV isolates differ from SLV and RRV and from each other, the Belgian isolate being closely related to one of the Dutch EV isolates. The serological differences found do not correspond with the geographical distances between the localities where the viruses were collected.Samenvatting Antisera werden bereid tegen het lepelbladvirus van rode bes (SLV), een isolatie van het Schotse raspberry ringspot-virus (RRV) en twee virusisolaties uit kersebomen met Eckelraderziekte (EV). Met behulp van deze antisera werden verschillende virusisolaties getoetst, waaronder één uit België van kers met Eckelraderziekte. De resultaten zijn vermeld in de tabellen 1 en 2. Ze duiden erop, dat we te maken hebben met een groep van virusisolaties met verschillende antigene eigenschappen. SLV is zeer nauw verwant aan RRV en is ongetwijfeld een stam van dit virus. Nederlandse EV-isolaties verschillen zowel van SLV en RRV, als van elkaar. De Belgische isolatie is nauw verwant aan één van de Nederlandse EV-isolaties. De grootte van de gevonden verschillen correspondeert niet met de geografische afstand tussen de plaatsen waar de virusisolaties werden verzameld.     

葡萄A病毒外壳蛋白原核表达及抗血清制备

 葡萄A病毒（Grapevine virus A,GVA）为线性病毒科（Flexiviridae）葡萄病毒属（Vitivirus）的代表种,是葡萄皱木复合病（rugose wood complex disease）的重要病原之一,可引起葡萄嫁接成活率下降、春季萌芽延迟、生长减弱甚至衰退死亡等危害\[1,2\]。GVA为线状单链RNA病毒,基因组共编码5个开放阅读框（ORF1\|5）,其中ORF4 编码外壳蛋白（coat protein, CP）,是病毒粒子包裹和系统移动所必需的功能蛋白\[3,4\]。GVA自然寄主为葡萄,机械摩擦可侵染本氏烟等草本寄主\[2\],由于嫁接和无性繁殖材料调运等因素造成该病毒远距离传播,目前在世界多个国家和地区均有发生。     

Host‐range studies,genetic diversity and evolutionary relationships of ACLSV isolates from ornamental,wild and cultivated Rosaceous species

A large‐scale survey was carried out to study the host range and genetic diversity of Apple chlorotic leaf spot virus (ACLSV) in various Rosaceae species, with a special emphasis on ornamentals and wild shrubs. Samples were tested by DAS‐ELISA using two different antisera, and RT‐PCR amplification of part of the CP gene. There was generally a poor correlation between the results obtained with the two sets of serological reagents and between serological and molecular detection assays. Using a nested RT‐PCR assay developed here, ACLSV was found to be widespread among cultivated, ornamental and wild species of the Rosaceae. The virus was detected for the first time in plum, wild cherry, Crataegus monogyna, Prunus spinosa and Prunus cerasifera in Greece. Sequences of a part of the CP encoding gene and the 3′ untranslated region from ACLSV isolates originating from various wild species and ornamentals were compared to those of isolates from cultivated hosts, showing similar divergence levels. Further phylogenetic analysis using the sequenced region indicated that the isolates from wild or ornamental hosts were not more closely related to each other than to isolates from cultivated hosts. The possible role of different factors in the spread of ACLSV on cultivated, ornamental and wild species is discussed.     

Real‐time and qualitative PCR for detecting Pseudomonas syringae pv. actinidiae isolates causing recent outbreaks of kiwifruit bacterial canker

Since 2008, Pseudomonas syringae pv. actinidiae virulent strains (Psa‐V) have quickly spread across the main areas of kiwifruit (Actinidia deliciosa and A. chinensis) cultivation causing sudden and re‐emerging outbreaks of bacterial canker to both species. The disease caused by Psa‐V strains is considered worldwide as pandemic. Recently, P. syringae strains (ex Psa‐LV, now called PsD) phylogenetically related to Psa‐V have been isolated from kiwifruit, but cause only minor damage (i.e. leaf spot) to the host. The different biological significance of these bacterial populations affecting kiwifruit highlights the importance of having a diagnostic method able to detect Psa‐V, which is currently solely responsible for the severe damage to the kiwifruit industry. In order to improve the specific molecular detection of Psa‐V, a real‐time PCR assay has been developed based on EvaGreen chemistry, together with a novel qualitative PCR (PCR‐C). Both methods are based on specific primer sets for the hrpW gene of Psa. The real‐time PCR and PCR‐C were highly specific, detecting down to 50 and 200 fg, respectively, and were applied to a range of organs/tissues of kiwifruit with and without symptoms. These methods are important tools for both sanitary and certification programmes, and will help to avoid the spread of Psa‐V and to check possible inoculum sources. In addition to being used as routine tests, they will also enable the study of the biology of Psa‐V and the disease that it causes, whilst avoiding the detection of other populations of related P. syringae present in kiwifruit.     

Orchid fleck symptoms may be caused naturally by two different viruses transmitted by <Emphasis Type="Italic">Brevipalpus</Emphasis>

Brevipalpus-transmitted viruses (BTV) cause chlorotic, necrotic and/or ringspot lesions in leaves and stems of orchids, citrus, coffee and several other plant species. There are two different types of BTVs, the nuclear and the cytoplasmic, based on maturation locale in the cell and particle morphology. The orchid fleck virus (OFV) is a BTV that infects orchids. Its short rodlike particles are 32–40 nm in diameter, 100–150 nm in length. OFV is found in the nucleus and is associated with intranuclear electronlucent viroplasms. In 1999, transmission electron microscopy analysis revealed a distinct type of virus causing orchid fleck symptoms. The bacilliform particles, 70–80 nm in diameter and 110–120 nm in length, induced electron-dense viroplasm inclusions in infected cells and resembled the cytoplasmic type associated with BTV, such as the citrus leprosis virus C. Our objective in the present study was to verify whether the cytoplasmic type virus found in orchids could be amplified using primers for other cytoplasmic BTVs, such as CiLV-C and Solanum violaefolium ringspot virus (SvRSV). Additionally, we aimed to differentiate the two BTVs found in orchids: the nuclear and the cytoplasmic types of OFV using microscopy and molecular and serological tools. This virus was not amplified by the CiLV-C and SvRSV primers, and neither the molecular nor the serological tools available to the OFV diagnosis reacted with it, demonstrating that they are definitely different viruses.     

玉米黄花叶病毒运动蛋白的原核表达纯化与抗血清制备

为实现对玉米黄花叶病毒（maize yellow mosaic virus,MaYMV）的血清学检测,丰富该病毒的检测方法,将编码MaYMV运动蛋白（movement protein,MP）的基因连接到原核表达载体pDBHis-MBP上,将构建成功的原核表达质粒转化到大肠杆菌Escherichia coli中诱导表达融合蛋白,将纯化后的融合蛋白对新西兰大白兔Oryctolagus cuniculus进行免疫并制备MaYMV MP多克隆抗血清,并采用Western blot对抗血清的效价、灵敏度和特异性进行检测。结果显示,利用成功构建的原核表达载体经诱导表达获得分子量大小约为62 kD的融合蛋白,纯化后对新西兰大白兔进行免疫获得MaYMV MP抗血清,该抗血清的效价为1∶128 000,灵敏度为1∶32,且该抗血清能够特异性地检测到本氏烟Nicotiana benthamiana中瞬时表达的MaYMV MP,而不与马铃薯卷叶病毒属Polerovirus及黄症病毒属Luteovirus的其他病毒发生血清学交叉反应,证明该抗血清具有良好的特异性。表明本研究制备的MaYMV MP抗血清能特异性...     

Characterization of Grapevine Algerian latent virus isolated from nipplefruit (Solanum mammosum) in Japan

Alfalfa mosaic virus (AMV), Cucumber mosaic virus (CMV), Potato virus Y (PVY), Tomato bushy stunt virus nipplefruit strain (TBSV-Nf), and an unknown spherical virus were isolated from nipplefruit (Solanum mammosum) cultivated in Chiba Prefecture, Japan. The spherical virus was identified as Grapevine Algerian latent virus nipplefruit strain (GALV-Nf) from the genus Tombusvirus, based on its physical properties, serological relationships, and analysis of genomic RNA. The genomic RNA of GALV-Nf is 4731 nucleotides long and encodes five open reading frames as well as those of other tombusviruses. Nipplefruit infected with GALV-Nf had severe stunting, leaf deformation, and clear mosaic symptoms. This is the first report of an isolation of GALV in Japan. An erratum to this article is available at .     

Development of a Non-radioactive Dot-blot Hybridisation Assay for the Detection of Pelargonium Flower Break Virus and Pelargonium line Pattern Virus

The ornamental geranium, Pelargonium×hortorum Bailey, is a traditional ornamental plant widely cultivated in Europe and Northern America. Vegetative propagation facilitates rapid spread of viral infections which have detrimental effects on the production and the quality of the crop. A non-radioactive nucleic acid hybridisation method was developed for detection of Pelargonium flower break virus (PFBV) and Pelargonium line pattern virus (PLPV) in infected host plants. This method was significantly more sensitive than the conventional ELISA test when using either purified viral preparations or crude plant extracts. The distribution of the viruses was studied by means of the non-isotopic hybridisation technique. The results indicated that the petioles and the apical blade regions of fully expanded leaves were the best source of test material. The hybridisation procedure enables the detection of PFBV and PLPV in a single assay, and its simplicity allows its application to routine large-scale indexing.     

Seed disinfection treatments do not sufficiently eliminate the infectivity of Cucumber green mottle mosaic virus (CGMMV) on cucurbit seeds

Tobamoviruses induce crop diseases that are responsible for significant economic losses around the world. Like other tobamoviruses, Cucumber green mottle mosaic virus (CGMMV) forms highly stable particles that can persist for long periods on plant debris, in soil and on seed surfaces. These particles serve as a primary source of infection, infecting seedlings from which the virus can then be mechanically transmitted to other neighbouring plants. Contaminated seeds also provide a route for the movement of the virus between countries and its introduction into new areas. Effective seed disinfection treatments and the use of uncontaminated seed may reduce the global prevalence of this virus. Several treatments based on the use of heat or chemicals have been reported to effectively eliminate CGMMV and other tobamoviruses from seeds. An evaluation of these treatments on highly contaminated seed lots revealed inconsistent results, which encouraged the construction of a more accurate detection method that combines morphological, serological, molecular and biological analyses in one protocol. The detection of viable (infectious) viral particles in seed treated with heat, trisodium phosphate or a combined treatment, indicates that these treatments are insufficient. The serological detection of CGMMV in the inner parts of infected seeds provides a possible explanation for the inconsistent efficacy of these treatments.     

Virus transmission by aphids in potato crops

This paper reviews the contribution of vector activity and plant age to virus spread in potato crops. Determining which aphid species are vectors is particularly important for timing haulm destruction to minimize tuber infection by potato virus Y (PVY). Alate aphids of more than 30 species transmit PVY, and aphids such asRhopalosiphum padi, that migrate in large numbers before flights of the more efficient vector,Myzus persicae, appear to be important vectors. Differences in methodology, aphid biotypes and virus strains prevent direct comparisons between estimates of vector efficiencies obtained for aphids in different countries in north western Europe.M. persicae is also the most efficient vector of potato leafroll virus (PLRV), but some clones ofMacrosiphum euphorbiae transmit PLRV efficiently toNicotiana clevelandii and potato test plants. The removal of infected plants early in the season prevents the spread of PLRV in cool regions with limited vector activity. The proportion of aphids acquiring PLRV from infected potato plants decreases with plant age, and healthy potato plants are more resistant to infection later in the season. Severe symptoms of secondary leafroll developed on progeny plants of cv. Maris Piper derived from mother plants inoculated with PLRV in June or July of the previous year. Progeny plants derived from mother plants inoculated in August showed only mild symptoms, but the concentration of PLRV in these plants was as high as that in the plants with severe symptoms.