Cucumber Vein Yellowing Virus Research Articles

Weed Plants of the Asteraceae and Malvaceae Families as Reservoirs of Harmful Viruses of Vegetable Crops in Ukraine and the World

The review provides an analysis of the current literature data on the prevalence of weeds of the Asteraceae and Malvaceae families, which act as reservoirs of agricultural plant viruses, in the agroecosystems of both Ukraine and the world. The main focus is on weeds that are common in the agrocenoses of agricultural crops. The primary sources of the main pathogens of viral diseases of vegetable crops (Tomato spotted wilt virus (TSWV), Tomato chlorosis virus (ToCV), Tomato yellow leaf curl virus (TYLCV), Cucumber mosaic virus (CMV), Cucumber vein yellowing virus (CVYV), Iris yellow spot virus (IYSV), and Pepino mosaic virus (PepMV)) in different climatic zones, as well as the main factors contributing to the spread of harmful viruses in agrophytocenoses are analyzed.

First report of Cucumber vein yellowing virus in Iraq

Courgette (Cucurbita pepo) is one of the main cucurbit crops grown in Iraq for local consumption. Viruses are a major threat to cucurbit production in Iraq, particularly whitefly-transmitted viruses (Mohammed et al., 2021). In the 2022 growing season, courgette plants with extensive leaf vein-yellowing symptoms (Figure 1), associated with whitefly infestation, were observed in fields around Al-Yusufiyah, Baghdad Province, Iraq. The disease incidence was 40–50%. Thirty leaf samples with vein-yellowing symptoms were collected randomly. One sample was sent in RNAprotect Tissue Reagent (Qiagen, Germany) for high throughput RNA sequencing (RNA-seq) at Macrogen Inc. (Seoul, South Korea). Overall, 39,549,599 paired-end reads (151 bp length) were obtained. The reads were first aligned to the complete genome sequence of Cucurbita pepo via Bowtie2 (v. 2.4.5) to deplete host sequence. The Velvet assembler (v. 1.2.10) was operated for de novo assembly of the unmapped reads (Lahuf, 2021). The contigs produced were compared with plant virus sequences retrieved from GenBank (https://www.ncbi.nlm.nih.gov/genome/viruses/) using BLASTn algorithms (Abass & Lahuf, 2023). The BLASTn analysis showed ≥99% pairwise nucleotide identity with the full genomes of five Cucumber vein yellowing virus (CVYV) isolates. Other viruses were also detected including Squash leaf curl virus (SqLCV) and Tomato leaf curl Palampur virus (ToLCPMV). Reference-based genome assembly was conducted using a sequence of CVYV (NC_006941.1). A total of 86,245 reads mapped to NC_006941.1 with 100% coverage and a depth coverage of 1.335× and BLAST analysis showed that the assembled genome of CVYV Iraq-1 shares 99.86% pairwise nucleotide identity with this isolate. The genome sequence of the CVYV isolate Iraq-1 was deposited in GenBank (Accession No. OQ685957.1). A phylogenetic analysis showed a close relationship between CVYV isolate Iraq-1 and isolates from diverse origins, particularly those from Spain (AY578085.1 and MK777994.1) and Portugal (MZ130935.1 and OK181771.1) (Figure 2). Total RNA was extracted from the thirty diseased courgette leaf samples, including the sequenced sample, using a Viral RNA/ Viral Nucleic Acid Mini Kit (Favorgen, Taiwan) and kept at -20°C for further analysis. RT-PCR was done using a OneStep RT-PCR kit (Qiagen, Germany) with CVYV-specific coat protein primers (CV+ and CV-) (Cuadrado et al., 2003). The amplicons were directly sequenced and CVYV infection was confirmed in all thirty leaves. Another fifty diseased leaf samples were collected randomly from different fields of courgette in Baghdad Province to confirm the presence of the virus in the region and 38 also tested positive using the CVYV-specific RT-PCR. This is the first report of CVYV in Iraq. Additional work is needed to reveal the distribution and prevalence of CVYV, SqLCV and ToLCPMV and to determine their role in causing disease in courgette and other curcurbit crops in Iraq. The authors are appreciative of the Plant Protection Department, Agriculture College, University of Kerbala and the Iraqi Ministry of Higher Education and Scientific Research for the facilities and financial support.

Musk mallow (Abelmoschus moschatus): a new host of Cucurbit aphid‐borne yellows virus

Musk mallow (Abelmoschus moschatus, family Malvaceae) is a medicinal plant cultivated across Asia, Africa and South America. It is found as a weed all over the Deccan region of India (Pawar & Vyawahare, 2017). The seeds of the plant are used for medicinal purposes and as a source of fragrant compounds (Gul et al., 2011). Musk mallow plants exhibiting yellowing of older leaves, midvein clearing, leaf reduction, mottling and slight downward curling (Fig. 1) were observed in October 2022 at the experimental research farm of the Indian Agricultural Research Institute in Pune, Maharashtra, India. The plants occurred as weeds and the disease incidence was 4% (c. 16 plants) in an eight-acre area. Ten diseased and four asymptomatic plants were sampled to ascertain the viruses associated with the symptoms. ELISA was done using antisera against Cucurbit aphid-borne yellows virus (CABYV) (DSMZ, Germany), Cucurbit yellow stunting disorder virus (CYSDV) (Arsh Biotech, India), Cucumber mosaic virus (CMV), Papaya ringspot virus (PRSV) and Zucchini yellow mosaic virus (ZYMV) (Agdia, USA). CABYV was detected in all diseased samples but CMV, CYSDV, PRSV and ZYMV were not detected. None of the five viruses were detected by ELISA in the asymptomatic samples. Total RNA was extracted from both diseased and asymptomatic samples using an RNeasy Plant Mini Kit (Qiagen, USA). Two-step RT-PCR assay was done using the extracted RNA and CABYV-specific primers which amplify c. 484 bp of the partial coat protein region (Boubourakas et al., 2006). RT-PCR was also performed using primers specific for CMV, CYSDV, PRSV, ZYMV, Beet pseudo-yellows virus and Cucumber vein yellowing virus. Amplicons of the expected size were obtained in all diseased plants with CABYV primers but not with primers for any of the other viruses. No amplification was obtained in the asymptomatic samples for any of the viruses. The amplicons of five samples were Sanger sequenced bidirectionally and found to be identical (GenBank Accession No. OP455156). A BLASTn search of the sequence revealed that it shared 100% identity with an Indian CABYV sequence from Praecitrullus fistulosus (OP455157). A phylogenetic tree was constructed using the neighbour-joining method (MEGA X program) with CABYV sequences from different hosts and geographies, and the sequence clustered with other Indian CABYV sequences (Fig. 2). CABYV primarily infects cucurbits but also infects other crops and weeds including three Malvaceae species, Abutilon theophrasti, Gossypium hirsutum and Malva parviflora (Lecoq et al., 2022). To our knowledge, this is the first report of CABYV infecting Abelmoschus moschatus in the world. The present finding is of epidemiological importance as it indicates the further broadening of the host range of CABYV and the possibility of infecting other economically important Malvaceae members, such as G. hirsutum which is grown for cotton in India. Furthermore, musk mallow plants could serve as an alternative / reservoir host for CABYV aiding its transmission to other commercial crops. The authors thank the Director, ICAR-IARI, New Delhi for providing lab facilities.

Research on Drawing Attention to Overlooked Viruses in Plant Viruses Causing Yellowing-Type Symptoms in Cucurbitaceae

A single-stranded, positive-sense plant RNA virus called the Cucurbit chlorotic yellows virus (CCYV, Crinivirus, Closteroviridae) is comprised of RNA1 and RNA2. It is semipersistently transmitted by the whitefly Bemisia tabaci biotypes MEAM1 and MED. In 2004, CCYV was discovered on melon plants in Japan. Several other cucurbit species, as well as a range of non-species, were subsequently reported from countries such as Saudi Arabia, California, Israel, Taiwan, Sudan, Lebanon, Iran, Greece, Türkiye, Egypt, Spain, and China. Whitefly populations are frequently encountered in cucurbit cultivating areas. Virus plant diseases attributed to whiteflies are common in squash cultivation in the open field and greenhouses in Türkiye, especially in cucumbers and squash. Cucumber vein yellowing virus (CVYV), Cucurbit yellow stunting disorder virus (CYSDV), Tomato leaf curl New Delhi virus (ToLCNDV), Squash vein-yellowing virus (SqVYV) are the leading virus diseases transmitted by Bemisia tabaci. Symptoms caused specifically by these viral diseases are of the yellowing type, although they differ as intervascular yellowing, yellowing of old or young leaves, and upward curling. Besides these viruses, CCYV, a problem in cucurbits, is carried by whitefly like others, causes yellowing type symptoms, and its first record in cucumber was reported in 2017 in Türkiye. However, this virus is ignored in the production of cucurbits, it is a problem in production areas. There are major viruses cause similar symptoms with the presence of the Cucumber chlorotic yellows virus is overlooked in the symptomatological observation. In this study, we tried to reveal the difference of CCYV, which is encountered in cucurbit growing areas in Antalya and whose presence was detected by RT-PCR, from other viruses and emphasized its importance as a virus that should be considered in classical breeding studies.

Analysis of the RNA-Dependent RNA Polymerase 1 (RDR1) Gene Family in Melon.

RNA-dependent RNA polymerase 1 (RDR1) plays a crucial defense role against plant viruses by secondary amplification of viral double-stranded RNA in the gene-silencing pathway. In this study, it was found that melon (Cucumis melo) encodes four RDR1 genes (CmRDR1a, b, c1 and c2) similar to the CsRDR1 gene family of cucumber (C. sativus). However, in contrast to cucumber, melon harbors a truncated CmRDR1b gene. In healthy plants, CmRDR1a was expressed, whereas the expression of CmRDR1c1/c2 was not detected. CmRDR1a expression level increased 20-fold upon cucumber mosaic virus (CMV) infection and was not increased in melon plants infected with zucchini yellow mosaic virus (ZYMV), cucumber vein yellowing virus (CVYV) and cucumber green mottle mosaic virus (CGMMV). The expression of CmRDR1c1/c2 genes was induced differentially by infection with viruses from different families: high levels of ~340-, 172- and 115-fold increases were induced by CMV, CVYV and CGMMV, respectively, and relatively low-level increases by potyvirus infection (4- to 6-fold). CMV mutants lacking the viral silencing suppressor 2b protein did not cause increased CmRDR1c/c2 expression; knockout of CmRDR1c1/c2 by CRISPR/Cas9 increased susceptibility to CMV but not to ZYMV. Therefore, it is suggested that the sensitivity of melon to viruses from different families is a result of the loss of function of CmRDR1b.

Specificity of Resistance and Tolerance to Cucumber Vein Yellowing Virus in Melon Accessions and Resistance Breaking with a Single Mutation in VPg.

Cucumber vein yellowing virus (CVYV) is an emerging virus on cucurbits in the Mediterranean Basin, against which few resistance sources are available, particularly in melon. The melon accession PI 164323 displays complete resistance to isolate CVYV-Esp, and accession HSD 2458 presents a tolerance, i.e., very mild symptoms despite virus accumulation in inoculated plants. The resistance is controlled by a dominant allele Cvy-11, while the tolerance is controlled by a recessive allele cvy-2, independent from Cvy-11. Before introducing the resistance or tolerance in commercial cultivars through a long breeding process, it is important to estimate their specificity and durability. Upon inoculation with eight molecularly diverse CVYV isolates, the resistance was found to be isolate-specific because many CVYV isolates induced necrosis on PI 164323, whereas the tolerance presented a broader range. A resistance-breaking isolate inducing severe mosaic on PI 164323 was obtained. This isolate differed from the parental strain by a single amino acid change in the VPg coding region. An infectious CVYV cDNA clone was obtained, and the effect of the mutation in the VPg cistron on resistance to PI 164323 was confirmed by reverse genetics. This represents the first determinant for resistance-breaking in an ipomovirus. Our results indicate that the use of the Cvy-11 allele alone will not provide durable resistance to CVYV and that, if used in the field, it should be combined with other control methods such as cultural practices and pyramiding of resistance genes to achieve long-lasting resistance against CVYV.

Cucumber vein yellowing virus (cucumber vein yellowing)

Cucumber vein yellowing virus (cucumber vein yellowing)

Unravelling cucumber resistance to several viruses via genome-wide association studies highlighted resistance hotspots and new QTLs.

The mapping and introduction of sustainable resistance to viruses in crops is a major challenge in modern breeding, especially regarding vegetables. We hence assembled a panel of cucumber elite lines and landraces from different horticultural groups for testing with six virus species. We mapped 18 quantitative trait loci (QTL) with a multiloci genome wide association studies (GWAS), some of which have already been described in the literature. We detected two resistance hotspots, one on chromosome 5 for resistance to the cucumber mosaic virus (CMV), cucumber vein yellowing virus (CVYV), cucumber green mottle mosaic virus (CGMMV) and watermelon mosaic virus (WMV), colocalizing with the RDR1 gene, and another on chromosome 6 for resistance to the zucchini yellowing mosaic virus (ZYMV) and papaya ringspot virus (PRSV) close to the putative VPS4 gene location. We observed clear structuring of resistance among horticultural groups due to plant virus coevolution and modern breeding which have impacted linkage disequilibrium (LD) in resistance QTLs. The inclusion of genetic structure in GWAS models enhanced the GWAS accuracy in this study. The dissection of resistance hotspots by local LD and haplotype construction helped gain insight into the panel's resistance introduction history. ZYMV and CMV resistance were both introduced from different donors in the panel, resulting in multiple resistant haplotypes at same locus for ZYMV, and in multiple resistant QTLs for CMV.

The Amino-Proximal Region of the Coat Protein of Cucumber Vein Yellowing Virus (Family Potyviridae) Affects the Infection Process and Whitefly Transmission.

Most plant viruses rely on vector transmission for their spread and specific interactions between vector and virus have evolved to regulate this relationship. The whitefly Bemisia tabaci- transmitted cucumber vein yellowing virus (CVYV; genus Ipomovirus, family Potyviridae) is endemic in the Mediterranean Basin, where it causes significant losses in cucurbit crops. In this study, the role of the coat protein (CP) of CVYV for B. tabaci transmission and plant infection was investigated using a cloned and infectious CVYV cDNA and a collection of point and deletion mutants derived from this clone. Whitefly transmission of CVYV was abolished in a deletion mutant lacking amino acids in position 93–105 of the CP. This deletion mutant caused more severe disease symptoms compared to the cDNA clone representing the wild-type (wt) virus and movement efficiency was likewise affected. Two virus mutants carrying a partially restored CP were transmissible and showed symptoms comparable to the wt virus. Collectively, our data demonstrate that the N-terminus of the CVYV CP is a determinant for transmission by the whitefly vector and is involved in plant infection and symptom expression.

An Importin-β-like Protein from Nicotiana benthamiana Interacts with the RNA Silencing Suppressor P1b of the Cucumber Vein Yellowing Virus, Modulating Its Activity.

During a plant viral infection, host–pathogen interactions are critical for successful replication and propagation of the virus through the plant. RNA silencing suppressors (RSSs) are key players of this interplay, and they often interact with different host proteins, developing multiple functions. In the Potyviridae family, viruses produce two main RSSs, HCPro and type B P1 proteins. We focused our efforts on the less known P1b of cucumber vein yellowing virus (CVYV), a type B P1 protein, to try to identify possible factors that could play a relevant role during viral infection. We used a chimeric expression system based on plum pox virus (PPV) encoding a tagged CVYV P1b in place of the canonical HCPro. We used that tag to purify P1b in Nicotiana-benthamiana-infected plants and identified by mass spectrometry an importin-β-like protein similar to importin 7 of Arabidopsis thaliana. We further confirmed the interaction by bimolecular fluorescence complementation assays and defined its nuclear localization in the cell. Further analyses showed a possible role of this N. benthamiana homolog of Importin 7 as a modulator of the RNA silencing suppression activity of P1b.

Genomic-Assisted Marker Development Suitable for CsCvy-1 Selection in Cucumber Breeding.

Cucumber is a widely grown vegetable crop plant and a host to many different plant pathogens. Cucumber vein yellowing virus (CVYV) causes economic losses on cucumber crops in Mediterranean countries and in some part of India such as West Bengal and in African countries such as Sudan. CVYV is an RNA potyvirus transmitted mechanically and by whitefly (Bemisia tabaci) in a semipersistent manner. Control of this virus is heavily dependent on the management of the insect vector and breeding virus-resistant lines. DNA markers have been used widely in conventional plant breeding programs via marker-assisted selection (MAS). However, very few resistance sources against CVYV in cucumber exist, and also the lack of tightly linked molecular markers to these sources restricts the rapid generation of resistant lines. In this work, we used genomics coupled with the bulked segregant analysis method and generated the MAS-friendly Kompetitive allele specific PCR (KASP) markers suitable for CsCvy-1 selection in cucumber breeding using a segregating F2 mapping population and commercial plant lines. Variant analysis was performed to generate single-nucleotide polymorphism (SNP)-based markers for mapping the population and genotyping the commercial lines. We fine-mapped the region by generating new markers down to 101 kb with eight genes. We provided SNP data for this interval, which could be useful for breeding programs and cloning the candidate genes.

First Report of Cucurbit Chlorotic Yellows Virus Infecting Cucumber and Zucchini in Algeria

This work was supported by the Spanish Ministerio de Ciencia, Innovacion y Universidades, cofunded with FEDER funds (project nos. AGL2017-85563-C2-1-R and RTA2017-00061-0O3-03 [INIA]) and the programa para grupos de investigacion de excelencia from the Conselleria d'Educacio, Investigacio, Cultura i Esport, (Generalitat Valenciana) (Prometeo Program 2017/078). A. Kheireddine thanks the Erasmus+ Programme of the European Union for her mobility project (KA107 2018-20). C. Saez is a recipient of a predoctoral fellowship from Generalitat Valenciana, cofunded by the Operational Program of the European Social Fund (FSECV 2014-2020) (grant no. ACIF/2016/188). Plant Dis. 104: 1264, 2020; published online as https://doi.org/10.1094/PDIS-10-19-2091PDN.Accepted for publication 19 December 2019.

Mapping Cucumber Vein Yellowing Virus Resistance in Cucumber (Cucumis sativus L.) by Using BSA-seq Analysis.

Cucumber vein yellowing virus (CVYV) causes severe yield losses in cucurbit crops across Mediterranean countries. The control of this virus is based on cultural practices to prevent the presence of its vector (Bemisia tabaci) and breeding for natural resistance, which requires the identification of the loci involved and the development of molecular markers for linkage analysis. In this work, we mapped a monogenic locus for resistance to CVYV in cucumber by using a Bulked Segregant Analysis (BSA) strategy coupled with whole-genome resequencing. We phenotyped 135 F3 families from a segregating population between a susceptible pickling cucumber and a resistant Long Dutch type cucumber for CVYV resistance. Phenotypic analysis determined the monogenic and incomplete dominance inheritance of the resistance. We named the locus CsCvy-1. For mapping this locus, 15 resistant and 15 susceptible homozygous F2 individuals were selected for whole genome resequencing. By using a customized bioinformatics pipeline, we identified a unique region in chromosome 5 associated to resistance to CVYV, explaining more than 80% of the variability. The resequencing data provided us with additional SNP markers to decrease the interval of CsCvy-1 to 625 kb, containing 24 annotated genes. Markers flanking CsCvy-1 in a 5.3 cM interval were developed for marker-assisted selection (MAS) in breeding programs and will be useful for the identification of the target gene in future studies.

Evidence for long‐term prevalence of cucumber vein yellowing virus in Sudan and genetic variation of the virus in Sudan and the Mediterranean Basin

Cucumber vein yellowing virus (CVYV) is emerging throughout the Mediterranean Basin, where it causes significant damage to cucumber and melon crops. It has been suggested that CVYV originated from the Middle East and has spread only recently to other areas. In this work, an isolate from Sudan was characterized, and surveys performed in that country between 1992 and 2012 revealed a long‐term presence of CVYV with a high molecular variability, showing that the virus has long been endemic in sub‐Saharan Africa. Comparison of the full‐length sequences of 11 CVYV isolates from different geographic origins revealed recombination events in CVYV populations from the Mediterranean Basin and the Middle East, and evidence for different selection pressures along the genome. These results shed a new light on the evolution of CVYV.

First report of Cucurbit aphid‐borne yellow virus infecting bitter gourd (Momordica charantia) and spiny gourd (Momordica dioica) in Sri Lanka

The rapid spread of a virus-like disease with severe leaf yellowing symptoms from bitter gourd and spiny gourd fields in Sri Lanka was observed in 2016-2017. Correct identification based on symptoms is difficult due to mixed infections of cucurbit viruses. Therefore, twenty bitter gourd samples and nine spiny gourd samples were selected from five geographically distinct areas in Sri Lanka (Agnukolapelessa, Balangoda, Kirindiwela, Mulathiuv and Thiththapaththara). The plants showed yellowing and thickening of basal leaves, necrosis of older leaves, reduction of plant growth and interveinal chlorosis (Fig. 1). The samples were tested for infection with Cucurbit chlorotic yellows virus, Cucurbit yellow stunting disorder virus and Zucchini yellow mosaic virus by RT-PCR but all results were negative. Additionally, the symptomatic plants were tested by TAS-ELISA using a monoclonal antibody for Cucurbit aphid-borne yellow virus (CABYV) (Agdia Inc., USA). The test was positive for CABYV in five bitter gourd and two spiny gourd samples. In order to confirm the serological results, total RNA was extracted from four of the samples which had tested positive using ELISA, using the size-fractionated silica extraction method (Boom et al., 2). Virus-specific primers CABYV- CP-5' (5'-CGCGTGGTTGTGGTCAACCC-3') and CABYV-CP-3' (5'- CCYGCAACCGAGGAAGATCC-3') (Bananej & Vahdat, 1) were used to amplify the coat protein gene of CABYV. An amplicon of approximately 500 bp was obtained from each of the four ELISA-positive samples and none from the symptomless samples. One RT-PCR product from spiny gourd and one from bitter gourd (GenBank Accession No. MH802612) were sequenced. The sequences were identical and a BLAST search showed 99% identity with a CABYV isolate from South Korea (LC413786). Additionally, an infected bitter gourd sample was analysed by electron microscopy. The presence of spherical particles, 25 nm in diameter, was observed in a partially purified preparation (Rowhani & Stace-Smith, 1979; Waterhouse & Murant, 5). CABYV has been reported to generally be present in mixed infection with other viruses, including the viruses tested for in this study and Beet pseudo-ellow virus, Cucumber vein yellowing virus and Watermelon mosaic virus. The significance of mixed infections in disease associated with CABYV in Sri Lanka is unclear and requires further investigation (Kassem et al., 3). To the best of our knowledge this is the first report CABYV on bitter gourd in Sri Lanka and the first report of its occurrence on spiny gourd in the world.

Characterization of a new cucurbit-infecting ipomovirus from Sudan.

Two members of the genus Ipomovirus (family Potyviridae) are known to infect cucurbits: cucumber vein yellowing virus (CVYV), which is emerging throughout the Mediterranean Basin, and squash vein yellowing virus (SqVYV), which has been described in America and the Caribbean Basin, and more recently in Israel. In this work, an ipomovirus different from CVYV and SqVYV, tentatively named coccinia mottle virus (CocMoV), was detected in a sample of the cucurbit Coccinia grandis collected in central Sudan in 2012. Sequence identity in nt was 68% with CVYV, 59-60% with SqVYV, cassava brown streak virus and Ugandan cassava brown streak virus, and less than 50% with other members of the family Potyviridae. Preliminary biological and epidemiological studies indicate that CocMoV has a narrow natural host range and a low prevalence.

Development of broad virus resistance in non-transgenic cucumber using CRISPR/Cas9 technology.

Genome editing in plants has been boosted tremendously by the development of CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) technology. This powerful tool allows substantial improvement in plant traits in addition to those provided by classical breeding. Here, we demonstrate the development of virus resistance in cucumber (Cucumis sativus L.) using Cas9/subgenomic RNA (sgRNA) technology to disrupt the function of the recessive eIF4E (eukaryotic translation initiation factor 4E) gene. Cas9/sgRNA constructs were targeted to the N' and C' termini of the eIF4E gene. Small deletions and single nucleotide polymorphisms (SNPs) were observed in the eIF4E gene targeted sites of transformed T1 generation cucumber plants, but not in putative off-target sites. Non-transgenic heterozygous eif4e mutant plants were selected for the production of non-transgenic homozygous T3 generation plants. Homozygous T3 progeny following Cas9/sgRNA that had been targeted to both eif4e sites exhibited immunity to Cucumber vein yellowing virus (Ipomovirus) infection and resistance to the potyviruses Zucchini yellow mosaic virus and Papaya ring spot mosaic virus-W. In contrast, heterozygous mutant and non-mutant plants were highly susceptible to these viruses. For the first time, virus resistance has been developed in cucumber, non-transgenically, not visibly affecting plant development and without long-term backcrossing, via a new technology that can be expected to be applicable to a wide range of crop plants.

Genetic variation and evolutionary forces shaping Cucumber vein yellowing virus populations: risk of emergence of virulent isolates in Europe

The genetic variation and evolutionary mechanisms shaping Cucumber vein yellowing virus (CVYV) populations were investigated by analysis of nucleotide sequences coding for P1b, P1b/P3 and coat proteins (CP) from isolates collected in different countries. The complete genome sequence of isolate ISM from Israel was also determined and compared to those of isolates Jor from Jordan and ALM32 from Spain. This isolate had overall nucleotide identities of 94·23 and 94·96% with ALM32 and Jor, respectively. Nucleotide variation among isolates was not homogeneously distributed, with the 5′ half of the genome being more variable than the 3′ half. A Bayesian phylogenetic tree of the CP showed that CVYV isolates clustered into two main clades: isolates from the Middle East region (Lebanon, Israel and Jordan) clustered in both clades whereas the isolate from Tunisia clustered in clade I and the European isolates clustered as a homogeneous phylogroup in Clade II. A similar topology was observed for P1b but with incongruences with respect to the CP, suggesting genetic exchange among virus isolates, which were confirmed with recombination algorithms. The low genetic diversity within the European phylogroup with respect to the other isolates, neutralist tests and genetic differentiation analyses suggest that the Middle East region is the cradle of CVYV and that a unique virus introduction event occurred in Europe, where the virus spread rapidly. Taken together, these findings indicate a risk of emergence of virulent CVYV isolates in Europe either through migration from the Middle East or by genetic changes of the European isolates.

Cucumber vein yellowing virus. [Distribution map].

Abstract A new distribution map is provided for Cucumber vein yellowing virus. Potyviridae: Ipomovirus. Hosts: Cucumis spp., Cucurbita spp. Information is given on the geographical distribution in Europe (Cyprus, France, Mainland France, Portugal, Spain), Asia (India, Uttar Pradesh, West Bengal, Iran, Israel, Jordan, Lebanon, Turkey), Africa (Egypt, Sudan, Tunisia).

Whitefly‐transmitted RNA viruses that affect intensive vegetable production

AbstractIntensive vegetable production is constantly facing the emergence of new viral diseases. Apart from the intrinsic features of viruses as plant pathogens, the highly dynamic turnover of cultivars and cultural practices, and the global trade of seeds and products characteristic of intensive vegetable production may favour the emergence of new viruses, as well as the expansion of the geographical range of vectors responsible for their dissemination. Indeed, the efficient transmission of viruses plays a major role in the impact and outcome of viral epidemics. Whiteflies (Hemiptera: Aleyrodidae) that belong to the genera Bemisia and Trialeurodes are efficient virus vectors. Whiteflies transmit viruses of at least four genera, one of DNA viruses, the genus Begomovirus, and three of RNA viruses, Crinivirus, Ipomovirus and Torradovirus. Begomoviruses have been the subject of recent reviews. In this article we review the genome structure, epidemiology and control of whitefly‐transmitted RNA viruses that belong to the genera Crinivirus, Ipomovirus and Torradovirus, with an extended discussion on the particular viruses within these genera that are currently causing important outbreaks, such are Cucumber vein yellowing virus (CVYV), Cucurbit yellow stunting disorder virus (CYSDV), Tomato chlorosis virus (ToCV) and Tomato torrado virus (ToTV).