Watermelon Mosaic Virus Isolates Research Articles

P3N-PIPO but not P3 is the avirulence determinant in melon carrying the Wmr resistance against watermelon mosaic virus, although they contain a common genetic determinant.

Viruses employ a series of diverse translational strategies to expand their coding capacity, which produces viral proteins with common domains and entangles virus-host interactions. P3N-PIPO, which is a transcriptional slippage product from the P3 cistron, is a potyviral protein dedicated to intercellular movement. Here, we show that P3N-PIPO from watermelon mosaic virus (WMV) triggers cell death when transiently expressed in Cucumis melo accession PI 414723 carrying the Wmr resistance gene. Surprisingly, expression of the P3N domain, shared by both P3N-PIPO and P3, can alone induce cell death, whereas expression of P3 fails to activate cell death in PI 414723. Confocal microscopy analysis revealed that P3N-PIPO targets plasmodesmata (PD) and P3N associates with PD, while P3 localizes in endoplasmic reticulum in melon cells. We also found that mutations in residues L35, L38, P41, and I43 of the P3N domain individually disrupt the cell death induced by P3N-PIPO, but do not affect the PD localization of P3N-PIPO. Furthermore, WMV mutants with L35A or I43A can systemically infect PI 414723 plants. These key residues guide us to discover some WMV isolates potentially breaking the Wmr resistance. Through searching the NCBI database, we discovered some WMV isolates with variations in these key sites, and one naturally occurring I43V variation enables WMV to systemically infect PI 414723 plants. Taken together, these results demonstrate that P3N-PIPO, but not P3, is the avirulence determinant recognized by Wmr, although the shared N terminal P3N domain can alone trigger cell death.IMPORTANCEThis work reveals a novel viral avirulence (Avr) gene recognized by a resistance (R) gene. This novel viral Avr gene is special because it is a transcriptional slippage product from another virus gene, which means that their encoding proteins share the common N-terminal domain but have distinct C-terminal domains. Amazingly, we found that it is the common N-terminal domain that determines the Avr-R recognition, but only one of the viral proteins can be recognized by the R protein to induce cell death. Next, we found that these two viral proteins target different subcellular compartments. In addition, we discovered some virus isolates with variations in the common N-terminal domain and one naturally occurring variation that enables the virus to overcome the resistance. These results show how viral proteins with common domains interact with a host resistance protein and provide new evidence for the arms race between plants and viruses.

First Report of Natural Infection of Watermelon mosaic virus (WMV) Infecting Bottle Gourd and Snake Melon

Cucurbitaceous crops, one of the main crops of agriculture, are sensitive to many plant viruses. In August 2019, virus-like symptoms were observed on some cucurbit plants grown in private home gardens in Antalya and Denizli provinces (Turkey). A total of 53 leaf samples were sampled from plants with the most symptoms (melon (Cucumis melo L.), watermelon (Citrullus lanatus L.), bottle gourd (Lagenaria siceraria (Molina) Standl.), and snake melon (Cucumis melo var. flexuosus) and tested by Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR) against possible watermelon mosaic potyvirus (WMV) infection. The coat protein gene (CP) specific primer sets amplified a gene product of nearly 820 bp fragment from symptomatic plants. WMV infections were detected in 31 individual cucurbit plants, including 11 melons, 8 watermelons, 7 snake melons and 5 bottle gourds. The presence of viral infection was found only in ornamental squash plants in Antalya province and in all cucurbits sampled in Denizli province. To better comprehend the molecular characteristics of virus isolates, the amplified viral DNA fragments were cloned in a proper prokaryotic plasmid, sequenced by Next Generation Sequencing (NGS) and recorded to GenBank. Bioinformatic analyses using the Basic Local Alignment Search Tool (BLAST) showed that the identified CP gene sequences exhibited significant nucleotide homogeneity, supported by a high nucleotide similarity index with that of other isolates around the world. In addition, Turkish isolates isolated from Antalya and Denizli regions showed approximately 94% nucleotide similarity among themselves. For phylogenetic inference, WMV sequences were subjected to multiple alignments with isolates from different geographic origins of the same viruses. Molecular phylogeny showed that all WMV isolates are closely related to other world WMV isolates at variable rates. WMV is wide host range viruses in cucurbit crops, however, this work is the first scientific report of WMV isolates detected in bottle gourd and snake melon from the South and West Regions of Turkey all over the world.WMV are broad spectrum viruses in cucurbit crops. This work is the first scientific report of Watermelon mosaic potyvirus isolates detected in bottle gourd and snake melon from the South-West Region of Turkey in all over the world.

Long-term monitoring of aphid-transmitted viruses in melon and zucchini crops: genetic diversity and population structure of cucurbit aphid-borne yellows virus and watermelon mosaic virus.

Understanding the emergence and prevalence of viral diseases in crops requires the systematic epidemiological monitoring of viruses, as well as the analysis of how ecological and evolutionary processes combine to shape viral population dynamics. Here, we extensively monitored the occurrence of six aphid-transmitted viruses in melon and zucchini crops in Spain for 10 consecutive cropping seasons between 2011 and 2020. The most prevalent viruses were cucurbit aphid-borne yellows virus (CABYV) and watermelon mosaic virus (WMV), found in 31 and 26% of samples with yellowing and mosaic symptoms. Other viruses, such as zucchini yellow mosaic virus (ZYMV), cucumber mosaic virus (CMV), Moroccan watermelon mosaic virus (MWMV), and papaya ring spot virus (PRSV) were detected less frequently (< 3%) and mostly in mixed infections. Notably, our statistical analysis showed a significant association between CABYV and WMV in melon and zucchini hosts, suggesting that mixed infections might be influencing the evolutionary epidemiology of these viral diseases. We then carried out a comprehensive genetic characterization of the full-length genome sequences of CABYV and WMV isolates by using the PacBio single-molecule real-time high-throughput technology, in order to assess the genetic variation and structure of their populations. Our results showed that most isolates clustered in the Mediterranean clade, with a fine-scale temporal structure, which was in part explained by the level of the variance between isolates from single and mixed infections. In contrast, the WMV population genetic analysis showed that most of the isolates grouped into the Emergent clade, with no genetic differentiation.

First Report of Mosaic Disease of Crape Myrtle Caused by Watermelon Mosaic Virus in Jiangsu Province in China

The crape myrtle ( Lagerstroemia indica) is a deciduous shrub that has become a popular landscape tree on public and private properties. However, crape myrtle is constantly subjected to multiple pathogen attacks, which severely affect the yield and quality and cause economic losses. In June 2019, foliar virus-like symptoms of chlorosis and mosaic were observed on crape myrtle in Yangzhou city, Jiangsu Province, East China. Leaf samples were collected from symptomatic plants. All samples were assayed by western blotting using a polyclonal antiserum to cucumber mosaic virus (CMV) and tobacco mosaic virus (TMV) and a double-antibody sandwich-ELISA assay for watermelon mosaic virus (WMV). The results revealed that all samples reacted positively with the WMV but negatively with CMV and TMV. RT-PCR was employed to confirm the obtained serological results. An amplicon of 288 bp was obtained from all the samples. Nucleotide BLAST analysis revealed that the sequence had 98.25 to 100% nucleotide identity to eight WMV isolate sequences available in GenBank. A pathogenicity assay was conducted using virus-free Nicotiana benthamiana seedlings inoculated with sap extracted from symptomatic crape myrtle leaves. Systemic infection of WMV was also confirmed in N. benthamiana by RT-PCR. On the basis of the data from serological and molecular analyses, the virus was identified as WMV. To our knowledge, this is the first report of WMV on crape myrtle in Jiangsu Province in China.

Detection and absolute quantitation of watermelon mosaic virus by real-time RT-PCR with a TaqMan probe

Watermelon mosaic virus (WMV) causes serious damage to several crops worldwide, mainly cucurbits. Disease control is based on preventing spread and search for natural resistances for plant breeding, which requires tools for sensitive detection and precise quantitation. We developed a procedure based on reverse transcription followed by real-time quantitative polymerase chain reaction (RT-qPCR) with a primer pair and a TaqMan® probe specific for WMV. The primers and probe were designed from conserved sequence stretches to target a wide range of WMV isolates. A standard curve performed with transcripts enabled estimation of WMV RNA copies per ng of total RNA, with a wide dynamic range and sensitivity (104 to 1011). This RT-qPCR was assayed with field samples from different cucurbits and used to evaluate the temporal accumulation in pumpkin plants.

Genetic Variability and Evidence of a New Subgroup in Watermelon Mosaic Virus Isolates.

Watermelon mosaic virus (WMV) is one of the important Potyviruses that infect cucurbits worldwide. To better understand the population structure of WMV in the United States (U.S.), 57 isolates were collected from cucurbit fields located in nine southern states. The complete coat protein gene of all WMV isolates was cloned, sequenced and compared with 89 reported WMV isolates. The nucleotide and amino acid sequence identities among the U.S. WMV isolates ranged from 88.9 to 99.7% and from 91.5 to 100%, respectively. Phylogenetic analysis revealed that all the U.S. WMV isolates irrespective of their geographic origin or hosts belonged to Group 3. However, the fifty-seven isolates made three clusters in G3, where two clusters were similar to previously reported subgroups EM1 and EM2, and the third cluster, containing nine WMV isolates, formed a distinct subgroup named EM5 in this study. The ratio of non-synonymous to synonymous nucleotide substitution was low indicating the occurrence of negative purifying selection in the CP gene of WMV. Phylogenetic analysis of selected 37 complete genome sequences of WMV isolates also supported the above major grouping. Recombination analysis in the CP genes confirmed various recombinant events, indicating that purifying selection and recombination are the two dominant forces for the evolution of WMV isolates in the U.S.

Detection and Molecular Characterization of Watermelon Mosaic Virus (WMV) Spread Along the Syrian Coast

Mouhanna, A.M., A.A. Ali Hasan and H.N.H. Alobaidi. 2021. Detection and Molecular Characterization of Watermelon Mosaic Virus (WMV) Spread Along the Syrian Coast. Arab Journal of Plant Protection, 39(1): 47-54. Identification of local isolates of Watermelon mosaic virus (WMV) was investigated using serological and molecular methods. A total of 293 leaf samples from watermelon, zucchini, pumpkin, cucumber, pepper, beans and potato, with symptoms suggestive of virus infection, were collected from fields in two Syrian governorates (Latakia, Tartus) along the Syrian coast. DAS-ELISA tests revealed the presence of WMV in watermelon, zucchini, pumpkin and cucumber samples, with an average relative incidence of 36.95, 26.31, 29.27 and 37.70%, respectively. The infection of pepper with Watermelon mosaic virus was reported for the first time in Syria, with an average relative incidence of 2.94%. WMV was not detected in potato and beans, and these results were confirmed by RT-PCR. The local WMV isolate Cu4 was grouped with an Iranian isolate [EU660584.1] with 98.9% sequence identity. A Turkish isolate [EU660579] was grouped with local WMV isolate Wa2 with 98.3% sequence identity. Furthermore, two local isolates Zu6 and Cu8 represented one sub-group with 99.3% sequence identity. Keywords: Watermelon mosaic virus, DAS-ELISA, RT-PCR, CI, Phylogenetic Tree.

Detection and Molecular Characterization of Two Potyvirus Species on Cucurbits from Northwestern of Iran

Cucurbit crops belonging to the family Cucurbitaceae are one the most important horticultural crops worldwide and cultivated widely in Iran. To aim detection and phylogenetic analysis of potyvirus members, during 2015-2016, 215 leaf samples from cucumber, melon, watermelon, and squash symptomatic with deforming and reduction in leaf size, blistering, mild and severe mosaic, fruit deformation, and stunting were collected from 10 major cucurbits-growing locations in West Azerbaijan province. Following mechanical inoculation of Cucurbita pepo as an indicator plant with symptomatic cucurbit crop extracts, a variety of symptoms developed on the plants. Then, total RNA extracted from 70 symptomatic leaf samples, and partial RNA-dependent RNA polymerase (NIb) (350 bp) was amplified using universal primer pairs (NIb2F/NIb3R) by reverse transcription-polymerase chain reaction (RT-PCR). The infection by potyviruses in 38.75% of the samples was confirmed based on the result. The five PCR products belonging to different hosts at the expected size (350bp) were sequenced. One sample (Ir-Na: MH491979) was determined to be infected by the Watermelon mosaic virus (WMV) whereas four samples (Ir-Ma:MH491979, Ir-Ng:MH491980, Ir-Pi:MH491981, and Ir-Ur:MH491982) infected by Zucchini yellow mosaic virus (ZYMV). In the phylogenetic analysis based on Maximum-likelihood, three ZYMV isolates (Ir-Ng, Ir-Pi, and Ir-Ur) were placed in subgroup I whereas one isolate (Ir-Ma) was placed in subgroup II belonging to group A. Also, WMV isolate (Ir- Na) was placed in CL phylogroup.

Assessment of the Current Status of Potyviruses in Watermelon and Pumpkin Crops in Spain: Epidemiological Impact of Cultivated Plants and Mixed Infections.

Viral infections on cucurbit plants cause substantial quality and yield losses on their crops. The diseased plants can often be infected by multiple viruses, and their epidemiology may depend, in addition to the agro-ecological management practices, on the combination of these viral infections. Watermelon mosaic virus (WMV) is one of the most prevalent viruses in cucurbit crops, and Moroccan watermelon mosaic virus (MWMV) emerged as a related species that threatens these crops. The occurrence of WMV and MWMV was monitored in a total of 196 apical-leaf samples of watermelon and pumpkin plants that displayed mosaic symptoms. The samples were collected from 49 fields in three major cucurbit-producing areas in Spain (Castilla La-Mancha, Alicante, and Murcia) for three consecutive (2018–2020) seasons. A molecular hybridization dot-blot method revealed that WMV was mainly (53%) found in both cultivated plants, with an unadvertised occurrence of MWMV. To determine the extent of cultivated plant species and mixed infections on viral dynamics, two infectious cDNA clones were constructed from a WMV isolate (MeWM7), and an MWMV isolate (ZuM10). Based on the full-length genomes, both isolates were grouped phylogenetically with the Emergent and European clades, respectively. Five-cucurbit plant species were infected steadily with either WMV or MWMV cDNA clones, showing variations on symptom expressions. Furthermore, the viral load varied depending on the plant species and infection type. In single infections, the WMV isolate showed a higher viral load than the MWMV isolate in melon and pumpkin, and MWMV only showed higher viral load than the WMV isolate in zucchini plants. However, in mixed infections, the viral load of the WMV isolate was greater than MWMV isolate in melon, watermelon and zucchini, whereas MWMV isolate was markedly reduced in zucchini. These results suggest that the impaired distribution of MWMV in cucurbit crops may be due to the cultivated plant species, in addition to the high prevalence of WMV.

Molecular characterization and population evolution analysis of Watermelon mosaic virus isolates on cucurbits of Northwest Iran.

One of the destructive potyviruses which cause economic damage and serious yield losses to cucurbit crops around the world is Watermelon mosaic potyvirus. In 2016, 305 leaf samples from different cucurbit cultivars with deformation and reduction in leaf size, blistering, mild and severe mosaic symptoms were collected from different cucurbits-growing regions in Northwest of Iran. Total RNA and their cDNA were tested by RT-PCR assay using two sets of specific primers corresponding to the partial sequences of CP and P1 genomic regions, in which approximately 80 out of 305 samples were found to be infected by WMV. DNA fragments of about 780bp and 545bp in length were amplified that belonged to the CP and P1 genes, respectively. Phylogenetic trees of WMV isolates were clustered into three main independent groups with significant F ST values (> 0.50 and > 0.55) for CP and P1 genes, respectively. dN/dS ratios obtained less than one (< 1) for CP gene that showed the WMV populations have been under the negative selection, whereas for P1 gene, the dN/dS values were calculated > 1 for EM clade containing; China, France, and Italy populations and < 1 for CL and G2 clades; South Korea and Iran populations. This results demonstrated that the WMV evolutionary selection pressure on the P1 gene is dependent on conditions such as the variety of cultivars and the type of cultivation.

Identification, genetic diversity and recombination analysis of Watermelon Mosaic Virusisolates.

Watermelon mosaic virus(WMV) is an important virus causing adverse effects on cucurbits throughout the world. In this study, we recorded WMV infection in the watermelon (Citrullus lanatus)-growing area of Alwar and Sikar in districts of Rajasthan, India. The RT-PCR-based detection was performed to confirm the presence of WMV, by using potyvirus-degeneratedcoat proteinprimers. Further, the complete genome sequences of two WMV isolates were compared with previously reported genome sequences. The complete genome of each isolate was 10,030 nt long, excluding the poly-A tails. Phylogeny relationships of the WMV isolates in the present study revealed the presence of uneven evolutionary pressure among the different WMV viral genomic segments. The analysis revealed that all the WMV isolates were divided into three clusters and the Indian WMV isolates cluster together with the French isolate. Recombination analysis of WMV exhibited significant recombination hotspots in the P1, NIa-Pro and Nib-CP regions. Our finding highlights the importance of genetic variability and recombination analysis to provide a better understanding of WMV molecular diversity.

Genetic variability of watermelon mosaic virus isolates infecting cucurbit crops in Italy

Watermelon mosaic virus (WMV; genus Potyvirus, family Potyviridae) is responsible for serious cucurbit yield losses worldwide. Different WMV genetic groups have been characterized so far. Among these, the "classical" (CL) group has been present in the Mediterranean basin for 40years, whereas the "emergent" (EM) group includes isolates that are associated with more-severe symptoms observed since 2000. Information on the spatial and temporal evolution of WMV isolates in Italy is currently sparse. In this study, 39 WMV isolates samples collected in different regions over the last two decades were analysed at two different genomic regions that are known to be highly variable and contain recombination breakpoints. Most of the isolates collected between 2002 and 2009 were found to belong to the CL group, whereas the isolates from 2012 onwards were classified as EM, indicating that EM isolates have progressively displaced the CL population in Italy. Although genetic variability was observed within both CL and EM groups and recombinant isolates were detected, no positive selection or haplotype geographic structure were inferred. This suggest that the shift from CL to EM populations was likely due to multiple introductions of EM isolates in different regions of Italy rather than from genetic differentiation of local populations. The progressive increase in prevalence of the highly virulent EM populations is a serious concern because of their symptom severity, and the presence of multiple EM variants that include recombinants necessitates new efforts to develop durable control strategies.

Molecular variability of watermelon mosaic virus isolates from Argentina

Watermelon mosaic virus (WMV) is an economically important virus of cucurbit crops in Argentina. The available information on genetic variability must be continuously updated. In this study, we assessed the molecular variability of WMV isolates in Argentina based on the partial sequences of the NIb-CP region and compared them with isolates previously reported from around the world. Forty-six WMV isolates were obtained from naturally infected cucurbit crops collected from 10 provinces between 2011 and 2018. At the molecular level, WMV isolates were grouped into three distinct major phylogenetic groups based on genetic distance. Majority of the Argentine isolates belonged to the emerging group (G3), whereas one isolate was included in G1 and another cluster in G2. G3 was further divided into 5 subgroups, named EM1, EM2, EM3, EM4, and a new group “EMArg”, composed exclusively of Argentine isolates with high bootstrap support and high level of significance. Tajima’s D and Fu were significantly negative for G3 and EMArg, indicating that the population of this subgroup has recently expanded. AMOVA analysis showed that the isolates was not well correlated with their geographic origin. The fixation index (FST) value between the WMV isolates from the different provinces in Argentina was lower than 0.33, indicating a relatively frequent gene flow between provinces. In every group, the predominant evolutionary pressure was negative with a mean dN/dS < 1, suggesting a slow replacement fixation rate. One recombination event was detected involving isolates of EM2 cluster from Argentina.

Genetic diversity and biological characterization of watermelon mosaic virus isolates from Iran and Iraq.

No abstract Keywords: genetic diversity; Iran and Iraq; water melon; mosaic virus; cucurbits.

Molecular diversity of main cucurbit viruses in Syria

Cucurbits are among the main crops and vegetables grown in Syria, including cucumber (Cucumis sativus), melon (C. melo), watermelon (Citrullus lanatus), and various squash species (Cucurbita pepo, C. moschata, and C. maxima). Cucurbit virus diseases are responsible for significant yield and quality losses to cucurbit crops. In the current study, we investigated the etiology of cucurbit virus diseases, and assessed the molecular diversity of the causal viruses in three major regions of cucurbit production of Syria. Out of 12 viruses and virus groups investigated, zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV),cucumber mosaic virus (CMV), cucurbit aphid-borne yellows virus (CABYV) and a new member of the genus Polerovirus, pepo aphid-borne yellows virus (PABYV) were detected in various cucurbit crops from plants displaying virus-like symptoms. Syrian ZYMV isolates were closely related and shared low diversity suggesting a relatively recent introduction. A diverse population of WMV with four classical and two emerging isolates of WMV were identified, which complicates the control program. Two CMV isolates were closely related to CMV isolates, reported previously from other crops in the same regions, which may indicate frequent movements of CMV among different hosts. The finding of an isolate of PABYV, a newly described species of the genus Polerovirus, reveals a wider distribution of this virus that may represent a potential emerging problem to cucurbit production.

A Watermelon mosaic virus clone tagged with the yellow visual maker phytoene synthase facilitates scoring infectivity in melon breeding programs

Watermelon mosaic virus (WMV), a plus-strand RNA virus that belongs to the family Potyviridae, is one of the most damaging viruses that infect cucurbit crops. However, isolates of this species frequently induce mild symptoms, which makes difficult to manage the disease in the field and breeding programs. A new generation of marker genes has been recently developed to visually track plant virus infection. Virus-mediated expression of the Pantoea ananatis phytoene synthase (crtB) induces accumulation in infected tissues of pigmented carotenoids that can be readily detected by the naked eye. Here we investigated whether this visual marker may facilitate visual diagnosis of WMV infection in cucurbits. First, we cloned a mild WMV isolate (WMV-Vera) and built a recombinant clone that expresses crtB (WMV-crtB). Next, we inoculated a series of cucurbit cultivars frequently used in breeding programs. We observed that WMV-mediated expression of crtB helps to visually score infection in two susceptible and highly appreciated melon cultivars, such as Piñonet Piel de Sapo and Vedrantais, but not in susceptible Cucurbita spp. cultivars. An increase in yellow pigmentation was experimentally confirmed in susceptible melon cultivars by measuring the Hue angle using a solid colorimeter. Carotenoid analyses in infected tissues explained why the visual crtB marker performs better in susceptible melon than in Cucurbita spp. cultivars. These results support that the visual marker crtB may facilitate visual diagnosis of WMV infection in melon breeding programs.

Genetic diversity and population structure of Watermelon mosaic virus

Watermelon mosaic virus (WMV) is one of the most important viruses infecting a wide range of plant species. Population genetic analysis of WMV was performed based on the virus coat protein (CP) gene sequences of ten isolates identified in this study and 89 additional isolates from five different countries (China, France, Iran, Spain and the USA) in three continents: Asia, Europe and North America. Phylogenetic analysis showed that WMV isolates clustered in three phylogroups: Classical, Group 2 and Emerging with significant F ST values (>0.43). Chinese, French, Iranian, Spanish and USA WMV populations were composed of multiple lineages. Genetic differentiation analysis of WMV populations showed that the Iranian and Spanish populations were statistically distinct from the other populations. The ratio of non-synonymous to synonymous nucleotide diversity (dN/dS = ω) was <1, indicating that the CP gene of WMV has been under negative selection. Most of the codons in the CP were under negative selection (ω < 1) except for codon 87, which were significantly under positive selection. This study suggests that host adoption selection and founder effect were important evolutionary factors driving the genetic diversification of WMV.

Molecular detection of watermelon mosaic virus associated with a serious mosaic disease on Cucurbita pepo L. in Shanxi, China.

With continued expansion of Cucurbita pepo L. cultivation, viral diseases affecting the crop have become more serious in recent years, causing enormous losses in yield and quality. A virus sample was obtained from Wenshui in Shanxi province, China. Double-stranded RNA technology and sequence-independent amplification (SIA) were used to identify the virus that induced C. pepo L. mosaic disease. SIA and sequencing results showed the presence of watermelon mosaic virus (WMV) in diseased C. pepo L. leaves. The complete sequence of WMV from the Shanxi isolate (i.e., WMV-WS) was cloned and analyzed for further characterization. The genomic RNA of WMV-WS is 10,040 nucleotides in length and encodes a putative polyprotein of 3218 amino acids. Phylogenetic analysis indicate that all WMV isolates were divided into four groups and WMV-WS isolate belong to Group 4. Further analysis showed that these WMV isolates were not only to a certain degree related to the host, but also related to geographical origin of isolates. Our results provide information for a better understanding of the genetic diversity of WMV isolates infecting C. pepo L. in Shanxi, China.

Host Reaction of Watermelon mosaic virus Isolates Infecting Melon from Different Geographical Origins in Xinjiang of China

Watermelon mosaic virus (WMV) is one of the major viruses infecting cucurbit crops worldwide. Although WMV is very common worldwide, little is known about the biological traits of WMV isolates from China. Hence, this study aimed to characterize 11 WMV isolates infecting melon from different geographical origins in Xinjiang based on experimental hosts. Sap inoculation of the 11 WMV isolates onto a range of 13 plant species revealed some differences compared to the WMV isolates collected from other countries. Our results showed that, overall, there were no obvious correlations of host responses to inoculation with WMV isolates from different geographical origins. However, isolate JS-1 caused mild mosaic on Cucurbita moschata, whereas the remaining 10 isolates were asymptomatic on this plant species. Moreover, in Datura stramonium, isolate TYG-1 induced mosaic, whereas the remaining 10 isolates did not infect this species. All isolates infected systemically Cucurbita pepo and Cucumis melo plants, causing severe symptoms. All isolates did not induce any symptoms on Cucumis sativus, but the virus could be detected using RT-PCR. Additionally, all isolates infected systemically Nicotiana tabacum plants, causing mild mosaics. Chenopodium amaranticolor and Chenopodium quinoa reacted to all isolates by chlorotic local lesions in the inoculated leaves, and the virus was detected in the inoculated leaves using RT-PCR. In addition, the attempts to transmit the isolates to Luffa cylindrica, Vicia faba, Phaseolus vulgaris, Vigna unguiculata or Pisum sativum failed as confirmed by negative RT-PCR. Our results would be useful for understanding the biological variability of WMV.

Occurrence of viruses infecting melon in Xinjiang of China and molecular characterization of Watermelon mosaic virus isolates

Cucurbit viruses have been associated with important economic losses in Xinjiang of China. Therefore, a comprehensive survey and sample collection was performed during the 2013 and 2014 growing seasons from the major melon-growing locations in Xinjiang which is the largest area for melon production in China. Samples were analyzed using reverse transcription-polymerase chain reaction (RT-PCR) to detect Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), Cucumber mosaic virus (CMV), Papaya ringspot virus (PRSV), Squash mosaic virus (SqMV), Tomato ringspot virus (ToRSV), Moroccan watermelon mosaic virus (MWMV), Tomato spotted wilt virus (TSWV), Watermelon silver mottle virus (WSMoV), Cucumber green mottle mosaic virus (CGMMV), and Zucchini yellow fleck virus (ZYFV). We collected 492 melon samples with virus-like symptoms. Out of these, 94.5 % of the samples were infected by at least one of these viruses. WMV was the most prevalent virus detected. WMV, CMV, and ZYMV were detected in 77.0 %, 60.0 %, and 41.1 % of infected samples, respectively, and the infection rate of these three viruses changed significantly among melon cultivars. Other viruses analysed were not detected in any sample tested. The number of multiple infections was high (average 57.2 %), with the most common double infection WMV + CMV (17.8 %), closely followed by WMV + ZYMV (14.4 %). Statistical analysis of the potential association among viruses showed that there was a strong association between several viruses for multiple infections. An analysis of WMV genetic diversity suggested that all isolates obtained in this study clustered into group A and that purifying selection was restricting variability in the population.