Occurrence, distribution and relative incidence of mosaic viruses infecting field--grown squash in Tehran province, Iran

Squash (Cucurbita pepo) belongs to Cucurbitaceae family. Every year Cucurbitaceae are planted world wide. They are one of the most important economic crops. Cucurbitaceae are threatened by viruses. Many viruses damage the plants of this family. Since nine viruses have been reported on squash from Iran. In this survey, during 2002--2003, to determine the distribution of Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV), 466 samples were collected from squash field in Tehran province. Infected plants showing symptoms such as: mosaic, yellowing, deformation, shoestring of leaves and fruit deformation and yield reduction. Distribution of CMV, ZYMV and WMV were determined by DAS-ELISA. Thepercentage of ZYMV, WMV and CMV were 35.6, 26.1 and 25.1% respectively. Triple infection (CMV+ZYMV+WMV) were found in 6.4% of samples. ZYMV were found the most frequently the viruses. This is the first report of WMV on squash in Tehran province.     

Increase in Cucurbit Aphid–Borne Yellows Virus Concentration by Co–infection with Sap–transmissible Viruses does not Increase its Aphid Transmissibility

The cucurbit aphid–borne yellows virus (CABYV) is a new tentative member of the luteovirus group which is transmitted persistently by Myzus persicae and Aphis gossypii.
In muskmelon plants, mixed infection with CABYV and zucchini yellow mosaic virus (ZYMV) induced an increase in CABYV concentration estimated by double antibody sandwich–enzyme linked immunosorbent assay (DAS–ELISA), which was maximum after 3 weeks, of co–infection.
Assays, conducted with other cucurbit hosts and sap–transmissible viruses showed that a similar increase occurred with most of the potyviruses tested. However, cucumber mosaic virus (CMV) and squash mosaic virus (SqMV) were inefficient for less efficient than potyviruses) in increasing CABYV concentration.
Aphid transmission experiments were conducted to check whether increased virus multiplication could either enhance transmission rates or modify the mode of CABYV acquisition by aphids. However, when A. gossypii was used, no increases in CABYV, transmissibility nor in its acquisition mode were detected.     

Comparative Epidemiology of Three Virus Diseases on Zucchini Squash

Zucchini yellow mosaic virus (ZYMV), Papaya ringspot virus – type W (PRSV‐W) and Zucchini lethal chlorosis virus (ZLCV) cause important diseases on zucchini squash crops in Brazil. ZYMV and PRSV‐W belong to the genus Potyvirus and are transmitted by aphids, whereas ZLCV belongs to Tospovirus and is transmitted by the thrips Frankliniella zucchini. These three viruses may occur simultaneously in the field, and the epidemiology of the corresponding diseases may be determined by interactions among viruses, hosts and vectors. In this work, the progress of the diseases caused by these viruses was studied over a temporal and geographic range for three planting seasons (PS). For the lethal chlorosis (ZLCV), a monomolecular model was found to be the best fit for the data, though only during the third PS. For data collected during the first two PS, the Gompertz model was found to fit the data best. The spatial distribution of disease indicated disease aggregation at the end of the crop cycle. For the yellow mosaic (ZYMV), the model that best fit in the 1st PS was the logistic and in the 2nd and 3rd PS was monomolecular. The spatial pattern of the disease was random when the disease incidence was low but aggregated when the disease incidence was high. The common mosaic (PRSV‐W) showed the lowest incidence in all three PS. An exponential model was the best fit for data collected during all PS, and the spatial pattern of the disease was random. Interactions among the three viruses apparently did not result in changes in the epidemiology of the diseases. Removal of sources of inoculum and planting at an unfavourable time for reproduction of virus vectors are the two main measures recommended for the control of these diseases. The use of insecticide is indicated only for the control of the F. zucchini.     

Epidemiology of an aphid nontransmissible potyvirus in fields of nontransgenic and coat protein transgenic squash

Spread of the aphid nontransmissible Zucchini yellow mosaicvirus virus (ZYMV) strain MV was monitored over two consecutive years in field plots of nontransgenic and transgenic squash expressing the coat protein (CP) gene of the aphid transmissible strain FL of Watermelon mosaic virus (WMV). The experimental approach was to mechanically inoculate plants with ZYMV strain MV and to assess subsequent transmissions, assumed to be vectored by aphids, of this strain to nonmechanically inoculated plants. Strain MV was distinguished from other ZYMV isolates by a threonine at position 10 of the CP or by a distinct electrophoretic pattern of a Nla IV-digested genomic cDNA fragment generated by RT-PCR. ZYMV strain MV was not detected in fields of nontransgenic plants, but was apparently aphid transmitted to 77 of 3,700 plants (2%) in transgenic fields. Despite the availability of numerous test plants and conditions of high disease pressure but low selection pressure, an epidemic of ZYMV strain MV did not develop in fields of transgenic plants. In contrast, the aphid transmissible ZYMV strain NY was aphid-transmitted to 99% (446/450) of transgenic plants under similar conditions. The relevance of these results in assessing environmental risks of transgenic plants expressing CP transgenes is discussed.     

Inheritance of resistance to watermelon mosaic virus in the cucumber line TMG-1: tissue-specific expression and relationship to zucchini yellow mosaic virus resistance

The inbred cucumber (Cucumis sativus L.) line TMG-1 is resistant to three potyviruses:zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), and the watermelon strain of papaya ringspot virus (PRSV-W). The genetics of resistance to WMV and the relationship of WMV resistance to ZYMV resistance were examined. TMG-1 was crossed with WI-2757, a susceptible inbred line. F₁, F₂ and backcross progeny populations were screened for resistance to WMV and/or ZYMV. Two independently assorting factors conferred resistance to WMV. One resistance was conferred by a single recessive gene from TMG-1 (wmv-2). The second resistance was conferred by an epistatic interaction between a second recessive gene from TMG-1 (wmv-3) and either a dominant gene from WI-2757 (Wmv-4) or a third recessive gene from TMG-1 (wmv-4) located 20–30 cM from wmv-3. The two resistances exhibited tissue-specific expression. Resistance conferred by wmv-2 was expressed in the cotyledons and throughout the plant. Resistance conferred by wmv-3 + Wmv-4 (or wmv-4) was expressed only in true leaves. The gene conferring resistance to ZYMV appeared to be the same as, or tightly linked to one of the WMV resistance genes, wmv-3.     

Endophytic colonisation of squash by the fungal entomopathogen Beauveria bassiana (Ascomycota: Hypocreales) for managing Zucchini yellow mosaic virus in cucurbits

We investigated the potential of endophytic Beauveria bassiana to provide protection against Zucchini yellow mosaic virus (ZYMV), one of the most economically important viral diseases in cucurbits. Four selected B. bassiana strains were able to successfully colonise squash plants following foliar inoculation with the conidial suspension of each respective strain. However, no significant difference in percentage colonisation was observed among the tested B. bassiana strains. Disease incidence (percentage of plants showing ZYMV symptoms) and severity (rating based on a 5-point scale), sampled weekly for four weeks following the challenge inoculation of plants with ZYMV, were significantly lower in B. bassiana-inoculated plants as compared to control plants, regardless of the inoculated strain. This is, to our knowledge, the first report on the potential of endophytic B. bassiana to confer protection against plant viruses. Further studies should be conducted to determine whether such endophytic B. bassiana-mediated protection against ZYMV in squash extends to other cucurbits.     

Serological diagnosis and host range studies of important viral diseases of a few cucurbitaceous crops in Maharashtra,India

Around 39 well characterised viruses affect cucurbits crops in developing countries and their viral diversity may be the consequence for genetic and ecological diversity of their hosts. Indeed, cucurbits are grown in variety of climatic, environmental and agricultural conditions, and this may provide more or less favourable conditions for the specific viruses or their hosts. The presence of various viral diseases caused by different viruses in Maharashtra was studied from the infected samples collected from cucurbits and melons during the survey conducted in 2009–2010 in different locations. The virus isolates collected from various cucurbitaceous crops were established and their host ranges were studied by sap transmission. The study revealed Cucumber Mosaic Virus (CMV), Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV) and Cucumber green mottle mosaic virus infections predominately found in Nashik region, and Watermelon bud necrosis virus (WBNV), CMV, ZYMV, WMV and Watermelon silver mottle virus (WSMoV) infections in Aurangabad and Paithan regions. In Sangamner region, the crop was mostly affected by WBNV, ZYMV and WSMoV, and CMV was found only in Sillod region. The protocols for performing sap transmission tests in assay hosts were standardised for ZYMV, CMV and WBNV. Using direct antigen-coating enzyme-linked immunosorbent assay, of all the plant parts, young leaves were found to have high concentration of virus and suitable for virus detection in screening programmes. CMV and ZYMV was found to have high concentration of virus and suitable for virus detection in screening programmes.     

Comparative spatial spread overtime of Zucchini Yellow Mosaic Virus (ZYMV) and Watermelon Mosaic Virus (WMV) in fields of transgenic squash expressing the coat protein genes of ZYMV and WMV, and in fields of nontransgenic squash

The spatial and temporal patterns of aphid-vectored spread of Zucchini Yellow Mosaic Virus (ZYMV) and Watermelon Mosaic Virus (WMV) were monitored over two consecutive years in plantings of nontransgenic and transgenic squash ZW-20H (commercial cv. Freedom II) and ZW-20B, both expressing the coat protein genes of ZYMV and WMV. All test plants were surrounded by nontransgenic plants that were mechanically inoculated with ZYMV or WMV, and served as primary virus source. Across all trials, none of the transgenic plants exhibited systemic symptoms upon infection by ZYMV and WMV but a few of them developed localized chlorotic dots and/or blotches, and had low mixed infection rates [4% (6 of 139) of ZW-20H and 9% (13 of 139) of ZW-20B], as shown by ELISA. Geostatistical analysis of ELISA positive transgenic plants indicated, (i) a lack of spatial relationship on spread of ZYMV and WMV for ZW-20H with flat omnidirectional experimental semivariograms that fitted poorly theoretical models, and (ii) some extent of spatial dependence on ZYMV spread for ZW-20B with a well structured experimental semivariogram that fitted poorly theoretical models during the first but not the second growing season. In contrast, a strong spatial dependence on spread of ZYMV and WMV was found for nontransgenic plants, which developed severe systemic symptoms, had prevalent mixed infection rates (62%, 86 of 139), and well-defined omnidirectional experimental semivariograms that fitted a spherical model. Geostatistical data were sustained by virus transmission experiments with Myzus persicae in screenhouses, showing that commercial transgenic squash ZW-20H alter the dynamics of ZYMV and WMV epidemics by preventing secondary plant-to-plant spread.     

Inheritance analysis and identification of SNP markers associated with ZYMV resistance in <Emphasis Type="Italic">Cucurbita pepo</Emphasis>

Cucurbit crops are economically important worldwide. One of the most serious threats to cucurbit production is Zucchini yellow mosaic virus (ZYMV). Several resistant accessions were identified in Cucurbita moschata and their resistance was introgressed into Cucurbita pepo. However, the mode of inheritance of ZYMV resistance in C. pepo presents a great challenge to attempts at introgressing resistance into elite germplasm. The main goal of this work was to analyze the inheritance of ZYMV resistance and to identify markers associated with genes conferring resistance. An Illumina GoldenGate assay allowed us to assess polymorphism among nine squash genotypes and to discover six polymorphic single-nucleotide polymorphisms (SNPs) between two near-isogenic lines, “True French” (susceptible to ZYMV) and Accession 381e (resistant to ZYMV). Two F₂ and three BC₁ populations obtained from crossing the ZYMV-resistant Accession 381e with two susceptible ones, the zucchini True French and the cocozelle “San Pasquale,” were assayed for ZYMV resistance. Molecular analysis revealed an approximately 90% association between SNP1 and resistance, which was confirmed using High Resolution Melt (HRM) and a CAPS marker. Co-segregation up to 72% in populations segregating for resistance was observed for two other SNP markers that could be potentially linked to genes involved in resistance expression. A functional prediction of proteins involved in the resistance response was performed on genome scaffolds containing the three SNPs of interest. Indeed, 16 full-length pathogen recognition genes (PRGs) were identified around the three SNP markers. In particular, we discovered that two nucleotide-binding site leucine-rich repeat (NBS-LRR) protein-encoding genes were located near the SNP1 marker. The investigation of ZYMV resistance in squash populations and the genomic analysis performed in this work could be useful for better directing the introgression of disease resistance into elite C. pepo germplasm.     

Characterization of sources of resistance to the watermelon strain of Papaya ringspot virus in cucumber: allelism and co-segregation with other potyvirus resistances

At least three sources of resistance to the watermelon strain of Papaya ringspot virus (PRSV-W) have been identified in cucumber (Cucumis sativus L.) including: ’TMG-1’, an inbred line derived from the Taiwanese cultivar, ’Taichung Mou Gua’; ’Dina-1’, an inbred line derived from the Dutch hybrid ’Dina’; and the South American cultivar ’Surinam’. In this investigation we sought to determine the inheritance of resistance to PRSV-W in ’Dina-1’, the allelic relationships among the three sources of PRSV-W resistance, and the relationship between PRSV-W resistance and known resistances to other cucurbit potyviruses. Like ’Surinam’ and ’TMG-1’, resistance in ’Dina-1’ is controlled by a single gene. Despite differences in dominance vs recessive performance and patterns of virus accumulation, all three sources of resistance complemented each other. ’TMG-1’ and ’Dina-1’ also possess co-segregating, single-gene resistances to Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus and Moroccan watermelon mosaic virus. Sequential inoculations and F₃ family analysis indicated that resistance to PRSV-W completely co- segregated with resistance to ZYMV in ’TMG-1’. Although PRSV-W resistances are at the same locus in both ’TMG-1’ and ’Surinam’, ’Surinam’ is only resistant to PRSV-W, and progeny of ’TMG-1’×’Surinam’ were resistant to PRSV-W but susceptible to ZYMV. Susceptibility to ZYMV and resistance to PRSV-W in ’Surinam’ was not influenced by co-inoculation or sequential in- oculations of the two viruses. Collectively, the co- segregation of resistances to PRSV-W, ZYMV, WMV and MWMV in ’TMG-1’ (within 1 cM), allelism of PRSV-W resistances in ’TMG-1’ and ’Surinam’, and resistance to only PRSV-W in ’Surinam’, suggest that multiple potyvirus resistance in cucumber may be due to different alleles of a single potyvirus resistance gene with differing viral specificities, or that the multiple resistances are conferred by a tightly linked cluster of resistance genes, of which ’Surinam’ only possesses one member. Received: 22 July 1999 / Accepted: 2 December 1999     

Multiple alleles for zucchini yellow mosaic virus resistance at the zym locus in cucumber

 Sources of resistance to several potyviruses have been identified and characterized within the cucumber (Cucumis sativus L.) germplasm. Resistance to zucchini yellow mosaic virus (ZYMV) is present in inbred lines derived from the Dutch hybrid Dina (Dina-1) and from the Chinese cultivar ‘Taichung Mou Gua’ (TMG-1). Tests of allelism indicated that the genes for resistance to ZYMV in TMG-1 and Dina-1 are at the same locus; however, the two genotypes exhibited different phenotypes in response to cotyledon inoculation with ZYMV. Dina-1 exhibited a distinct veinal chlorosis and accumulation of virus limited to the first and/or second true leaves, while TMG-1 remained symptom-free and did not accumulate virus. The distinct veinal chlorosis phenotype in Dina-1 was dominant to the symptom-free phenotype in TMG-1 and was shown not to be due to a separate gene. These results indicate that a series of alleles differing in effectiveness and dominance relationships occurs at the zym locus such that Zym>zym ^Dina>zym ^TMG-1. In addition to ZYMV resistance, TMG-1 is also resistant to watermelon mosaic virus (WMV), the watermelon strain of papaya ringspot virus (PRSV-W) and the Moroccan watermelon mosaic virus (MWMV); the WMV and MWMV resistances are at the same locus, or tightly linked to the zym locus. Dina-1 also was found to be resistant to PRSV-W and MWMV. The gene for MWMV resistance in Dina-1 appeared to be at the same locus or tightly linked (<1% recombination) to the gene for ZYMV resistance. In contrast to the response to ZYMV inoculation, Dina-1 does not exhibit distinct veinal chlorosis when inoculated with PRSV-W or MWMV. Collectively, these observations suggest that the gene(s) conferring resistance to ZYMV, WMV, and MWMV may be part of a gene cluster for potyvirus resistance in cucumber. Received: 12 November 1996 / Accepted: 25 April 1997     

The incidence and distribution of viruses infecting lettuce, cultivated Brassica and associated natural vegetation in Spain

A virus survey was conducted during the spring and autumn of 2001 and 2002 to determine the presence, prevalence and distribution in Spain of the viruses that are most commonly found infecting lettuce and Brassica worldwide. Crop plants showing virus symptoms from the principal lettuce and Brassica-growing regions of Spain, and some samples of the annual and perennial flora nearby, were tested by enzyme-linked immunosorbent assays using specific commercial antibodies against the following viruses: Alfalfa mosaic virus (AMV), Broad bean wilt virus 1 (BBWV-1), Beet western yellows virus (BWYV), Cauliflower mosaic virus (CaMV), Cucumber mosaic virus (CMV), Lettuce mosaic virus (LMV), Pea seed-borne mosaic virus (PSbMV), Turnip mosaic virus (TuMV) and Tomato spotted wilt virus (TSWV). Samples were also tested with a Potyvirus genus antibody. Virus incidence was much lower in spring than in autumn, especially in 2001. In spring 2002, CMV and LMV were the most prevalent viruses in lettuce, while CaMV was the most important virus present in Brassica crops grown in Navarra, followed by CMV and BWYV. In the autumn, the spectrum of viruses was different; potyviruses were widespread in lettuce grown in Madrid, but TSWV and BWYV were predominant in the Murcia region. The prevalent Potyvirus detected in lettuce fields was LMV, but none of the samples collected were positive for PSbMV or TuMV. In Brassica crops, TSWV was the most abundant in autumn-sown crops, especially in the Navarra region. All of the viruses present in lettuce and Brassica were also frequently detected in their associated natural vegetation at the same time, suggesting that they probably play an important role as virus reservoirs. Sonchus spp. were particularly common and were frequently infected with CMV, LMV and BWYV. Another common species, Chenopodium album, was often infected with TSWV and BWYV. Multiple infections were common, especially in non-crop plants, and the most common combination was BWYV and TSWV. The role of weeds in the epidemiology of viruses that infect lettuce and Brassica crops in Spain is discussed.     

Aphids secrete watery saliva into plant tissues from the onset of stylet penetration

Aphid feeding requires the secretion of two types of saliva: gelling saliva (from the principal gland) that forms an intercellular sheath for the penetrating stylet, and watery saliva [from accessory salivary glands (ASGs)] that facilitates intracellular penetration and phloem feeding. Plant viruses can be used as salivary markers to investigate key steps in aphid feeding, and penetration can be monitored electrically using the electrical penetration graph (EPG) approach. We conducted a series of EPG‐controlled transmission experiments using Cucurbit aphid‐borne yellows virus [CABYV; Polerovirus spec. (Luteoviridae)], which is retained in the ASGs, as a marker for watery saliva secretions. The melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae), was used as a vector and melon seedlings, Cucumis melo L. (Cucurbitaceae), as host plants. Viruliferous aphids were interrupted at various stages during stylet penetration, i.e., during intercellular penetration prior to intracellular puncture and following a potential drop within the first probe. Viruliferous aphids and leaf disc samples obtained from the stylet penetration site were used to detect CABYV by quantitative real‐time RT‐PCR. Approximately half of the inoculated leaf discs were found to be infected with CABYV after very brief (12.9 ± 1.9 s) intercellular stylet probes and before intracellular stylet puncture. The number of virus particles ejected during such probes was similar to the number ejected by aphids during longer probes including a single intracellular puncture. Our results therefore suggest that watery saliva is secreted by aphids from the onset of stylet penetration.     

Occurrence,distribution and seasonal changes of viruses infecting common bean in northwestern Iran

Many surveys were conducted during 2003–2005 to study the identity, prevalence and fluctuation of bean infecting viruses in northwestern Iran. In total, 649 bean samples with virus- like symptoms were collected and analysed by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and tissue-print immunoassay to detect infectious viruses. Serological tests revealed the presence of Bean common mosaic virus (BCMV), Bean common mosaic necrosis virus (BCMNV), Bean yellow mosaic virus (BYMV), Cucumber mosaic virus (CMV), Alfalfa mosaic virus (AMV), Bean leaf roll virus (BLRV), Bean pod mottle virus (BPMV) and Southern bean mosaic virus (SBMV), with some co-infection occurred, with prevalence of BCMV, BCMNV and BYMV (17–29% infection rate). The incidence of viruses showed variation in over 3 years of research including more than double increase in CMV from 2004 to 2005 and obvious one-third decrease in AMV from 2003 to 2005. SBMV and BPMV were detected sporadically in the fields and the response of some differential test plants was analysed by mechanical inoculation. Western immunoblotting analysis of SBMV infected bean leaf total proteins using SBMV-specific polyclonal antibody revealed viral CP with molecular mass of 28.5 kDa which confirmed the presence of SBMV as a new threat for bean production.     

Distribution and impact of virus associated diseases of common bean (Phaseolus vulgaris L.) in northern Iran

Different viral diseases infect common bean crops in Iran. A total of 248 symptomatic samples were collected from common bean fields throughout main growing fields of Guilan province in Iran during the summer of 2006. Eight viruses were detected using double antibody-sandwich – enzyme-linked immunosorbent assay (DAS-ELISA). Bean common mosaic virus – BCMV (1%), Bean leaf roll virus – BLRV (9%), Cowpea mild mottle virus – CpMMV (6%), Southern bean mosaic virus – SBMV (3%), Cucumber mosaic virus – CMV (15%), Bean golden mosaic virus – BGMV (2%), Bean common mosaic necrosis virus – BCMNV (1%) and Bean yellow mosaic virus – BYMV (1%) were detected. Comparatively CMV (15%) was found to be more prevalent in Guilan province. Multiple infections of viruses were recorded in many samples. Weed species belonging to Chenopodiaceae, Solanaceae, Malvaceae and Amaranthaceae families were also found to be infected with the viruses.