Molecular,biological and serological variability of Zucchini yellow mosaic virus in Tunisia

A study was conducted to better understand the population structure of Zucchini yellow mosaic virus (ZYMV), a severe virus affecting cucurbit crops worldwide, in Tunisia and to estimate whether the use of resistant cultivars may provide durable control. Analysis of the polymerase and coat protein (NIb‐CP) partial sequences of 83 isolates collected in the three main cucurbit‐growing areas in Tunisia showed that ZYMV grouped into two distinct clusters within ZYMV molecular group A. An important variability was observed in the MREK motif of the P3 protein, a motif associated with tolerance breaking in ZYMV‐tolerant zucchini squash cultivars. Interestingly, significant differences were found in the distribution of the MREK variants in the two clusters defined by the partial NIb‐CP sequences, MREK and MKEK sequences being more common in cluster 1 and cluster 2, respectively. When combining NIb‐CP and P3 sequence information, ZYMV molecular variability was shown to be significantly higher in the Cap Bon region than in the Bizerte area. An important biological variability was observed in a subset of 23 isolates regarding symptomatology in susceptible or resistant cucurbits. Some isolates overcame ZYMV tolerance or resistance in zucchini squash and melon, but not in cucumber. Three serotypes were differentiated using a set of 13 monoclonal antibodies (MAbs). Seven parameters characterizing the 23 isolates, including molecular, serological and biological properties, were used for a multiple component analysis (MCA). This analysis revealed that symptom intensity of a given isolate was similar in different susceptible cucurbit hosts, suggesting similar degrees of aggressiveness in different hosts.     

Biological characteristics and nucleotide sequences of three Korean isolates of Zucchini yellow mosaic virus

Zucchini yellow mosaic virus (ZYMV) is one of the most economically important viruses of cucurbit crops, causing severe mosaic, necrosis, and malformation. Three ZYMV isolates were obtained from pumpkins at Andong (ZYMV-PA), Euiryung (ZYMV-PE), and Suwon (ZYMV-PS), and their biological variability was determined on different hosts, including cucurbit crops as well as other indicator plants. ZYMV-PA caused the most severe symptoms, including severe mosaic, size reduction, and deformation, in oriental melon (Cucumis melo) and cucumber (Cucumis sativus) leaves. In contrast, ZYMV-PE and ZYMV-PS caused mild mosaic symptoms on oriental melon and cucumber. The nucleotide sequences of the genomic RNAs were determined and compared to the sequences of other potyviruses, including ZYMV isolates Reunion Island and TW-TN3. Each ZYMV Isolate had a genome of 9593 nucleotides, excluding the poly(A) tail, and contained 139 and 214 nucleotides in the 5- and 3-untranslated regions, respectively. Each had one large open reading frame encoding a protein of about 351kDa. The nucleotide sequences of ZYMV-PA, ZYMV-PE, and ZYMV-PS were more than 96.0% and the deduced amino acid sequences were more than 98.1% identical. When compared with other ZYMV isolates in a phylogenetic analysis, these three viruses formed a distinct virus clade and were more distantly related to other potyviruses (43.5%–62.8% identity).The nucleotide sequence data reported are available in the GenBank database under the accession numbers AY278998 to AY279000 for ZYMV-PA, ZYMV-PE and ZYMV-PS     

甘肃省南瓜及西葫芦小西葫芦黄花叶病毒病鉴定

利用双抗夹心酶联免疫吸附测定(DAS-ELISA)的方法对甘肃出入境南瓜、西葫芦种子及采自河西地区显症病株叶片进行检测,在种子及病叶组织中均检测到ZYMV病毒,其中南瓜种子带毒批次占12.5%,西葫芦种子带毒批次占11.8%。根据已报道的小西葫芦黄花叶病毒(Zucchini yellow mosaic virus)基因组核苷酸序列,设计引物扩增其外壳蛋白(CP)基因,以ELISA阳性种子或病叶组织总RNA为模板,进行RT-PCR扩增,对预期大小的扩增产物进行测序,结果表明扩增获得的核苷酸序列与世界各地的ZYMV分离物CP基因具有高度一致性,综合ELISA检测和RT-PCR的结果,确定南瓜、西葫芦种子可携带ZYMV,且ZYMV是侵染甘肃瓜类作物的重要病毒种类。     

Characterization of Hungarian isolates of zucchini yellow mosaic virus (ZYMV,potyvirus) transmitted by seeds of Cucurbita pepo var Styriaca

Zucchini yellow mosaic virus (ZYMV) has emerged as an important pathogen of cucurbits within the last few years in Hungary. The Hungarian isolates show a high biological variability, have specific nucleotide and amino acid sequences in the N-terminal region of coat protein and form a distinct branch in the phylogenetic tree. The virus is spread very efficiently in the field by several aphid species in a non-persistent manner. It can be transmitted by seed in holl-less seeded oil pumpkin (Cucurbita pepo (L) var Styriaca), although at a very low rate. Three isolates from seed transmission assay experiments were chosen and their nucleotide sequences of coat proteins have been compared with the available CP sequences of ZYMV. According to the sequence analysis, the Hungarian isolates belong to the Central European branch in the phylogenetic tree and, together with the ZYMV isolates from Austria and Slovenia, share specific amino acids at positions 16, 17, 27 and 37 which are characteristic only to these isolates. The phylogenetic tree suggests the common origin of distantly distributed isolates which can be attributed to widespread seed transmission.     

Increase in Zucchini yellow mosaic virus Symptom Severity in Tolerant Zucchini Cultivars Is Related to a Point Mutation in P3 Protein and Is Associated with a Loss of Relative Fitness on Susceptible Plants

ABSTRACT Zucchini yellow mosaic virus (ZYMV, Potyvirus) is a very damaging cucurbit virus worldwide. Interspecific crosses with resistant Cucurbita moschata have led to the release of "resistant" zucchini squash (C. pepo) F(1) hybrids. However, although the resistance is almost complete in C. moschata, the commercial C. pepo hybrids are only tolerant. ZYMV evolution toward increased aggressiveness on tolerant hybrids was observed in the field and was obtained experimentally. Sequence comparisons and recombination experiments revealed that a point mutation in the P3 protein of ZYMV was enough to induce tolerance breaking. Competition experiments were performed between quasi-isogenic wild-type, and aggressive variants of ZYMV distinguished by monoclonal antibodies. The aggressive mutants were more fit than wild-type strains in mixed infections of tolerant zucchini, but they presented a drastic fitness loss in mixed infections of susceptible zucchini or melon. Thus, the ability to induce severe symptoms in tolerant zucchini is related to a genetic load in susceptible zucchini, but also on other susceptible hosts. This represents the first quantitative study of the fitness cost associated with tolerance breaking for a plant virus. Thus, although easily broken, the tolerance might prove durable in some conditions if the aggressive variants are counterselected in susceptible crops.     

Barriers to gene flow between emerging populations of Watermelon mosaic virus in Southeastern France

Since 1999, "emerging" (EM) strains of Watermelon mosaic virus (WMV) have been detected in cucurbit crops of southeastern France, probably as a result of recent introductions. Population genetic approaches were used to study the structure of EM isolates in southeastern France and to identify factors involved in their spatial distribution. A population clustering method (SAMOVA) and a maximum-difference algorithm (Monmonier's algorithm) were combined to visualize and quantify barriers to gene flow between populations. Both methods yielded similar results and two main barriers were identified. A North/South oriented barrier may be related to physical obstacles to gene flow (Rh?ne River, presence of an area with few cucurbit crops). Although the barrier was very strong, some "crossing" events were detected. A second barrier, oriented Northwest to Southeast, was not correlated with obvious geographical features. The two methods used here are complementary and confirm the limited spread of WMV-EM isolates. This approach can be useful in epidemiology studies to characterize the structure of viral populations and identify barriers to gene flow.     

Characterization and occurrence of Zucchini Yellow Mosaic Virus in Sudan

Zucchini yellow mosaic potyvirus (ZYMV) was isolated in 1993 from a squash plant ( Cucurbita pepo cv. Eskandrani) showing severe leaf and fruit distortions, collected in the Gezira region (Sudan). This isolate (ZYMV-Su) was found to be very closely serologically related if not identical to the type strain from Italy. The host range was mostly limited to Cucurbitaceae but systemic infection was found to occur on sesame ( Sesamum indicum ), an important cultivated crop in Sudan. ZYMV-Su induced mosaic symptoms on the resistant melon accession PI 414723, indicating that it belongs to pathotype 2, but did not cause wilting of melon cv. Doublon. ZYMV-Su was efficiently transmitted by Myzus persicae and Aphis gossypii in a non-persistent manner. Surveys conducted from 1993 to 1995 revealed that ZYMV occurred in the major cucurbit growing areas in Sudan, in a diversity of crops and agroecosystems.     

Biological and molecular characterization of two Zucchini yellow mosaic virus isolates from Syria

Zucchini yellow mosaic virus (ZYMV) is the most prevalent virus in cucurbits in Syria. Two Syrian ZYMV isolates, SYZY-1 and SYZY-3, collected from a courgette field in 2006 were characterized using molecular and biological means for the first time. These isolates showed biological diversity with regard to their pathogenicity and symptoms. SYZY-1 was more aggressive in cucurbits, but could not induce any infection in Fabaceae. On the contrary, SYZY-3 could not infect cucumber and melon plants, induced milder symptoms in courgette and watermelon but induced local and occasional systemic infection in Fabaceae tested. Nonetheless, according to their molecular characteristics, SYZY-1 and SYZY-3 were closely related. The SYZY-1 CP nucleotide and amino acid sequences had similarity of 99.5% and 100% with those of SYZY-3, respectively. The high similarity of the CP nucleotide sequences of SYZY-1 and SYZY-3 with that of a ZYMV isolate from Germany suggests a common origin. Adaptation to different hosts might have caused the variable biological properties of these Syrian ZYMV isolates.     

Viruses of vegetable crops in Albania

Field surveys were carried out in the main vegetable-growing areas of Western and Central Albania to evaluate the sanitary status of open-field and protected cultivations of capsicum, tomato, potato, watermelon, cucumber, courgette, aubergine, lettuce, cabbage, chicory, leek and celery. The following viruses were detected: Alfalfa mosaic alfamovirus (AMV), Cucumber mosaic cucumovirus (CMV), Potato Y potyvirus (PVY), Tomato spotted wilt tospovirus (TSWV) and Watermelon mosaic potyvirus 2 (WMV-2). The virus found most frequently was CMV and all the isolates identified were of subgroup IA. AMV was also detected in several areas and all isolates were of subgroup II, suggesting a French origin. Finally, at the time of this survey, TSWV infections appeared to be moderately relevant and absent in protected crops. This is the first documented record of AMV, CMV, PVY, TSWV and WMV-2 in Albania. No infection by Tomato yellow leaf curl begomovirus (TYLCV) or Zucchini yellow mosaic potyvirus (ZYMV) was detected during this survey.     

United States Department of Agriculture-Agricultural Research Service research on pre-harvest prevention of mycotoxins and mycotoxigenic fungi in US crops

Mycotoxins (ie toxins produced by molds) are fungal metabolites that can contaminate foods and feeds and cause toxic effects in higher organisms that consume the contaminated commodities. Therefore, mycotoxin contamination of foods and feeds results is a serious food safety issue and affects the competitiveness of US agriculture in both domestic and export markets. This article highlights research accomplished by Agricultural Research Service (ARS) laboratories on control of pre-harvest toxin contamination by using biocontrol, host-plant resistance enhancement and integrated management systems. Emphasis is placed on the most economically relevant mycotoxins, namely aflatoxins produced by Aspergillus flavus, Link, trichothecenes produced by various Fusarium spp and fumonisins produced by F verticillioides. Significant inroads have been made in establishing various control strategies such as development of atoxigenic biocontrol fungi that can outcompete their closely related, toxigenic cousins in field environments, thus reducing levels of mycotoxins in the crops. Potential biochemical and genetic resistance markers have been identified in crops, particularly in corn, which are being utilized as selectable markers in breeding for resistance to aflatoxin contamination. Prototypes of genetically engineered crops have been developed which: (1) contain genes for resistance to the phytotoxic effects of certain trichothecenes, thereby helping reduce fungal virulence, or (2) contain genes encoding fungal growth inhibitors for reducing fungal infection. Gene clusters housing the genes governing formation of trichothecenes, fumonisins and aflatoxins have been elucidated and are being targeted in strategies to interrupt the biosynthesis of these mycotoxins. Ultimately, a combination of strategies using biocompetitive fungi and enhancement of host-plant resistance may be needed to adequately prevent mycotoxin contamination in the field. To achieve this, plants may be developed that resist fungal infection and/or reduce the toxic effects of the mycotoxins themselves, or interrupt mycotoxin biosynthesis. This research effort could potentially save affected agricultural industries hundreds of millions of dollars during years of serious mycotoxin outbreaks.     

小西葫芦黄花叶病毒山东南瓜分离物的分子特性

 Zucchini yellow mosaic virus (ZYMV) was detected by RT-PCR from pumpkin (Cucurbita moschata) plant showing yellowing and mosaic symptom from Liaocheng, Shandong Province. The 3'-termial 1 684 bp genomic sequence covered 633 bp of NIb encoding sequence, 840 bp of cp gene and 211 bp of 3'-untranslated region of the isolate ZYMV-Liaocheng was determined. The cp gene of ZYMV-Liaocheng shared identities of 81.4%-98.8% and 89.4%-99.5% at nucleotide and amino acid levels, respectively, with other ZYMV sequences available in the GenBank. Phylogenetic analysis indicated that ZYMV could be clustered to 6 genotypes. ZYMV-Liaocheng belonged to genotypeⅠ, which contained isolates from Asia, Europe and America. Genotypes Ⅲ and Ⅴ were unique and contained only isolates from East Asia. The isolates from East Asia had the highest variability.     

Cucurbit downy mildew (<Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis>)—biology,ecology, epidemiology,host-pathogen interaction and control

Cucurbit downy mildew, caused by the oomycete Pseudoperonospora cubensis, is a devastating, worldwide-distributed disease of cucurbit crops in the open field and under cover. This review provides recent data on the taxonomy, biology, ecology, host range, geographic distribution and epidemiology of P. cubensis. Special attention is given to host-pathogen interactions between P. cubensis and its economically-important cucurbit hosts (Cucumis sativus, C. melo, Cucurbita pepo, C. maxima, and Citrullus lanatus); pathogenic variability in P. cubensis at the species, genus, and population levels; and, differentiation of pathotypes and races. Genetics and variability of host resistance and cellular and molecular aspects of such resistance are considered. A focus is given to methods of crop protection, including prevention and agrotechnical aspects, breeding for resistance—classical and transgenic approaches, chemical control and fungicide resistance. Novel technologies in biological and integrated control are also discussed. This review also summarizes the most important topics for future research and international collaboration.     

Aphid-borne viruses infecting cultivated watermelon and squash in Spain: Characterization of a variant of cucurbit aphid-borne yellows virus (CABYV)

Aphid-borne viruses are responsible for major cucurbit diseases and hamper the sustainability of crop production. Systematic monitoring can reveal the occurrence and distribution of these viruses, in addition to unadvertised viruses, facilitating the control of diseases. For three consecutive (2018–2020) seasons, the presence of aphid-borne viruses was monitored from a total of 292 samples of watermelon and squash plants that showed yellowing symptoms in three major cucurbit-producing areas (Castilla La-Mancha, Alicante, and Murcia) in Spain. We observed that cucurbit aphid-borne yellows virus (CABYV) was the most common virus found (29%) in the plants from both crops. Likewise, except for squash samples from Castilla La-Mancha and Alicante, watermelon mosaic virus (WMV) was also found (23%) with a relatively high frequency. Furthermore, we observed the exacerbation of bright yellowing symptoms in watermelon plants that was often accompanied by considerable fruit abortion. CABYV was the only causative agent for this new yellowing disease, and two infectious cDNA clones (one from watermelon, CABYV-LP63, and another from melon, CABYV-MEC12.1) were constructed to further compare and characterize this CABYV disease. Based on the full-length genome, both isolates were grouped phylogenetically together within the Mediterranean clade. However, the Koch's postulates tests were only successfully completed for the LP63 isolate, which also showed several amino acid changes and two potential recombination events, as compared to MEC12.1. Remarkably, the LP63 isolate caused more severe symptoms and showed higher RNA accumulation than MEC12.1 in five cucurbit plant species. These results suggest that a novel CABYV variant that causes severe yellowing symptoms may be causing outbreaks in cucurbit crops.     

西葫芦环斑病病原鉴定及葫芦科作物对西瓜花叶病毒抗性筛选

 西瓜花叶病毒(watermelon mosaic virus,WMV)是危害我国葫芦科作物生产的重要病原。培育和种植抗病品种是防治病毒病最经济有效的措施。本研究利用RT-PCR和血清学方法在表现环斑症状的西葫芦果实上检测到WMV,未检测到番木瓜环斑病毒(papaya ringspot virus,PRSV)。接种WMV侵染性克隆到西葫芦品种绿源冬宝,果实表面产生环斑症状,表明WMV是引起西葫芦果实表面环斑症状的重要病原。利用间接ELISA方法对山东泰安的西瓜、黄瓜、甜瓜、西葫芦和南瓜等46个样品检测发现33个样品表现WMV血清学阳性(检出率71.74%),薛庄采集的带有环斑症状的西葫芦均检测到WMV。对山东省81份葫芦科作物种质资源抗WMV鉴定发现西葫芦品种万盛丰宝、盛丰金珠表现中抗(MR);西瓜品种绿宝新秀和浪潮一号表现中抗(MR);甜瓜品种黄皮面瓜表现抗病(R);黄瓜品种星君贝贝表现中抗(MR);南瓜品种爱维80南瓜表现高抗(HR),蜜本南瓜、传统蜜本南瓜、七叶早南瓜、玲珑二号和绿贝贝迷你南瓜等5个品种表现抗病(R);瓠瓜品种均表现为感病(S)。研究结果对合理布局葫芦科作物品种防控WMV具有重要意义。     

Biological control of pigweeds (Amaranthus retroflexus, L. A. Powellii, S. Watson and A. bouchonii Thell.) with phytophagous insects, fungal pathogens and crop management

Pigweeds (Amaranthus spp.) are of economic importance worldwide. In Europe, Amaranthus retroflexus is one of the ten weed species of greatest economic importance. It is a serious problem weed in several field crops (e.g. maize), as well as in vegetables, orchards and grape vines. It is an annual spreading by seeds which have a long viabilityand are dispersed principally by wind and water, but also by machinery. There is great variability in seed germination which renders control with post-emergence herbicides difficult. In addition, triazine herbicide-resistant populations occur in ten European countries. The aim of this subproject of COST action 816 is to investigate the possibilities of classical and inundative biological control of Amaranthus spp., to characterize potentialbiological control agents and to develop methods for their integration with current phytosanitary measures in the target crops. The project was initiated with an extended literaturesurvey followed by field surveys for insects and pathogens associated with Amaranthus spp. in several European countries. Promising isolates of fungal pathogens have been tested ondetached leaves and whole plants, and initial studies on the application of pathogens causing damping off in seedlings have been made. Further, the variability of different provenances ofAmaranthus spp. in response to fungal attack has been investigated     

Biological and Serological Characterization of Zucchini Yellow Mosaic and Watermelon Mosaic Virus-2 Isolates in Israel

Cucurbit potyviruses were collected in the field in Israel and subcultured in indicator plants in a greenhouse. Partial characterization of the Israeli cucurbit potyviruses was done on the basis of host reaction using cucurbits, peas andChenopodium spp. as hosts. Further classification of potyviruses was done by enzyme-linked immunosorbent assay (ELISA) and serological specific electron microscopy (SSEM). By these methods it was possible to identify three of the four isolates as strains of the zucchini yellow mosaic virus, while the fourth was identified as watermelon mosaic virus-2. Two of the ZYMV isolates were nonaphid-transmissible following prolonged mechanical transmission in a greenhouse. Both of these isolates were found to produce helper components capable of assisting the transmission of virions from a transmissible isolate but not those of their own.     

Resistance to ascochyta blights of cool season food legumes

Ascochyta blights are the most important diseases of cool season food legumes (peas, lentils, chickpeas, and faba beans) and are found in nearly all production regions. Despite having the same common disease name, the pathogen species differ for each of the crops. These diseases cause serious yield losses under favourable cool and humid conditions. Planting resistant cultivars is often the first choice and most economical means in managing the diseases. Therefore breeding for resistance to ascochyta blights has been an important objective of many cool season food legume research programmes. Systematic screening of germplasm collections at international research centres and other national research programmes have identified useful resistance sources that have been used successfully to breed resistant or tolerant cultivars. Genetic studies have revealed inheritance patterns of the resistance genes. Genetic linkage analyses and QTL mapping have identified molecular markers that could be useful for marker-assisted selection and gene pyramiding. In general, research towards developing resistance to ascochyta blights in cool season food legume faces mainly two limitations: the lack of availability of efficient resistance sources and the lack of a good understanding of the variability of the pathogen populations. Research efforts to alleviate these limitations should be pursued. Given that modern technologies of marker development and genomics are available, further advances in deploying resistance to manage ascochyta blights in this group of legume crops will depend on concerted efforts in developing accurate screening procedures with adequate knowledge of pathogen variability and identification of additional sources of resistance.