Zucchini yellow mosaic virus

Zucchini yellow mosaic potyvirus (ZYMV), first isolated in Italy in 1973, described in 1981, and then identified in all continents within a decade, is one of the most economically important viruses of cucurbit crops. It is efficiently aphid-transmitted in a nonpersistent manner and it is also seed-borne in zucchini squash, which could have contributed to its rapid spread worldwide. Biological variability has been observed among ZYMV isolates, concerning host range, symptomatology and aphid transmissibility. More recent studies also revealed a serological and molecular variability. The survival of ZYMV in areas where cucurbits are not grown throughout the year remains to be elucidated, because very few natural over-wintering hosts have been identified so far. Partial control of ZYMV can be achieved by limiting transmission of the virus to the crops by aphids, using adapted cultural practices. Cross-protection with a mild strain has been shown to be effective against most ZYMV isolates. Resistance genes found in cucurbit germplasms are currently being introduced into cultivars with good agronomical characteristics. Pathogen-derived resistance strategies using the expression of ZYMV genes in transgenic plants have also been developed and appear promising. Nevertheless, the high biological variability of ZYMV justifies a careful evaluation of the deployment of genetic control strategies in order to increase their durability.     

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.     

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。     

Importance of cucurbits in the epidemiology of Papaya ringspot virus type P

Papaya ringspot virus type P (PRSV‐P) systemically infects Carica papaya and species belonging to the family Cucurbitaceae. Attempts to recover PRSV‐P from naturally infected cucurbit plants grown near or among diseased papaya trees have shown conflicting results worldwide. This study aimed to evaluate the natural infection of cucurbit species grown among and near papaya trees infected with PRSV‐P in Brazil. Natural infection of cucurbits with PRSV‐P occurred in zucchini squash but not in watermelon and cucumber. However, several attempts to recover PRSV‐P from numerous Cucurbita pepo cv. Caserta (zucchini squash) plants grown 5–80 m from diseased papaya trees in the field failed. Mechanical inoculations of Cucurbita pepo cv. Caserta, Cucurbita maxima cv. Exposição (pumpkin), Cucumis sativus cv. Primepack Plus (cucumber) and Citrullus lanatus cv. Crimson Sweet (watermelon) with five Brazilian PRSV‐P isolates showed that zucchini squash was the most susceptible species followed by watermelon and cucumber, while pumpkin was not infected. The results confirmed the variable susceptibility of cucurbit species to experimental and natural PRSV‐P infection. Given these facts, the control of the disease through roguing should focus mainly on diseased papaya plants, as has been practised successfully in Brazil for many years, and on those cucurbits particularly known to be susceptible to natural infection with PRSV‐P.     

Penetration and reproduction of root-knot nematodes on cucurbit species

Cucurbits are often cultivated in rotation with Solanaceae in double-cropping systems. Most cucurbits have been described as susceptible to root-knot nematodes (RKN) but little is known on their relative levels of susceptibility. Because RKN species differ in rates of root invasion and reproductive traits, isolates of M. arenaria, M. incognita and M. javanica were compared on five cucurbit hosts in experiments run in a climate growth chamber. They included zucchini squash cv Amalthee, cucumber cv Dasher II, melon cv Pistolero, pumpkin cv Totanera and watermelon cv Sugar Baby. All cucurbits were susceptible to the three RKN isolates although M. javanica showed higher invasion rates, faster development and higher egg production than M. arenaria on the selected cucurbits. Apparent differences among cucurbits were primarily due to root invasion rates and formation of egg masses. Both Cucumis species (cucumber and melon) were better hosts for nematode invasion and reproduction than zucchini squash, followed by watermelon. Large invasion rates followed by small reproduction traits were linked to M. incognita on zucchini squash. Reduced invasion rates and egg mass formation along with delayed early development were shown on watermelon.     

小西葫芦黄花叶病毒北京分离物的鉴定及其基因组3''端特性分析

在北京东郊自然感病的南瓜Cucurbita moschata上获得一病毒分离物（BJ-1），经生物学、血清学和分子生物学鉴定，确定为小西葫芦黄花叶病毒（Zucchini yellow mosaic virus，ZYMV）。为分析其基因组3’端特性，以发病叶片中提取的总RNA为模板，对基因组3’端进行RT-PCR扩增，产物克隆到pMD18-T栽体上进行序列分析，共测定了该病毒分离物包括全部CP基因在内的1269bp。该分离物CP基因由837个核苷酸组成，编码279个氨基酸。对包括该分离物在内的30个序列的760bp（含NIb基因3’端56bp和CP基因中的704bp）片段、NIb蛋白与CP蛋白的切割位点、蚜传必需基序的变异、寄主来源及地域来源进行了分析。结果表明，ZYMV不同分离物的基因分型与上述五个因素无明显关系。     

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.     

Biological characterization of Tomato leaf curl New Delhi virus from Spain

Tomato leaf curl New Delhi virus (ToLCNDV; family Geminiviridae, genus Begomovirus) is an emerging virus in horticulture crops in Asia, and has recently been introduced in Spain, Tunisia and Italy. No betasatellite DNA was detected in infected tomato and zucchini squash samples from Spain, and agroinoculated viral DNA‐A and DNA‐B were sufficient to reproduce symptoms in plants of both crop species. Infected tomato and zucchini squash plants also served as inoculum sources for efficient transmission either mechanically or using Bemisia tabaci whiteflies. Cucumber, melon, watermelon, zucchini squash, tomato, eggplant and pepper, but not common bean, were readily infected using viruliferous whiteflies and expressed symptoms 8–15 days post‐inoculation. New full‐length sequences from zucchini squash and tomato indicated a high genetic homogeneity (>99% sequence identity) in the ToLCNDV populations in Spain, pointing to a single recent introduction event.     

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.     

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     

Characterization of Synergy Between Cucumber mosaic virus and Potyviruses in Cucurbit Hosts

ABSTRACT Mixed infections of cucurbits by Cucumber mosaic virus (CMV) and potyviruses exhibit a synergistic interaction. Zucchini squash and melon plants coinfected by the potyvirus Zucchini yellow mosaic virus (ZYMV) and either Fny-CMV (subgroup IA) or LS-CMV (subgroup II) displayed strong synergistic pathological responses, eventually progressing to vascular wilt and plant death. Accumulation of Fny- or LS-CMV RNAs in a mixed infection with ZYMV in zucchini squash was slightly higher than infection with CMV strains alone. There was an increase in CMV (+) strand RNA levels, but no increase in CMV (-) RNA3 levels during mixed infection with ZYMV. Moreover, only the level of capsid protein from LS-CMV increased in mixed infection. ZYMV accumulated to similar levels in singly and mixed infected zucchini squash and melon plants. Coinfection of squash with the potyvirus Watermelon mosaic virus (WMV) and CMV strains increased both the Fny-CMV RNA levels and the LS-CMV RNA levels. However, CMV (-) strand RNA3 levels were increased little or not at all for CMV on coinfection with WMV. Infection of CMV strains (LS and Fny) containing satellite RNAs (WL47-sat RNA and B5*-sat RNA) reduced the accumulation of the helper virus RNA, except when B5*-sat RNA was mixed with LS- CMV. However, mixed infection containing ZYMV and the CMV strains with satellites reversed the suppression effect of satellite RNAs on helper virus accumulation and increased satellite RNA accumulation. The synergistic interaction between CMV and potyviruses in cucurbits exhibited different features from that documented in tobacco, indicating there are differences in the mechanisms of potyvirus synergistic phenomena.     

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。     

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.     

Diversity of Plum pox virus isolates in Bosnia and Herzegovina

Sixteen Plum pox virus (PPV) isolates from several stone fruit cultivars, host species, orchards and geographical areas of Bosnia and Herzegovina were selected for typing, using serotype-specific monoclonal antibodies (MAbs) and PCR–RFLP, targeting the 3' terminal region of the coat protein (CP) and P3-6K₁ with restriction enzymes Rsa I and Dde I. Four PPV isolates were identified as PPV-M by serology and PCR; eight isolates were identified as PPV-D based on PCR–RFLP on both genomic regions, but were not recognized by the D-specific MAb4DG5. Four isolates from plum were identified as natural D/M recombinants (PPV-Rec), based on conflicting results of CP and P3-6K₁ typing. To investigate the genetic diversity of Bosnian PPV isolates in more detail, five isolates (three PPV-Rec, one PPV-M and one PPV-D) were partially sequenced in the region spanning the 3' terminal part of the NIb gene and the 5'-terminal part of the CP gene, corresponding to nucleotides 8056–8884. Nucleotide sequence alignment of recombinant isolates showed that they were closely related at the molecular level to previously characterized recombinants from other European countries, and shared the same recombination break point in the 3' terminal part of the NIb gene. This is the first report of naturally infected Prunus trees with PPV-M, PPV-D and PPV-Rec in Bosnia and Herzegovina. The high variability of the Bosnian PPV isolates fits with the presence of this virus in the country over a long period.     

Differences in virulence of <Emphasis Type="Italic">Phytophthora capsici</Emphasis> isolates from a worldwide collection on host fruits

Phytophthora capsici causes root, crown, and fruit rot of vegetable and tropical hosts. Cucumber, zucchini, tomato, and pepper fruits were inoculated using 6-mm-diameter agar plugs of P. capsici, incubated in clear plastic boxes at room temperature (25 ± 2°C and 100% relative humidity), and virulence was estimated by measuring the lesion diameter, pathogen growth diameter, and pathogen sporulation density three (cucumber, zucchini) or four (tomato, pepper) days later. When isolates were grouped by genetic cluster, significant differences in virulence were observed on cucumber and zucchini, with isolates belonging to genetic cluster five causing larger lesions than isolates from genetic cluster six. On tomato, no significant differences were observed for isolates grouped by genetic cluster, but isolates from vegetable crops were generally more virulent than isolates from tropical hosts. Isolates from fabaceous hosts sporulated better on cucumber fruits than isolates from solanaceous hosts. Isolates from vegetable hosts sporulated better on zucchini than isolates from tropical hosts. No significant differences in lesion diameter were noted on pepper when isolates were grouped by host family of origin or genetic cluster, but differences in pathogen sporulation were apparent by host family. Our findings suggest that isolate characteristics such as host family of origin and genetic cluster membership may be used to guide initial isolate selection for cucurbit fruit resistance screening. Final isolate selection should incorporate the phenotypic and genetic diversity of P. capsici, including isolates with differing virulence to the host organ of interest.     

Comparison of the nucleotide and amino acid sequences of parental and attenuated isolates of Zucchini yellow mosaic virus

To identify possible sites of viral attenuation, the complete nucleotide sequences of two isolates of Zucchini yellow mosaic virus (ZYMV) were determined; a severe isolate Z5-1 and an attenuated isolate from Z5-1 (designated ZYMV-2002). The viral genome of both isolates consisted of 9593 nucleotides in size and contained an open reading frame encoding a single polyprotein of 3080 amino acids. Comparison of the nucleotide sequences for Z5-1 and ZYMV-2002 revealed 14 nucleotide mutations, resulting in seven amino acid substitutions with four in the HC-Pro region, two in the CI region, and one in the NIb region. These results provide a genetic basis for future manipulation of the ZYMV reverse genetics system. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB188115 and AB188116     

Purification, serology and properties of five zucchini yellow mosaic virus isolates

Five zucchini yellow mosaic virus (ZYMV) isolates designated ZYMV-1, -3, -5, -7 and -FL were purified from zucchini plants grown under the same environmental conditions. Isolates were divided into three groups on the basis of yield of purified virus: group one (ZYM V-5 and -7) yielded 18-24 mg/100 g tissue, group two (ZYMV-3) 5.0-5.7 mg/100 g tissue, and group three (ZYMV-1 and -FL) low yields of 0-5-1-5 mg/100 g tissue. The yield of purified virus was positively correlated with the number of local lesions produced by inoculation of Chenopodium amaranticolor with extracts from infected zucchini leaf tissue. No serological differences were exhibited among the isolates in SDS-immunodiffusion tests. Results of ELISA tests indicated that ZYMV-FL differed from the other isolates and that antiserum to ZYMV-7 absorbed with ZYMV-FL failed to react with ZYMV-FL but retained some serological activity to ZYMV-7 and the other three Taiwanese isolates. The relative molecular masses of capsid proteins for the four ZYMV isolates from Taiwan and ZYMV-FL were similar.