Papaya Ringspot Virus Type W Research Articles

Cyclanthera pedata var. edulis: New Host of Papaya ringspot virus-type W in Brazil.

Stuffing cucumber (Cyclanthera pedata var. edulis Schrad.) is native to the Americas, where it often occurs as an escape. The species is monoecious, with small flowers and large and deeply palmately lobed leaves. Fruits are puffy, partially hollow, and measure 5 × 15 cm long. The plant has soft spines, a tapered neck, and black seeds. The species has long been cultivated in Asia, where fruits are eaten raw as a substitute for cucumber or cooked (1). One plant showing intense mosaic, without leaf malformation, was found near a squash crop (Cucurbita moschata) in Anhembi County, State of São Paulo. Electron microscopic examination of a negatively stained sap preparation from leaves of this plant showed that it contained numerous flexuous rod-shaped particles, approximately 700 × 760 nm long, similar to those of potyviruses. Extracts from symptomatic leaves were rub-inoculated to zucchini squash (Cucurbita pepo), Carica papaya, Chenopodium amaranticolor, C. quinoa, Gomphrena globosa, and Phaseolus vulgaris cv. Black Turtle 2. Only zucchini squash was infected and developed severe mosaic with intense leaf malformation. Extracts from field infected stuffing cucumber and experimentally inoculated zucchini squash were tested by plate-trapped antigen enzyme linked immunosorbent assay (PTA-ELISA) with antisera against the following potyviruses: Papaya ringspot virus-type W (PRSV-W), Zucchini yellow mosaic virus (ZYMV), and Watermelon mosaic virus-2 (WMV-2). Samples were also tested with antisera against a tospovirus (Zucchini lethal chlorosis virus) and a cucumovirus (Cucumber mosaic virus). Both samples were positive in PTA-ELISA only with PRSV-W antiserum. This is the first report of C. pedata var. edulis as a natural host for PRSV-W in Brazil.

Occurrence, Distribution, and Relative Incidence of Five Viruses Infecting Cucurbits in the State of São Paulo, Brazil.

Cucurbits species grown in 38 of 40 agricultural regions in the state of São Paulo, Brazil, were surveyed for the relative incidence of Cucumber mosaic virus (CMV), Papaya ringspot virus-type W (PRSV-W), Watermelon mosaic virus-2 (WMV-2), Zucchini lethal chlorosis virus(ZLCV), and Zucchini yellow mosaic virus (ZYMV) during May 1997 and June 1999. Samples from 621 plants, representing eight cultivated species, six wild species, and one commercial hybrid (Cucurbita moschata × C. maxima), were analyzed by plate trapped antigen enzyme-linked immunosorbent assay (PTA-ELISA). PRSV-W and ZYMV were the most frequently found viruses, accounting for 49.1 and 24.8%, respectively, of 605 samples tested. ZLCV, CMV, and WMV-2 were detected in 7.8, 6.0, and 4.5% of 612, 497, and 423 samples tested, respectively. Double infection was found in 97 samples, and triple infection was found in 10 samples. Quadruple infection was detected in one C. pepo sample. Plants that were symptomatic but negative by PTA-ELISA might be due to abiotic agents, infection by virus for which antiserum was not available, such as Squash mosaic virus, or infection with an as yet uncharacterized virus.

Efeitos da premunização da abóbora 'Menina Brasileira' com estirpes fracas do vírus-do-mosaico-do-mamoeiro - estirpe melancia

Neste trabalho avaliou-se o efeito da premunização com duas estirpes fracas do vírus-do-mosaico-do-mamoeiro - estirpe melancia ("papaya ringspot virus - type W", PRSV-W), combinada com a tolerância das plantas, no controle do mosaico e na produtividade da abóbora 'Menina Brasileira'. Testes realizados em casa de vegetação mostraram que as plantas dessa cultivar premunizadas com as estirpes fracas PRSV-W-1 e 2 ficaram totalmente protegidas contra a infecção por uma estirpe severa de Campinas. Em condições de campo avaliou-se comparativamente a produção de plantas premunizadas, infectadas com a estirpe severa de Campinas, e sadias e expostas à infecção natural (controle). A proteção foi medida com base na produção individual das plantas, cujos frutos foram classificados em comerciais e não-comerciais. As plantas premunizadas tiveram uma produção média de frutos comerciais (peso) 33% superior à daquelas naturalmente infectadas em campo. Quanto ao número de frutos comerciais, o aumento foi da ordem de 50%. A premunização combinada com a tolerância da abóbora 'Menina Brasileira' permitiu um melhor controle do mosaico, com ganhos na produção de frutos comerciais.

Cayaponia tibiricae: New Host of Zucchini Yellow Mosaic Virus in Brazil.

Cayaponia tibiricae Cogn. (CT) is a wild Cucurbitaceae species found in secondary forests in the State of São Paulo, Brazil. The species has indefinite growth and bears oblong dark green fruits, 15 to 20 mm long (1,2). CT plants showing yellow mosaic symptoms were found in Atibaia County. Extracts from symptomatic plants were rub inoculated to zucchini squash (Cucurbita pepo L.) and Chenopodium amaranticolor Coste & Reyn. Zucchini squash plants developed severe yellow mosaic with intense leaf malformation, while C. amaranticolor showed necrotic local lesions. Extracts from naturally infected CT, zucchini squash, and C. amaranticolor were tested by plate trapped antigen-enzyme-linked immunosorbent assay (PTA-ELISA) with antisera against papaya ringspot virus type W (PRSV-W), zucchini yellow mosaic virus (ZYMV), zucchini lethal chlorosis virus (ZLCV), watermelon mosaic virus 2 (WMV-2), and cucumber mosaic virus (CMV). All samples were positive in PTA-ELISA only with ZYMV antiserum. Also, in Western blot (immunoblot) assay, ZYMV antiserum labeled a protein of approximately 36 kDa. Electron microscopic examination of ultrathin sections from infected CT tissue revealed the presence of pinwheel inclusions typical of potyvirus (type 1) infection in the cytoplasm of the cell. CT seedlings were susceptible to mechanical inoculation with the ZYMV isolated from this species. This is the first report of CT as a natural host for ZYMV in Brazil.

Control of Papaya Ringspot Virus-Type W in Zucchini Squash by Cross-Protection in Brazil.

Two mild strains of papaya ringspot virus-type W (PRSV-W) were tested under greenhouse and field conditions to study the potential of cross-protection for control of zucchini squash mosaic. Protected plants of zucchini squash cultivars Caserta and Clarinda were challenged with three severe strains from different geographic regions of the country in tests carried out in the greenhouse. Challenge inoculations were done mechanically 10 and 20 days after the protective inoculation. The mild strains did not have a visible negative effect on the development of the plants and offered effective protection against the severe strains. Field tests of protected Caserta plants were carried out in Piracicaba County, São Paulo. Comparative evaluation based on the symptoms and development of protected and unprotected plants of zucchini squash showed that both mild strains effectively protected the plants against the effects of the severe strain present in the field. Yield of marketable fruits harvested from protected plants was only 10% less than that of the healthy plants in one field trial. Compared with the yield from plants infected with the severe strains, protected plants showed an increase of 511 and 633% in the number and weight of marketable fruits, respectively, in a test in 1994. In a second experiment in 1995, an increase of 327% in the number and 344% in the weight of marketable fruits was recorded. These studies demonstrate the effectiveness of cross-protection for the control of the mosaic disease caused by PRSV-W in zucchini squash and offer growers a method for large-scale application of this technology.

Use of Acetone to Facilitate Aphid Harvesting for Plant Virus Transmission Assays

Acetone as an aphid anesthetic was compared with mechanical removal of aphids from leaves to enhance the harvesting and handling of large populations of the aphid Myxus persicae. The effect of these two procedures on aphid virus transmission efficiency was assessed with a persistent and a nonpersistent virus using potato leafroll virus (PLRV) and papaya ringspot virus type W (PRSV-W), respectively. The use of acetone was 8-10 times faster and about 30% more efficient than the camel's-hair brush technique for harvesting M, persicae from leaves of turnip, Malva parviflora, and sweet pepper. Even small nymphs could be collected and handled easily, indicating an additional benefit of the acetone method

Serological and Biological Variability Among Papaya Ringspot Virus Type-W Isolates in Florida

Six distinct monoclonal antibodies (MAbs) were obtained to the viral structural protein of a Florida isolate of papaya ringspot virus type-W (PRSV-W). These MAbs were distinguished by their reactivity in indirect ELISA with 10 Florida isolates of PRSV-W, five additional isolates of PRSV-W, and with single isolates of the papaya strain of PRSV (PRSV-P) and a strain of PRSV from Guadeloupe (PRSV-T). MAb-1 and MAb-2 reacted with all 15 of the PRSV-W isolates and with PRSV-P. MAb-1 reacted with PRSV-T but MAb-2 did not (...)

Inheritance of resistance to papaya ringspot virus type W in hybrids between Cucurbita ecuadorensis and C. maxima

Papaya ringspot virus type W (PRV-W) causes foliar mosaic, deformed fruit and reduced yield in crops of Cucurbita maxima cv. Queensland Blue in Queensland. Cucurbita ecuadorensis is highly resistant to PRV-W. Using crosses between these 2 cucurbits we studied inheritance of resistance to PRV-W in mechanically inoculated parental, F1, F2, backcross and inbred backcross populations under glasshouse and/or field conditions. Disease severity was assessed on each plant as the proportion of the young leaf area which was chlorotic. Inheritance of resistance, following inoculation of cotyledons with either of 2 isolates that differed in the severity of symptoms produced, was most consistently described as polygenic. Analysis of means of generations indicated additive gene effects were predominant. However simpler inheritance could not be entirely discarded as a 13:3 digenic model based on epistasis and modifiers described some distributions. No strong associations existed between high resistance to PRV-W and undesirable characteristics so that transfer of high levels of resistance from C. ecuadorensis to commercially acceptable lines of C. maxima should be possible.

Dot-immunobinding assay for zucchini yellow mosaic virus using polyclonal and monoclonal antibodies.

The application of dot-immunobinding assay (DIA) for detecting zucchini yellow mosaic virus (ZYMV) was described. The virus showed the same binding activity to nitrocellulose membrane (NCM) in three kinds of coating buffers tested. Antigenicity of ZYMV in DIA could be maintained in leaf extract-dotted NCM which had been stored at -20C, 6C, or 20C at least for six months. The methods were developed for sending samples using infected leaves extract-dotted NCM in replace of fresh leaves and for simplifying the procedure for direct deposition of the samples onto NCM. Seven protocols of DIA tested proved to be applicable to discriminate between healthy and infected pumpkin, with limits of detection ranging from 10-3∼10-5 dilution of leaf extracts. Rabbit polyclonal antibody against ZYMV cross-reacted with watermelon mosaic virus 2 (WMV-2) in two-step direct-DIA and indirect-DIA but not in DAS-DIA. It did not also cross-react with papaya ringspot virus, type W (PRSV-W) in three DIA protocols. When the three DIA protocols were used with monoclonal antibody against ZYMV, the assays resulted in the same sensitivity as those obtained by using polyclonal antibody, and could also be used to discriminate ZYMV from PRSV-W and WMV-2.

Inhibition of mechanical transmission of virus by sap, and infection of Cucurbita ecuadorensis with papaya ringspot virus type W

Dilutions of Cucurbita ecuadorensis sap were mixed with dilutions of sap from C. maxima infected with papaya ringspot virus type W (PRV-W), and the mixtures mechanically inoculated to seedlings of C. pepo cv. Small Sugar or Cucumis sativus cv. Supermarket. Plants inoculated with C. maxima sap plus C. ecuadorensis sap (at 1/8 when C. pepo was the test plant, or 1/16 when C. sativus was the test plant) showed reduced infection compared with plants not receiving C. ecuadorensis sap. The reduction caused by C. ecuadorensis sap was greater at a lower virus concentration (1 g infected C. maxima/400 mL sodium-potassium phosphate buffer 0.1 mol/L) than at a higher virus concentration (1 g/25 mL). It was concluded that C. ecuadorensis sap contains an inhibitor of infection, that tissue derived from this species should be diluted at least 1 g/ 10 mL buffer before use in inoculations, and that C. pepo, which was 5 times more sensitive than C. sativus, should be used as the test seedling in reisolations. When C. ecuadorensis, C. maxima and the F1 (C. maxima x C. ecuadorensis) were inoculated on their cotyledons with a severe isolate of PRV-W, symptoms were expressed on at least 1 plant of each species and the F1, and the virus was reisolated in seedlings of C. pepo cv. Small Sugar from the uninoculated leaves of all plants. Severity of symptoms and the proportion of plants infected at reisolation were least for C. ecuadorensis, intermediate for the F1 and most for C. maxima. This is the first report of infection of C. ecuadorensis by PRV-W.