Aphid-borne Virus Research Articles

Comparative Susceptibility of Two Banana Cultivars to Banana Bunchy Top Virus Under Laboratory and Field Environments

Field and laboratory experiments were carried out on the island of Oahu, HI, to compare the susceptibility of the two most commonly grown banana (Musa sp.) cultivars in the state ('Dwarf Brazilian' or Santa Catarina [locally known as dwarf apple] and 'Williams') to the aphid-borne Banana bunchy top virus (genus Babuvirus, family Nanoviridae, BBTV). Several morphological and physiological features of the two cultivars were monitored to determine whether the banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), transmits BBTV to both cultivars at a similar rate; and whether after successful inoculation, does each cultivar respond similarly to viral infection. Results from the laboratory experiment showed that a similar percentage of both cultivars were infected with BBTV by aphid vectors (> 90% for both cultivars). However, field results showed a significantly lower percentage of dwarf apple (39%) infected with BBTV compared with Williams (79%). We also found that all physiological and morphological features measured (i.e., plant height, leaf area, canopy, chlorophyll level, and moisture content) for both cultivars were impacted similarly by BBTV. The incubation period, or the time between plant infection and initial appearance of disease symptoms, was similar for both cultivars. Results also showed that BBTV transmission efficiency was lower in the field than in the laboratory, despite that more aphids per plant were used for field than laboratory inoculation tests. The results highlight the potential use of less susceptible cultivars to help manage BBTV and the importance of screening banana varieties in the field to determine their response to vectors and associated diseases.

Epidemiology and integrated management of persistently transmitted aphid-borne viruses of legume and cereal crops in West Asia and North Africa

Cool-season food legumes (faba bean, lentil, chickpea and pea) and cereals (bread and durum wheat and barley) are the most important and widely cultivated crops in West Asia and North Africa (WANA), where they are the main source of carbohydrates and protein for the majority of the population. Persistently transmitted aphid-borne viruses pose a significant limitation to legume and cereal production worldwide. Surveys conducted in many countries in WANA during the last three decades established that the most important of these viruses are: Faba bean necrotic yellows virus (FBNYV: genus Nanovirus; family Nanoviridae), Bean leafroll virus (BLRV: genus Luteovirus; family Luteoviridae), Beet western yellows virus (BWYV: genus Polerovirus; family Luteoviridae), Soybean dwarf virus (SbDV: genus Luteovirus; family Luteoviridae) and Chickpea chlorotic stunt virus (CpCSV: genus Polerovirus; family Luteoviridae) which affect legume crops, and Barley yellow dwarf virus-PAV (BYDV-PAV: genus Luteovirus; family Luteoviridae), Barley yellow dwarf virus-MAV (BYDV-MAV: genus Luteovirus; family Luteoviridae) and Cereal yellow dwarf virus-RPV (CYDV-RPV: genus Polerovirus; family Luteoviridae) which affect cereal crops. Loss in yield caused by these viruses is usually high when infection occurs early in the growing season. Many aphid vector species for the above-mentioned viruses are reported to be prevalent in the WANA region. In addition, in this region many wild species (annual or perennial) were found infected with these viruses and may play an important role in their ecology and spread. Fast spread of these diseases was always associated with high aphid vector populations and activity. Although virus disease management can be achieved by combining several control measures, development of resistant genotypes is undoubtedly one of the most appropriate control methods. Over the last three decades barley and wheat genotypes resistant to BYDV, faba bean genotypes resistant to BLRV, and lentil genotypes resistant to BLRV, FBNYV and SbDV have been successfully identified. Moreover, progress has been made in disease management of some of these viruses using a combination of management options. Experience gathered over the last few decades clearly showed that no single method of virus disease control suffices to reduce yield losses in legume and cereal crops.

Reflective Plastic Mulch but not a Resistance-Inducing Treatment Reduced Watermelon Mosaic Virus Incidence and Yield Losses in Squash

Plant viruses, especially those transmitted by aphids in a nonpersistent manner, cause significant yield losses in cucurbit crops. Studies have shown that UV-reflective mulches can reduce insects from entering a crop with coincidental reductions in virus incidence. Treatment of plants with various forms of resistance-inducing agents have also shown promise for their ability to reduce plant virus incidence and associated losses. In this article, we describe a two-trial study that evaluated the integration of UV-reflective plastic mulch and a commercially available resistance-inducing treatment, BioYield™, to reduce the incidence and disease-related yield losses in summer squash [Cucurbita pepo var. melopepo (L.) Alef.] caused by the aphid-borne plant virus, Watermelon mosaic virus (WMV). In the spring trial, there was significantly reduced WMV incidence and whole treatment average enzyme-linked immunosorbent assay (ELISA) values among squash plants grown on silver-on-black (UV-reflective) mulch compared with plants grown on nonreflective black mulch. Significantly greater squash fruit yields were obtained for plants grown on the silver-on-black mulch relative to the black mulch treatment. In the fall trial, highly UV-reflective silver mulch was used in addition to silver-on-black and black mulches. WMV incidence and whole treatment average ELISA values were significantly lower for squash plants in the silver mulch treatment compared with silver-on-black and black mulch treatments. The silver-on-black treatment resulted in lower WMV incidence and whole treatment average ELISA values compared with the black mulch treatment. Squash plant yields were significantly greater for plants in the silver-on-black mulch treatment than for those in the silver or black mulch treatments. Treatment of squash plants with BioYield™ did not reduce virus incidence, or whole treatment average ELISA values, nor did it result in higher squash fruit yields compared with the nontreated control in spring or fall trials.

Certification scheme for strawberry

Certification scheme for strawberry

Inter-row Soil Cover to Reduce Incidence of Aphid-borne Viruses in Pumpkin

ABSTRACT Inter-row soil cover used in conjunction with vegetable crop production has the potential to reduce aphid-borne plant virus incidence while also reducing the need for pesticide applications and preserving inter-row soil structure. In this study, inter-row soil covers were compared with a conventional, bare soil treatment for their ability to reduce aphid-borne virus incidence and associated yield loss in pumpkin (Cucurbita pepo L. var. pepo). In 2006, inter-row soil cover crops included Sericea lespedeza [Lespedeza cuneata (Dumont de Courset)] G. Don], and sunn hemp (Crotalaria juncea L.). Sericea lespedeza was used in the 2007 trial, but naturally occurring weed species were used instead of sunn hemp. Watermelon mosaic virus (WMV) was detected in the 2006 trial and Papaya ringspot virus (PRSV) and WMV were detected in the 2007 trial. In 2006, no differences were observed for WMV incidence among treatments, although significantly more aphids were identified on pumpkin plants in the Sericea lespedeza treatment. Enzyme-linked immunosorbent assay absorbance values for WMV accumulation in pumpkin plants for whole treatment, and for samples shown to be infected, were significantly lower in the Sericea lespedeza treatment, indicating less virus accumulation in these samples. No differences were observed among treatments for marketable pumpkin fruit number or yield. In the 2007 trial, WMV incidence was significantly less in pumpkin plants in the weed treatment compared with Sericea lespedeza early in the season, but incidence did not differ among treatments later in the season. PRSV incidence did not differ among treatments early in the season but was significantly lower in pumpkin plants in the Sericea lespedeza treatment than the bare soil treatment later in the season. Significantly more aphids occurred on pumpkin plants in the weed treatment than in the Sericea lespedeza and bare soil treatments. Significantly more aphids occurred on pumpkin plants in the Sericea lespedeza treatment than the bare soil treatment. Marketable pumpkin fruit numbers and yield were significantly greater for the Sericea lespedeza treatment than the bare soil and weed treatments. These data indicate that pumpkin plants grown with an inter-row soil cover may have less aphid-borne virus despite greater numbers of aphids.

Ocorrência generalizada do Lettuce mottle virus em três regiões produtoras de alface comercial do Estado de São Paulo

Os sequivírus são vírus isométricos transmitidos por afídeos. Lettuce mottle virus (LeMoV), um provável sequivirus foi descrito no Brasil em 1982 e causa sintomas de mosaico semelhantes aos observados pelo Lettuce mosaic virus (LMV). Um levantamento para ocorrência do LeMoV nos campos de produção de alface de três diferentes regiões do Estado de São Paulo (Mogi das Cruzes, Campinas e Bauru) foi realizado durante 2002 a 2005. RNA total foi extraído e utilizado na detecção, em RT-PCR, com oligonucleotídeos específicos para o LeMoV. Do total de 1362 amostras, 137 (10,05%) foram positivas para o LeMoV. Infecção mista com o LMV foi verificada em 43 amostras (31,4%). Foi verificada a ocorrência do LeMoV nas três diferentes regiões analisadas, porém sua ocorrência foi baixa nas diferentes épocas do ano.

Characterization and Recent Advances in Detection of Strawberry Viruses.

Characterization and Recent Advances in Detection of Strawberry Viruses.

Mulches reduce aphid-borne viruses and whiteflies in cantaloupe

We compared reflective plastic and wheat straw mulches with conventional bare soil for managing aphid-borne virus diseases and silverleaf whitefly in cantaloupe. The occurrence of aphid-borne virus diseases was significantly reduced with both mulches as opposed to bare soil, and reflective plastic performed better than wheat straw. Silverleaf whitefly numbers, both adults and nymphs, were reduced equally by plastic mulch and wheat straw, and were significantly lower than with bare soil. Reflective plastic produced mature melons sooner and more cartons per acre than the other production systems. The reflective plastic system also produced a greater number of large-size melons, which are favored in the late-season market. Plants grown over straw mulch produced higher overall yields, including large-size melons, than those grown over bare soil.

Management of Aphid-Borne Viruses andBemisia argentifolii(Homoptera: Aleyrodidae) in Zucchini Squash by Using Uv Reflective Plastic and Wheat Straw Mulches

Plastic UV resective mulch (metalized mulch) and wheat straw mulch delayed colo- nization by Bemisia argentifolii Bellows & Perring and the incidence of aphid-borne viruses in zucchini squash. No insecticides were used in either mulch treatment. The mulches were compared with a preplant treatment of imidacloprid and an untreated, unmulched control. In 2000, yield of marketable fruit in the plastic and straw mulched plots was approximately twice that from the imidacloprid plot. In 2001, yield from the straw mulch plots was twice that of the imidacloprid and plastic mulch plots. Yields from both mulched plots and from the imidacloprid plots ranged from 3 to 12 times higher than those from the control plots. The mulches were more effective than a preplant application of imidacloprid in reducing the incidence of both B. argentifolii and aphid-borne viruses. Plants growing over the plastic mulch and the straw mulch grew more rapidly and reached a larger size, as determined by plant dry weight, than did those growing over bare soil, with or without imidacloprid. The spectral quantum sux from the plastic averaged between 80 and 90% of ambient spectral quantum sux values in the UV (300 Ð 400-nm) range. Spectral quantum sux values of wheat straw were similar to those of the resective mulch and ambient near 300 nm but were virtually identical to bare soil beyond 320 nm. The metalized mulch resected 94% of the incoming photosynthetically active radiation (PAR) in the 400 Ð700-nm range compared with ambient, whereas the straw mulch resected 85%. Bare soil resected only 41% of incoming PAR compared with ambient.

Sweetpotato Whitefly (Homoptera: Aleyrodidae), Aphid (Homoptera: Aphididae) Populations, and Complex of Viruses in Watermelon on Different Planting Dates in Jalisco, Mexico

The goals of this study were to determine the population dynamics of sweetpotato whitefly, Bemisia tabaci (Gennadius); green peach aphid, Myzus persicae (Sulzer); and the cotton/melon aphid, Aphis gossypii Glover, as well as to explore the incidence of the complex of aphid-borne viruses of watermelon, Citrullus lanatus L., on different planting dates. Four (1998–1999) and six (1999–2000) watermelon plots were monitored under grower management conditions in La Huerta and Casimiro Castillo, Mexico. Plant growth, sweetpotato whitefly, and aphid (adult and nymph) populations, and percentage of virus-infected plants were measured in fall–winter watermelon plots planted at different dates. The population of sweetpotato whitefly varied significantly by planting date and showed two different population patterns. Watermelon planted in early October had higher population density at young developmental stages, whereas plantings from mid-October had more adults at flowering or harvesting. Aphid species may be present at any time in fall–winter watermelon. However, higher levels of infected plants and more damage caused by viruses occurred when watermelon was planted on 16 November or later. Several factors acting separately or interactively may influence the population dynamics of vector populations and the complex of viruses in watermelon. Current levels of vector populations (nymphs) may not be high enough to produce direct damage to watermelon plants, but adults may be important factor in the viruses’ infection process. Planting before mid-November may aid in getting lower levels of infected plants and improving yield.

DIFFERENT RATES OF SPREAD OF RASPBERRY BUSHY DWARF VIRUS AND SOME APHID-BORNE VIRUSES INTO RED RASPBERRY CULTIVARS CONTAINING DIFFERENT RESISTANCE GENES

The incidence of infection with the pollen-borne Raspberry bushy dwarf virus (RBDV) and some aphid-borne viruses was assessed in 6 red raspberry cultivars in a field experiment at Invergowrie, Dundee. The cultivars differed in their resistance to RBDV, and to strains of the main aphid virus vector, Amphorophora idaei. Six years after planting as healthy plants, cv. Glen Clova, that contains the RBDV-resistance gene Bu, was not infected with RBDV, whereas all 5 RBDV-infectible cultivars became infected with RBDV but the virus incidence varied greatly from 2 - 78%. Seemingly, factors other than the presence of gene Bu influence the level of resistance to natural infection with RBDV under field conditions. All cultivars contained genes for resistance to strains of Am. idaei present in the UK and, in PCR assays for Rubus yellow net virus (RYNV) transmitted by this aphid species, the incidence of infection varied greatly. The percent infection with RYNV in cvs Glen Rosa and Leo, that contain the strongest resistance gene A10, was 0 and 9 respectively, in cvs Glen Ample, Glen Prosen and Malling Landmark, that contain gene A1, it was 9, 53 and 19 respectively, and in cv. Glen Clova, that has only minor gene resistance, it was 22. In the four cultivars sensitive to the viruses inducing Raspberry leaf spot mosaic disease, the lowest incidence of disease was 0.6% in the gene A10-containing cv. Glen Rosa and the highest was 80% in the gene A1-containing cv. Malling Landmark. Clearly, there are factors other than the major aphid resistance genes that influence resistance to virus inoculation by Am. idaei under field conditions. None of the raspberry cultivars studied were resistant to Raspberry vein chlorosis virus (RVCV) or to its aphid vector, Aphis idaei. Based on symptomatology, all cultivars became infected with RVCV but the incidence of infection varied from 1 - 100%.

Evaluation of Plastic Reflective and Wheat Straw Mulches for Pest and Disease Control in Cucurbit Production Systems

Trials were conducted in 2002 and 2003 in California's San Joaquin Valley to determine the efficiency of reflective plastic and wheat straw in managing silverleaf whitefly and aphid-borne virus diseases in late planted cantaloupes. In 2002, the incidence of aphid-borne viruses was lowest in plants growing over reflective plastic followed by those growing over wheat straw and then those growing over bare soil. Wheat straw mulch was as effective as reflective plastic during the early part of the growing season in reducing the incidence of virus disease, but by mid-season, the reflective plastic was superior. The incidence of virus diseases in plants growing over wheat straw was significantly (P < 0.05) lower than that in plants growing over bare soil throughout the season. Whitefly numbers (nymphs per cm2) and aphid numbers were significantly reduced on plants growing over both reflective mulch and wheat straw mulch compared to those growing over bare soil. Yields of all sizes of melons were significantly higher in the reflective mulch plots and yield for the straw mulched and bare soil plots were not significantly different. Results in 2003 were similar to those of 2002. Both whitefly numbers and aphid numbers were significantly lower in plants growing over both mulches than in those growing over bare soil. Virus incidence was initially low but following an aphid flight in late August, the number of infected plants increased rapidly. Both the reflective plastic and straw provided equal protection form aphid-borne viruses throughout the growing season. Yields were highest in the reflective plastic plots, followed by the straw mulch and finally the bare soil. Differences were significant (P < 0.05) among all three treatments.

NON-CHEMICAL INSECT AND DISEASE MANAGEMENT IN CUCURBIT PRODUCTION SYSTEMS

NON-CHEMICAL INSECT AND DISEASE MANAGEMENT IN CUCURBIT PRODUCTION SYSTEMS

Real-time NASBA for Detection of Strawberry Vein Banding Virus

An assay for the detection of Strawberry vein banding virus (SVBV) in Fragaria spp. based on nucleic acid sequence based amplification (NASBA) and real-time detection using molecular beacons (real-time NASBA) is described. This assay was compared both with biological indexing, the current method for certification of SVBV, and a newly optimised PCR-based detection method. Performance of the assay was tested on three SVBV isolates in Fragaria indicator plants and 317 field strawberries from five European countries. The assay was shown to be SVBV-specific, testing negative for other common aphid-borne strawberry viruses. The virus was detected in purified total RNA preparations diluted a millionfold, which is an amount equivalent to ∼1 ng of fresh material. The real-time NASBA method developed here offers the potential of a fast, sensitive and reliable approach for the routine diagnosis of strawberry stock material.

Control strategies for sweet potato virus disease in Africa

Sweet potato virus disease (SPVD), caused by dual infection with the whitefly-borne Sweet potato chlorotic stunt virus (SPCSV) and the aphid-borne Sweet potato feathery mottle virus (SPFMV), is the most serious disease of sweet potato in Africa. SPVD has been known there since at least the 1940s, although it took several decades to elucidate its aetiology. It occurs throughout Africa and is particularly prevalent in the Great Lakes region. Production of sweet potato is largely by resource-poor farmers, growing mostly local landraces and for home consumption and so control strategies need to be appropriate to these circumstances. Most high yielding and/or early maturing landraces in Uganda are susceptible to SPVD and most resistant landraces are low-yielding, forcing farmers to compromise between the conflicting requirements of large and/or early yields, and food security. Accordingly, two strategies were tested to avoid the disadvantages associated with such compromises. These were deploying high-yielding SPVD-resistant cultivars and phytosanitation practices to enable susceptible landraces to be grown successfully. In on-farm trials in Masaka and Rakai Districts of Uganda, some SPVD-resistant cultivars bred at Namulonge Agricultural and Animal Research Station (NAARI), in Wakiso District, out-yielded local landraces. Other trials at NAARI and at nearby farms showed that roguing diseased cuttings within 1 month of planting and isolation from diseased crops, even by as little as 15 m, can considerably decrease spread of SPVD to susceptible cultivars. This indicates that phytosanitation can protect desirable susceptible cultivars, even if adopted only locally. A dual approach of deploying both resistant varieties and phytosanitation provides farmers with a valuable increase in their choice of control strategies for SPVD.

Comparative fitness of a wild squash species and three generations of hybrids between wild×virus-resistant transgenic squash

We compared some fitness components of the wild squash species Cucurbita pepo spp. ovifera var. texana (C. texana) and three generations of hybrids (F1, BC1, and BC2) between C. texana and commercial transgenic squash CZW-3 over three consecutive years under field conditions of low (LDP) and high disease pressure (HDP) by Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV). Transgenic squash CZW-3 expresses the coat protein (CP) genes of CMV, ZYMV, and WMV, and is resistant to these three aphid-borne viruses. Across all HDP trials, transgenic BC1 and BC2 hybrids expressing the three CP genes grew more vigorously, displayed resistance to CMV, ZYMV, and WMV, and produced a greater number of mature fruits and viable seeds than nontransgenic hybrid segregants and C. texana. Transgenic F1 hybrids behaved similarly to BC1 and BC2 hybrids but grew less vigorously than C. texana. In contrast, across all LDP trials, C. texana outperformed the transgenic and nontransgenic hybrid segregants. Further, only one back cross was necessary to recover individuals with most of the C. texana characteristics and yet maintain virus resistance. Our data suggest that C. texana acquiring CP transgenes upon hybridization and introgression could have a selective advantage if CMV, ZYMV, and WMV are severely limiting the growth and reproductibility of wild squash populations.

Movement of coat protein genes from a commercial virus-resistant transgenic squash into a wild relative

We monitored pollen-mediated transgene dissemination from commercial transgenic squash CZW-3 into its wild relative Cucurbita pepo ssp. ovifera var. texana (C. texana). Transgenic squash CZW-3 expresses the neomycin phosphotransferase II (nptII) gene and the coat protein (CP) genes of Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV), and Watermelon mosaic virus (WMV); thereby, it is resistant to these three aphid-borne viruses. The rate of NPT II and CP transgene introgression increased with overlapping flowering patterns and a high ratio of transgenic F1 hybrids (C. texana x CZW-3) to C. texana. Transgene transfer also readily occurred from transgenic F1 hybrids into C. texana over three generations in field settings where test plants grew sympatrically and viruses were not severely limiting the growth, and fruit and seed production of C. texana. In contrast, introgression of the transgenes into C. texana was not sustained under conditions of high viral disease pressure. As expected, C. texana progeny that acquired the CP transgenes exhibited resistance to CMV, ZYMV, and WMV. This is the first report on transgene dissemination from a transgenic crop that exhibits disease resistance and hybridizes with a wild plant species without loss of fertility.

Potential Sources of Resistance for Melon to Nonpersistently Aphid-borne Viruses.

Two hundred and sixty-eight Cucumis melo and wild relative accessions were evaluated for resistance to Cucumber mosaic virus (CMV), Papaya ringspot virus strain W (PRSV-W), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV). Symptom development and systemic infection based on double antibody sandwich enzyme-linked immunosorbent assays were monitored. Sources of resistance were scarce. However, a number of them were found among the C. melo accessions tested. Thus, the accession C-189 behaved similarly to PI 161375 and showed resistance to "common" CMV strains although it was infected by a "song" type CMV. For WMV, the accessions C-768 and C-425, although infected, exhibited very mild symptoms, and recovery from infection occurred in some occasions in the former. A similar trait was also found in C-105, although in this case symptoms rarely appear and part of the plants are not infected. In addition, C-105 was highly resistant to virus transmission by Aphis gossypii, similarly to PI 161375. Accessions C-885 and C-769 exhibited resistance to PRSV-W, WMV, and ZYMV; therefore they are potential sources of multiple resistance. Resistance traits were also found in wild relatives that could be exploited when interspecific barriers with C. melo can be circumvented.

Multiplex RT-PCR detection of four aphid-borne strawberry viruses in Fragaria spp. in combination with a plant mRNA specific internal control

The principal aphid-borne viruses infecting Strawberry ( Fragaria spp.) Strawberry crinkle virus (SCV), Strawberry mild yellow edge virus (SMYEV), Strawberry mottle virus (SMoV) and Strawberry vein banding virus (SVBV) can cause serious crop losses. In this paper, a multiplex reverse transcriptase polymerase chain reaction (RT-PCR) method is described for the simultaneous detection of all four viruses in combination with a plant mRNA specific internal control which can be used as an indicator of the effectiveness of the extraction and RT-PCR. In total, 18 strawberry isolates infected naturally were analysed by this method. Every combination of RNA virus was able to be detected and a full complement of all four viruses were found together in three isolates, all taken from wild strawberry ( Fragaria chiloensis (L.) Duch.) in Chile. The upper detection limit for the four viruses was at an extract dilution of 1/200. The broad applicability of the RNA specific internal control primers—which produced a PCR fragment of the expected size in 25 of 27 plant species tested—combined with improvements, made in extraction methods described provides potentially a standard method for comparable RT-PCR analyses in a wide variety of plant species.

Experimental layout, data analysis, and thresholds in ELISA testing of maize for aphid-borne viruses

Several aspects of enzyme-linked immunosorbent assay (ELISA) procedures and data analysis have been examined in an attempt to find a rapid and reliable method for discriminating between ‘positive’ and ‘negative’ results when testing a large number of samples. A layout of ELISA plates was designed to reduce uncontrolled variation and to optimize the number of negative and positive controls. A transformation using the fourth root ( A 1/4) of the optical density readings corrected for the blank ( A) stabilized the variance of most ELISA data examined. Transformed A values were used to calculate the true limits, at a set protection level, for false positive ( C) and false negative ( D). Methods are discussed to reduce the number of undifferentiated samples, i.e. the samples with response falling between C and D. The whole procedure was set up for use with an electronic spreadsheet. With the addition of few instructions of the type ‘if…then…else’ in the spreadsheet, the ELISA results were obtained in the simple trichotomous form ‘negative/undefined/positive’. This allowed rapid analysis of more than 1100 maize samples testing for the presence of seven aphid-borne viruses—in fact almost 8000 ELISA samples.