Cucumber Mosaic Virus Symptoms Research Articles

Characterization of Cucumber Mosaic Virus Isolated from Passion Fruit (<ii>Passiflora edulis) in Korea

In July 2020, total RNA was extracted from passion fruit (<i>Passiflora edulis</i>) leaves showing virus symptoms such as chlorotic spots and vein banding in Haenam, South Korea. Cucumber mosaic virus (CMV)-HN2 was identified through reverse transcription polymerase chain reaction and sequencing analysis. To confirm the biological characteristics of the CMV infecting passion fruit, 10 indicator plants were inoculated with CMV-HN2, and the results showed a typical CMV symptoms. Phylogenetic analysis based on the amino acid of the coat protein (CP) of CMVs revealed that the CMV passion fruit isolates belonged to subgroup I, among which CMV-HN2 belonged to subgroup IA. Additionally, CMVs isolated from passion fruit in Korea have amino acid sequence variation between the subgroup. Among them, CMV-HN2 had four to eight amino acid differences in CP from other CMV isolates from passion fruit. These results confirm the presence of genetic diversity in the CPs of passion fruit CMV isolates.

Effect of Foliar Humic Acid on Water Productivity: Biochemical Parameters and Biotic Stress on Geranium Yield

During the 2017/2018 and 2018/2019 seasons, a study was conducted on the effect of humic acid at 1.0, 1.5, and 2.0 ml L-1 and water productivity on essential oils and proline content, biotic stress caused by Cucumber Mosaic Virus (CMV) and yield of geranium plants. The study was conducted in El Kanater El Khairia of Qalubia Governorate. It was aimed at determining the appropriate concentration of humic acid that attains the highest water productivity (WP), the highest production of essential oils, and highest proline content as well as reducing the symptoms of CMV. Results indicate that the highest fresh yield was obtained with a foliar application of 2.0 ml L-1 humic acid and 120% evapotranspiration (ETo). Applied irrigation water was 15155, 12168, and 9334 m3 ha-1 in the first growing season and 15218, 12298, and 9678 m3 ha-1 in the second growing season with 120, 100, and 80% ETo in both seasons. The highest average of WP 9.31 kg ha-1 both seasons was attained with 80% ETo and, 2.0 ml L-1 humic acid. While, the highest percentage of geranium essential oils and proline content, 68.16 and 3.73%, respectively were found with 2.0 ml L-1 humic. On the contrary, there was a significant reduction in CMV symptoms in plants treated with 2.0 ml L-1 humic acid compared to untreated controls. Thus, it is recommended that geraniums be irrigated with 80% ETo and application of 2.0 ml L-1 humic acid. Additionally, these treatments increased WP and resulted in the highest production of essential oils. It also increased the concentration of proline which acts as an endogenous osmoprotectants, against CMV.

Myricetin Derivative LP11 Targets Cucumber Mosaic Virus 2b Protein to Achieve In Vivo Antiviral Activity in Plants.

Cucumber mosaic virus (CMV) 2b protein plays a key role in the process of CMV infecting plants and symptom formation and is a potential molecular target for the control of this important plant virus. The exploitation of antiviral compounds is one of the strategies with the highest input: output ratio in plant protection. In this study, the CMV 2b recombinant protein was cloned, purified, and identified as the target protein by mass spectrometry. Subsequently, we carried out preliminary functional screening of the LP series of myricetin derivatives designed and synthesized in our laboratory and commercial antiviral compounds by microscale thermophoresis (MST), which showed that LP compounds LP4, LP11, LP13, and LP20 interacted well with CMV 2b, with dissociation constant (Kd) values of 1.39, 0.88, 1.52, and 1.77 μM, respectively. Among the commercially available antiviral compounds, ningnanmycin (NNM) was the most active, with a Kd value of 4.09 μM. Then, the strongest binding force to CMV 2b was identified to be from LP11 by isothermal titration calorimetry (ITC) experiments, with a Kd of 1.19 μM. Among the commercial compounds, NNM had the strongest binding force with CMV 2b, with a Kd of 4.62 μM. Through the screening of commercial compounds and LP series compounds by MST and ITC, LP11, NNM (positive control), LP16 (negative control), and the blank control group were selected to test the in vivo impact of LP11 on CMV. Specifically, the screened compounds were sprayed onto CMV-inoculated Nicotiana benthamiana plants to determine their impact on the regulation of CMV pathogenic gene expression, symptoms, and virus titer. The results showed that LP11 had a strong ability to inhibit CMV infection of tobacco at the transcriptional and translational levels. By mutating the CMV 2b protein, the 15th amino acid leucine and the 18th amino acid methionine at the N-terminal region were shown to be potential sites for binding to compound LP11. This finding provided a theoretical basis for screening and developing anti-CMV agents.

Binding immunoglobulin 2 functions as a proviral factor for potyvirus infections in Nicotiana benthamiana.

Infection of viruses from the genera Bromovirus, Potyvirus, and Potexvirus in Nicotiana benthamiana induces significant up-regulation of the genes that encode the HSP70 family, including binding immunoglobulin protein 2 (BiP2). Three up-regulated genes were knocked down and infection assays with these knockdown lines demonstrated the importance of the BiP2 gene for potyvirus infection but not for infection by the other tested viruses. Distinct symptoms of cucumber mosaic virus (CMV) and potato virus X (PVX) were observed in the BiP2 knockdown line at 10 days postagroinfiltration. Interestingly, following inoculation with either soybean mosaic virus (SMV) or pepper mottle virus (PepMoV) co-expressing green fluorescent protein (GFP), neither crinkle symptoms nor GFP signals were observed in the BiP2 knockdown line. Subsequent reverse transcription-quantitative PCR analysis demonstrated that knockdown of BiP2 resulted in a significant decrease of SMV and PepMoV RNA accumulation but not PVX or CMV RNA accumulation. Further yeast two-hybrid and co-immunoprecipitation analyses validated the interaction between BiP2 and nuclear inclusion protein b (NIb) of SMV. Together, our findings suggest the crucial role of BiP2 as a proviral host factor necessary for potyvirus infection. The interaction between BiP2 and NIb may be the critical factor determining susceptibility in N.benthamiana, but further studies are needed to elucidate the underlying mechanism.

Effects of β-Glucans from Aureobasidium pullulans on Cucumber Mosaic Virus Infection in Chili Pepper

Cucumber mosaic virus (CMV), the most prevalent virus in chili pepper (Capsicum annuum L.), negatively affects chili pepper production in South Korea. In this study, foliar spraying with β-glucans obtained from the mycelial walls of the yeast-like fungus Aureobasidium pullulans inhibited CMV infection of chili pepper if applied before virus inoculation. At three concentrations, β-glucans from A. pullulans significantly ameliorated CMV symptoms in treated chili pepper; the effect was greater in plants treated with 0.01% β-glucans than 0.005% or 0.001% β-glucans. Double antibody sandwich enzyme-linked immunosorbent assay showed that these β-glucans treatments resulted in 1.7- to 10-fold reductions in CMV accumulation in the treated chili pepper. The glucans did not act directly on the virus and did not interfere with virus disassembly or replication. Foliar spraying with 0.01% β-glucans from A. pullulans at 24 hr intervals for 3 days significantly increased plant height, the total number of fruit, and the fresh weight of chili pepper fruit. However, the stem diameter of chili pepper treated with β-glucans did not increase significantly. These results indicate that foliar spraying with β-glucans from A. pullulans acts an antiviral agent against CMV infection and stimulates chili pepper growth.

Foliar application of liquiritin protects Chinese flowering cabbage against cucumber mosaic virus and increases health-promoting compounds

ABSTRACT Decades of research have revealed notable similarities between the immune systems of the plant and animal kingdoms. Liquiritin has long been used to stimulate the body immunity in animals against an array of diseases. Considering the homology of some induced immune responses between animals and plants, we examined the effects of exogenously applied liquiritin to stimulate defense responses in Chinese flowering cabbage plants against cucumber mosaic virus (CMV) infection under greenhouse and field conditions. Foliar application of liquiritin (200 ppm) effectively suppressed the development of CMV symptoms by not less than 40% compared with the control in cabbage plants in both greenhouse and field trials along with the significant increases in the marketable yield and nutritional quality of cabbage. Liquiritin application enhanced the production of phenolic compounds and different defense-related enzymes in treated plants. Moreover, quantitative real-time PCR analysis revealed that liquiritin significantly up-regulated the expression of different defense-related genes upon pathogen inoculation, indicating an induction of the salicylic acid-mediated defense system. Collectively, the findings of this study indicate that liquiritin can effectively control CMV in cabbage plants.

Antiviral Activity of 2-Nitromethyl Phenol, Zinc Nanoparticles and Seaweed Extract Against Cucumber mosaic virus (CMV) in Eggplant

Cucumber mosaic virus (CMV) considers the most important viral pathogen affecting the production of vegetable crops all over the world. The potentials of 2-nitromethyl phenol, zinc nanoparticles and an extract (0.2%) of the seaweed Ascophyllum nodosum (SW) to reduce disease severity and incidence of Cucumber mosaic virus were evaluated under greenhouse conditions. Disease severity and incidence were significantly reduced in eggplants treated with 2-nitromethyl phenol, zinc nanoparticles and seaweed extract. CMV symptoms were suppressed in treated plants compared with the non-treated control. Coat protein of CMV was not discovered in treated plants in comparison with control plants. CMV titre was significantly reduced in plants treated with 2-nitromethyl phenol, zinc nanoparticles and seaweed extract using ELISA. The amounts of total phenols and free phenols were significantly increased in treated plants after virus inoculation compared with control plants. All treatments exhibited significantly increased growth and yield parameters of eggplants relatively to control plants. This is the first report of the antiviral activity of seaweed extract against plant viruses.

Cucumber mosaic virus infection of chickpea stands: temporal and spatial patterns of spread and yield‐limiting potential

Patterns of spread and yield losses were examined when migrant aphid vectors transmitted Cucumber mosaic virus (CMV) within chickpea (Cicer arietinum) plots. When numbers of chickpea plant infection foci were varied to provide initial infection incidences of 0·3–2%, rate of virus spread and its final incidence increased in proportion to initial virus incidence and pathogen progress curves reflected a polycyclic pattern of spread. Chickpea seed yields decreased by 44–45% when CMV incidence reached 61–74% at final assessment in plots with simulated 1–2% initial incidence. In chickpea plots with or without introduced lupin plant infection foci, cumulative spatial data for diseased plants were assessed using spatial analysis by distance indices (sadie). When CMV spread within a plot, infection was concentrated in large patch clusters and was consistent with comprehensive localized spread around primary infection foci. When introduced infection foci were absent, there was more diffuse spread with many isolated clusters. In individual plants that developed CMV symptoms at different growth stages, shoot and pod dry weight were reduced by 60–65% and 77–79% (early infection) and 44 and 66% (late infection), respectively. Seed yield losses were 78–80% (early) and 65–67% (late), and reduction in 50‐seed weight was 20–25% regardless of time of infection, so seed number was reduced more by early than late infection. Infection also reduced seed quality as, in addition to smaller seed size, seed coats were discoloured and malformed: the proportions of malformed seeds were 9–11% (early), 3–6% (late) and 0·5% (healthy).

Note: Occurrence and distribution ofCucumber mosaic virus infecting danshen (Salvia miltiorrhiza) in China

Cucumber mosaic virus (CMV) has resulted in much damage to Danshen (Salvia miltiorrhiza Bunge) crops in China. A 5-year survey was conducted in Hebei, Shandong, Sichuan, Shanxi, Henan and Gansu Provinces, all major Danshen-growing areas. A total of 156 Danshen plant samples with CMV symptoms were collected and tested for the presence of CMV by a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using polyclonal antibodies against CMV and a positive control, according to the supplier’s instructions (Agdia). They were confirmed to be CMV by amplification of complete coat protein gene and analysis of the gene sequence. The results showed that 122 samples were infected by CMV and all of these CMV isolates belonged to subgroup IB.

Variation in the Pathogenicity of Lily Isolates of Cucumber mosaic virus

Two isolates of Cucumber mosaic virus (CMV) originated from lily plants, named Ly2-CMV and Ly8-CMV, were compared with their pathological features in several host plants. Ly2-CMV and Ly8-CMV could induce systemic mosaic symptom in Nicotiana benthamiana, but Ly2-CMV could not systemically infect tomato and cucumber plants that have been used for CMV-propagative hosts. While Fny-CMV used as a control infected systemically the same host plants, producing typical CMV symptoms. Ly8-CMV could infect systemically two species of tobacco (N. tabacum cv. Xanthi-nc and N. glutinosa) and zucchini squash (Curcubita pepo), but Ly2 failed systemic infection on these plants. As resulted from tissue-print immunoblot assay, different kinetics of systemic movement between Ly2-CMV and Ly8-CMV were crucial for systemic infection in tobacco (cv. Xanthi-nc). Sequence analysis of full-length genome of two lily isolates showed Ly2 and Ly8 belonged to subgroup IA of CMV. The lily isolates shared overall 98 % sequence identity in their genomes. Coat protein, 3a protein, and 2b protein involved in virus movement was highly conserved in genomes of the isolates Ly2 and Ly8. Although there is the low frequency of recombinants and reassortants in natural CMV population, phylogenetic analysis of each viral protein among a number of CMV isolates suggested that genetic variation in a defined population of CMV lily isolates was stochastically produced.

Limited movement of Cucumber mosaic virus (CMV) in yellow passion flower in Brazil

Symptoms of Cucumber mosaic virus (CMV) on yellow passion flower (Passiflora edulis f. flavicarpa) are characterized by bright yellow mottling on leaves, starting at random points on the vine and diminishing in intensity towards the tip, which becomes symptomless as it grows. To determine whether symptomless portions of vines are CMV‐free or represent latent infection, leaves with and without symptoms were collected from infected vines in the field. Biological, serological (plate‐trapped antigen enzyme‐linked immunosorbent assay, PTA‐ELISA), Western blot and dot‐blot hybridization assays showed that portions of the vines without symptoms were CMV‐free. Vegetatively propagated vines with symptoms showed remission of symptoms on newly developed leaves. One year later, no CMV was detected in the upper leaves of these plants. Mechanically inoculated passion flower seedlings behaved similarly; symptoms were shown by few leaves after inoculation. Afterwards, plants became symptomless and CMV was not detected in the upper leaves or root system, 40 or 85 days after inoculation. The mechanism responsible for remission of symptoms accompanied by CMV disappearance is not known.

Further studies on the effects of insecticides on aphid vector numbers and spread of cucumber mosaic virus in narrow-leafed lupins ( Lupinus angustifolius)

Narrow-leafed lupin ( Lupinus angustifolius) was sown in five field experiments over three years to investigate the effects of applying imidacloprid, alpha-cypermethrin, triazamate and methamidophos insecticides on aphid vector numbers, spread of cucumber mosaic virus (CMV), resulting yield losses and CMV transmission to seed. Of the colonising aphid species, Acyrthosiphon kondoi and Aphis craccivora were most effectively controlled by alpha-cypermethrin and Myzus persicae by imidacloprid. Methamidophos and triazamate had similar effects on colonising aphid numbers to those of alpha-cypermethrin. In one experiment, >82% of the CMV vector M. persicae were insecticide resistant (R1 or R2 E4 esterase resistant types). In two experiments, numbers of colonising aphids were greater in plots in which CMV was spreading from seed-infected plants than in plots where healthy seed had been sown. Visual assessment of plants with CMV symptoms under-estimated actual incidence measured by ELISA tests more than three-fold. Alpha-cypermethrin applied at 25 g a.i./ha decreased CMV incidence by up to 62%, but imidacloprid, methamidophos and triazamate did not significantly diminish it. Increasing incidences of current-season CMV-infected plants were positively correlated with the magnitude of yield losses and extent of CMV transmission through harvested seed. Direct aphid feeding damage did not influence grain yield. However, application of alpha-cypermethrin to control the aphid vectors of CMV in plots sown with infected seed increased yield by up to 60%, but did not give consistent enough control to be recommended for general use. Sowing healthy seed and using recommended integrated cultural management practices that minimise CMV spread should remain the mainstays of successful CMV management in lupins.

Cucumber Mosaic Virus on Asiatic Hybrid Lilies in India.

Asiatic hybrid lilies are popular cut flowers with a range of bright colors. Of the several viruses reported from lily (2,3), cucumber mosaic virus (CMV) reduces flower quality and yield (1). Classical symptoms of CMV were observed in recently introduced plants of Asiatic hybrid lilies in Kangra Valley, Himachal Pradesh. The symptoms were mild leaf mosaic, ring spot, transient vein yellowing, occasionally with growth deformation, and flower breaking. Leaf samples from cvs. MonteNegro, Yellow Present, Apeldoorn, Toscana, Connecticut King, and Adelina were collected randomly on the basis of symptom expression. Viral-associated double-stranded RNA (dsRNA) analysis was used to analyze tissue from symptomatic and asymptomatic plants for evidence of a possible cucumovirus. dsRNA analysis resulted in a banding profile typical of that seen with cucumoviruses. There was no evidence of dsRNA in the asymptomatic tissue. Presence of CMV in the symptomatic plants was also confirmed by enzyme-linked immunosorbent assay with antiserum from Agdia (Elkhart, IN). Virus from symptomatic tissues was purified and 30 nm polyhedral, viruslike particles were observed that were subsequently tested for CMV with counter immunoelectrophoresis with antibodies of CMV-C and CMV-D (antibodies obtained from H. A. Scott, University of Arkansas) and ATCC CMV antisera PVAS 242-A. Our isolate differs from other prevalent CMV isolates of Kangra Valley, having a narrow host range and not being readily sap transmissible. However, this isolate is normally transmitted to progeny bulblets. Lack of fallow periods, continuous cropping of other CMV-susceptible bulbous crops, and occasional sprouting of uncollected lily bulblets enhance inoculum build-up. Planting of CMV-tested lilies is recommended to avoid disease losses and to reduce viral inoculum floriculture fields. This is the first report of CMV in Asiatic hybrid lilies in India.

Salicylic Acid Can Induce Resistance to Plant Virus Movement

Salicylic acid (SA) treatment has recently been reported to inhibit replication of tobacco mosaic virus (TMV) in inoculated tissue. Furthermore, resistance is induced via a novel defensive signal transduction pathway sensitive to inhibition by salicylhydroxamic acid (SHAM; S. Chivasa, A. M. Murphy, M. Naylor, and J. P. Carr, Plant Cell 9: 547–557, 1997). The goals of this study were to determine if replication of viruses other than TMV could be inhibited by SA and, if so, whether the resistance to other viruses could also be prevented by SHAM. Potato virus X (PVX) RNA accumulation in inoculated tobacco leaf tissue was reduced by SA treatment and resistance was dependent on the SHAM-sensitive signaling pathway. However, although symptoms of cucumber mosaic virus (CMV) infection were delayed in SA-treated tobacco plants, this was not due to inhibition of replication but rather to inhibition of systemic movement of the virus.14CO2-feeding experiments indicated that SA-induced interference with long-distance virus movement is not a by-product of disrupted photosynthate translocation. Significantly, SA-induced resistance to CMV was abolished by SHAM. Thus, the SHAM-sensitive signaling pathway activates both resistance mechanisms: inhibition of long-distance CMV movement and inhibition of TMV and PVX replication.

Viral Satellite RNA Expression in Transgenic Tomato Confers Field Tolerance to Cucumber Mosaic Virus.

Field trials of transgenic tomato plants expressing an ameliorative satellite RNA of cucumber mosaic virus (CMV) were conducted to test the efficacy of satellite-transgenic technology to protect against CMV infection. Three transgenic tomato lines derived from two susceptible genotypes were evaluated over two growing seasons for viral symptoms and titers, satellite RNA expression, and fruit yield. Satellite-transgenic lines exhibited mild or no CMV symptoms and low viral titers relative to nontransformed plants. A significant negative correlation between satellite RNA levels and disease severity was evident in transgenic lines. Total marketable yield of CMV-infected satellite-transgenic lines was 40 to 84% greater than that of CMV-infected parent lines. Importantly, yield of CMV-infected satellite-transgenic lines did not differ significantly from mock-inoculated parent lines. Risk assessment results demonstrated low levels of satellite RNA transmission within the test site and no evidence of satellite RNA-induced damage on surrounding plants.

Effects of applying insecticides to control aphid vectors and cucumber mosaic virus in narrow-leafed lupins Lupinus angustifolius)

Summary. Narrow-leafed lupins (Lupinus angustifolius) were sown in 4 field experiments to investigate the effects of applying organophosphorus and carbamate insecticides on the spread of cucumber mosaic virus (CMV), which is transmitted non-persistently by aphids. The seed sown carried 0 or 5% CMV infection and seed-infected plants were the primary source for subsequent virus transmission by aphids. Virus incidence was gauged by calculating the percentage of plants per plot showing typical current-season CMV symptoms. At final assessment in plots sown with 5% infected seed, recorded CMV incidence was always significantly smaller (up to 3-fold less) when they received sprays of pirimicarb and/or methamidophos every 2 weeks than when they received no insecticide. When single or double strategic sprays of methamidophos or a mixture of pirimicarb/thiometon were applied in late August or early September, they either decreased recorded CMV incidence (up to 2-fold less infection) or had no significant effect on it. Recorded CMV incidence was not significantly diminished by dressing seed with disulfoton or by single- or double-foliar applications of pirimicarb used alone. However, pirimicarb sprays applied every 2 weeks improved grain yield (24% increase), as also did single or double applications of pirimicarb (14%). In one experiment, applications of methamidophos every 2 weeks to plots originally sown with 5% infected seed resulted in increased grain yield (35%) and yields were increased in plots sown with healthy seed whether sprayed every 2 weeks with methamidophos or left unsprayed (42–61%). Pirimicarb suppressed numbers of colonising Acyrthosiphon kondoi and Aphis craccivora to a greater extent than those of Myzus persicae, especially when sprayed every 2 weeks. Single-, double- and sprays of methamidophos every 2 weeks also decreased numbers of Acyrthosiphon kondoi, but had less effect on M. persicae. When different insecticides were tested for their abilities to kill colonising, insecticide-resistant M. persicae, methamidophos was the most effective. This work suggests that single or double strategic foliar sprays of organophosphorus or carbamate insecticides cannot be relied on to control CMV adequately to be recommended for use in increasing grain yields in CMV-infected lupin grain crops.

Screening of Capsicum Accessions for Resistance to Cucumber Mosaic Virus

Eighty-three sweet or hot pepper accessions (Capsicum annuum L.) and 57 other Capsicum spp. accessions were screened for resistance to cucumber mosaic virus (CMV). Most C. annuum accessions developed symptoms after the first inoculation with CMV but 45 plants in 22 accessions were symptomless. When the latter were reinoculated, 15 symptomless plants in 10 accessions were selected for progeny testing. The resistance of some progenies derived from symptomless plants was higher than that of the parents. The resistant progenies are preserved as seed stocks.Of the 57 Capsicum spp. accessions, most showed CMV symptoms after the first inoculation. Five, 21, 7, and 7 symptomless plants were observed in accessions of C. chinense Jacquin, C. frutescens L., C. baccatum L., and C. pubescens Ruiz & Pavon, respectively. Of the symptomless plants which were reinoculated, 19 symptomless plants mostly of C. frutescens were progeny tested. As a result, five progenies of C. frutescens and one of C. baccatum were selected as seed stocks for future testing.

CMV resistance developed in vigorous-growing lateral shoots from virus infected plants of Capsicum annuum L.

Vigorous-growing lateral shoots were observed emerging from certain pepper cultivars infected with cucumber mosaic virus (CMV) about 2 years after infection. They exhibited no CMV symptoms. When checked by enzyme-linked immunosorbent assay (ELISA), CMV was not detected in the vigorous-growing lateral shoots which emerged from Capsicum annuum L. ‘Af-5’ plants infected with CMV, in spite of a high concentration of CMV in the infected shoots. Vigorous-growing cuttings from ‘Af-5’ plants did not express CMV symptoms, regardless of either the renewal frequency by cutting propagation or the duration of growing. In these cuttings, CMV was never detected when checked by either ELISA or the grafting method. Vigorous-growing cuttings inoculated with CMV by aphids showed no symptoms of CMV, with a CMV concentration index of 0. When tested by the grafting inoculation method, ‘Af-5’ vigorous-growing cuttings were resistant to CMV.

Efficacy of Endogenous Satellite Expression to Confer Resistance to CMV in Satellite Transgenic Tomato under Field Conditions

Viral satellite RNA associated with cucumber mosaic virus (CMV) is know to modulate CMV symptomology. Virulent CMV associated RNA 5 (CARNA 5) satellites may intensify crop disease. Naturally occurring variants of these satellites, however, attenuate CMV symptoms. Satellite transgenic tomato plants expressing the S-CARNA 5 or 1-CARNA 5 ameliorating forms of the satellite were evaluated under simulated CMV epidemic conditions in USDA–APHIS approved field trials. Trials conducted at Beltsville, Md., in 1994 and 1995 demonstrated that CMV can be effectively controlled under field conditions in satellite transgenic plants. Yields of transgenic lines infected with CMV were 50%–65% greater than that of non-transgenic infected controls. Yields of noninfected transgenic lines ranged from 5% greater than, to 33% less than, noninfected nontransgenic controls. Expression of CARNA 5 in inoculated transgenic plants greatly reduced CMV foliar symptoms and virus titers when compared to inoculated control plants. Levels of CARNA 5 were detected at varying levels in infected transgenic plants throughout the growing season. Virus or satellite was not detected in samples collected from tomato border plants and weeds growing inside and outside a nonhost crop border surrounding the test plot. Field tests conducted in 1996 will evaluate transgenic tomato plants with a double construct coding for the CMV coat protein gene and 1-CARNA 5 satellite.

Effects of sowing seed with different levels of infection, plant density and the growth stage at which plants first develop symptoms on cucumber mosaic-virus infection of narrow-leafed lupins (Lupinus angustifolius)

During 1990-92, narrow-leafed lupins (Lupinus angustifolius) cv. Gungurru, were grown in six field experiments in which plots were sown with healthy seed or seed that carried 0.5-5% infection with cucumber mosaic virus (CMV). Seed-infected plants were the primary source for subsequent virus spread by aphids. The rate of CMV spread and the extent of infection in plots depended on the level of infection in the seed sown, the proportion of infected seeds that successfully developed into established plants and the time of arrival and number of aphid vectors. In general, higher seed infection levels, better establishment of seed-infected plants and early aphid arrival favoured greater virus spread, yield loss and infection in the harvested seed. In 1991, in two experiments, late arrival of aphids resulted in minimal CMV spread, no effect on yield and much less infection in the harvested seed than in the seed sown. In the other four experiments, significant yield losses (25-42%) always resulted when seed with 5% or 3% infection was sown. Sowing 1% infected seed resulted in significantly decreased yields in two experiments, while 0.75% and 0.5% infected seed caused significant losses in one experiment (16-19% losses). Yield decreases were due to both fewer seeds being formed and decreased seed size. Levels of infection in harvested seed did not exceed 15%. In a further field experiment in 1991, individual plants that developed CMV symptoms before initiation of flowering or during flowering had significantly smaller yields than those that developed symptoms after flowering had finished. In four field experiments during 1990-91, 10-15% CMV-infected lupin seed was sown at rates of 20-150 kg ha-1 to generate a range of plant densities. The numbers of seed-infected plants were recorded at different times. The extent of loss of seed-infected plants due to shading by neighbouring healthy plants depended on plant density and the time when canopy closure developed. Where no canopy formed there was little or no loss of seed-infected plants, while early canopy formation at high plant density was most effective in removing them. Current-season spread was also decreased by early canopy formation and high plant density, but this effect was smaller when aphids arrived early. This work supports recommendations for management of CMV infection in lupins by sowing seed with low infection (<0.5%) to minimize infection sources, and sowing early at high seeding rates to remove seed-infected plants through improved canopy formation.