Spread Of Cucumber Mosaic Virus Research Articles

Transcriptional Comparison Reveals Differential Resistance Mechanisms between CMV-Resistant PBC688 and CMV-Susceptible G29.

The Cucumber mosaic virus (CMV) presents a significant threat to pepper cultivation worldwide, leading to substantial yield losses. We conducted a transcriptional comparative study between CMV-resistant (PBC688) and -susceptible (G29) pepper accessions to understand the mechanisms of CMV resistance. PBC688 effectively suppressed CMV proliferation and spread, while G29 exhibited higher viral accumulation. A transcriptome analysis revealed substantial differences in gene expressions between the two genotypes, particularly in pathways related to plant-pathogen interactions, MAP kinase, ribosomes, and photosynthesis. In G29, the resistance to CMV involved key genes associated with calcium-binding proteins, pathogenesis-related proteins, and disease resistance. However, in PBC688, the crucial genes contributing to CMV resistance were ribosomal and chlorophyll a-b binding proteins. Hormone signal transduction pathways, such as ethylene (ET) and abscisic acid (ABA), displayed distinct expression patterns, suggesting that CMV resistance in peppers is associated with ET and ABA. These findings deepen our understanding of CMV resistance in peppers, facilitating future research and variety improvement.

Infeksi Cucumber mosaic virus dan Chilli veinal mottle virus pada Cabai di Kabupaten Rejang Lebong, Bengkulu

Mosaic disease caused by Cucumber mosaic virus (CMV) and Chilli veinal mottle Virus (ChiVMV) has been distributed widely in chilli in Indonesia and considered as important disease. A research was conducted to investigate the spread and incidence of CMV and ChiVMV in Rejang Lebong, Bengkulu and to identify its insect vector. Symptomatic and asymptomatic leaf samples were collected systematically from several chillipepper fields for further detection by DAS-ELISA (Double antibody sandwich-enzyme linked immunosorbant assay) using specific antibody for CMV and ChiVMV. The result showed that infection of both CMV and ChiVMV was found with disease incidence reached 20-50%, whereas infection only by ChiVMV or CMV were 50-80% and 20-50%, respectively. One species of aphid, i.e. Aphis gossypii was found from the fields.Key words: Aphis gossypii, CMV, ChiVMV, disease incidence

The effect of Chrysoperla carnea (Neuroptera: Chrysopidae) and Adalia bipunctata (Coleoptera: Coccinellidae) on the spread of cucumber mosaic virus (CMV) by Aphis gossypii (Hemiptera: Aphididae).

The effects of two aphidophagous predators, the larvae of Chrysoperla carnea and adults of Adalia bipunctata, on the spread of cucumber mosaic virus (CMV) transmitted in a non-persistent manner by the cotton aphid Aphis gossypii were studied under semi-field conditions. Natural enemies and aphids were released inside insect-proof cages (1 m × 1 m × 1 m) with a central CMV-infected cucumber plant surrounded by 48 healthy cucumber seedlings, and the spatiotemporal dynamics of the virus and vector were evaluated in the short and long term (1 and 5 days) in the presence and absence of the natural enemy. The spatial analysis by distance indices methodology together with other indices measuring the dispersal around a single focus was used to assess the spatial pattern and the degree of association between the virus and its vector. Both natural enemies significantly reduced the number of aphids in the CMV-source plant after 5 days but not after 1 day. The CMV transmission rate was generally low, especially after 1 day, due to the limited movement of aphids from the central CMV-source plant, which increased slightly after 5 days. Infected plants were mainly located around the central virus-infected source plant, and the percentage of aphid occupation and CMV-infected plants did not differ significantly in absence and presence of natural enemies. The distribution patterns of A. gossypii and CMV were only coincident close to the central plant. The complexity of multitrophic interactions and the role of aphid predators in the spread of CMV are discussed.

Natural cucumber mosaic virus reservoirs in seed farms in Primorskii krai

The spread of cucumber mosaic virus in natural flora is studied. It is revealed that it is found mainly in natural cenoses where vegetables, especially those of the Cucurbitaceous family, have been cultivated for a long time. It is shown that an epiphytotic can occur under favorable conditions.

Spatio-temporal dynamics of viruses are differentially affected by parasitoids depending on the mode of transmission.

Relationships between agents in multitrophic systems are complex and very specific. Insect-transmitted plant viruses are completely dependent on the behaviour and distribution patterns of their vectors. The presence of natural enemies may directly affect aphid behaviour and spread of plant viruses, as the escape response of aphids might cause a potential risk for virus dispersal. The spatio-temporal dynamics of Cucumber mosaic virus (CMV) and Cucurbit aphid-borne yellows virus (CABYV), transmitted by Aphis gossypii in a non-persistent and persistent manner, respectively, were evaluated at short and long term in the presence and absence of the aphid parasitoid, Aphidius colemani. SADIE methodology was used to study the distribution patterns of both the virus and its vector, and their degree of association. Results suggested that parasitoids promoted aphid dispersion at short term, which enhanced CMV spread, though consequences of parasitism suggest potential benefits for disease control at long term. Furthermore, A. colemani significantly limited the spread and incidence of the persistent virus CABYV at long term. The impact of aphid parasitoids on the dispersal of plant viruses with different transmission modes is discussed.

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).

Patterns of spread of two non‐persistently aphid‐borne viruses in lupin stands under four different infection scenarios

SummaryPatterns of spread of Bean yellow mosaic virus (necrotic type, BYMV‐N) and Cucumber mosaic virus (CMV) were examined in stands of narrow‐leafed lupin (Lupinus angustifolius) where naturally occurring aphid vectors moved them from external or internal primary virus sources. The lupin stands were: commercial crops near BYMV‐infected clover pasture with or without an intervening non‐host barrier crop; a large rectangular block with BYMV‐N and CMV sources on opposite sides and a narrow, non‐host barrier crop facing the BYMV‐N source; and a plot within which seed‐infected lupin plants acted as internal CMV sources. When BYMV‐N spread into commercial crops in the absence of a non‐host barrier, there was a steep decline in its incidence with distance from the crop edge. However, when a 20 m‐wide perimeter barrier of oats intervened between the two, there was only a shallow decline. When CMV and BYMV‐N spread from opposite directions into a block with a 0.25 m‐wide oat barrier between it and the BYMV‐N source, the BYMV‐N incidence gradient was shallow but in the opposite direction the CMV gradient was steep. When CMV spread from primary sources within a plot, infection was concentrated in large internal patches. Spread of BYMV‐N was more diffuse with more isolated symptomatic plants and small clusters than occurred with CMV, spread of which was more comprehensive, reacting the near monocyclic and polycyclic patterns of spread with BYMV‐N with CMV respectively. Spread of both viruses was greater along than across rows, especially with CMV. With BYMV‐N, three different phased cycles of secondary spread were evident in the individual symptomatic plants within the small clusters that formed away from the edges of lupin stands. These findings help validate inclusion of perimeter non‐host barriers within an integrated disease management strategy for BYMV‐N in lupin.

Forecasting aphid outbreaks and epidemics of Cucumber mosaic virus in lupin crops in a Mediterranean-type environment

Cucumber mosaic virus (CMV) causes a serious disease of narrow-leafed lupin ( Lupinus angustifolius). It is seed-borne in lupin and seed-infected plants act as the primary virus source for secondary spread by aphid vectors within crops. Infection with CMV causes yield losses of up to 60% in epidemic years, but has little impact on yield in years when spread is limited. Aphids also cause sporadic yield losses due to direct feeding damage. A simulation model was developed to forecast aphid outbreaks and epidemics of CMV in lupin crops growing in the ‘grainbelt’ of south–west Australia, which has a Mediterranean-type climate. The model uses rainfall during summer and early autumn to calculate an index of aphid build-up on weeds, crop volunteers and self-regenerating annual pastures in each ‘grainbelt’ locality before the growing season commences in late autumn. The index is used to forecast the timing of aphid immigration into crops. The subsequent aphid build-up and movement within the crop, spread of CMV from virus-infected source plants within the crop, yield losses and percentage of harvested seed-infected are then calculated. The model evaluates the effects of different sowing dates, percentages of CMV infection in seed sown and plant population densities on virus spread. The model simulations were validated with 14 years’ field data from six different sites in the ‘grainbelt’, representing a wide range of pre-growing season rainfall scenarios, sowing dates, percentages of infection in seed sown and plant population densities. The model was incorporated into a decision support system (DSS) for use by lupin farmers and agricultural consultants in planning CMV management and targeting sprays against aphids to prevent direct feeding damage. The inputs required from the user are lupin cultivar, anticipated emergence date, percentage CMV infection in seed sown, plant density and location. The output consists of a personalised risk forecast for the user and includes predictions for date of first aphid arrival, aphid numbers, CMV spread, final virus incidence, yield loss due to infection and percentage infection in harvested seed. Predictions from the DSS are accessible via an Internet site and from other information sources. The model can serve as a template for modelling similar virus/aphid vector pathosystems in other regions of the world, especially those with Mediterranean-type climates.

Acibenzolar-S-methyl induces resistance to Colletotrichum lagenarium and cucumber mosaic virus in cantaloupe

Acibenzolar-S-methyl (ASM) is a synthetic analogue of salicylic acid developed for use in a novel strategy for crop protection through systemic acquired resistance (SAR). ASM protected cantaloupe against a fungal pathogen, Colletotrichum lagenarium, and a viral pathogen, cucumber mosaic virus (CMV). ASM induced the systemic accumulation of chitinase, a marker protein for SAR, in both greenhouse and field grown seedlings. ASM at 50 or 100 μg/ml provided almost complete protection against the fungal pathogen and effectively delayed the spread of CMV in greenhouse trials. In two field trials, ASM had no negative effect on fruit production in the absence of CMV disease pressure.

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.

Are Tubules Generated by the 3a Protein Necessary for Cucumber Mosaic Virus Movement?

The 3a movement protein of cucumber mosaic virus (CMV), fused to the jellyfish green fluorescent protein (3a-GFP) generated surface punctate aggregates as well as tubules protruding from infected tobacco and Nicotiana benthamiana protoplasts. Fluorescent tubules also appeared on the surface of protoplasts prepared from transgenic tobacco plants expressing 3a-GFP, indicating that the 3a protein is the only viral component required for the formation of the tubules. CMV with a mutation in the gene encoding the 3a protein, M8 CMV, could infect tobacco systemically, but tubules were not detected protruding from infected protoplasts when the mutated 3a protein was fused to the GFP [(M8)3a-GFP]. This indicates that the ability of the 3a protein to generate tubules in the surface of protoplasts is not a function required for the spread of CMV in tobacco. On the other hand, the (M8)3a-GFP did not traffic through plasmodesmata interconnecting tobacco epidermal cells, in contrast to the wild-type 3a-GFP. This suggests that there may be a correlation between the ability of the 3a protein to assemble tubules in protoplasts and its ability to promote movement within certain tissues.

Effects of different cultural practices on spread of cucumber mosaic virus in narrow-leafed lupins (Lupinus angustifolius)

Lupinus angustifolius (narrow-leafed lupin) was sown in 7 field experiments to examine the effects of cultural practices on incidence of cucumber mosaic virus (CMV). The factors investigated were row spacing, banding fertiliser below seed, straw groundover, and tillage. The seed sown carried 5–15% CMV infection. Seed-infected plants were the primary source for subsequent virus spread by aphids. Incidence of seed-infected plants and the extent of virus spread were gauged by counting numbers of lupin plants showing typical seed-borne and current-season CMV symptoms. Due to greater competition with other plants within wide than narrow rows, wide row spacing diminished the survival of seed-infected plants by 46%. Increased plant growth from banding superphosphate below seed did not significantly decrease numbers of seed-infected plants surviving. Straw spread on the soil surface suppressed final CMV incidence by 25–40% and, when applied at different rates, diminished recorded CMV incidence more at 4 than 2 t/ha and least at 1 t/ha. Where there was no straw, CMV incidence increased faster with narrow spacing than wide spacing. Soil disturbance from sowing seed with double discs instead of tynes significantly increased incidences of both seed-borne and current-season infection and diminished grain yield. Neither straw nor row spacing treatments significantly affected grain yield, but the decrease in CMV spread due to straw ground cover significantly increased individual seed weight once and overall yields were greater with straw. Myzus persicae was the main colonising aphid species but Aphis craccivora and Acyrthosiphon kondoi also colonised the lupins. There were significantly fewer colonising M. persicae in plots with 4 t/ha of straw than in those with none. This work suggests that stubble retention, minimum tillage, and wide row spacing should be included as components of an integrated disease management strategy for CMVin L. angustifolius crops.

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.

Resistance to seed transmission of cucumber mosaic virus in narrow-leafed lupins (Lupinus angustifolius)

Cucumber mosaic virus (CMV) is seed-transmitted in L. angusti,folius (narrow-leafed lupin) and plants that grow from infected seed are the primary source of inoculum for field epidemics. Resistance to seed transmission of CMV was sought in cultivars, breeding lines and wild types of this species. The field screening method developed was based on spreader rows, where a susceptible cultivar (Wandoo) with high intrinsic seed infection levels was grown on either side of every test row, and CMV spread occurred by natural aphid transmission. Inoculum pressure was so great that spreader and test rows became virtually 100% infected. Harvested seed from each test row was assessed for the level of infection present by testing for the presence of CMV in the radicles of newly germinated seeds or in leaves of seedlings by ELISA. This method was used successfully from 1987 to 1992 to screen lines for relative resistance/susceptibility to CMV seed transmission. Based on their intrinsic CMV seed transmission rates during the experiments test lines were categorized into four groups: moderately resistant (1-6% seed transmission, as in cvv. Danja and Frost), moderately susceptible (6-20% seed transmission, as in cvv. Illyarrie, Yorrel and Gungurru), susceptible (20-35% seed transmission, as in cv. Wandoo), and very susceptible (35-75% seed transmission, as found in some breeding lines and wild types). No lines were highly resistant (<l% seed transmission) or immune (0%). Differences in seed transmission rates between lines were highly significant and stable from year to year. Resistance or susceptibility was not related to alkaloid content or flowering date of lines but appeared to be polygenically controlled. Breeding for low CMV seed transmission rates is recommended for use in L. angustifolius breeding programs. Also, advanced breeding lines with unacceptably high intrinsic seed transmission rates (i.e. >20%) should be culled out.

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.

Partial Resistance of Bell Pepper to Cucumber Mosaic Virus Movement within Plants: Field Evaluation of its Efficiency in Southern France

AbstractThe spread of cucumber mosaic virus (CMV) was followed during three years in field plots of bell pepper varieties Yolo Wonder (susceptible) and Milord and Vania (partially resistant to CMV movement within plants). During the three test years, CMV spread was delayed 4 to 6 weeks in var. Milord and in var. Vania as compared to var. Yolo Wonder. Final CMV incidence and the apparent infection rate, the latter calculated from Van der Plank logistic analyses, were lower in var. Milord and in var. Vania than in var. Yolo Wonder. The resistance of var. Milord and var. Vania, expressed as a delay of spread and a reduced CMV incidence over the past three years, provides practical disease control.

Resistance of Pepper Lines to the Movement of Cucumber Mosaic Virus

AbstractThe multiplication and the migration of cucumber mosaic virus (CMV) were studied in greenhouse conditions in one susceptible ‘Yolo wonder’ and two resistant ‘Milord’ and ‘Vania’ pepper varieties. DAS‐ELISA tests have revealed that the virus is replicated in inoculated leaves of the resistant varieties as high as in the susceptible variety. In the susceptible variety ‘Yolo wonder’, CMV migrated from the leaf lamina to the petiole two days after inoculation and it became systemic three days later regardless the season. In ‘Milord’ the virus migrated from the leaf lamina to the petiole five days after inoculation and it became systemic during the winter 16 days after inoculation. Whereas plants of the same genotype were not infected systemically during the summer. In ‘Vania’, during the two seasons, CMV spread from the blade to the petiole five days after inoculation, but the virus was not detected beyond the inoculated leaf. These results show that ‘Milord’ and ‘Vania’ are resistant to CMV migration. Therefore, the resistance to CMV migration is affected by plant genotype and temperature. The study of effect of pepper plant phenology on infection has revealed that resistance to CMV migration is also affected by the development stage of the plants.

Further studies on cucumber mosaic virus infection of narrow‐leafed lupin (Lupinus angustifolius): seed‐borne infection, aphid transmission, spread and effects on grain yield

SUMMARYFour field trials were done with narrow‐leafed lupins (Lupinus angustifolius) in 1988 ‐ 1989, to examine the effect of sowing seed with 5% and 0.5% cucumber mosaic virus (CMV) infection on subsequent virus spread, grain yield and percentage of infection in harvested seed. A proportion of the CM V‐infected seed failed to produce established plants and thus, plots sown with 5% and 0.5% infected seed contained 1.5‐2.9% and 0.2‐0.3% of seed‐infected plants respectively. The rate of virus spread by aphids was faster and resulted in more extensive infection at maturity in plots sown with 5% infected seed than with 0.5% infected seed. In three trials, sowing 5% infected seed resulted in yield losses of 34 ‐ 53% and CMV infection in the seed harvested of 6 ‐ 13%. The spread of CMV infection resulting from sowing 0.5% infected seed did not significantly decrease yield. However, late CMV spread in these plots caused > 1% seed infection. In the fourth trial, which was badly affected by drought, CMV spread only slowly, there was no significant effect of CMV on grain yield and the percentage of infected seed harvested was 3–5 times less than that in the seed sown.When CMV‐infected seed was sown at different depths, target depths of 8 and 11 cm decreased the incidence of seed‐infected plants by c. 15% and c. 50% respectively compared with sowing at 5 cm. However, in glasshouse tests, treatment with the pre‐emergence herbicide simazine failed to selectively cull out seed‐infected plants.The field trials were colonised by green peach (Myzus persicae), blue‐green (Acyrthosiphon kondoi) and cowpea (Aphis craccivora) aphids. When the abilities of these aphid species and of the turnip aphid (Lipaphis erysimi) in transmitting CMV from lupins to lupins were examined in glasshouse tests, short acquisition access times favoured transmission. With 5–10 min acquisition access times, overall transmission efficiencies were 10.8%, 9.4%, 6.1% and 3.9% for the green peach, cowpea, blue‐green and turnip aphids respectively.

Increase in cucumber mosaic virus concentration in Japanese radish plants co-infected with turnip mosaic virus.

Dual infection of turnip mosaic virus (TuMV) and cucumber mosaic virus (CMV) causes a severe mosaic disease in Japanese radish plants. This paper deals with the interactions between these viruses in radish plants. TuMV caused mild mosaic symptoms of Japanese radish plants by itself, but CMV did not. Plants inoculated with both viruses displayed more severe mosaic symptoms than plants inoculated only with TuMV. Indirect ELISA tests indicated that CMV accumulation was significantly enhanced in the presence of TuMV, but TuMV levels were little affected by co-infection with CMV. The enhanced accumulation of CMV in plants infected with TuMV as well as CMV was evident in systemically infected leaves rather than the inoculated cotyledons and this suggested that systemic transport and spread of CMV in radish plants were enhanced in the presence of TuMV.

Model for the spread of non-persistent virus diseases

This study considers the buildup of virus infection within a crop area. The virus is transmitted by aphid vectors which acquire virus from source plants and inoculate the sensitive crop. The model relates the increase of infection to the behaviour of incoming vectors and of vectors moving from plant to plant within the crop area. The model is implemented using some data available on spread of cucumber mosaic virus in a pepper plot in Israel. The effect of control means is considered.