Virus diseases of garden lupin in Great Britain

Two viruses occur widely in lupins in Britain. Alfalfa mosaic virus (AMV), of which two strains were isolated, was found mainly in named Russell varieties. Lupin mottle virus (LMV), a previously undescribed strain of the bean yellow mosaic virus (BYMV) common pea mosaic virus (CPMV) complex, was found more commonly in seedling lupins. Cucumber mosaic virus (CMV) was isolated once. The AMV strains were differentiated by their reaction in Phaseolus vulgaris; they were serologically closely related. Both AMV and LMV were aphid transmitted but not transmitted in lupin seed. LMV was distantly serologically related to both BYMV and CPMV. It cross-protected against BYMV but not against CPMV and it differed from both these viruses in some host reactions. The CMV isolate from lupins was similar to type CMV. It was transmitted both mechanically and by aphid, easily from cucumber to cucumber, but with difficulty from cucumber to lupin.     

Resistance to six viruses in the legume goat's rue {Galega orientalis Lam.)

Plants from 2nd to 6th year leys of the legume goat's rue (Galega orientalis Lam.) were tested for infection with bean yellow mosaic (BYMV), bean common mosaic (BCMV), alfalfa mosaic (AMV), broad bean stain (BBSV), red clover mottle (RCMV) and cucumber mosaic (CMV) viruses by enzyme-linked immunosorbent assay (ELISA), electron microscopy, and by sap-inoculation to various test plant species. No virus infections were observed in goat's rue in the field. Glasshouse-grown seedlings of goat's rue were inoculated with the above viruses. No virus was detected in the inoculated plants. The results suggest that goat's rue is extremely resistant to the above six viruses which are important in other forage legumes.     

Occurrence,distribution and seasonal changes of viruses infecting common bean in northwestern Iran

Many surveys were conducted during 2003–2005 to study the identity, prevalence and fluctuation of bean infecting viruses in northwestern Iran. In total, 649 bean samples with virus- like symptoms were collected and analysed by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and tissue-print immunoassay to detect infectious viruses. Serological tests revealed the presence of Bean common mosaic virus (BCMV), Bean common mosaic necrosis virus (BCMNV), Bean yellow mosaic virus (BYMV), Cucumber mosaic virus (CMV), Alfalfa mosaic virus (AMV), Bean leaf roll virus (BLRV), Bean pod mottle virus (BPMV) and Southern bean mosaic virus (SBMV), with some co-infection occurred, with prevalence of BCMV, BCMNV and BYMV (17–29% infection rate). The incidence of viruses showed variation in over 3 years of research including more than double increase in CMV from 2004 to 2005 and obvious one-third decrease in AMV from 2003 to 2005. SBMV and BPMV were detected sporadically in the fields and the response of some differential test plants was analysed by mechanical inoculation. Western immunoblotting analysis of SBMV infected bean leaf total proteins using SBMV-specific polyclonal antibody revealed viral CP with molecular mass of 28.5 kDa which confirmed the presence of SBMV as a new threat for bean production.     

国家种质库保存大豆和菜豆种质的种传病毒检测

以国家种质中期库提供的300份大豆、100份菜豆种质为材料,分别采用血清学和分子生物学方法,对种传病毒的种类进行了检测。结果表明:在大豆种质中检测出大豆花叶病毒(SMV)、黄瓜花叶病毒(CMV)、苜蓿花叶病毒(AMV)3种病毒,阳性检出率分别为25.33%(76份)、13.67%(41份)和4.67%(14份)。大豆种质中还存在大豆花叶病毒与黄瓜花叶病毒、大豆花叶病毒与苜蓿花叶病毒的复合侵染。在菜豆种质中检测出菜豆普通花叶病毒(BCMV)阳性材料92份,种质带毒率高达92%。这些信息将会对今后采取相关措施提高国家种质库保存的豆类种质的质量提供帮助。     

Distribution and impact of virus associated diseases of common bean (Phaseolus vulgaris L.) in northern Iran

Different viral diseases infect common bean crops in Iran. A total of 248 symptomatic samples were collected from common bean fields throughout main growing fields of Guilan province in Iran during the summer of 2006. Eight viruses were detected using double antibody-sandwich – enzyme-linked immunosorbent assay (DAS-ELISA). Bean common mosaic virus – BCMV (1%), Bean leaf roll virus – BLRV (9%), Cowpea mild mottle virus – CpMMV (6%), Southern bean mosaic virus – SBMV (3%), Cucumber mosaic virus – CMV (15%), Bean golden mosaic virus – BGMV (2%), Bean common mosaic necrosis virus – BCMNV (1%) and Bean yellow mosaic virus – BYMV (1%) were detected. Comparatively CMV (15%) was found to be more prevalent in Guilan province. Multiple infections of viruses were recorded in many samples. Weed species belonging to Chenopodiaceae, Solanaceae, Malvaceae and Amaranthaceae families were also found to be infected with the viruses.     

Recognition and differentiation of seven whitefly-transmitted geminiviruses from India, and their relationships to African cassava mosaic and Thailand mung bean yellow mosaic viruses

Particles resembling those of geminiviruses were found by immunosorbent electron microscopy in extracts of plants infected in India with bhendi yellow vein mosaic, croton yellow vein mosaic, dolichos yellow mosaic, horsegram yellow mosaic, Indian cassava mosaic and tomato leaf curl viruses. All these viruses were transmitted by Bemisia tabaci whiteflies, all reacted with at least one out of ten monoclonal antibodies to African cassava mosaic virus (ACMV), and all reacted with a probe for ACMV DNA-1, but scarcely or not at all with a full-length probe for ACMV DNA-2. Most of the viruses were distinguished by their host ranges when transmitted by whiteflies, and the rest could be distinguished by their pattern of reactions with the panel of monoclonal antibodies. Horsegram yellow mosaic virus was distinguished from Thailand mung bean yellow mosaic virus by its lack of sap transmissibility, ability to infect Arachis hypogaea, failure to react strongly with the probe for ACMV DNA-2 and its pattern of reactions with the monoclonal antibodies. Structures resembling a ‘string of pearls’, but not geminate particles, were found in leaf extracts containing malvastrum yellow vein mosaic virus. Such extracts reacted with two of the monoclonal antibodies, suggesting that this whitefly-transmitted virus too is a geminivirus. All seven viruses from India can therefore be considered whitefly-transmitted geminiviruses.     

Biological properties of necrotic and non-necrotic strains of bean yellow mosaic virus in cool season grain legumes

A collection of 51 bean yellow mosaic virus (BYMV) isolates was transmitted from infected Trifolium subterraneum (subterranean clover) to Lupinus angustifolius (narrow‐leafed lupin) by Myzus persicae (green peach aphid). Depending on isolate and L. angiistifolius genotype used, two distinct responses developed in L. angustifolius plants, either systemic necrosis and plant death or non‐necrotic reactions of varying severity. Ten isolates caused necrosis and plant death in cv. Danja. However, when nine of these were inoculated to breeding line 90L423‐07‐13, seven induced non‐necrotic reactions, while two caused necrosis and plant death. Thirty seven isolates always produced non‐necrotic reactions regardless of genotype of L. angustifolius inoculated. Non‐necrotic and necrotic isolates originally came both from lupins and other species, and the non‐necrotic isolates were no less efficiently transmitted by M. persicae than the necrotic ones. When one isolate of each type was inoculated together to T. subterraneum and nine months later this culture was used as an acquisition source for aphid transmission to L. angustifolius, only the necrotic type was detected. Previous infection of L. angustifolius plants with a non necrolic isolate prevented subsequent infection by a necrotic one. All necrotic and non‐necrotic isolates reacted with BYMV antiserum in ELISA but only two cross‐reacted with antiserum to clover yellow vein virus (CYVV). When selected necrotic and non‐necrotic isolates were inoculated to differential hosts, all behaved like BYMV and not CYVV. When three isolates of each type were transmitted to 11 other cool season grain legume species, except in Cicer arietinum (chickpea), there were no necrotic reactions, but symptom severity varied with the isolate and species inoculated. The two isolates that caused necrosis in C. arietinum did not do so in L. angustifolius. The six isolates from Vicia faba (faba bean) all caused non‐necrotic reactions in L. angustifolius cv. Danja and 90L423‐07‐13. These and two necrotic isolates readily infected five genotypes of V. faba always causing severe symptoms. However, three non‐necrotic isolates from L. angustifolius and a further necrotic isolate were poorly infectious on V. faba in which they generally induced mild symptoms. These results show that at least three strain groups of BYMV can be distinguished by their reactions in different L. angustifolius genotypes, one causing necrosis and death in cv. Danja and 90L423‐07‐13, one causing necrosis and death in Danja but not 90L423‐07‐13, and one causing non‐nccrotic reactions in both. These strain groups could not be distinguished when representative necrotic and non‐necrotic isolates were inoculated to other grain legume species. However, inoculation to V. faba distinguished two other BYMV strain groupings differing in severity of symptoms and ability to infect this species.     

The effect of insecticides and a plant barrier row on aphid populations and the spread of bean yellow mosaic potyvirus and subterranean clover red leaf luteovirus in Vicia faba in South Australia

The effect of the insecticides malathion, demeton-S-methyl and disulfoton, and a barley barrier row on the rate and pattern of spread of bean yellow mosaic potyvirus (BYMV) and subterranean clover red leaf luteovirus (SCRLV) in Vicia faba was investigated in field plots with artificially introduced sources of viruses and vectors. The systemic insecticide treatments reduced aphid populations in the plots and this was associated with reduced spread of SCRLV, but not of BYMV. The barley barrier did not affect aphid populations in plots; however, it reduced the spread of BYMV to rows 1 · 1 m from the source but had only a minor effect on the spread of SCRLV. Apterae rather than alates of Aulacorthum solani were implicated in the spread of SCRLV. Spread of BYMV was attributed mainly to alate migrants of Myzus persicae and Macrosiphum euphorbiae, but other aphid species and morphs which occurred in high populations at the times of most rapid virus spread may also have had an active role as vectors of BYMV.     

Reflective mulch decreases the spread of two non-persistently aphid transmitted viruses to narrow-leafed lupin (Lupinus angustifolius)

Trials were done in 1987–1989, to investigate the effect of a reflective aluminium painted polythene mulch in protecting rows of narrow-leafed lupin ( Lupinus angustifolius ) from infection with two non-persistently aphid-transmitted viruses, bean yellow mosaic (BYMV) and cucumber mosaic (CMV). The mulch greatly decreased the rate and extent of spread of BYMV from external sources into mulch-protected rows in two trials, but was somewhat less effective in a third. The rate and extent of spread of CMV from an adjacent external source into reflective mulch-protected rows was also greatly decreased in one trial in which the mulch also decreased spread within rows and was effective even when the primary infection source was only 2.5 m away. In a trial sown with CMV-infected seed ( c . 2% seed transmission), the mulch decreased CMV spread from primary foci within rows. Reflective mulch can be used to protect breeders' single row plots of lupins from infection with CMV and BYMV.     

Split Personality of a Potyvirus: To Specialize or Not to Specialize?

Bean yellow mosaic virus (BYMV), genus Potyvirus, has an extensive natural host range encompassing both dicots and monocots. Its phylogenetic groups were considered to consist of an ancestral generalist group and six specialist groups derived from this generalist group during plant domestication. Recombination was suggested to be playing a role in BYMV''s evolution towards host specialization. However, in subsequent phylogenetic analysis of whole genomes, group names based on the original hosts of isolates within each of them were no longer supported. Also, nine groups were found and designated I-IX. Recombination analysis was conducted on the complete coding regions of 33 BYMV genomes and two genomes of the related Clover yellow vein virus (CYVV). This analysis found evidence for 12 firm recombination events within BYMV phylogenetic groups I–VI, but none within groups VII–IX or CYVV. The greatest numbers of recombination events within a sequence (two or three each) occurred in four groups, three which formerly constituted the single ancestral generalist group (I, II and IV), and group VI. The individual sequences in groups III and V had one event each. These findings with whole genomes are consistent with recombination being associated with expanding host ranges, and call into question the proposed role of recombination in the evolution of BYMV, where it was previously suggested to play a role in host specialization. Instead, they (i) indicate that recombination explains the very broad natural host ranges of the three BYMV groups which infect both monocots and dicots (I, II, IV), and (ii) suggest that the three groups with narrow natural host ranges (III, V, VI) which also showed recombination now have the potential to reduce host specificity and broaden their natural host ranges.     

Occurrence and distribution of lettuce mosaic disease in Tehran province from Iran

Lettuce mosaic virus (LMV) Cucumber mosaic virus (CMV) and Tomato spotted wilt virus (TSWV) were identified in fields of Tehran province. In this study 452 leaf samples were collected from the fields throughout the Tehran province during 2002 and 2003. Distribution of Lettuce mosaic virus (LMV), Cucumber mosaic virus (CMV), Tomato spotted wilt virus (TSWV)and Arabis mosaic virus (ArMV) was determined with DAS-ELISA. Percentage of single Infection to LMV. CMV or TSWV was 20.58, 15.93 and 9.96% respectively. Also 15.28% of samples were co- infected with LMV+CMV, 8.19% with LMV+TSMV and 7.74% with CMV+TSWV. 4.65% of samples were Infected to all of these three viruses. LMV was found in 48.69%, CMV in 43.59% and TSWV in 30.54% of samples totally. Therefore LMV is major dominant agent of lettuce mosaic disease in Tehran province. This is the first report of occurrence of TSWV on lettuce in Iran and first report of CMV and LMV in Tehran province.     

Detection of Three Plant Viruses by Dot-Blot and Tissue-Blot Immunoassays Using Chemiluminescent and Chromogenic Substrates1

Detection of bean yellow mosaic virus (BYMV), impatiens necrotic spot virus (INSV) and lily symptomless virus (LSV) by dot-blot and tissue-blot immunoenzymatic assay was compared by using either chromogenic or chemiluminescent substrates. Testing was conducted on infected-leaf extracts and on purified virus preparations. Both types of substrates gave comparable results with leaf extracts. However, with purified virus, the use of chemiluminescent substrates led to a more sensitive detection of the three viruses.     

Serological and molecular characterisations of the Egyptian isolate of Bean common mosaic virus

Bean common mosaic virus (BCMV) was isolated from the naturally infected bean plants collected from the Kafr El-Sheikh and El-Gharbia Governorates. BCMV induced sever mosaic, vein banding, malformation, leaf curling and stunting on bean plants cv. Giza 6. The isolated virus was propagated in bean plants cv. Giza 6. The identification of BCMV was carried out serologically by an indirect enzyme-linked immunosorbent assay using BCMV antiserum. Positive reaction indicated that the virus under study was related serologically to Potyvirus. The molecular biology techniques were used to identify and characterise the coat protein gene of BCMV. Oligonucleotide primers were designed for BCMV according to the published nucleotide sequences of BCMV and were successfully amplified with a DNA fragment (300 bp) from BCMV CP gene by RT-PCR. The total RNA was extracted from bean leaves and was reverse-transcribed and amplified using the oligonucleotide primer. The amplified product was analysed by gel electrophoresis. Also, Southern and dot blot hybridisations were used to establish the authenticity and specificity to the RT-PCR-amplified products of BCMV. The nucleotide sequences of the Egyptian isolate of BCMV/CP showed similarity with an isolate (BCMV-NY 15) which belongs to Puerto Rico.     

Detection of Four Seed-borne Plant Viruses by the Enzyme-Linked Immunosorbent Assay (ELISA)

This study was conducted to evaluate the sensitivity of the ELISA technique in detecting four economically important viruses, namely barley stripe mosaic (BSMV), cucumber green mottle mosaic (CGMMV), bean common mosaic (BCMV), and squash mosaic (BSMV) viruses in single seeds as well as in batches of barley, cucumber, bean and squash seeds, respectively. Results indicated the suitability of the technique in detecting the above viruses in single germinated seeds or embryos. Accordingly, seed transmission rates of BSMV, CGMMV, BCMV and SqMV were found to be 67 %, 17%, 17% and 12%, respectively. In artificially contrived mixtures of infected: healthy seeds or embryos, BSMV, CGMMV, BCMV and SqMV were successfully detected at ratios of 1 : 500, 1 : 25, 1 : 10 and 1 : 10, respectively. Sensitivity of detection was increased in the ease of BSMV by using germinated rather than ground dry BSMV-infected barly seeds; and in the case of SqMV, by using whole germinating emybryos rather than coleoptiles only. Trials on re-using the enzyme-γ-globulin conjugate indicated that CGMMV conjugate used once can be re-used with little loss in reactivity.     

Genome affinities and epitope profiles of whitefly-transmitted geminiviruses from the Americas

The relationships among fifteen isolates of whitefly-transmitted geminiviruses (WTGs) from North, Central and South America and six from other continents were assessed (a) in nucleic acid hybridisation tests with sulphonated DNA probes for eight of the viruses, and/or (b) in triple-antibody-sandwich ELISA with panels of monoclonal antibodies (MAbs) to particles of African cassava mosaic virus (ACMV) and Indian cassava mosaic virus (ICMV). Probes specific for DNA-A of four American viruses, abutilon mosaic (AbMV), bean golden mosaic (BGMV), squash leaf curl (SLCV) and tomato golden mosaic (TGMV), detected virtually all the American viruses but reacted weakly if at all with ICMV, ACMV or tomato yellow leaf curl virus from Thailand (TYLCV-T). Conversely, the probe for ACMV DNA-A did not detect any of the American viruses, and that for TYLCV-T DNA-A reacted weakly with SLCV and TGMV0020but did not detect the others. In contrast, probes specific for DNA-B of the four American viruses or ACMV detected only the homologous virus, except for slight reactions between the AbMV DNA-B probe and both chino del tomate virus (CdTV)-DNA and SLCV-DNA. However, a probe for DNA-B of bean calico mosaic virus (BCMoV) reacted weakly with BGMV-PR DNA, and a probe for DNA-B of CdTV from Mexico detected several American viruses. Six out of 17 MAbs specific for ACMV and six out of 10 MAbs specific for ICMV reacted with one or other of the 14 American virus isolates tested. Two and-ACMV MAbs reacted with all, and one anti-ACMV MAb and two anti-ICMV MAbs reacted with nearly all the American viruses, one anti-ACMV MAb reacted with about half the American viruses and six other MAbs reacted with only one or two of them. Of the American viruses, CdTV and AbMV were the least closely related to the others. The epitope profiles of BCMoV, BGMV, cotton leaf crumple virus, serrano golden mosaic virus and SLCV were virtually indistinguishable. TGMV, potato yellow mosaic virus (PYMV) and an euphorbia virus had profiles intermediate between those of the BGMV cluster and AbMV-CdTV. In general, the epitope profiles and the results of hybridisation tests with DNA-A probes show that the similarities among the American viruses are greater than those between the American viruses and the viruses from other continents; the hybridisation tests with DNA-B probes show that substantial differences exist between individual American viruses. In America, geminivirus evolution seems to have proceeded convergently from different progenitor viruses, or divergently from one ancestral form, with DNA-B diverging to a greater extent than DNA-A and its particle-protein gene.     

Protective action of salicylic acid against bean yellow mosaic virus infection in Vicia faba leaves

In this study, morphological, ultrastructural and physiological modifications of faba bean (Vicia faba cv Giza 461) leaves in response to bean yellow mosaic virus (BYMV) infection and salicylic acid (SA) treatments were examined. Under BYMV stress, leaves showed symptoms including severe mosaic, mottling, crinkling, size reduction and deformations. Three weeks after virus inoculation, photosynthetic rate, pigment contents and transpiration rate were significantly reduced in response to BYMV infection.

Ultrastructural investigations of BYMV-infected leaves demonstrated that most chloroplasts with increased stromal area became spherical in shape and some lost their envelopes, either partially or totally. The internal structures of chloroplast, grana and thylakoids were dilated. Two kinds of inclusions were detected in BYMV-infected leaves: straight or slightly curved bands sometimes coiled or looped at the end, and electron opaque crystals with varied shapes. BYMV-infected cells showed lower chloroplast number in comparison to the control.

Spraying of SA on faba bean leaves helped to reduce or prevent the harmful effects produced after virus infection. Application of 100 μM SA three days before inoculation restored the metabolism of infected leaves to the levels of healthy controls. SA treatment improved plant health by increasing the photosynthesis rates, pigment contents and levels of other parameters studied similar to control values.

Moreover, SA treatment increased plant resistance against BYMV. This was observed through induction of chloroplast number, reduction in percentage of infected plants, decrease in disease severity and virus concentration of plants treated with SA prior to BYMV inoculation. Cells of SA-treated samples showed well-developed chloroplasts with many starch grains and well-organized cell organelles.

The present results provide an overview of the negative effects on faba bean leaves due to BYMV infection from physiological and subcellular perspectives. Also, a role of SA involved in induction of resistance against BYMV infection in bean plants is discussed.     

莴苣病毒病病毒的分离及鉴定

从陕西省关中地区春季和秋季自然发病的109个莴苣病株上分离到3种不同的病毒。经寄主范围与症状反应、抗性测定、传播途径、血清学反应以及电镜观察等鉴定表明,侵染莴苣的3种病毒是莴苣花叶病毒(LMV)、黄瓜花叶病毒(CMV)及蒲公英黄色花叶病毒(D YMV),其中DYMV在我国是首次报道。     

Alfalfa mosaic and cucumber mosaic virus infection in chickpea and lentil: incidence and seed transmission

Samples collected in 1994 and 1995 from commercial crops of chickpeas and lentils growing in the agricultural region of south-west Western Australia were tested for infection with alfalfa mosaic (AMV) and cucumber mosaic (CMV) viruses, and for members of the family Potyviridae using enzyme-linked immunosorbent assay (ELISA). In 1994 no virus was detected in the 21 chickpea crops tested but in 1995, out of 42 crops, AMV was found in two and CMV in seven. With lentils, AMV and/or CMV was found in three out of 14 crops in 1994 and 4 out of 13 in 1995, both viruses being detected in two crops in each year. Similar tests on samples from chickpea and lentil crops and plots growing at experimental sites, revealed more frequent infection with both viruses. No potyvirus infection was found in chickpeas or lentils in agricultural areas either in commercial crops or at experimental sites. However, bean yellow mosaic virus (BYMV) was detected along with AMV and CMV in irrigated plots of chickpeas and lentils at a site in Perth. When samples of seed from infected crops or plots of chickpeas and lentils were germinated and leaves or roots of seedlings tested for virus infection by ELISA, AMV and CMV were found to be seed-borne in both while BYMV was seed-borne in lentils. The rates of transmission found through seed of chickpea to seedlings were 0.1–1% with AMV and 0.1–2% with CMV. Seed transmission rates with lentil were 0.1–5% for AMV, 0.1–1% for CMV and 0.8% for BYMV. Individual seed samples of lentil and chickpea sometimes contained both AMV and CMV. With both species, infection with AMV and CMV was sometimes found in commercial seed stocks or seed stocks from multiplication crops of advanced selections nearing release as new cultivars. Seed-borne virus infection has important practical implications, as virus sources can be re-introduced every year to chickpea and lentil crops or plots through sowing infected seed stocks leading to spread of infection by aphid vectors, losses in grain yield and further contamination of seed stocks.     

Interaction of Cucumber mosaic virus and Bean yellow mosaic virus in co-infected plants of bean and broad bean

After evaluation of the responses of bean and broad bean common cultivars against an isolate of Cucumber mosaic virus (CMV-K) and Bean yellow mosaic virus (BYMV-K), interaction of isolates was statistically studied on co-infected plants of bean cv. Bountiful and broad bean cv. Lahijan at two trials. Based on viral relative concentration determined by quantitative enzyme-linked immunosorbent assay, BYMV interacts synergistically with CMV in bean at 14 days post inoculation, while in co-infection with BYMV, CMV interacts antagonistically in both host plants at least in one of the two trials. This suggests that CMV/BYMV interaction is dependent on host species and developmental stage of plant. Co-infection like single infection with CMV in bean plants led to significantly decrease in plants’ height and fresh weight than BYMV singly infected and healthy plants, while viral infection of broad bean plants did not significantly affect growth parameters. Decline effect of viral infection (especially co-infection) on chlorophyll and carotenoids value of bean plants was greater than those of broad bean. Viral infection (singly or doubly) caused irregular changes in nutrient elements values of both hosts compared with healthy ones.     

Patterns of spread of the non-persistently transmitted bean yellow mosaic virus and the persistently transmitted subterranean clover red leaf virus in Vicia faba

Patterns of spread of two aphid borne viruses, the non-persistently transmitted bean yellow mosaic virus (BYMV) and the persistently transmitted subterranean clover red leaf virus (SCRLV), were compared simultaneously in field plots of Vicia faba minor grown in a Mediterranean climate (winter-spring growing season, and dry summer). Spread from a primary source was mapped following the artificial introduction of virus alone, or virus with vector, at the centre of the plots. BYMV spread rapidly from the virus source whether or not vectors were introduced with the virus. By contrast, SCRLV spread from the source only when plants were also artificially infested with the vector Aulacorthum solani. An attempt was made to evaluate the importance of secondary spread of both viruses by assessing the degree of clumping of infected plants that occurred outside the primary sites of virus introduction. BYMV-infected plants were clumped in each treatment irrespective of whether the virus was introduced alone or with vector, as well as in control plots. Clumping of SCRLV occurred only when the vectors were introduced on virus source plants at the beginning of the experiment. Times of spread were determined both by exposing trap plants at 4-weekly intervals throughout the 30 month trial period, and by analysing the rates of spread in experimental plots between June and November in one growing season. Both viruses spread in the spring when vectors were flying, but negligible spread of the viruses was observed in the autumn despite aphid flight activity. Times of flight of the four main aphid vector species were continuously monitored with yellow water traps. A major spring and a minor autumn flight peak were observed for Aphis craccivora, Macrosiphum euphorbiae, Aulacorthum solani and Myzus persicae. Aphid flights occurred predominantly in weeks when the mean temperature was in the range 13–17°C. Rainfall above 7 mm per week appeared to affect flights only when mean weekly temperatures were outside the range 13–17°C.