Relative efficiency of a number of aphid species in the transmission of potato virus YN in the Netherlands

This paper reports the results of live-trapping winged aphids in an Ashby (1976) trap in potato crops in the Netherlands from 1983–1987. During this period, a total of 122 aphid species were trapped. Although only four of those species were able to colonise potato, 26 of them were able to transmit PVY^N from potato to potato test plants. The transmission rates and relative efficiency factors (REF's) of those transmitters were determined. Aphis sambuci, Cryptomyzus galeopsidis, Dysaphis spp.,Hyadaphis foeniculi, Hyalopterus pruni andMyzus cerasi were recorded for the first time as vectors of PVY^N in the Netherlands.The numbers of aphids per species caught per season differed very much, also the virus transmission results of some fluctuated from year to year, e.g.Brachycaudus helichrysi. The REF's in various reports differ greatly, thus the value of a universal REF is doubtful. Assessment of the rate of virus spread in a potato crop is discussed.Samenvatting Van de in Nederland voorkomende aardappelvirussen wordt het aardappelvirus Y^N (PVY^N) als het meest schadelijke bij de pootgoedproduktie beschouwd. Dit virus kan op non-persistente wijze door een aantal bladluissoorten worden overgebracht. De groene perzikluis,Myzus persicae wordt geacht dit het meest efficiënt te kunnen doen.In de periode 1983–1987 is onderzocht welke bladluissoorten, geregistreerd in aardappelpercelen te Wageningen, Y^N-virus kunnen overbengen. In deze periode werden 122 gevleugelde bladluissoorten met behulp van een Ashby-val levend gevangen en op hun vermogen om Y^N-virus van aardappel naar aardappel over te brengen getoetst. 26 soorten hiervan zijn potentiële Y^N-virusoverbrengers. De relatieve efficiëntiewaarden (REF) voor elk van deze soorten werden opnieuw berekend.De REF-waarde voorBrachycaudus helichrysi werd berekend op 0,21, in afwijking van de waarde (0,01) die Van Harten (1983) aan deze toekende na waarnemingen gedurende slechts één seizoen.40% van het totaal aantal geregistreerde bladluizen bestond uitCavariella aegopodii, M. persicae, Metopolophium dirhodum, Rhopalosiphum insertum, R. padi enSitobion avenae. Minder talrijk (6,5%) was de groepB. helichrysi, Brachycandus spp. enMacrosiphum euphorbiae. De groepAphis nasturtii, Myzus certus enPhorodon humuli had een aandeel van 3,2% in de totale vangst. BehalveC. aegopodii zijn de genoemde soorten in staat het PVY^N over te brengen van aardappel naar aardappel. Van de rest zijn echter ook een aantal soorten in staat PVY^N over te brengen maar die zijn slechts in geringe mate gevangen. A. nasturtii, Brachycaudus spp.,M. certus enM. persicae besmetten vaker dan andere soorten aardappelplantjes met PVY^N. Van de soortenAphis sambuci, Cryptomyzus galeopsidis, Dysaphis spp.,Hyadaphis foeniculi, Hyalopterus pruni andMyzus cerasi werd voor de eerste keer in Nederland overdracht van PVY geconstateerd.     

Aphid vectors of potato virus YN

BesideMyzus persicae a dozen other species were found to be vectors of potato virus Y^N. Eleven other species did not transmit the virus.White Burley tobacco and A6 potato are equally suitable as test plant to monitor the efficency ofRhopalosiphum padi as vector of PVY^N, but as PVY^N source tobacco is not suitable for this aphid species.Between some aphid species rather large differences exist in retention periods of PVY^N. WithR. insertum andAphis fabae transmission after a 1 h starvation period was still 50% of that without starvation. WithPhorodon humuli, M. certus andM. persicae this value was only 15, 30 and 30%, respectively.Samenvatting Van 12 bladluissoorten werd vastgesteld dat zij, evenalsMyzus persicae, vectoren van het aardappelvirus Y^N (PVY^N) zijn. Van 11 andere soorten kon dit niet worden vastgesteld. Nicotiana tabacum cv. White Burley enSolanum tuberosum cv. A6 bleken beide goed bruikbaar als toetsplant voor het vaststellen van de efficiëntie vanRhopalosiphum padi als vector van het PVY^N; voor deze bladluissoort is tabak ongeschikt als bron van PVY^N.De retentieperiode van het PVY^N lijkt bij verschillende bladluissoorten aanzienlijk te variëren. BijRhopalosiphum insertum enAphis fabae bracht één uur vasten na de acquisitie de overbrenging terug tot 50% van die welke zonder vasten werd verkregen. BijPhorodon humuli was de reductie in overbrenging na één uur vasten 85%, bijMyzus certus enM. persicae was deze 70%.     

Molecular characterization of potato virus YN isolates by PCR-RFLP

Based on the sequence polymorphism in the 5 terminal part of the viral genome, a range of PVY^N isolates were characterized by polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP). Three pairs of primers selected in the 5 non-translated and P1 protein region were tested. Two of them yielded PCR products of about 1Kb from all isolates tested. Restriction analysis of the PCR products gave two distinct electrophoretic patterns, whichever of the three enzymes was used. In this way, the 18 isolates were separated into two easily identifiable subgroups. All tuber necrosing isolates (PVY^NTN) were clustered in the same subgroup.     

Characterization of potato potyvirus Y (PVY) isolates from seed potato batches. Situation of the NTN, Wilga and Z isolates

A collection of 38 PVY isolates from seed potato batches, originating from several Western European countries, was characterized by using current biological, serological and molecular tools differentiating PVY strains and groups. The correlation between the three kinds of tests was good but not absolute. No single serological or PCR method was able to discriminate among the five isolate groups found. Twenty-nine isolates belonged to the PVY^N strain and six to the PVY^O strain. No PVY^C was found. Two other isolates reacted serologically like PVY^O, but were unable to elicit a hypersensitive response from the Ny_tbr gene and probably represent the PVY^Z group. At the molecular level, these two isolates showed a combination of both PVY^O and PVY^N and could be recombinants of these strains. Another isolate reacted serologically like PVY^O, but induced vein necrosis in tobacco, like PVY^N-Wilga. Some PVY^N isolates caused tuber ring necrosis in glasshouse conditions. These might belong to the PVY^NTN group. The PVY^NTN, PVY^N-Wilga and PVY^Z groups probably represent pathotypes within strains PVY^N and PVY^O, respectively. The present study also confirms previous reports showing a high genetic variation at the 5 end within the PVYN strain.     

Flight behaviour of the aphidMyzus persicae during its maiden flight

The assumption that the first flight of aphids from their secondary host is several kilometers long, followed by short hops, is mainly based on research done withAphis fabae. The validity of these observations has not been proved satisfactorily in the case of the peach aphidMyzus persicae. By using radiolabelled aphids their behaviour during the maiden flight was studied. The results indicate that the first flight can be as short as 1 to 100 m, which might have consequences for our views on the spread of viruses in the crop.Samenvatting Op grond van onderzoek dat in hoofdzaak is verricht met de bladluisAphis fabae, wordt algemeen aangenomen dat de eerste vlucht vanaf de secundaire waardplant over een grote afstand plaatsvindt, gevolgd door meerdere korte vluchten. De juistheid van deze veronderstelling is voorMyzus persicae niet afdoende bewezen. Door gebruik te maken van radioactief gemerkte perzikluizen is getracht hun gedrag tijdens de eerste vlucht te volgen. Uit dit onderzoek blijkt dat de eerste vlucht van deze bladluis wel degelijk kort kan zijn. Deze resultaten kunnen consequenties hebben voor onze inzichten omtrent de verspreiding van virussen in het gewas.     

Infection pressure of potato virus YN

Potato virus Y^N (PVY^N) infection was determined by the tobacco test in Swifterbant (Eastern Flevoland). In plots with beet, wheat and seed potatoes the infection exhibited an identical course. No differences were found either between PVY^N infection in the border and that in the middle of a field planted with ware potatoes, although infection pressure was clearly higher here than in the plot with seed potatoes. A barrier crop of 10 rows of wheat did not decrease the infection pressure of the virus.From August onwards, the spread of PVY^N in Lienden (Betuwe) was followed. Here virus transmission was found continuously, even until mid-November.Potato volunteers outside as well as in potato fields are serious infection sources. In 1976 and in 1977 virus spread was detected before the flight ofMyzus persicae, as determined with yellow Moericke traps. Infection pressure can be measured more efficiently by the tobacco test than by aphid trapping. The effect of rogueing at the time of virus spread should be reconsidered.If infection pressures in different areas or successive years are to be compared, the tobacco test should be standardized. A proposal to this effect is made.Samenvatting In Swifterbant (Oostelijk Flevoland) werd de infectie met het aardappel-Y^N-virus (PVY^N) bepaald met behulp van de tabakstoests. In percelen met bieten, tarwe en pootaardappelen bleek de infectie hetzelfde verloop te hebben. Tussen het infectieverloop van PVY^N in de rand en in het midden van een veld consumptieaardappelen werd eveneens geen verschil gevonden. Wel was de infectiedruk hier duidelijk hoger dan in het pootgoedperceel. Een barrier crop van 10 rijen tarwe verminderde de infectiedruk niet.De volgende conclusies kunnen worden getrokken. Aardappelopslag buiten en in aardappelvelden vormt een zeer belangrijke infectiebron. Zowel in 1976 als in 1977 vond de virusverspreiding plaats vóór de vlucht vanMyzus persicae begon, zoals deze werd bepaald met behulp van de gele Moericke vangbakken. Het effect van opzuiveren ten tijde van de virusverspreiding dient aan een nader onderzoek te worden onderworpen. De infectiedruk kan met de tabakstoets op meer directe wijze worden vastgesteld dan met bladluisvangsten mogelijk is.Wil men overgaan tot het vergelijken van de infectiedruk in verschillende gebieden of in verschillende jaren, dan dient de tabakstoets te worden gestandaardiseerd. Een voorstel hiertoe wordt gedaan.     

Spread of potato virus Y in potato cultivars (Solanum tuberosum L.) with different levels of sensitivity

The aim of this work was to correlate the appearance of the symptoms, multiplication and spread of virus after mechanical inoculation of potato (Solanum tuberosum L.) cultivars showing different levels of susceptibility and sensitivity to Potato virus Y^NTN (PVY^NTN). The potato cultivars used were the resistant cultivar Sante and susceptible cultivars Igor, Pentland squire and Désirée. The spread of the virus PVY^NTN in infected plants was monitored using different methods: DAS-ELISA, tissue printing, immuno-serological electron microscopy and real-time PCR. In all three susceptible cultivars, the virus was detected in the inoculated leaves 4–5 days after inoculation. From there virus spread rapidly, first into the stem, then more or less simultaneously to the upper leaves and roots. Real-time PCR was shown to be very sensitive and enabled viral RNA to be detected in non-inoculated leaves of susceptible cultivar Igor earlier than other methods. Therefore, for exact studies of plant–virus interaction, a combination of methods which detect viruses on the basis of their different properties (coat protein, morphology or RNA) should be used to monitor the spread of viruses.     

New aphid vectors and efficiency of transmission of Potato virus A and strains of Potato virus Y in the UK

The aphid‐transmitted viruses Potato virus Y (PVY) and Potato virus A (PVA) commonly affect seed potatoes in the UK. The transmission efficiency for aphid species is used to calculate a potential transmission risk and is expressed as a relative efficiency factor (REF). These REFs have not previously been calculated for UK strains of viruses or aphid clones. Using a previously published method, REFs have been calculated for the aphid species and viruses commonly occurring in UK potatoes. The efficiency of transmission of Myzus persicae is nominally set to a REF of 1 and REFs for other species are calculated relative to this. These data represent the first set of REFs calculated for PVA transmission. Macrosiphum euphorbiae (REF 0.91) was almost as efficient as M. persicae at PVA transmission. The data were further analysed to compare transmission rates of PVY and PVA using a binomial (logit) generalized mixed model to take into account the potential influence of variation in virus titre between leaves. This approach found that there is little variation between the efficiency of transmission between clones of each aphid species or between strains within a virus species. This is a first report that Aphis fabae, Metopolophium dirhodum, Sitobion avenae, Acyrthosiphon pisum and Cavariella aegopodii have the ability to vector PVA. This study also represents a first report that C. aegopodii has the ability to vector PVY and confirms the potential of S. avenae, A. fabae, M. euphorbiae and Rhopalosiphum padi as important PVY vectors.     

Prospects for improving potato crop protection against aphid vectors

Conventional ways to control aphid vectors on potato crops rely essentially on cultural and chemical methods. The extensive use of insecticides, too often applied regardless of real needs and consequences, has resulted in more and more failures in both controlling aphids and virus spread. This paper stresses the need to introduce more rationale in the operation of existing methods by improving the efficiency of some of them like forecasting systems, to assess the potential of others like fertilization and semiochemicals and to put most efforts on resistant cultivars so that integrated pest management can be operated in the near future.     

Characteristics of a resistance-breaking isolate of potato virus Y causing potato tuber necrotic ringspot disease

An Austrian isolate of potato virus Y^NTN, the causal agent of potato tuber necrotic ringspot disease (PTNRD), was serologically compared with seven Dutch PVY^N isolates. Using polyclonal and monoclonal antibodies, it was found indistinguishable from PVY^N. Determination of the nucleotide sequence of the coat protein cistron and comparison of the deduced amino acid sequence with coat protein sequences of other potyviruses revealed a high level of homology with PVY^N coat protein sequences. This confirmed the close taxonomic relationship of PVY^NTN with the PVY^N subgroup of potato virus Y. PVY^NTN is able to overcome all resistance genes known so far in commercial potato cultivars. Remarkably, transgenic PVY-protected tobacco plants are also resistant to PVY^NTN infection upon mechanical and aphid-mediated inoculation. These experiments indicate that genetically engineered resistance offers great potential in protection of potato to new aggressive strains of PVY^N.     

Potato Virus Y from Petunia can cause Symptoms of Potato Tuber Necrotic Ringspot Disease (PTNRD)

A potyvirus known to be an important agent involved in causing a disease of trailing petunias, was identified as being a member of the necrotic strain of potato virus Y (PVY) using a number of monoclonal antibodies. The sequence of the coat protein gene for the PVY isolate was determined and when compared with sequences for other PVY strains it was shown to cluster closely with isolates of PVY^NTN and to have a recombination point present within the coat protein common with other isolates of PVY^NTN. When inoculated onto potato tuber necrotic ringspot disease (PTNRD) susceptible potato cultivars the petunia isolate was found to be capable of causing necrotic tuber symptoms, consistent with those caused by other isolates of PVY^NTN. Due to the number of similarities it is thought the petunia isolate belongs to the PVY^NTN group of isolates. Out of 24 species of bedding and pot plant crops tested, 19 were shown by mechanical inoculation to be susceptible to PVY, highlighting not only a clear risk to a number of commercially important plant species from PVY^NTN infected trailing petunias, but also other susceptible crops grown in these areas.     

Control of potato virus Y (PVY) in seed potatoes by oil spraying,straw mulching and intercropping

Potato virus Y (PVY) is the potato virus with the highest economic impact on seed potato production. Insecticides are efficient in controlling aphids, which are the vectors of this virus, but rarely limit virus spread in the field. Straw mulching and mineral oil spraying are known as alternatives to insecticides to reduce PVY incidence, but important year‐to‐year variation in efficacy has been observed with both of these techniques. Preliminary studies revealed the efficacy of intercropping in controlling PVY spread, but more data are needed to validate this observation. A four‐year field trial was conducted in Switzerland to assess the potential synergistic effect of combining mineral oil spraying with straw mulching to increase the protection of seed potato crops against PVY spread. Furthermore, the efficacy of intercropping with oat and hairy vetch was examined as a novel way to control in‐field PVY spread. The present work demonstrates that the modes of action of mineral oil and straw mulching are complementary and reduce the year‐to‐year variation observed with oil and straw when used alone as PVY control agents. The results also demonstrate the efficacy of intercropping for the control of PVY, and the mode of action of this novel control method is discussed. Overall, this work shows that it is possible to increase the protection of potato fields against PVY spread by combining control strategies with different modes of action that complement each other, such as mulching, oil spraying and intercropping.     

Stability of the aphid transmission phenotype in cucumber mosaic virus

The stability of the aphid transmission phenotype in seven field isolates of cucumber mosaic virus (CMV) was studied, using aphids Aphis gossypii and Myzus persicae . Field isolates, obtained from four vegetable crops, were propagated in squash and Nicotiana glutinosa , and passaged by either aphid transmission or mechanical transfer. All seven isolates were transmissible by both aphids and this aphid transmission phenotype was stable after 20–24 mechanical passages. Upon further mechanical passaging, one of the seven isolates, CMV-2 A1-MT 60x, lost its transmissibility by Myzus persicae but was still transmissible by Aphis gossypii , although at a reduced rate. Isolates maintained by both aphid transmission and mechanical transfer were transmitted more efficiently by Aphis gossypii than by Myzus persicae . A comparison of the RNA profiles showed no major differences among the CMV isolates before and after mechanical passage.     

The characteristics of mineral oils in relation to their inhibitory activity on the aphid transmission of potato virus Y

In greenhouse trials paraffinic mineral oils, characterized by a viscosity gravity constant (VGC) of 0.790–0.819, and with viscosities between 12 and 30 cSt at 37°C (66–150 SUS) proved to have the best aphid transmission inhibiting activity of potato virus Y to red peppers. The activity decreased rapidly with decreasing viscosities but only slowly with increasing values.Effective oils are further characterized by an unsulfonated residue (USR) of 95–100, indicating the near or total absence of aromatic structures, which are inactive and known to be phytotoxic. The paraffine-pourpoint should be below 0°C, indicating that n-paraffines do not form a very important part of the oil, since they are also inactive. Naphthenic structures seem equally inert, their percentage in the oil depending on the origin of the crude oil, because they cannot be separated from the paraffinic structures by refining procedures.Mineral oils which one commercialize for agricultural practice normally have an USR above 95 and a paraffine-pourpoint below 0°C. Therefore, the information on the classification, based on a VGC value and on the viscosity, is already sufficient to allow an evaluation of those oils of their suitability as inhibitor of the virus transmission by aphids.Samenvatting In kasproeven bleken minerale paraffine oliën, gekenmerkt door een VGC (viscositeits-dichtheidsconstante) van 0.790–0.819 en een viscositeit tussen 12 en 30 cSt bij 37°C (66–150 SUS) de beste werking te bezitten tegen de overdracht van aardappelvirus Y naar paprika door bladluizen. De werking verminderde snel bij afnemende viscositeiten beneden 12 cSt, slechts langzaam bij toenemende waarden boven 30 cSt.De minerale olie met de meest gunstige eigenschappen met betrekking tot verhindering van de virusoverdracht wordt verder nog gekenmerkt door een USR (nier-sulfoneerbare rest) van 95–100. Dit betekent het geheel of bijna geheel afwezig zijn van aromatische verbindingen, die bekend zijn om hun fytotoxische eigenschappen en bovendien niet werkzaam zijn. Het stollingspunt moet bij voorkeur onder 0°C liggen wat betekent dat n-paraffinen geen al te belangrijk bestanddeel van de olie vormen, aangezien deze eveneens onwerkzaam zijn. Naphthenische structuren bleken ook onwerkzaam te zijn. Het gehalte hiervan in de oliefractie hangt echter van de herkomst van de ruwe olie of, omdat ze niet door raffineren van de paraffinestructuren kunnen worden gescheiden.Minerale oliën die aanbevolen worden voor landbouwkundige doeleinden, bezitten normalerwijze een USR boven 95 en een stollingspunt onder 0°C. Dit betekent dat informatie over de aard der oliën op grond van een VGC waarde en over de viscositeit voldoende is om dergelijke oliën te beoordelen op hun geschiktheid de virusoverdracht door bladluizen te kunnen verhinderen.     

The effect of insecticide application sequences on the control and insecticide resistance status of the peach-potato aphid, Myzus persicae (Hemiptera:Aphididae), on field crops of potato

Experiments were done on commercial potato crops in the UK to investigate the effect of different insecticide sequences on the control and insecticide resistance status of Myzus persicae (Sulzer). The work was done to provide field validation of similar laboratory studies done in 'field simulators'. To ensure adequate aphid populations and to influence the initial resistance status of the aphid population, cultured M. persicae from a clone of known resistance status (esterase R1, kdr heterozygote, non-MACE (modified acetylcholinesterase)) were inoculated into both experiments. Two-spray programmes starting with lambda-cyhalothrin (a pyrethroid insecticide) gave poor control in comparison with programmes starting with pirimicarb (a carbamate insecticide) or pirimicarb-containing mixtures. This concurred closely with the results obtained from single applications in field simulator studies. Treatment sequences containing pymetrozine (a pyridine azomethine insecticide) were also effective, though slower-acting. This again concurs with field simulator studies. The proportions of aphids carrying different resistance mechanisms were largely unaffected by treatment in these experiments. The implications of these results for field control strategies are discussed.     

Localization of potato leafroll virus in leaves of secondarily-infected potato plants

Potato leafroll virus (PLRV) antigen was localized by immunogold labelling in semi-thin leaf sections of secondarily-infected potato plants cv. Bintje. Viral antigen was present in all cell types of the phloem tissue. but occurred most abundantly in the companion cells. Detectable amounts of PLRV antigen were found only in the sieve elements in veins with a large number of infected companion cells. Occasionally, parenchyma cells were also found to be infected. PLRV was not exclusively limited to the phloem tissue in the infected potato plants, but was also found in mesophyll cells neighbouring minor phloem vessles. Spread of virus from cell to cell in the mesophyll was not observed. The distribution of PLRV in the potato leaf tissue has implication on its availability, for acquisition by aphids.     

Characterisation of a Tobamovirus from Trailing Petunias

A tobamovirus has been identified as being involved in a devastating disease of trailing petunia. Results from indicator plants and ELISA suggested that the tobamovirus was a strain of Tobacco mosaic virus (TMV). This was confirmed from the full sequence of the coat protein gene and a partial sequence of the replicase gene. Sequence analysis revealed that TMV isolated from diseased petunia had high identity (ca. 98–99) with TMV vulgare type sequences reported from Korea and Japan. Mechanical inoculation of 23 varieties, representing 21 species of pot and bedding plants with the petunia isolate of TMV confirmed that 11 were infected by the petunia isolate of TMV, although several species remained symptomless after three weeks. This highlights a clear risk to a number of commercially important pot and bedding plant species from TMV infected trailing petunias.