Biological factors influencing the transmission of potato leafroll virus by different aphid species

Summary Macrosiphum euphorbiae, collected in the field from potato plants infected with potato leafroll virus (PLRV), transmitted the virus to fewer potato plants in a field trial than did laboratory-rearedMyzus persicae. In the laboratory,M. persicae was the only efficient vector of PLRV fromPhysalis floridana seedlings, potato sprouts or excised leaves toP. floridana. Two clones ofM. euphorbiae and one clone ofAulacorthum solani transmitted PLRV from infected potato plants toNicotiana clevelandii as effeciently asM. persicae but a clone ofAphis gossypii was an inefficient PLRV vector. An isolate of PLRV, whichM. persicae transmitted inefficiently from potato toN. clevelandii, was also transmitted inefficiently byM. euphorbiae andA. solani.     

The infection pressure of potato leafroll virus and potato virus Y in relation to aphid populations in Cyprus

Summary The infection pressure of two viruses, potato leafroll (PLRV) and potato virus Y (PVY), both common in seed potatoes grown in Cyprus, was determined in three experiments in 1982–83. Virus-free bait plants, of potato and four other species, were exposed weekly to field infection during the growing season (March–June), and then returned to an aphid-free glasshouse for symptom expression. Only tobacco plants produced clear symptoms enabling reliable assessment of PVY infection pressure. When assessed with ELISA or by tuber indexing, the potato plants were efficient baits for both viruses whose infection period commenced at emergence (mid March to early April) and ended within 6–7 weeks. The seasonal trend of aphid populations, determined with Moericke traps or 100-leaf counts, correspond to that of virus spread. Correlation and regression analysis of aphid and virus data implicated the alate form ofMyzus persicae as the principal vector of both viruses.     

Progeny tests to identify diploid potato clones homozygous at loci controlling resistance to PLRV

Summary Using potato parental lines homozygous at a locus or loci controlling resistance to potato leafroll virus (PLRV) can give advantages in the selection of resistant forms. In order to identify homozygous diploid clones their test-cross families were evaluated. All the clones that were test-crossed expressed resistance in primarily- and secondarily-infected plants and etiolated sprouts, and were derived from mating genotypes highly resistant to PLRV. Genotypes from test-cross families varied in resistance to PLRV, and one family was found which had only resistant genotypes, suggesting that the resistant parent of this progeny was homozygous at resistance loci. Evidence was gathered that resistance in some diploid clones may result from resistance to virus multiplication as well as restricted virus transport from leaves to tubers.     

Transmission of potato leafroll virus to or from tuber slices by aphids feeding through a membrane

Summary Eye-bearing slices, cut from healthy potato tubers and placed between Parafilm membranes, were inoculated with potato leafroll virus (PLRV) byMyzus persicae. PLRV was detected by ELISA and by transmission tests in tuber slices and in plants grown from the slices of the susceptible cv. Désirée, but not in those of the resistant cv. Arkula. These results suggest that PLRV replication and transport within tuber phloem is controlled by specific mechanisms of resistance.M. persicae was also able to acquire and transmit PLRV toPl floridana from slices cut from tubers of infected plants. The aphids effectively transmitted PLRV from slices cut from the sprouting rose end but they failed to transmit it from slices cut from the heel end of tubers.     

Host genes and transgenes that confer resistance to a Scottish isolate of potato leafroll virus are also effective against a Peruvian isolate

Summary Potato genotypes with host gene-mediated resistance (host-MR) and coat protein-mediated transgenic resistance (CP-MR) to potato leafroll virus (PLRV), were inoculated with a Scottish and a Peruvian isolate of PLRV. The coat protein transgene had been cloned from the Scottish PLRV isolate which had also been used during the screening and selection of genotypes with host resistance. Significantly less PLRV accumulated in plants with either host-MR or CP-MR than in plants of susceptible genotypes or in non-transformed control plants, but the two forms of resistance were equally effective against both PLRV isolates.     

Transmission of potato leaf roll virus byMyzus persicae (Sulz.) from leaves and plants of different ages

Summary Young potato plants were a better source of potato leaf roll virus (PLRV) for aphids,Myzus persicae (Sulz.), than old ones. For plants 6, 7.5 and 9 weeks old, the best sources of PLRV were the lower, middle and upper leaves, respectively. The frequency of PLRV transmission from upper leaves did not change much with increasing age of plants nor did it change with different leaflets from the same leaf.     

Resistance to potato leaf roll virus inSolanum brevidens

Summary Plants ofSolanum brevidens graft-inoculated with potato leaf roll virus (PLRV) grew vigorously and had a normal healthy appearance. Although presence of the virus was confirmed in all inoculated plants by graft tests to potato and/orDatura stramonium, recovery of PLRV fromS. brevidens PI 218228 usingPhysalis floridana and the aphidMyzus persicae was erratic and only few test seedlings became infected. Ease of recovery of the virus using aphids was not influenced by presence of a continuous graft union with infected potato. Testing ofS. brevidens PI 245763 withM. persicae was not possible due to poor aphid survival on plants of this accession.     

The development of mature plant resistance in four potato cultivars against aphid-inoculated potato virus YO and YN in four potato cultivars

Summary Field-grown potato plants of cvs King Edward, Record, Maris Piper and Désirée were inoculated on seven different dates during the growing season of 1987 and 1988 with either potato virus Y^O (PVY^O) or PVY^N, using three viruliferous peach-potato aphids (Myzus persicae) per plant. In each cultivar, the proportion of progeny tubers infected with PVY^O or PVY^N was high in plants inoculated during the four weeks following emergence, the proportion declining to zero or close to zero in the subsequent 4–6 wks.     

Epidemiology of potato leaf roll virus in the Fraser River delta of British Columbia

The spread of potato leaf roll virus (PLRV) and the resulting phloem necrosis in the tubers has been a limiting factor in the production of the Netted Gem (Russet Burbank) variety in southwestern British Columbia, Canada. Steckling sugar beets are an important overwintering host for nymphs and adults of the green peach aphid,Myzus persicae (Sulzer). By June, aphids are widely disseminated to the florets and new leaves of sugar beet and other hosts, including potato. Colonies with alates are produced on summer hosts which are not treated with insecticides. The peak of the flight of alates from the colonies on the summer hosts occurs during the first half of August. Those alates that were produced on PLRV-infected potato and which travel to other potatoes transmit the virus as soon as they feed. By the end of August, the sugar beet seed crops and the early and mid-season potato crops have been defoliated or harvested. Thus many colonies ofM. persicae are destroyed and the threat of PLRV spread diminishes. Crop and weed plants which serve as overwintering hosts become infested during late summer with alate aphids. Their offspring survive the winter in numbers which are determined by the weather and survival of host plants.     

Influence of the duration of acquisition and inoculation feeding on the effectiveness of potato leafroll virus transmission byMyzus persicae Sulz

Summary In laboratory experiments PLRV transmission byMyzus persicae Sulz was shown to be possible even during a very brief feeding period onPhysalis floridana Rydb, in both acquisition and inoculation feeding. When the acquisition feeding time (AFT) was varied between 30 sec and 48 h the inoculation feeding time (IFT) was constant (48h) and vice versa: when the AFT was constant (48 h), the IFT was variable. The rate of infection was 2.2% following 30 sec AFT and 1.1% after 30 sec IFT. After 1 min feeding these infection rates increased to 7.9% and 1.8% respectively. The capacity for virus transmission was closely correlated with the increase in feeding time for both acquisition and inoculation feeding.     

Production of seed potatoes in Cyprus: the effects of roguing and planting date on the spread of potato leaf roll virus,tuber yield,and infestation by potato tuber moth

Summary Field experiments during 1984–6 tested the effects of planting date on the development of aphid infestations and the spread of potato leaf roll virus (PLRV) in rogued or unrogued plots of potatoes, cv. Spunta. Plantings were made each month from December to April, the customary time for planting being February. Aphid infestation in early-planted plots was severe throughout the growing season; plots planted in February were also severely infested early in the growing season but the populations later gradually declined to undetectable levels. Nevertheless, the incidence of PLRV in the latter plots was as high as in those planted in December-January. Late-planted crops escaped aphid infestation and PLRV infection, either in part (March planting) or completely (April planting). Such crops, however, were uneconomical due to poor yields and heavy losses from potato tuber moth infestation. Roguing significantly reduced the spread of PLRV in all years but its interaction with planting date was insignificant.     

A rapid technique for assessing the resistance of families of potato seedlings to potato leaf roll virus

Summary A technique is described by which families of potato seedlings can be rapidly screened for resistance to potato leaf roll virus (PLRV) in the greenhouse with a minimum expenditure of labour and bench space. Seed of different families was sown in rows in four replicated blocks and the seedlings produced were exposed to viruliferousMyzus persicae when very young. Symptoms resembling those typical of secondary infection with PLRV developed within a few weks and families with few affected seedlings compared with the susceptible control were classed as resistant. Tests done at different times with similar sets of families gave similar results. Applying infectiveM. persicae by shaking heavily colonised potato shoots above the seedlings was more effective and far less time consuming than transferring them individually by hand using a fine paint brush.     

Volunteer potatoes as a source of potato leafroll virus and potato virus X

Volunteer potatoes were investigated as infection sources for potato leafroll virus (PLRV) and potato virus X (PVX) in a high elevation seed potato growing area of eastern Idaho. Population densities ofMyzus persicae were assessed. Percentage of PLRV and PVX infection of the volunteers and seed potato crops was determined, as well as density of volunteers and certain parameters of volunteer growth and reproduction. Volunteers apparently harbored no more PLRV than the potato crop from which they originated. But they were found to be an important reservoir of PVX with the infection increasing as much as 12.43% in one year. No aphids capable of transmitting PLRV were found although one species that can transmit potato virus Y was recorded. The mean density of volunteers varied from 0 to 84,880 stems/ha. The number of tubers remaining in the field after harvest and winter weather conditions appeared to be the only factors affecting volunteer density. Volunteer plants arising from seed pieces at an average depth of 6.1 cm were found to set an average of 2.1 new tubers per plant at an average depth of 4.0 cm. These results suggest that volunteer potatoes are a significant source of PVX infection in subsequent seed potato crops.     

The effect of feeding time on potato virus S transmission byMyzus persicae (Sulz.) andAphis nasturtii Kalt, aphids

Summary The relationship between the feeding time and potato virus S (PVS) transmission byMyzus persicae andAphis nasturtii was studied. The optimal acquisition feeding time forM. persicae was at 30 sec to 2 min (2.9% infected plants). For transmission byA. nasturtii the highest level of infection was after acquisition feeding at 15 sec (11%), 30 sec and 2 min (9.6% each) and there was a significant linear decrease of plant infection as feeding time extended from 7 sec to 64 min. A different relationship has been obtained for inoculation feeding. In PVS transmission byM. persicae the plant infection increased from 0% at 7 sec feeding to 2.9% at 8 and 32 min. In virus transmission byA. nasturtii the infection was 4% after 7 sec feeding and increased significantly to 12.2% at 64 min feeding time.     

Diploid genotype DW.84-1457, highly resistant to potato leafroll virus (PLRV)

Summary The diploid clone DW.84-1457 which has outstanding resistance to potato leafroll virus (PLRV), has been selected at the Mlochów Centre of the Institute for Potato Research. It has in its pedigree PLRV-resistant clones from the Max Planck Institute nos. MPI 44.1016/10, MPI 44.335/130 and MPI 49.540/2. Its behaviour in the field and response to aphid inoculation indicate high resistance to infection, and the low concentration of the virus in graft-inoculated plants indicates high resistance to multiplication. This combination within one genotype of two aspects of resistance is not connected with hypersensitivity, and is heritable. Clone DW.84-1457 has other desirable characters such as extreme resistance to potato virus X (PVX), high resistance to potato virus M (PVM) and good table and processing quality. It is being utilized in the development of parental lines, both at the diploid and tetraploid level.     

Domyzus (nectarosiphon) species other thanm persicae pose a threat to the idaho potato crop?

Green peach aphids (Myzus persicae (Sulzer) ) pose a threat to the Idaho potato (Solanum tuberosum L.) crop primarily because they transmit potato leafroll virus (PLRV). Only colonizing vectors are epidemiologically significant because PLRV is persistently transmitted. Additionally, Idaho winters are severe enough that most permanently anholocyclic aphid species do not establish. It is now accepted that the taxon that has been known asMyzus (Nectarosiphon)persicae (Sulzer) is in fact at least three species (M. persicae, Myzus nicotianae Blackman andMyzus antirrhinii (Macchiati) ). It was not known whether the newly designated species had the potential to damage the Idaho potato crop. The objectives of our research were to determine whetherMyzus (Nectarosiphon) spp. other thanM. persicae occurred naturally in Idaho, whether they could colonize potato and transmit PLRV, and whether they were potentially holocyclic. NoMyzus (Nectarosiphon) spp. other thanM. persicae were found in Idaho in trap nurseries; howeverMyzus ascalonicus Doncaster recently has been found on stored bulbs and in suction trap collections in north Idaho. Laboratory bioassays for PLRV vector potential usingPhysalis floridana Rydb. indicator plants show thatM. nicotianae can transmit PLRV as efficiently asM. persicae. Similarly,M. nicotianae colonized potato as well asM. persicae in a replicated laboratory experiment comparing two clones ofM. nicotianae and one clone ofM. persicae. Our observations indicate that North AmericanM. nicotianae may be capable of a limited facultative holocycle. Thus, in laboratory experiments,M. nicotianae is as damaging asM. persicae with respect to PLRV vector potential; however,M. nicotianae may not occur naturally in areas like Idaho that have no tobacco production. A summary of allMyzus (Nectarosiphon) spp. with respect to PLRV epidemiology is provided.     

The infection pressure of potato virus Yo and the occurrence of winged aphids in potato fields in Sweden

Summary Water-filled yellow trays sited in a potato field were used to catch different species of winged aphids. The catches, enumerated weekly, were compared with the spread of potato virus Y^o (PVY^o), detected by bait plants of tobacco and potato, during the growing season for four years. The first detection of PVY^o, at about the same time as the first catch of winged aphids, varied from the middle of June to the middle of July in different years. In three of the four years,Rhopalosiphum padi was the dominant aphid in the beginning of the growing season and, presumably, it was responsible for the early spread of PVY^o in those years.Aphis spp. andMyzus persicae generally appeared later in the season and wingless aphids on the potato leaves were not common before the middle of July.

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Zusammenfassung Der Infektionsdruck durch das Kartoffel-Y^o-Virus (PVY^o) und das Auftreten geflügelter Blattl?use verschiedener Arten in Kartoffelfeldern wurde in den vier Jahren von 1978 bis 1981 untersucht (Tab. 1). Der Infektionsdruck wurde durch junge K?derpflanzen in Form von Tabak und Kartoffeln (Sorten Bintje und King Edward), welche w?chentlich der Virusinfektion im Feld ausgesetzt waren, gemessen. Die geflügelten Blattl?use wurden in gelben Wasserschalen (YWT) gefangen, ungeflügelte Blattl?use wurden an 60 zuf?llig ausgew?hlten Kartoffelbl?ttern ausgez?hlt. Die erste Entdeckung von PVY^o und der erste Fang geflügelter Blattl?use koinzidierten; dies erfolgte in den verschiedenen Jahren zu unterschiedlichen Zeiten von Mitte Juni bis Mitte Juli (Abb. 1).Rhopalosiphum padi war die dominierende Blattlaus am Anfang der Wachstumsperiode in drei von vier Jahren, in denen es vermutlich Ursache für die frühe Ausbreitung von PVY^o war.Aphis spp. undMyzus persicae erschienen in der Jahreszeit generell erst sp?ter. Ungeflügelte Blattl?use auf Kartoffelbl?ttern erschienen bis zur Mitte des Jahres nur selten.

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Résumé On étudie la pression d'infection du virus Y^o de la pomme de terre (PVY^o) en relation avec la présence dans un champ de pomme de terre de pucerons ailés de plusieurs espèces, dans le cadre d'un essai conduit durant 4 années entre 1978 et 1981 (tableau 1). La pression d'infection est déterminée au moyen de jeunes plantes de tabac et de pomme de terre (variétés King Edward et Bintje), qui sont exposés chaque semaine dans le champ à l'infection virale. Les pucerons ailés sont capturés dans un piège à bac jaune, et les pucerons aptères sont comptés directement sur 60 feuilles de pommes de terre, choisies au hasard. La première détection du PVY^o et la première capture de pucerons ailés co?ncident, ce qui a été observé à différentes époques de plusieurs années, de la mi-juin à la mi-juillet (fig. 1).Rhopalosiphum padi a été le puceron le plus abondant au commencement de la période de croissance, dans trois des quatre années où il fut présumé responsable de l'extension précoce du PVY^o.Aphis spp. etMyzus persicae apparaissent généralement plus tard dans la saison. Les pucerons aptères sur les feuilles de pomme de terre sont peu fréquents avant la mi-juillet.

     

Relationship between potato cyst nematodes and their principal host. IV. Tolerance of potato cultivars and the effect of potato cyst nematode on initial plant growth

Summary Greenhouse experiments on the effects of white potato cyst nematode infestations (Globodera pallida Stone) on initial growth and development of a series of potato cultivars are compared with the results of field experiments on sandy and sandy-peat soils on the effect of nematode density on tuber yield. A simple greenhouse test, assessing root growth response to potato cyst nematode infection, provided a good insight into a cultivar's tolerance performance in the field early in the growing season. As a very limited number of plants is needed for the greenhouse test, screening for tolerance can be conducted in the early stages of a breeding programme.     

An approach to field screening potato genotypes for potato leaf roll virus resistance

Eight potato cultivars and two advanced breeder selections were assessed for field resistance to the potato leaf roll virus (PLRV) following field exposures in which PLRV-infected Russet Burbank plants were used as inoculum sources within treatments. This screening protocol provided consistent PLRV resistance ratings despite year-to-year variation in PLRV pressure. Secondary disease incidence based on enzyme-linked immunosorbent assay (ELISA) of foliage from tuber progeny ranged from 0–87% in 1990 and 0–67% in 1991, and was consistent with reported PLRV resistance ratings for eight of ten genotypes. Agreement between visual assessment and ELISA on plants from harvested tubers was 94% in 1990 and 83% in 1991, for all genotypes. However, agreement data were inconsistent from year-to-year, with the exception of three genotypes. In both years, current season infection, based on ELISA of foliage, was detected in less than two percent of the plants and, was inadequate as a measure of secondary PLRV incidence. Green peach aphid (GPA) populations did not differ among genotypes at sampling times during the season, but the PLRV concentration in GPA colonizing Russet Burbank plots was significantly higher than in GPA colonizing any other genotype.     

Environmental factors influencing aphid transmission of potato virus Y and potato leafroll virus

Summary The effect of temperature, relative humidity (RH) and light on aphid transmission of potato virus Y (PVY) and potato leafroll virus (PLRV) was studied using as vectorsMyzus persicae Sulz. andAphis gossypii Glov. Host susceptibility was enhanced by 48 h pre-inoculation exposure at 25°C and by 48 h post-inoculation exposure to 30°C. High RH (80%) in both pre- or postinoculation phases enhanced host susceptibility. Continuous fluorescent light (4000 lux) did not alter the rate of transmission of either virus. High RH (80–90%) and high temperature (25–30°C), when combined, increased virus transmission by 30–35%. Transmission rates were reduced by nearly 50% if RH was maintained at 50% in either of the two phases even if the temperature was 25 or 30°C. Both viruses were acquired by aphids earlier (13–20 days after inoculation) when the source plants were incubated at 25 or 30°C. Most virus was transmitted from plants inoculated with PVY 13 to 16 days and with PLRV 15 to 20 days previously. Transmission rates of PVY were enumerated from symptom expression on test plants and by Enzyme Linked Immunosorbent Assay (ELISA) whereas those of PLRV were enumerated from symptom expression alone.