The relative efficiency of some aphid species as vectors of potato virus Yo (PVYo)

Summary The relative efficiency of 7 aphid species as vectors of potato virus Y^o (PVY^o) was investigated. Winged aphids of one species were released in a net cage containing PVY^o-infected potato plants as a virus source and healthy young potato plants as test plants. After 35 hours the glasshouse chamber was fumigated and the young plants tested for PVY^o by ELISA at 10-days intervals.Myzus persicae andAcyrthosiphon pisum were the most effective vectors, infecting 26 and 25% of the test plants, respectively.Aphis fabae, Aphis nasturtii andRhopalosiphum padi infected only 1–7% test plants.Sitobion avenae andBrevicoryne brassicae did not transmit PVY^o. Relative ‘efficiency factors’ are suggested from these and other results.

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Zusammenfassung Um die relative Wirksamkeit einiger Blattlausarten als Vektoren für PVY^o zu untersuchen, wurden Versuche in den Jahren 1980 und 1981 durchgeführt. Geflügelte Blattl?use einer Art wurden in einem Netzk?fig (Bodenfl?che 1 m², H?he 0,5 m) ausgesetzt, in dem gesunde junge Kartoffelpflanzen und als Virusquelle PVY^o-infizierte Kartoffelpflanzen standen. Die K?fige befanden sich in einem Gew?chshaus mit künstlichem Licht als Erg?nzung zum Sonnenschein. Die durchschnittliche Tagesl?nge betrug 17 Stunden (16–18) und die durchschnittliche Temperatur 25°C (16–18°C) 35 Stunden nach dem Aussetzen wurden die Gew?chshauskabinen ger?uchert und die jungen Kartoffelpflanzen in 10-t?gigem Abstand mit ELISA auf das Vorhandensein von PVY^o geprüft. In ungef?hr 90 Versuchen wurden folgende Blattlausarten getestet:Myzus persicae, Acyrthosiphon pisum, Aphis fabae, Aphis nasturtii, Rhopalosiphum padi, Brevicoryne brassicae undSitobion avenae. Als wirksamste Vektoren mit Infektionserfolgen von 26 bzw. 25% der Testpflanzen erwiesen sichM. persicae undA. pisum. Weniger wirksam mit 1–7% Infektionserfolgen warenA. fabae, A. nasturtii undR. padi, w?hrendS avenae undB. brassicae PVY^o überhaupt nicht übertrugen (Tab. 1). Entsprechend diesen und anderen Ergebnissen werden für die 7 geprüften Blattlausarten ‘Wirksamkeitsfaktoren’ vorgeschlagen. Die h?chsten Faktoren wurdenM. persicae undA. pisum mit 1,0 bzw. 0,8 gegeben. Bei den anderen virusübertragenden Blattlausarten liegen die Wirksamkeitsfaktoren zwischen 0,3 und 0,1. Die Zeit zwischen dem Versuchsbeginn und der Auffindung von PVY^o im Saft der oberen Bl?tter der Testpflanzen betrug ca. 4 Wochen. Wenn PVY^o mit ELISA in den Kartoffelbl?ttern entdeckt werden kann, ist die Konzentration wahrscheinlich hoch genug, um den Blattl?usen die Virusaufnahme durch kurzfristige Einstiche in infizierte Pflanzen zu erm?glichen und es dann auf gesunde Pflanzen zu. übertragen. Diese Ergebnisse scheinen mit denen von Beemster (1979) übereinzustimmen, wobeiM. persicae 4 Wochen nach der Inokulation PVY^N von nicht inokulierten Spitzenbl?ttern aufnehmen konnte. Betrachtet man die Gefahr der Virusausbreitung, so ist sowohl die H?ufigkeit als auch die relative Wirksamkeit der verschiedenen Blattlausarten als Vektoren für PVY wichtig. Darüber hinaus spielt die Zeit von der Inokulation bis zu dem Moment, wo die Pflanze wiederum als Infektionsquelle dienen kann, eine bedeutende Rolle. Für die Entwicklung von Prognosemethoden w?ren bessere Kenntnisse über Virusvektoren, vor allem für nicht-persistente Viren, sehr hilfreich.

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Résumé En 1980–1981, des expériences ont porté sur l'efficacité relative de certaines espèces de pucerons en tant que vecteurs du virus PVY^o. Des pucerons ailés ont été lachés dans une cage appropriée (surface de base 1 m², hauteur 0,5 m) sous laquelle des plantes atteintes du virus PVY^o sont placées avec témoins sains. Les expériences ont lieu sous serre avec un complément de luminosité par éclairage artificiel. La longueur moyenne de jour est 17 heures (16–18) et la température moyenne +25°C (16–28°C). Après 35 heures, une fumigation est réalisée puis des test ELISA sont effectués à 10 jours d'intervalle sur les jeunes plantes. Environ 20 expériences ont été ainsi menées et les espèces de pucerons testés ont été les suivants:Myzus persicae, Acyrthosiphon pisum, Aphis fabae, Aphis nasturtii, Rhopalosiphum padi, Brevicoryne brassicae etSitobion avenae. M. persicae etA. pisum sont les plus efficaces vecteurs de PVY^o, contaminant respectivement 26 et 25 pour cent des témoins.A. fabae, A. nasturtii et R. padi le sont moins avec 1 à 7 pour cent de plantes contaminées etS. avenae etB. brassicae ne transmettent aucunement le virus (tableau 1). Des facteurs ‘d'éfficacité’ relative sont accordés aux sept espèces de pucerons étudiées, en fonction d'autres résultats et de ceux-ci. Les plus élevées se rapportent àM. persicae etA. pisum, respectivement 1,0 et 0,8. Des facteurs compris entre 0,3 et 0,1 sont donnés aux autres espèces de pucerons transmettant le virus. La détection du virus PVY^o est réalisée 4 semaines après la mise en place de l'expérience, à partir du jus prélevé sur les feuilles supérieures des plantes testées. Si le virus est détecté par la méthode ELISA dans les feuilles des pommes de terre, la concentration du virus est probablement suffisante pour tester les pucerons au niveau de l'acquisition des virus à partir de plantes déjà contaminées et leur transmission à des plantes saines. Ces résultats semblent corroborer ceux de Beemster (1979), oùM. persicae pouvait acquérir PVY^N après 4 semaines à partir des feuilles supérieures non-inoculèes de plantes préalablement contaminées. La fréquence et l'éfficacité relative de différentes espèces de pucerons en tant que vecteurs de PVY sont importants à prendre en compte dans le risque de transmission du virus. De plus, la durée entre la contamination et le moment où la plante de pomme de terre peut agir comme source d'infection est un facteur important. Une meilleure connaissance des vecteurs des virus, notamment des virus non persistants, serait très utile à l'avenir, pour développer des méthodes d'avertissements.

     

Inheritance of extreme resistance to potato virus Y in potato

Summary Segregation for extreme resistance to PVY was evaluated in progenies derived from crossing two extremely resistant potato clones with parents differing in resistance. Resistance was evaluated after mechanical inoculation with PVY^O and PVY^N, and after graft inoculation with PVY^O. Biological and serological tests (ELISA) were used for virus detection. The extreme resistance is governed by a single dominant gene, but observed segregations deviated from the expected ratios. Considerable modifying effects were detectable, depending on the potato genotype and virus isolate, for a significant excess of susceptible genotypes was observed in some progenies. Moreover, genotypes with non-parental types of resistance to PVY were observed.     

Spread of potato virus Y (PVY) in relation to aphid population trends in potato fields in Israel

Summary Test of field spread of potato virus Y (PVY) were carried out in the coastal plain of Israel during the autumn growing seasons of 1964 and 1965. These included twice-weekly samplings of the winged aphid population. PVY-infected tubers of the varietyUp-to-Date, were planted at predetermined points in a trial plot, simultaneously with PVY-free ones. Virus spread to progeny was determined by indexing plants grown from tubers that had been collected at different distances from the infector plants. In 1965, a fair correlation was established between the incidence of naturally-spread PVY and distance from the source of inoculum. In 1964, however, the number of aphids trapped were exceptionally high, resulting in a PVY incidence more than double that of 1965 but with practically no apparent relation to the distance from the infector plants. This can be partly explained by the additional infection arising from sources outside the trial plot through the activity of an increased number of vector individuals.

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Zusammenfassung Im Anschluss an Studien über die Feldausbreitung von PVY, die vor 7 Jahren begannen, wurden in der Küstenzone von Israel w?hrend der zwei Herbstanbauperioden 1964 und 1965 besondere Untersuchungen angestellt. Halbw?chentlich wurden die geflügelten Individuen der Familie Aphididae in der Versuchsparzelle mit Hilfe der Moericke-Falle gesammelt. Vom gesamten Fang wurde nurMyzus persicae identifiziert, da diese Art der Hauptübertr?ger des PVY in Israel ist. Knollen der SorteUp-to-Date, mit dem gew?hnlichen Isolat von PVY infiziert, wurden an vorher bestimmten Stellen der Versuchsparzelle gleichzeitig mit PVY-freien Knollen gepflanzt (Abb. 1) Das Auftreten des Virus auf Knollen der neuen Generation wurde auf folgende Weise festgestellt: Knollen, die in verschiedenen Entfernungen von der Inokulumquelle gesammelt wurden, wurden in der Augenstecklingsprüfung nicht nur visuell beurteilt, sondern auch im A6-Test (Einreiben von Blattsaft) und mittels verschiedenen Testpflanzen überprüft. Zu diesem Zweeke wurden Stecklinge unter insektenfreien Bedingungen angezogen. Im Herbst 1965, wie auch in den Frühjahren 1960 und 1961 und im Winter 1961 (Zimmerman-Gries undNitzany, 1964), wurde eine ziemlich gute Korrelation zwischen Feldauftreten des PVY und der Entfernung von der Inokulumquelle beobachtet (Abb. 2). Im Jahre 1964 waren die Fallenergebnisse aussergew?hnlich gross. Dies nun verursachte ein mehr als doppelt so starkes Auftreten von PVY wie im Jahre 1965, und dies stand praktisch in keiner augenscheinlichen Wechselbeziehung zur Entfernung von der ausgepflanzten Inokulumquelle (Abb. 2). Das Verwischen eines solchen Korrelationsbildes im Jahre 1964 wird teilweise durch die weitere Ansteckung erkl?rt, die, von Quellen ausserhalb der Versuchsparzellen kommend, durch die vermehrte Zahl von übertr?gerindividuen (Abb. 3), die im Felde vorhanden waren, verursacht wurde.

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Résumé Des recherches particulières ont été effectuées dans la zone c?tière d'Isra?l durant les deux saisons automnales de culture 1964 et 1965, en jonction à des études sur la propagation au champ du PVY qui débutèrent il y a sept ans. Les individus ailés de la famille des Aphides étaient récoltés dans les parcelles d'essais deux fois par semaine, au moyen de pièges de Moericke. Parmi toutes les captures seuls les puceronsMyzus persicae étaient identifiés, puisque cette espèce est le principal transmetteur du PVY en Isra?l. Des tubercules de la variétéUp-to-Date, infectés avec l'isolat ordinaire de PVY, ont été plantés à des emplacements déterminés à l'avance dans la parcelle d'essais en même temps que les tubercules libres de PVY (Fig. 1). La présence du virus sur les tubercules de la génération suivante fut déterminée de la fa?on suivante: aux tubercules récoltes à diverses distances de la source d'infection était appliqué le test de bouture d'oeil de même que le test sur folioles détachées de l'hybride pomme de terre A6, comme aussi sur une séric de plantes-test. Pour la réussite de l'épreuve les pousses de tubercules étaient élevées dans des conditions libres de pucerons. En automne 1965, comme au printemps 1960 et 1961, et en hiver 1961 (Zimmerman-Gries etNitzany, 1964), on a observé une corrélation passablement bonne entre l'apparition au champ du PVY et l'eloignement de la source d'inoculum (Fig. 2). En 1964, les produits des pièges étaient exceptionellement élevés. Ce qui, dès lors, occasionna une apparition de PVY à un degré plus que double de celui de 1965, et engendra aussi ce fait que pratiquement il n'y avait aucune corrélation avec l'éloignement des sources d'inoculum plantées (Fig. 2). Cet effacement d'une telle image de corrélation en 1964 sera partiellement expliquée par une contagion plus grande causée par le nombre accru d'individus vecteurs (Fig. 3) qui étaient présents dans les champs, à partir de sources extérieures aux parcelles d'essais.

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Contribution from the National and University Institute of Agriculture, Rehovot, Israel. 1966 Series, No. 1051-E.

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Paper read to the Virology Section of the Third Triennial Conference of the European Association for Potato Research, Zürich, September 1966.     

An enhanced multiplication of potato virus X is not related to a synergistic reaction between the potato viruses X and Y

Summary Greenhouse experiments demonstrated a differential interaction between potato viruses X and Y in two potato cultivars. Enhancement of PVX synthesis in doubly infected plants occurred only in the PVY-susceptible potato cv. Ulla, whereas PVX multiplication was almost completely inhibited in the doubly infected PVY-resistant cv. Franzi. However, a synergistic effect was also evident in the latter cultivar in the form of a growth inhibition of the plants. An increased multiplication of one or both of the viruses is, therefore, not related to a synergistic reaction.     

Use of the virus strain group concept to characterize the resistance to PVX and PVYo in the potato cv Allegany

Resistance to the potato viruses X (PVX), Y (PVY) and A (PVA) was examined in the potato cv Allegany released by Cornell University in 1990. Standard potato cultivars from North America and Europe were included for characterization of the resistance response. Allegany was extremely resistant to a strain group 3 isolate of PVX and reacted with hypersensitivity to an ordinary strain isolate of PVY (PVY^o). However, Allegany was susceptible to an isolate of PVY causing necrosis in tobacco (PVY^N), and to an isolate of PVA. No symptoms appeared following infection with PVY^N and PVA. Identification of existing virus strain groups in a geographic area is an important aspect of predicting cultivar response to inoculation in the field.     

Enzyme-linked immunosorbent assay (ELISA) for the detection of potato leafroll virus and potato virus Y in potato tubers after artificial break of dormancy

Summary Conditions necessary for the detection of potato leafroll virus (PLRV) and potato virus Y (PVY) in tubers from primary and secondary infected plants were investigated. Tubers were analysed before and after breaking dormancy by rindite treatment. PLRV was reliably detected indormant tubers whereas PVY was readily detected only when tubers had been rindite-treated and held for two to three weeks at 22°C and high humidity in the dark. PLRV occurred in higher concentration at the heel end than at the rose end of infected tubers and the concentration remained nearly unchanged during the experimental period of 35 days, whereas PVY was found to be more concentrated at the rose end and was rapidly accumulating in the tubers after the break of dormancy. In dormant tubers PVY concentration dropped during storage at 22°C. The use of ELISA for tuber indexing is discussed.     

Use ofNicotiana debneyi to detect viruses S,X and Y in potato seed stocks and relative susceptibility of six common varieties to potato virus S

Summary Nicotiana debneyi Domin. proved a reliable test plant for potato viruses S, X, and Y. Test plants with several leaves 6 cm long, were dusted with carborundum and rubbed with potato leaf sap, or with raw surfaces of cut tubers. The plants were then held at 20°C under approximately 250 ft cd light intensity on a 16–18 h photoperiod. Each of the 3 viruses, or X and Y combined, could be distinguished, but symptoms of S were obscured by those of X or Y. At two elite seed farms, virus S spread into virus-free stocks of the varietyNetted Gem. but little intoKatahdin. In greenhouse tests, 3 older varieties,Green Mountain, Irish Cobbler andNetted Gem, as a group, were more susceptible to PVS, when inoculated with infective sap, than the newer varieties,Katahdin, Kennebec andSebago.     

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.     

Incidence of potato virus Y and potato leaf roll virus in autumn potatoes in Israel

Summary Random sampling of autumn grown potatoes in Israel revealed potato virus Y incidences of 2.7, 2.5 and 3% during the years 1976, 1977 and 1978, respectively, figures only slightly higher than those found in spring-planted fields (2.3% in 1976), and which agree with visual estimates by the Inspection Service. Assaying random samples for potato leaf roll virus (PLRV) by aphid transmission to test plants, detected incidences as high as 38.8, 28.9, 36.7 and 33.3% during 1976, 1977, 1978 and 1979, respectively, although only minor levels were visable, indicating symptom masking in the autumn. Most of the infection was found to be secondary; ca. 25% of the local seeds for autumn planting, grown during spring, are PLRV-infected. The effect of the high incidences of PLRV on autumn yields is not known, but they are consistently lower than spring yields of the same varieties. Contribution No 315-E, 1980 Series, The Volcani Center, Bet Dagan, Israel.     

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.     

The incidence of potato viruses X,Y and S in the Chilota potato collection

The 530 potato clones of the Chilota collection of the germplasm bank from the Universidad Austral de Chile were tested for potato viruses X (PVX), Y (PVY) and S (PVS) by means of NCM-ELISA (nitrocellulose membrane enzyme-linked immunosorbent assay). Four clones (0.8%) healthy for all 3 viruses simultaneously were detected. These clones could be resistant to the above mentioned viruses.     

Detection of potato leaf roll virus and potato viruses M,S, X and Y by dot immunobinding on plain paper

Summary Potato leafroll virus and potato viruses M, S, X and Y in green leaves were detected by dot immunobinding (DIB) on plain paper and on nitrocellulose membranes. On both materials, DIB could detect the presence of very small amounts of virus, e.g. 30 pg of purified PVX. The sensitivity of the DIB test on plain paper and on nitrocellulose was compared to Double Antibody Sandwich ELISA (DAS-ELISA) by serial dilutions of infected plant sap made in healthy plant sap. Detection of potato viruses by DIB on plain paper and nitrocellulose was found to be equally sensitive whereas DAS-ELISA was 2 to 8 times more sensitive. Possible simplifications of the DIB procedure to suit the requirements of a routine method were examined. The use of the DIB method for routine testing of potato viruses is discussed.     

Oxygen and carbon dioxide treatment to break potato tuber dormancy for reliable detection of potato virus Y (PVY) by enzyme-linked immunosorbent assay (ELISA)

Summary Dormant tubers of the potato cv. Bintje were treated for 7 or 14 days in an atmosphere enriched to either 40% O₂ plus 1% CO₂, or 40% O₂ plus 20% CO₂, or they were stored in closed plastic bags for identical periods. Rindite-treated and untreated tubers served as references. Treatment with 40% O₂ plus 20% CO₂ for 7 days was nearly as efficient as rindite for inducing sprouting. Both the O₂ plus CO₂ treatments, for 7 and 14 days, considerably increased virus concentration in tubers and had an effect similar to that of rindite 40 days after treatment, but the plastic bag treatment was not as efficient. It is concluded that O₂ plus CO₂ enriched atmospheres could be used for breaking tuber dormancy in order to detect reliably PVY in tuber extracts.     

Elimination by chemotherapy of potato virus S from potato plants grown in vitro

Summary Potato virus S was eliminated from systemically infected stem cuttings of five potato cultivars after three passages in nutrient media containing 0.003% of the synthetic riboside ribavirin (Virazole). Treatment effects could be detected after only two passages which also revealed differences in cultivar response. Treated plants transferred to ribavirin-free culture media and to soil remained PVS-free. This simple method is less time-consuming than the usual meristem (axillary) tip culture procedures combined with chemotherapy or heat treatment.     

The spread of PVYo in New Brunswick potato fields: Timing and vectors

Field tests at three sites over a period of three to four years have shown that PVY^o spread in New Brunswick starts in mid-to late July when plants reach maximum height. Some 62 different genera or species of aphids were collected in experimental plots. Only seven of these were known vector species. Of the colonizing species, the alate green peach aphid,Myzus persicae (Sulzer), seems to be the most important vector. However, because it is not always present when disease spread starts, non-colonizing aphids are probably responsible for the early spread of PVY^o. Five of these species of aphids were tested in the laboratory to determine their vector efficiency. A list of potential vectors is presented. The impact of these findings on the management of PVY^o is discussed.     

Guar (Cyamopsis tetragonoloba) as a potential differential host of potato virus Y

Summary Guar is reported for the first time as a host of potato virus Y. The virus produced no symptoms, or occasional faint chlorotic spots on inoculated cotyledons and unifoliate leaves. No symptoms were observed on new growth, but the virus was consistently recovered from these leaves by back-inoculation to tobacco. Neither potato virus X nor cucumber mosaic virus infected guar.