Reaction to the potato leafroll virus (PLRV) in diploid potatoes

Summary Diploid parents with some resistance to PLRV, were intercrossed to give 3 families with 191 clones which were evaluated for reaction to PLRV and yielding ability. After inoculation with PLRV the clones could be separated into those: 1) resistant, 2) susceptible, 3) intolerant, reacting with low virus concentration, 4) tolerant and 5) intermediate in reaction. Both the ELISA test and the evaluation of external disease symptoms were necessary to separate the clones. No correlation was found between resistance to PLRV and tuber yielding ability.     

Inhibition of potato tuber sprouting: Low levels of cytosolic pyrophosphate lead to non-sprouting tubers harvested from transgenic potato plants

Summary ExpressingE. coli inorganic pyrophosphatase in transgenic plants demonstrated that long distance sucrose transport is dependent on cytosolic pyrophosphate. It was speculated that removal of cytosolic pyrophosphate would impair sucrose utilization during storage of potato tubers and thereby prevent tuber sprouting. To explore this hypothesisSolanum tuberosum var. Désirée plants were transformed with a chimeric PPa gene. FollowingAgrobacterium mediated transformation, metabolite and carbohydrate contents of growing and stored tubers were measured. There was a large accumulation of soluble sugars and a decrease of starch at all developmental stages investigated. The PPase activity in PPaII tubers was parallel with a decrease of PPa, an increase of fructose-2,6-bisphosphate and an increase of UDP-glucose. As expected the amount of hexose-6-phosphates and glycolytic intermediates decreased. As a consequence PPaII tubers did not sprout even after a prolonged storage period of two years. Since the energy status of PPaII tubers is unaltered inhibition of sprouting is most likely due to reduced sucrose export and its subsequent utilization.     

Transmission of potato virus Y by cereal aphids

Summary The cereal aphidRhopalosiphum padi transmitted PVY^O and PVY^N from and to both tobacco and potato. However, it transmitted much less frequently thanMyzus persicae, even when aphids making single probes were compared.R. padi andM. persicae retained PVY for a similar duration. Both alatae and apterae ofR. padi transmitted infrequently, as also did progenies of individual aphids that had transmitted PVY.Metopolophium dirhodum also transmitted PVY infequently butSitobion avenae did not transmit.

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Zusammenfassung In Laborversuchen übertrugen ca, 1% der Getreideblattl?useRhopalosiphum padi undMetopolophium dirhodum, nicht jedochSitobion avenae das Kartoffel-Y-Virus (PVY). 65% vonMyzus persicae übertrugen PVY.R. padi übertrugauch dann weniger h?ufig alsM. persicae, wenn die Aphiden bei Einzelentnahmen untersucht wurden.R. padi übertrug PVY^O und PVY^N von und auf die Tabaksorte White Burley und die Kartoffelsorte King Edward. Zwei oder zehn Minuten Einwirkung waren optimal fürM. persicae, um PVY zu erlangen, w?hrendR. padi PVY h?ufiger nach l?ngeren Entwirkungszeiten übertrug (Tabelle 1).R. padi undM. persicae beinhalteten PVY für eine ?hnliche Zeitdauer (Tabelle 2). Sowohl alatae als auch apterae vonR. padi übertrugen unregelm?ssig, ebenso Nachkommen von individuellen Aphiden, welche PVY übertragen hatten.

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Résumé En tests de laboratoire, environ 1% des pucerons des céréalesRhopalosiphum padi etMetopolophium dirhodum, aucun deSitobion avenae et environ 65% deMyzus persicae transmettent PVY.R. padi transmet également moins fréquemment queM. persicae lorsque les pucerons sont mis en comparaison par piq?re unique.R. padi acquiert PVY^O et PVY^N à partir des variétés de tabac White Burley et de pomme de terre King Edward et les transmet à ces deux mêmes variétés. Deux ou 10 minutes d'acquisition sont optimum pour queM. persicae acquiert PVY tandis queR. padi transmet PVY plus fréquemment après une plus longue période d'acquisition (tableau 1).R. padi etM. persicae conservent PVY dans les mêmes délais (tableau 2). Les ailés et les aptères deR. padi transmettent rarement PVY comme les descendants de pucerons ayant transmis PVY.

     

Transmission of potato virus Y by aphids trapped in potato crops in southern England

Summary Harrington et al. (1986) assessed the relative efficiency with which different aphid species transmitted potato virus Y (PVY), by trapping flying aphids on a net downwind of a plot of infected potatoes and transferring the aphids to tobacco seedlings. This paper reports the extension of that work over further seasons and identifies three more vector species,Aphis sambuci, Myzus cerasi andDysaphis sp. A method for determining the proportion of those aphids caught on the net that had landed and probed in the crop is suggested. The use of such information to improve a model of virus spread is discussed.     

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.     

Acquisition of potato leafroll virus byMyzus persicae from secondarily-infected potato plants of different genotypes

Summary The acquisition of potato leafroll virus (PLRV) byMyzus persicae nymphs from the top leaves of potato plants was studied throughout a growing season in relation to the antigen titre in those leaves and the feeding behaviour of the aphid. Secondarily-infected plants of eight potato genotypes with different levels of field resistance served as virus sources. Early in the growing season, plants were efficient sources for virus acquisition. The amount of viral antigen detected inM. persicae nymphs fed on the top leaves was strongly correlated with the titres of viral antigen in these leaves. Virus acquisition from the top leaves of older potato plants was markedly impaired and could not be correlated with their virus titre. With increasing age of the potato plants and the development of virus symptoms, the virus titre in the leaves declined and the initial weak correlation between the virus titre and field resistance ratings disappeared. Thus, screening secondarily-infected potato plants for field resistance to PLRV based on the concentration of viral antigen in leaves or in aphids fed on them should be avoided later in the growing season. The feeding rate ofM. persicae, measured by the number of honeydew droplets excreted, did not account for the reduced uptake of virus from older plants since it was not influenced by the age of the plant. Throughout the growing season, the feeding rate ofM. persicae nymphs on PLRV-infected plants was higher on genotypes with low levels of field resistance to PLRV than on genotypes with high ones.     

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.     

Evidence that resistance to potato leafroll virus accumulation in tetraploidsolarium tuberosum L. is controlled by one or few major genes that are not complementary

Summary Previous investigations into the inheritance of resistance to accumulation of potato leafroll virus indicated a dominant major-gene effect, but the segregation ratios in progenies of crosses were a closer fit to a model involving two complementary genes (both required for resistance and one present in the susceptible parent cultivar, Maris Piper) than to a single gene model. In this study, we tested the complementary gene hypothesis by backcrossing susceptible segregants from one of these progenies to their susceptible parent, Maris Piper. No resistant segregants were found in the five backcross progenies examined, so the complementary gene hypothesis was not supported. There was significant variation between susceptible progeny-members in these backcrosses. The progeny of another, highly resistant parent clone, G. 8107(1), selfed, was also examined: all members were resistant. Whilst there is evidently a dominant major-gene effect involved, this is not the whole picture and there are other unidentified genetic effects.     

Sporulation ofPhytophthora infestans (Mont.) de Bary on the surface of diseased potatoes and tuber to tuber spread of infection during handling

Summary Laboratory experiments and observations in commercial stores showed that viable sporangia ofPhytophthora infestans can be produced on infected potato tubers of different cultivars. Infection was also found to spread from diseased to healthy tubers during handling.     

Effect of applying nitrogen fertilizer to a potato seed crop on the susceptibility of the daughter plants toErwinia carotovora subsp.atroseptica

Summary Seed potatoes of cvs Record and Bintje were grown with 30, 80 or 130 kg N/ha. In the subsequent growing season the seed tubers, which were inoculated or not with two concentrations ofErwinia carotovora subsp.atroseptica (Eca), were subjected to the same fertilization treatment. The incidence of blackleg and the level of seed tuber decay increased from the uninoculated treatment to the higher inoculum level, but the degree varied considerably from one year to another. Cv. Bintje was more susceptible to blackleg and yield loss caused by Eca than cv. Record. In 1990, when disease incidence was high, the proportion of blackleg stems increased with increasing doses of nitrogen fertilizer which had been applied to the seed crop, but was not significantly affected in 1988 and 1992. Seed tuber decay was retarded by the lowest nitrogen dose. The yield of the subsequent crop was not affected by the nitrogen dose applied to the seed crop.     

Penetration of potato tuber lenticels by bacteria in relation to biological control of blackleg disease

Summary In a glasshouse experiment three potato cultivars were grown to maturity in wet or dry compost. The number of lenticels per tuber was greater with larger tubers but was unaffected by the cultivar or soil moisture regime. The frequency of lenticel penetration by a water soluble stain, safranin O, remained high as tubers developed to maturity in wet soil. In dry soil penetration declined markedly as the tubers matured. When tubers, harvested just before the onset of haulm senescence, were inoculated withErwinia carotovora ssp.atroseptica, the frequency of lenticel rotting was less than the rate of stain penetration, indicating that additional factors were involved in the bacterial infection process. Inoculating mature tubers with bacteria and incubating them in anaerobic conditions frequently resulted in rotting of the lenticels. Comparable tubers incubated in aerobic conditions showed no rotting or invasion by bacteria. The results are discussed in relation to the biological control of blackleg.     

The feasibility of predicting the number of stems per tuber produced by potato seed stocks from measurements made before planting

Summary The number of stems per seed tuber produced by 17 seed stocks of cv. Record was determined in glasshouse and field experiments to assess the feasibility of predicting the number of stems produced in the field. Multiple regression analysis showed that seed tuber weight alone gave the most satisfactory fit to stems produced in the field, which was not improved by adding terms involving the number of stems produced in the glasshouse. Quadratic relationships between the number of above-ground stems per tuber and tuber weight were most appropriate for each stock, with the fitted curves for individual stocks differing only in the constant term. However, there were significant rank correlation coefficients between the constant terms for relationships between field stems and tuber weight and glasshouse stems and tuber weight, suggesting that in other cultivars and seed stocks a predictive glasshouse test might still be useful.     

Varietal differences to infection of potato stems by the gangrene pathogen,Phoma exigua var.foveata

Summary Thirteen cultivars were tested for presence ofPhoma exigua var.foveata in stems and green leaves. The frequency of segments yielding the pathogen increased with time during the growing season and varied between cultivars from 13 to 36% and their distribution pattern was irregular. There were significant differences between cultivars to this symptomless invasion of the green shoots. The value of such cultivar differences depends on the interpretation of the importance of stem inoculum in carrying the disease to the next tuber generation.

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Zusammenfassung Es wurden 13 Kartoffelsorten auf das Vorhandensein vonPhoma exigua var.foveata in Stengeln und grünen Bl?ttern untersucht. Pflanzknollen, die nach künstlicher Infektion faulten, wurden im Feld ausgepflanzt; nach 5, 12 und 17 Wochen wurden pro Sorte vier Stengel mit Bl?ttern nach dem Zufallsprinzip ausgew?hlt, wobei jeder Stengel eine Pflanze repr?sentierte. Die Stengel wurden gewaschen, getrocknet und in 5 cm-Segmente geteilt. Nach Oberfl?chensterilisation wurden die Segmente und die Blattschnitte in Petrischalen auf ein selektives Agarmedium gebracht, das zur F?rderung der Pyknidienentwicklung Paraquat enthielt.P. exigua var.foveata wurde auf Malzextraktagar bestimmt, der Thiophanatmethyl und Chloramphenicol enthielt. Die Sorten reagierten unterschiedlich auf die Infektion, wie an der Anzahl der Schnitte, die das Pathogen lieferten, zu ersehen ist. Die Nachweish?ufigkeit war am niedrigsten bei der ersten und am h?chsten bei der letzten Probenahme (Tab. 2). Die mittleren Prozentwerte varierten von 13% bis 36%, die Reihenfolge war zwischen den Jahren ?hnlich (Tab. 1). Das Verteilungsmuster der Schnitte, die das Pathogen lieferten, war unregelm?ssig; es wurde überall in Stengelschnitten und Bl?ttchen vom oberirdischen Trieb nachgewiesen und in nur wenigen F?llen auch in Stengelsegmenten unterhalb der Bodenoberfl?che (Tab. 3). Die Werte zeigen, dass die Anf?lligkeit der Sorten zur symptomlosen Invasion der grünen Triebe differiert. Inwieweit in dieser Phase des Lebenszyklus des Pilzes eine Resistenzauslese lohnend ist, h?ngt von der m?glichen Bedeutung des Stengelinokulums als Quelle für die Infektion der Knollennachkommenschaft ab. Es war mit dieser Untersuchung nicht beabsichtigt, Fragen, die sich auf die Ausbreitung des Pilzes beziehen, zu beantworten; ein besseres Verst?ndnis der Biologie dieses Krankheitserregers ist aber entscheidend zur rationalen Anwendung der Ergebnisse in der Pflanzenzüchtung.

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Résumé La présence dePhoma exigua var.foveata dans les tiges et les feuilles vertes est étudiée sur treize variétés de pommes de terre. Des tubercules de semence pourris après contamination artificielle, sont plantés au champ. Après 5, 12 et 17 semaines, 4 tiges avec les feuilles de chaque variété sont prélevées au hasard, chaque tige représentant une plante. Les tiges sont lavées, séchées et coupées en segments de 5 cm. Après une stérilisation de surface les segments et des sections de folioles sont placés en boites de pétri sur un milieu sélectif à base d'agar contenant du paraquat afin de favoriser le développement des pycnides.Phoma exigua var.foveata est identifié sur malt agar contenant du thiophanate-méthyl et chloramphenicol. Les variétés répondent différemment à l'infection, comme le montre le nombre de sections hébergeant le pathogène. La fréquence de détection est la plus faible à la première date d'échantillonnage et la plus élevée à la dernière (tableau 2). Le pourcentage moyen varie entre 13 et 36%, le classement est similaire entre les années (tableau 1). La distribution du pathogène hébergé par les échantillons est irrégulière. Il est détecté sur des sections de tiges et des folioles au dessus du sol et dans quelques cas sur des segments de tiges en dessous de la surface du sol (tableau 3). Les données montrent que la sensibilité des variétés à l'infection des parties aériennes est variable. L'intérêt d'une sélection à la résistance pour cette phase du cycle du champignon dépend de l'importance potentielle de l'inoculum sur tige en temps que source de contamination des tubercules-fils. Cette étude n'a pas pour but d'expliquer la dissémination du champignon, mais une meilleure connaissance de la biologie du pathogène est fondamentale pour une application rationnelle des résultats de la multiplication variétale.

     

The response of potatoes to a single transient heat or drought stress imposed at different stages of tuber growth

Summary The effects of a single treatment of heat or drought stress imposed at different stages of tuber growth, were investigated in two potato cultivars, Désirée and Cara. Both stresses impaired dry matter accumulation in tubers, and tuber yields. Stress imposed at early stages of tuber growth, when tubers were less than 20 mm in diameter, had little effect on dry matter accumulation, whereas stress imposed later resulted ingnificant losses of dry matter in tubers. Stress imposed during later tuber growth increased the percentage of tubers sprouting in the soil. Tuber malformation was less affected. The adverse effects of heat on tuber yield and quality seemed to be greater than those of drought. Drought increased the content of total soluble solids (TSS) and lowered the osmotic potential in the tuber tissue of both cultivars. These effects were detectable even 55 days after stress relief. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No 984-E, 1984 Series. This investigation was sponsored by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

Reducing potato leaf roll virus (PLRV) in potato by means of baiting aphids to yellow surfaces and protecting crops by coarse nets

Summary Surrounding half of the perimeter of potato plots with sticky yellow polyethylene sheets (HPS) stretched vertically at a height of 0.6 m above the soil, reduced the number, of winged aphids by ca. 70% and of PLRV infection by ca. 38%. A YPS mulch cuased an increase in aphid population, PLRV incidence and percentage of misshapen tubers. Covers of white coarse net (2.5×8.0 mesh per inch square ≈ 1×3.1 per mesh per cm square) reduced landing aphids to ca. 2% of those trapped in unprotected plots but increased by factors of ca. 5 to 6000 the number of apterae. PLRV incidence was greatly reduced in protected plots provided that no secondary infection occurred under the net. In plots planted with secondarily PLRV-infected seeds subsequent incidence under the nets was even higher than in the unprotected controls. The use of aphicides in addition to net covers completely prevented the spread of PLRV.

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Zusammenfassung Um die Infektion mit PLRV in Kartoffelfeldern zu vermindern, wurde versucht, die anfliegenden L?use mit gelben Poly?thylenfolien (YPS) zu k?dern (die besonders im 500–700 nm Bereich des Spektrums reflektieren) und den Bestand mit weissen, grobmaschigen (1×3,1 F?den/cm²) und relativ billigen Netzen zu schützen. Eine Abdeckung mit YPS erh?hte die Zahl der insgesamt anfliegenden L?use und die Zahl der gefangenenMyzus persicae (Abb. 1). Der Befall mit PLRV war in behandelten Parzellen 2,1% im Gegensatz zur Kontrolle mit 0,6%, die Zahl der missgestalteten Knollen verdoppelte sich durch diese Behandlung. Wurde die halbe Parzelle mit einer klebrigen YPS (2m×0,5m) abgeschirmt, die ausserhalb der Parzelle senkrecht in einer H?he von 0,6 m über dem Boden aufgespannt war, so verringerte sich sowohl die Blattlauspopulation als auch der Befall mit PLRV. Die Zahl der insgesamt anfliegenden L?use und die Zahl der geflügeltenM. persicae betrug in den geschützten Parzellen nur ca, 30% der in den Kontrollen gefangenen (Abb. 1, Tabelle 5) und der Befall mit PLRV wurde in 5 von 6 Versuchen auf 29–87% des in den entsprechenden Kontrollen beobachteten gesenkt (Tabelle 1). Dennoch war der Befall in den geschützten Parzellen noch h?her als in der Pflanzgutverordnung erlaubt (Tabelle 1). Abdeckungen mit doppelten Lagen von Netzen reduzierten den L?useanflug auf ca, 1% der in den unbedeckten Kontrollen gefangenen (Tabelle 5) und verhinderten vollst?ndig die Ausbreitung des PLRV. Billigere Abdeckungen mit einfachen Lagen von Netzen wurden in gr?sserem Umfang getestet (9 Versuche). In allen Versuchen wurde die Zahl der geflügelten L?use signifikant auf 1,4–2,6% der in den Kontrollen landenden gesenkt. Unter dem Netz stiegen jedoch, vor allem gegen Ende der Wachstumsperiode die Populationen der ungeflügelten L?use stark an, (Tabelle 3). Die Ausbreitung des PLRV war unter den Netzen stark eingeschr?nkt, unter der Voraussetzung, dass keine Sekund?rinfektion vorhanden war, im anderen Fall führte die unter dem Netz entstehende starke Blattlauspopulation zu einer verst?rkten Virusausbreitung (Tabelle 2). Die Netzabdeckung hatte keinen Einfluss auf den Gesamtertrag (Tabelle 6). Eine Kombination zwischen Netzabdeckung und Insektizideinsatz verhinderte die Ausbreitung des PLRV vollst?ndig, w?hrend in den ungeschützten und nicht gespritzten Parzellen 16% Knollen mit PLRV gefunden wurden (Tabelle 4). Es sollte daher m?glich sein, unter dem Netz und mit Insektizideinsatz Pflanzgut mit geringem PLRV-Befall zu erzeugen.

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Résumé Des essais ont été réalisés pour réduire l’infection d?e au virus de l’enroulement (PLRV) dans les parcelles de pommes de terre, soit en attirant les pucerons par des baches en polyéthylène jaune (ces baches jaunes réfléchissent la lumière dans la zone des 500–700 nm), soit en protégeant la culture par des filets blancs grossiers (1×3,1 fils par cm²). Un paillis réalisé avec les baches en polyéthylène jaune augmente le nombre total de pucerons et le nombre deMyzus persicae piégés (fig. 1). L’incidence du PLRV dans les parcelles traitées est plus importante que dans les parcelles témoins non traitées: 2,1% contre 0,6%, et le nombre de tubercules difformes est doublé par ce traitement. On entoure la moitié du périmètre des parcelles avec des baches de polyéthylène jaune (2m×0,5m), enduites de colle, placées à une hauteur de 0,6 m au-dessus du sol. Ceci réduit à la fois la population aphide et l’incidence du PLRV. Dans les parcelles protégées, le nombre total de pucerons et le nombre deM. persicae ailés représentent 30% de la population piégée dans les parcelles témoins (fig. 1, tableau 5). Dans cinq des six essais, l’incidence du PLRV est réduite à 29–87% par rapport à celle détectée dans les parcelles témoins (tableau 1). Cependant, l’incidence du PLRV dans les parcelles protégées est encore plus élevée que les niveaux permis pour la certification des semences (tableau 1). Dans des parcelles couvertes d’une double épaisseur de filet, le nombre de pucerons ailés représente 1% du nombre piégé dans les parcelles témoins (non couvertes) (tableau 5); l’infection d?e au PLRV ne se propage pas. La protection des parcelles avec une seule épaisseur de filet (cela revient moins cher) a été testée sur neuf essais. Dans tous ces essais, le nombre total de pucerons ailés est réduit de fa?on significative à 1,4–2,6% par rapport au nombre obtenu dans les parcelles témoins. Cependant, les populations de pucerons aptères augmentent sous le filet, notamment à la fin de la saison (tableau 3). La propagation du PLRV, favorisée par le développement d’importantes populations d’aptères (tableau 2) est notablement réduite sous le filet si aucune infection secondaire ne se manifeste. En outre, les filets n’affectent pas le rendement total (tableau 6). En combinant la protection des parcelles par des filets avec un traitement aphicide, on empêche totalement la propagation du PLRV, alors que dans les parcelles non protégées et non traitées on détecte 16% de tubercules virosés (tableau 4). Donc, une protection par des filets plus un traitement aphicide permettraient aux plants de pommes de terre de se développer avec un taux d’infection relativement faible.

     

Use of the polymerase chain reaction to clone the potato leafroll virus coat protein gene directly from the total RNA of infected plants

Summary The potato leafroll virus (PLRV) coat protein (CP) gene was directly cloned from the total RNA extracted from virus-infected plants. First strand cDNA synthesis was not necessarily specific; it was equally efficient using either random or CP-specific primers. The viral sequence encoding the coat protein was specifically amplified from the total population of cDNA molecules by polymerase chain reaction (PCR), using specific primers bordering the CP gene. The unique amplified product thus obtained was cloned blunt-end into the pT7T318U plasmid vector, and the authenticity of the cloned gene verified by sequence analysis. This cloning strategy obviates the need for virus purification. Sequence comparison of the CP gene of the Italian isolate and those of five other PLRV isolates revealed a close similarity to the three European and the Canadian isolates, and a more distant relationship with the Australian one.     

Comparative detection of mild strains of potato spindle tuber viroid from the dormant potato tubers by Return-polyacrylamiee gel electrophoresis and nucleic acid hybridization

Summary Using a modified procedure of Return-polyacrylamide gel electrophoresis (R-PAGE) mild strains of potato spindle tuber viroid (M-PSTV) were detected reliably from dormant tubers. The sensitivity of R-PAGE detection of M-PSTV was equivalent to that of nucleic acid hybridization. Both methods detected M-PSTV when infected tissue was mixed with healthy tissue in a ratio of 1 to 100. When extracted nucleic acid was diluted with buffer, R-PAGE detected PSTV at a dilution of 1:256 and nucleic hybridization only up to 1:64 PSTV was readily detected from 18 potato cultivars. In addition, mild, ‘intermediate’ and severe strains were separated by R-PAGE, on the basis of their mobility on the electrophorogram.     

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.     

Progeny testing for resistance to potato virus Y: a comparison of susceptible potato cultivars for use in testcrosses with resistant parents

Summary For potato breeding or genetical research purposes, the number of copies of a dominant major gene for resistance to potato virus Y in a parent clone can be determined by test-crossing with a susceptible parent and observing the segregation ratio of resistant to susceptible seedlings in the progeny. In a comparison of different susceptible cultivars for use in test-crosses for this purpose, their progenies differed in the clarity of symptoms and parental phenotype proved an unreliable guide. Cvs Maris Piper, Arran Peak and Dr MacIntosh were found to be suitable tester parents, Pentland Squire less so and cv. Désirée was confirmed as having a major gene conferring incomplete resistance. It was found advisable to test-cross with more than one susceptible parent.