A comparison of some methods for detecting potato leaf roll virus in potato tubers in Israel

Summary The results obtained by four methods for detecting PLRV in potato tubers grown in Israel were compared with the results obtained by aphid transmission to test plants. The correlation coefficients for potatoes lifted in July (seed for autumn) and September (seed for spring) were: Igel-Lange test, 0.18 and 0.25; datura grafting with tuber sprouts, 0.71 and 0.63; aphid transmission from sprouts to test plants, 0.89 and 0.81; and visual assessment in the Florida test (for spring seed), Up-to-Date 0.58, Blanka 0.67 and Désirée 0.33. The Igel-Lange test proved unreliable; datura grafting is time consuming and PLRV symptoms were similar to reactions ofDatura stramonium to wounding and to stress. The results of the Florida test were somewhat variable and were obtained too late. The sprout test was deemed the most suitable as it is accurate and the results can be obtained within two months. Contribution No 156-E, 1979 series, Volcani Center.     

Selection of first-year potato seedlings for resistance to potato leaf roll virus

Summary In families obtained from crossing pairs of parents with high resistance to potato leaf roll virus (PLRV), individual clones differ greatly in their level of resistance. Inoculation of first-year seedlings was effective in selecting more resistant families, but it was not so effective in selecting more resistant individual clones.     

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.     

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.     

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.     

Effect of potato leaf roll virus on autumn potatoes in Israel

Summary In field trials simulating commercial conditions, secondary PLRV infection of autumn-grown potato crops in Israel significantly reduced yield, although symptoms were not perceptible. Plots containing 7.3% PLRV-infected seed showed an increase in yield per plant of 17%, compared with plots with 36.2% infected seed; in plots with only 1.3% infected seed the increase of yield was 21%. In a second experiment, where individual plants were assayed, the yield of PLRV-infected plants of cv. Blanka was only 68.7% of that of PLRV-free plants; corresponding figures for cv. Up-to-Date and Désirée were 79.2 and 58% respectively. PLRV infection was not associated with reduced emergence or with the yield of deformed tubers.

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Zusammenfassung W?hrend der ersten zwei Monate der im Herbst liegenden Wachstumszeit der Kartoffel (August-Januar) sind in Israel sehr hohe Temperaturen (mittleres Maximum 34,7° C) und hohe Sonneneinstrahlung; anschliessend fallen die Temperaturen und die Lichteinstrahlung stark ab. Unter diesen Bedingungen bleibt die Infektion mit PLRV meist symptomlos und es gibt vom Pflanzenwuchs her keine Anzeichen dafür anzunehmen, dass der Ertrag beeintr?chtigt ist. Imersten Versuch (A) wurden die Ertr?ge von Best?nden verglichen, die die gleiche Pflanzgutgr?sse (Sorte Désirée) hatten, aber von drei Herkünften I, II und III stammten. Der Anteil der PLRV infizierten Knollen in diesen Herkünften betrug 1,3, 7,8 und 32,6% (Abb. 1A). Der durchschnittliche Ertrag pro Parzelle für Herkunft I, II und III lag bei 12,6 kg, 10,0 kg und 7,6 kg (Abb. 1C); die Differenzen zwischen den Herkünften waren signifikant (P<0,05). Der Unterschied zwischen Herkunft I und II gibt vielleicht die unterschiedlichen Auflaufraten wieder (Abb. 1B), aber die Differenz zwischen den Herkünften II und III scheint eine Folge der Virusinfektion zu sein, und ?hnliche Differenzen wurden beim Vergleich des Ertrages pro Pflanze gefunden (Abb. 1D). Diese Annahme wurde im Versuch B best?tigt, in dem der Ertrag PLRV-infizierter Pflanzen mit dem PLRV-freier Pflanzen verglichen wurde. Die Infektion mit PLRV war nicht mit einer verringerten Auflaufrate oder dem Ertrag an deformierten Knollen verbunden, aber infiziertes Pflanzgut der Sorte Blanka ergab nur 68,7% des Ertrages virusfreien Pflanzgutes, Up-to-Date 79,2% und Désirée 58%; die Verluste waren statistisch signifikant (Abb. 3). Diese Ergebnisse lassen annehmen, dass betr?chliche Ertragsverluste durch die Infektion mit PLRV in den im Herbst gepflanzten Kartoffeln eintreten k?nnen, obwohl die Symptome nicht wahrnehmbar sind. Im Hinblick auf den hohen PLRV-Befall in den Herbstbest?nden (Marco, 1981b), kann es von Vorteil sein die im Frühjahr gepflanzten Best?nde vor einer PLRV-Infektion zu schützen, da sie das Pflanzgut für den Herbst stellen.

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Résumé Pendant les deux premiers mois de végétation des pommes de terre cultivées à l'automne en Israel (Ao?t-Janvier), les températures sont très élevées (moyenne maximale de 34,7°C) et la luminosité très forte. Puis les températures et l'intensité lumineuse diminuent rapidement. Sous de telles conditions, la contamination par le virus de l'enroulement est généralement existante mais sans l'apparition de sympt?mes; rien ne permet donc d'indiquer en végétation que le rendement est affecté. Dans une première expérience (A), le rendement est comparé pour trois cultures obtenues à partir de plants de même calibre (variété Désirée), mais de sources différentes (I, II et III). Suivant l'origine I, II et III les pourcentages de la contamination par le virus de l'enroulement est respectivement 1,3, 7,8 et 32,6% (fig. 1A). Le rendement moyen obtenu par parcelle est respectivement 12,6, 10 et 7,6 kg (fig. 1C), la différence entre les trois origines étant significative (P<0,05). L'écart de rendement entre les plants de source I et II s'explique sans doute par le taux de levée différent (fig. 1B); mais entre les plants de source II et III, la différence semble provenir de la contamination par le virus et ceci est également observé pour le rendement par pied (fig. 1D). Cette hypothèse est confirmée par l'expérience B ou le rendement obtenu à partir de plants contaminés est comparé à celui du témoin planté avec des tubercules indemnes de virus. L'incidence de la contamination n'est pas correlée au manque à la levée et au rendement des tubercules difformes. Les plants contaminés ont donné pour les variétés Blanka, Up-to-Date et Désirée respectivement 68,7%, 79,2% et 58% du rendement obtenu à partir de tubercules sains, la diminution de rendement étant significative (fig. 3). Les résultats montrent qu'il peut y avoir des

     

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.