Relationship between potato cyst nematodes and their principal host. II. Evaluation of mathematical descriptors relating potato yield and nematode density

Summary  To describe the relationship between nematode density and yield, four equations of increasing complexity are found in the literature. They concern a linear regression curve, a log linear regression curve, a regression curve based on an exponential relation and an inverse linear regression curve. The yield to PCN density responses of these equations are shown on a linear and on a logarithmic scale. Considerable differences are shown in the way they respond to the same data. None of these equations is able to explain or forecast yield decrease caused by potato cyst nematodes.     

Effects of soil characteristics on the relationship between potato cyst nematodes and yield. II. Acidity (soil pH)

Summary The sandy and sandy peat soils of the northeast of The Netherlands are mineralogically very poor and acid. Independently of potato cyst nematode infestations, there is a considerable negative effect of increasing soil pH on potato tuber yield. Potato cyst nematode infections aggravate the effect of soil pH in depressing yield. It was shown that both potato cyst nematode infection and increasing soil pH values reduce the buffering capacity of the root system. Testing for yield as well as for tolerance to potato cyst nematode infection should be made at a range of soil pH values, similar to those found in the target area. This refers to active breeding programmes as well as to the selection of cultivars for yield trials.     

Effects of soil characteristics on the relationship between potato cyst nematodes and yield. I. Water retention

Summary Data from five long-term field experiments on sandy and sandy peat soils were analyzed for the effect of soil type on damage caused by potato cyst nematodes to potato crops. It was shown that the water retention of the topsoil and the subsoil largely determined the potential yield level in the different fields. According to Oostenbrink's equation the slopes of the curves are steeper with increasing yield level, indicating that the higher the potential yield level, the higher the absolute yield loss. However, when yield was expressed as percentage of maximum yield, yield reduction related to potato cyst nematode density did not differ significantly, except when tolerant cultivars were grown. Increasing tolerance of cultivars to nematode damage was reflected in less steep slopes of the yield/nematode density curves.     

A method of assessing potato seedling progenies for resistance to the white potato cyst nematode

Summary The resistance expressed by progenies of potato seedlings to the white potato cyst nematode (Globodera pallida) has been assessed on bulk sowings of seedlings and on individual plants raised from tubers, and a positive correlation between the seedling and plant tests has been established. The use of such a seedling test as an addition to other methods of screening is discussed.     

Formation of microsclerotia ofVerticillium dahliae Kleb. on various plant parts of two potato cultivars

Summary Potato plants of cvs Element and Mirka were artificially infected withV. dahliae in two greenhouse experiments. Leaf blade, petiole, aerial stem, subterranean stem, stolon and root mass were separately harvested both when the canopy was still green and at maturity. After 4 weeks incubation, the plant tissue was air-dried and the numbers of microsclerotia per mg tissue and per plant were determined. The highest numbers of microsclerotia were observed in the haulm when harvest took place at maturity. Cultivar Element yielded significantly more microsclerotia in the haulm than cv. Mirka, whilst there were no cultivar differences in the microsclerotial production on subterranean parts. The petiole and the aerial stem contributed most to the total microsclerotial production, whereas roots were much more important for formation of microsclerotia than stolons.     

The use of single,spaced potato plants to assess their tolerance of damage by potato cyst nematodes

Summary Potato clones and cultivars differ in their ability to tolerate damage by the potato cyst nematodes:G. rostochiensis andG. pallida. This paper reports a simplified field assessment whereby single, spaced plants are grown in heavily infested soils. These trials identified those clones which are either very sensitive to damage or those that grow and yield well in the presence of nematodes. The use of such a screening procedure in a breeding programme is discussed.     

Interrelationships of the number of initial sprouts,stems, stolons and tubers per potato plant

Summary The relationships between the number of initial sprouts, the number of main stems, stolons and tubers per plant are depicted in 4-quadrant figures. The number of sprouts per seed tuber varied because of different pre-sprouting conditions and/or because of the use of different cultivars. Good linear relationships are shown between the numbers of sprouts and stems, stolons and tubers, and sprouts and tubers, but especially between stolons and tubers within each trial with the one cultivar. When comparing different experiments with the one cultivar the linear relationship between the numbers of stems and stolons disappeared. When comparing different cultivars, no relation was found between the numbers of sprouts and stems. These two cases also led to a statistically less significant relation between the number of sprouts planted and the number of tubers harvested.     

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.     

Verification of sap flow by heat balance method on three potato cultivars

Summary A heat balance method for measuring sap flow in actively growing plants was tested on three potato (Solanum tuberosum L.) cultivars Monona, Norchip and Atlantic. The method is based on applying a known heat source to the stem of an intact plant: by measuring the axial and radial heat dissipation the magnitude of sap flow can be quantified. The technique shows promise as 24 h accumulated sap flow measurements were highly correlated (r²=0.935, n=36) with gravimetric measurements of transpiration and produced an average root mean square error (RMSE) of 20 g d⁻¹. The accuracy of the method improved as daily accumulated flow increased. Under low daily flow rates overall RMSE increased, supporting the need for a heat storage term in the heat balance equation. Short term flow rates were less significantly correlated (r²=0.764, n=1572) and produced an average RMSE of 2.89 g h⁻¹. Identification of these short term flow rates during high flow periods may be difficult. The presence of water potential gradients and the likelihood of re-hydration during high flow events may have also affected the short term performance of the method. At low flow rates, many different errors may be introduced.     

Resistance to potato cyst nematodes,Globodera spp., in wild and primitiveSolanum species

Summary This paper summarizes the results, up to June 1986, of screening the Dutch-German potato collection at Braunschweig Genetic Resources Centre (BGRC) for resistance toGlobodera pallida andG. rostochiensis virulence groups. Resistance toG. pallida was detected in 4.1 of the 78Solanum species tested. The number of accessions with a pathotype-specific high-level resistance was high but accessions with resistance to allG. pallida andG. rostochiensis virulence groups were rare. Four accessions had a high level of resistance to all virulence groups and 26 had partial resistance. The partially resistant genotypes differed in the average number of larvae per root and of eggs per cyst.

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Zusammenfassung Die Suche nach Quellen für Resistenz gegen Zystennematoden der Kartoffel,Globodera pallida undG. rostochiensis, wird bei der Stiftung für landwirtschaftliche Pflanzenzüchtung (SVP) durchgeführt. In einem kooperativen Programm werden die Neuzug?nge bei der ‘Niederl?ndisch-Deutschen Abteilung Kartoffeln der Genbank in Braunschweig’ (BGRC) in S?mlingstests intensiv auf Resistenz gegenG. pallida undG. rostochiensis in Münster (Institut für Nematologie) und in Wageningen (SVP) geprüft. Die Ergebnisse sind in den Tabellen 1, 2 und 3 zusammengefasst. Insgesamt 699 Neuzug?nge von 78Solanum-Spezies wurden auf Resistenz gegen die Virulenzgruppe Pa3 untersucht. In 260 Zug?ngen von 41Solanum-Spezies wurden resistente Genotypen beobachtet, Genotypen mit m?ssiger Resistenz (RS) in 65 Zug?ngen. Die Frequenz von Spezies mit Resistenz gegen Pa2 war ebenfalls hoch (28 von 58 Spezies). Resistenz gegen Virulenzgruppen vonG. rostochiensis wurde weniger h?ufig gefunden (Tabellen 1 und 2). Die Zahl der Zug?nge mit Resistenz gegen eine, zwei oder drei Virulenzgruppen zeigt Tabelle 3. Die H?ufigkeit von Zug?ngen mit Resistenz sowohl gegen Pa2 als auch Pa3 war hoch. Zug?nge mit kombinierter Resistenz gegen Pa2, Pa3 und Ro5 ergaben sich beiS. acaule, S. gourlayi, S. leptophyes, S. megistacrolobum, S. multidissectum, S. oplocense, S. spegazzinii, S. sucrense undS. vernei. SVP-Genotypen unter den Zug?ngen mit kombinierter Resistenz gegen die Virulenzgruppen Pa2 und Pa3 wurden zus?tzlich mit Isolaten von Pa2, Pa3, Ro1.4, Ro2.3 und Ro5 getestet. Genotypen mit Resistenz gegen eine oder mehrere Virulenzgruppen waren gegen andere Virulenzgruppen oft anf?llig. Dies deutet auf Gen-für-Gen-Verh?ltnisse hin. Nur vier Zug?nge konnten gefunden werden, die in hohem Ma?e gegen alle Virulenzgruppen Resistenz aufwiesen. Zug?nge mit partieller Resistenz gegen alle Virulenzgruppen wurden ebenfalls untersucht. Genotypen mit partieller Resistenz unterschieden sich in der durchschnittlichen Zahl von Larven pro Wurzel und von Eiern pro Zyste (Tabelle 4).

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Résumé La Fondation pour l'Amélioration des Plantes Cultivées (SVP) a entrepris des recherches de sources de résistance àGlobodera pallida et àG. rostochiensis dans la collection germanonéerlandaise du centre de Ressources Génétiques de Braunschweig (BGRC). En collaboration, l'Institut für Nematologie de Münster et le SVP de Wageningen ont réalisés des tests de résistance à ces deux nématodes sur des plantules issues de graines provenant de diverses introductions. On trouvera la synthèse des résultats en tableaux 1, 2 et 3, 699 introductions appartenant à 78 espèces deSolanum ont été testées vis-à-vis de Pa3: des génotypes résistants ont été trouvés dans 260 introductions de 41 espèces deSolanum et des génotypes modérément résistants (RS) ont été trouvés dans 65 introductions. La fréquence d'espèces possédant une résistance à Pa2 est également élevéc (28 sur 58 espèces). La résistance àG. rostochiensis est trouvée plus rarement (tableaux 1 et 2). Le tableau 3 indique le nombre d'introductions possédant une résistance à un, deux ou trois groupes' de virulence. La fréquence des introductions possédant une résistance à la fois à Pa2 et à Pa3 est élevée. Des résistances à la fois à Pa2, Pa3 et Ro5 sont trouvées dans des introductions appartenant àS. acaule, S. gourlayi, S. leptophyes, S. megistacrolobum, S. multidissectum, S. oplocense, S. spegazzinii, S. sucrense etS. vernei. Ultérieurement, les génotypes combinant la résistance à Pa2 et Pa3 ont été testés au SVP vis-à vis de différentes populations de Pa2, Pa3, Ro1,4, Ro2,3 et Ro5. Souvent, les génotypes résistant au moins un groupe de virulence ne sont pas résistans aux autres groupes de virulence. Ceci montre que la résistance est basée sur une réaction gène pour gène. Un haut niveau de résistance à tous les groupes de virulence n'a été trouvé que dans quatre introductions. Des introductions possédant une résistance partielle à tous les groupes de virulence ont été trouvées. Les génotypes partiellement résistants diffèrent entre eux par le nombre moyen de larves par racine et d'oeufs par kyste.

     

An early generation screen for combined cyst nematode (Globodera spp.) and blight (Phytophthora infestans) resistance in potato

Summary A technique is described which enables potato clones to be screened for resistance to both species of potato cyst nematode (Globodera rostochiensis andG. pallida) and to blight (Phytophthora infestans) in the foliage during the winter and first spring following harvest of seedlings grown from true seed. A container test, used to assess resistance to both species ofGlobodera in a mixed inoculum, is followed by an assessment of resistance to foliage blight, using the same plants in the glasshouse. This screen can be completed in time for duplicate tubers of the resistant clones to be planted for multiplication in the second growing season. The close correlation between results obtained using this system and those predicted from the known inheritance of the characters selected and the gain in efficiency achieved in breeding, are illustrated by examples. In Kartoffelzuchtprogrammen müssen viele Eigenschaften berücksichtigt werden. Die Reihenfolge ihrer Selektion kann grossen Einfluss auf die gesamte Arbeitsleistung haben. Dort wo die Aufspaltung der Nachkommenschaft bedeutsam ist, kann eine frühe Selektion leicht erkennbarer Eigenschaften, wie Resistenz gegenüber Sch?dlingen und Krankheiten, die Populationsgr?sse wirkungsvoll verringern. Dies k?nnte den starken Selektionsdruck auf Knolleneigenschaften als erste Hauptprüfung in Kartoffelzuchtprogrammen ersetzen. In dieser Arbeit wird eine Technik zur Prüfung auf kombinierte Resistenz gegenüber Kartoffelnematoden und Krautf?ule beschrieben, und es werden die Ergebnisse für Nachkommen aus typischen Kreuzungen mitgeteilt (Tabelle 1). Die Nematodenresistenz wurde mit Hilfe eines Gef?sstestes ermittelt, bei dem ein Inokulumgemisch aus Larven vonGlobodera rostochiensis undG. pallida verwendet wurde. Dies ergab die in Tabelle 2 dargestellten Befunde und eine Verteilung der Zystenproduktion, wie sie in den Abbildungen 1A und 1B gezeigt wird. Diese Ergebnisse best?tigten, dass die nicht wiederholten Tests Reaktionen ergaben, wie sie von der bekannten Vererbung der Eigenschaften erwartet wurden, und ein Chi-Quadrat-Test (Tabelle 2) ergab bei drei von vier Familien, dass keine Abweichung von den erwarteten Verh?ltnissen für H1, von dem sich dieG. rostochiensis-Resistenz herleitet, vorlag. Eine vorkommende Abweichung (Tabelle 2, Familie 4) liess sich mit der ungenügenden Unterscheidung der unreifen Zysten von beidenGlobodera-Arten erkl?ren. Bei der Selektion auf Resistenz gegenüber den beiden Arten ist diese Fehlerquelle unbedeutend. Die als nematodenresistent ermittelten Pflanzen wurden in T?pfen bei hoher Luftfeuchtigkeit in einem Polythen-Tunnel in Gew?chshaus angezogen und mit einer Zoosporensuspension aus einem Isolatkomplex vonPhythophthora infestans besprüht. Die Anf?lligkeit wurde ermittelt, indem die ungef?hre Blattfl?che der entstehenden nekrotischen L?sionen bewertet wurde. Die Ergebnisse in Tabelle 3 und die Verteilung der resistenten Klone (Abb. 1C) weisen—wie erwartet—auf die polygene Vererbung hin. Bei den angewandten Selektionsstufen erhielt man ungef?hr 15% der Nachkommen mit hinreichender Resistenz gegenüber den drei vorgegebenen Eigenschaften. Die Teste wurden in der Lagerzeit der Knollen, die ursprünglich von S?mplingspflanzen stammten, abgeschlossen, so dass sie in der der Aussaat nachfolgenden Saison ausgepflanzt werden konnten. Dans les programmes de sélection de la pomme de terre, de nombreux caractères sont pris en compte et le choix de la succession de leurs mesures a une forte importance sur l'efficacité globale du travail. Quand il y a ségrégation pour des caractères importants et facilement mesurables comme la résistance aux ravageurs et aux maladies, on peut réduire le travail de maintenance du matériel en réalisant des cribles précoces pour ces caractères. Ces tests peuvent être d'abord réalisés à la place des tests de qualité, classiquement effectués en début de programme. Les auteurs décrivent ici une technique de tests de résistance à la fois vis-à-vis des nématodes à kyste et du mildiou. Les résultats de tests de descendance de quatre croisements sont détaillés. La résistance aux nématodes est mesurée par des tests en conteneours dans lesquels le substrat est infesté par un mélange de larves infestantes deGlobodera rostochiensis et deG. pallida. On trouve les résultats globaux en Tableau 2 et les distributions exprimées en valeur relative du nombre de kystes neoformés sont représentées en figures 1A et 1B. Malgré l'absence de répétitions, ces résultats sont en accord avec ceux espérés: le {ie67-1} (Tableau 2) ne montre pas de différence significative pour 3 familles sur 4 avec les résultats théoriques quand c'est la résistance due au gène H1 qui est mesurée. Le cas de non concordance (Tableau 2, famille 4) est explicable par une possible confusion des espèces à la lecture. Cependant, cette source d'erreurs est peu importante quand la sélection est dirigée en même temps contre ces deux espèces. Les clones jugés résistants sont alors testés vis-à-vis dePhytophthora infestans. Ils sont placés en pots et cultivés en serre sous tunnel de polyethylène pour entretenir une forte humidité relative. Une suspension de zoospores d'un isolat complexe est pulvérisée et la sensibilité est appréciée par la surface approximative des lésions nécrotiques du feuillage. Les résultats du Tableau 3 et la distribution relative de la fréquence des clones résistants confirment l'hérédité polygénique de la résistance au mildiou. Environ 15% des familles sont ainsi retenues comme ayant un bon niveau de résistance aux deux espèces deGlobodera et àP. infestans. Les tests, réalisés en hiver, sont achevés à temps pour que les duplicatats, conservés à basse température, identifiés comme résistants puissent être plantés au champ en temps utile, l'année qui suit les semis de graines.     

The effect of a seaweed concentrate on the in vitro growth and acclimatization of potato plantlets

Summary The seaweed concentrate ‘Kelpak’ is used commercially in the greenhouse and field to improve plant quality. ‘Kelpak’ was added to the in vitro culture medium of potato cv. ‘BP1’ and also applied as a leaf/soil drench immediately after transplanting. The addition of 0.25% seaweed concentrate to the medium improved plantlet quality and led to better establishment in the greenhouse. No beneficial effect of seaweed concentrate in the tissue culture medium was observed if a second cutting was part of the micropropagation process. Additional application of 0.5% seaweed concentrate in the greenhouse to plantlet cuttings derived from tissue culture was not beneficial.     

Screening potato cultivars for common scab of potato in a naturally infested field

Summary Twenty seven cultivars of potato were screened for common scab grown in a commercial field in two successive years (1996–97 and 1997–98). Eight cultivars were least susceptible and the others ranged from medium susceptible to very highly susceptible. None of the cultivars was resistant. Most showed a stable resistance reaction in both years.     

The effect of boron on calcium uptake and growth in micropropagated potato plantlets

Summary Boron (B) requirements differ widely among plant species and the concentration range between toxicity and deficiency is less for B than for any other nutrient. Excess B can adversely affect calcium (Ca) uptake and plant growth. Potato cvs Bintje and Norland plantlets were micropropagated on Murashige & Skoog (MS) nutrient medium, supplemented with 3 (MS control level) or 9 mM Ca, and a range of H₃BO₃ levels (0.025 to 0.300 mM B). Medium B levels of 0.100 and 0.300 mM decreased Ca content in leaves and shoots of cv. Norland, but not Bintje. Medium B level of 0.025 mM, which is 25% of the control MS level, enhanced Ca uptake in cv. Norland and did not compromise normal plantlet growth in either cultivar. This lower H₃BO₃ level (0.025 mM B), and a B-free gelling agent such as Gelrite, could be used for micropropagation of potato and possibly other species susceptible to Ca defifiency disorders.     

Effect of haulm treatments on the formation of microsclerotia ofVerticillium dahliae Kleb. on potato

Summary In four pot experiments, potato plants of cv. Element were artificially infected withV. dahliae. At an early and a late harvest haulms were killed chemically, by burning or by various other treatments, including cutting them into pieces of different lengths and keeping the debris on the soil surface or covering with soil. After 4 weeks the plant material was air-dried and the number of microsclerotia per mg was determined. At the early harvest, in two experiments, the chemical treatment yielded more microsclerotia than the cutting treatments. Covering colonised haulm tissue with non-sterilised soil was effective in inhibiting microsclerotia formation. Shorter haulm pieces led to fewer microsclerotia at the later harvest if the material was kept on the soil surface. The variation in microsclerotial yield and in treatment effects among the different experiments was large.     

Effects of soil-borneRhizoctonia solani Kühn on yield and quality of ten potato cultivars

Summary The effects of soil-borneRhizoctonia solani on yield and quality of potato were studied by an extensive individual plant sampling procedure. From 1983 to 1986, stem canker and stolon pruning were examined in 10 768 plants growing on a sandy soil. Tuber yield and quality and haulm yield per plant were also recorded. The degree of attack byR. solani depended on the cropping frequency of potato. Severe and very severe stem and stolon attacks decreased fresh yield, dry matter yield and dry matter content of tubers and increased the number of deformed and small tubers, whereas the effect on haulm yield and stem number was small. Potato cultivars differed in susceptibility toR. solani, but yield response did not differ significantly between cultivars at the same levels of stem and stolon infection.     

Assessing potato cultivars in Tunisia for susceptibility to leak caused byPythium aphanidermatum

Summary The susceptibility of 21 potato cultivars to leak (watery wound rot) caused byPythium aphanidermatum was compared. Whole tubers were inoculated after wounding by dipping into a water suspension of 10³ oospores/ml and incubated for 3 days at 25°C. The mean penetration of tissue calculated from the recording of lesion width and depth and the qualitative assessment of rot extension were highly correlated. For 10 of 12 cultivars tested at least twice, consistent reactions were obtained: cvs Korrigane. Superstar, Safrane and Yesmina were moderately susceptible, whereas Atlas, Diamant, Mondial, Obélix, Spunta and Timate were susceptible to highly susceptible. Tubers originated from two locations and/or two cropping seasons: thus, the performance of these cultivars under different production conditions reveals a satisfactory level of agreement with the test. Moreover, ratings assigned are supported by field or store observations.     

Ring rot symptom development on potato cultivars and lines in southern Alberta

Summary Plants were grown in the field from seed pieces of potato cultivars injected with ring rot bacteria (Corynebacterium sepedonicum). Symptoms were produced with both 18 and 180 colony forming units (cfu) on cvs Norchip and Red Pontiac and with 180 cfu on cv. Belrus plants. Tuber symptoms were detected in all cultivars except Belrus and Teton. Tuber progeny produced plants that developed top symptoms on all cultivars except those of cv. Nooksack, Russet Burbank, and Teton. Tuber progeny of the second crop produced both plants and tubers with symptoms developing only in the cv. Nooksack. In another 3-year experiment, variability in the disease response of selected cultivars and lines was examined following knife-inoculation of tuber seed with a high level of ring rot bacteria. Significant correlations between top and tuber symptoms were detected, but they were not high enough to make unnecessary the examination of both top and tuber symptoms in ring rot disease selection studies. Contribution no. 3879111     

The expression of resistance to the white potato cyst nematode (Globodera pallida) by individual potato seedlings under different inoculation treatments

Summary The resistance toGlobodera pallida of individual potato seedlings from three progenies derived fromSolanum tuberosum ssp.andigena CPC 2802 was assessed using three inoculation treatments. Plants grown from tubers from the seedlings were used to reassess resistance. All the seedling test inoculation treatments over-estimated the proportion of clones classified as resistant compared to the results from tuber-grown plants. However, the mean relative resistance of progenies estimated by both tests showed good agreement, and it is suggested that seedlings are best used for assessing the resistance of progenies of crosses to identify promising combinations rather than individual clones.