PUCREC/PUCTRI – a decision support system for the control of leaf rust of winter wheat and winter rye*

During a three‐year project from 2003 to 2006, two models have been developed to predict leaf rust (Puccinia recondita and P. triticina) occurrence and to simulate disease incidence progress curves on the upper leaf layers of winter rye (PUCREC) and winter wheat (PUCTRI). As input parameters the models use air temperature, relative humidity and precipitation. PUCREC and PUCTRI firstly calculate daily infection favourability and a cumulative infection pressure index and, in a second step, disease incidence is estimated. An ontogenetic model (SIMONTO) is used to link disease predictions to crop development. PUCREC and PUCTRI have been validated with data from 2001 to 2005. Both models give satisfactory results in simulating leaf rust epidemics and forecasting dates when action thresholds for leaf rust control are exceeded.     

A preliminary study of changes in the content of gibberellin-like substances in the potato plant in relation to the tuberization mechanism

Summary Changes in the content of gibberellin-like substances were followed in shoots and roots during different periods of the vegetative cycle (pre-tuberization; tuber initiation; tubers 1–2 cm in diameter; tubers fully grown). The extractions were made with ethyl alcohol and the extracts were divided into acid and neutral fractions after previous treatment with ethyl acetate. Before tuberization the shoots contained large quantities of gibberellin-like substances which decreased after tuberization. On the other hand, the roots contained high concentrations of antigibberellin-like substances which disappeared after tuber initiation. It is suggested that these substances are of importance in the control of the mechanism of tuberization, on the basis of a hypothesis previously propounded.

---

Zusammenfassung Aufgabe dieser Arbeit war, die Entwicklung der gibberellinisch oder antigibberellinisch wirkenden Stoffe in der Kartoffelpflanze (SorteBintje) sowie ihre m?glichen Beziehungen zum Mechanismus der Knollenbildung zu studieren. Der Inhalt dieser Stoffe im Laub und im Wurzelsystem wurde in folgenden Zeitpunkten der vegetativen Entwicklung der Pflanze analysiert: vor der Knollenbildung (20–25 Tage nach Pflanztermin); Beginn der Knollenbildung (Vergr?sserung der Stolonenspitze); Knollen mit 1–2 cm Durchmesser; abgeschlossene Knollenbildung (15–18 Tage vor dem Vergilben der Pflanzen). Die erw?hnten Stoffe wurden 24 Stunden im Dunkeln und bei 2–3 C mit 75 prozentigem Aethylalkohol extrahiert. Nach Entfernung des Alkohols im Vakuum und anschliessender Aethylazetatbehandlung wurden die Extrakte in neutrale und saure Fraktionen getrennt. Nach ihrer Konzentrierung wurden alle Extrakte papierchromatographisch (Whatman's Papier Nr. 4) untersucht. Die Zonen, die im ultravioletten Licht (2537 ?) Fluoreszens oder Absorption zeigten, wurden markiert. Die üblichen Zonen wurden nach herk?mmlichen Rf eingeteilt und ebenso wie die ersten mit Phosphat-Zitronens?urepuffer (pH 5) 24 Stunden im Dunkeln und bei 2–3 C eluiert. Um Stoffe mit gibberellinischer oder anti-gibberellinischer Wirkung zu entdecken, wurde der Reis-Test verwendet. Die Ergebnisse (Abb. 1 und 2) zeigen, dass vor der Knollenbildung das Laub verh?ltnism?ssig hohe Konzentrationen der gibberellinisch wirkenden Stoffe enth?lt, die sich nach Beginn der Knollenbildung verringern. Die Wurzeln ihrerseits zeigen mehrere Fraktionen mit anti-gibberellinischer Wirkung, die nach Einsetzen der Knollenbildung verschwinden. Gestützt auf die in einer früheren Arbeit dargestellten Hypothese glauben die Verfasser, dass diese Stoffe m?glicherweise eine Rolle in der Kontrolle der Knollenbildung spielen k?nnten. Laut dieser Hypothese dürften ein oder einige dieser anti-gibberellinisch wirkenden, durch die Wurzeln synthetisierten Stoffe (Wurzel-Faktor?) nicht nur die Knollenbildung, sondern auch die Erscheinung und das Wachstum der Stolonen am Anfang des Vegetationszyklus hemmen. Unterhalb einer gewissen Konzentrationsgrenze oder dank einer Wechselwirkung dürften ein oder mehrere gibberellinisch wirkende Stoffe des Laubes die Knollenbildung weiter hemmen, jedoch die Erscheinung des Stolonensystems f?rdern. Die Knollenbildung würde unter einer bestimmten kritischen Schwellen konzentration dieser natürlichen Gibberelline eintreten. Gleichfalls geben die Verfasser die M?glichkeit eines Eingriffs des hypothetischen ‘Knollenbildungsfaktors’ in den Mechanismus der Knollenbildung zu; nach einigen Autoren soll sich dieser unter bestimmten thermischen und photoperiodischen Verh?ltnissen synthetisieren.

---

Résumé Le travail avait pour but d'étudier l'évolution de substances d'activité gibbérellinique ou antigibbérellinique dans la plante de Pomme de terre (variétéBintje) et ses rapports possibles avec le mécanisme de tubérisation. La présence de ces substances dans le feuillage et le système radiculaire a été analysé à certains moments du cycle végétatif de la plante (prétubérisation 20–25 jours après plantation); début de la tubérisation (grossissement de l'apex stolonifère); moment où les tubercules ont atteint 1–2 cm de diamètre; et pleine tubérisation (15–18 jours avant le jaunissement des plantes). L'extraction de ces substances a été faite avec de l'alcool éthylique 75% pendant 24 heures à 2–3 C et à l'obscurité. Aprés élimination sous vide de l'alcool, les extraits ont été divisés en fractions neutres et acides par un traitement à l'acétate d'éthyle. Après concentration de tous les extraits, ceux-ci furent chromatographiés sur papier Whatman No. 4. On a marqué les régions qui se sont révélées être fluorescentes ou absorbantes à la lumière ultraviolette (2537 ?). Les autres régions ont été divisées selon des Rf conventionnels, et, comme les autres, ont été éluées avec un tampon phosphateacide citrique pH 5, pendant 24 heures, à 2–3 C et à l'obscurité. Tout de suite on a utilisé le test riz afin de détecter des substances d'action gibbérellinique ou antigibérellinique. Les résultats (Fig. 1 et 2) montrent que, avant la tubérisation, feuillage contient des concentrations relativement élevées de substances d'action gibbérellinique lesquelles diminuent après l'installation du phénomène de tubérisation. D'ailleurs les racines montrent plusieurs fractions d'action antigibbérellinique. Enfin, elles disparaissent lorsque la plante commence à tubériser. Les auteurs pensent que ces substances peuvent jouer un r?le dans le contr?le de la tubérisation, tenant compte d'une hypothèse exposée dans un travail antérieur. Selon cette hypothèse l'une ou certaines substances d'action antigibbérellinique synthétisées par les racines (‘facteur radiculaire’?) empêcheraient, au début du cycle végétatif de la plante, non seulement la tubérisation, mais aussi l'apparition et croissance des stolons. Au-dessous d'une certaine limite ou par interaction avec elles, une ou certaines substances d'action gibbérellinique du feuillage continueraient à empêcher la tubérisation mais elles stimuleraient l'apparition du système stolonifère. Au-dessous d'une certaine limite critique de concentration de ces gibberellines naturelles se produirait la tubérisation. On admet encore la possibilité de l'intervention dans ce mécanisme, de l'hypothétique ‘facteur de tubérisation’ qui, selon certains auteurs, se synthétiscrait dans certaines conditions photopériodiques et thermiques.

     

Differences in natural antibody titres comparing free-ranging guanacos (Lama guanicoe) and capybaras (Hydrochoerus hydrochaeris)

Natural antibodies are an important component of innate humoral immunity but have not been investigated to any great extent in wild mammals. In the current study, serum natural antibody titres were measured by hemagglutination assay for two South American herbivores, the guanaco (Lama guanicoe) and the capybara (Hydrochoerus hydrochaeris). Results indicated that capybaras had antibody titres on average more than four times higher than guanacos (median titres 1:256 and 1:4, respectively), suggesting differences in investment in constitutive humoral immunity between the two species.     

Impact of climate change on the temporal and regional occurrence of Cercospora leaf spot in Lower Saxony

Journal of Plant Diseases and Protection - The effect of climate change on the temporal and regional occurrence of Cercospora leaf spot (CLS) of sugar beet in Lower Saxony is analysed using the...     

A simulation model for the development of brown rust epidemics in winter wheat

A model simulating the progress of Puccinia recondita severity, expressed as a percentage of rusted leaf area (both as average and its 95% confidence interval) on individual wheat leaves over the course of a growing season, with a time step of one day, was elaborated using laboratory and field data from literature. Data on the stages of each infection cycle (uredospore germination, penetration, latency, uredium eruption and infectiousness) were transformed into model parameters by curve fitting, Montecarlo stochastic procedures, corrections and empirical assumptions. Data on host growth, like the timing of all phenological stages, the dynamic of the green area of each leaf from appearance to complete senescence, and tillering were obtained from a specific sub-model. Model validation was performed on actual data not used in model building and representing a wide range of conditions (several winter wheat cultivars grown at eight locations in northern Italy between 1990 and 1994) by using subjective, non-parametric and parametric tests: it revealed a satisfactory agreement between the data simulated by the model and actual data.     

CERCBET 3 – a forecaster for epidemic development of Cercospora beticola*

Cercospora beticola is the most prevalent and damaging fungal disease in German sugar beet growing. Control strategies are based on action thresholds. A model has been developed which forecasts epidemic development (expressed as disease incidence) and signals when action thresholds are overridden. The plot‐specific model, CERCBET 3 uses as input meteorological parameters (temperature, relative humidity), easily accessible agronomic field characteristics and a single recording of C. beticola disease incidence. Extensive validation in 2001–03 showed that, in 80–95% of the cases, CERCBET 3 correctly forecasted the dates when thresholds were overridden. Cultivar diversity in German sugar beet growing is increasing, thus a module has been included into CERCBET 3 which reflects susceptibility to C. beticola by introducing a sporulation factor. In some cases a second or even third fungicide treatment could be necessary to control Cercospora leaf spot and so a further module which models fungicide efficacy has been elaborated. CERCBET 3 is available for sugar beet growers in an interactive form on the Internet platform ISIP, which is provided by the governmental crop protection services of Germany.     

Modelling some aspects of the monocyclic phase of <Emphasis Type="Italic">Stemphylium vesicarium</Emphasis>, the pathogen causing purple spot on asparagus (<Emphasis Type="Italic">Asparagus officinalis</Emphasis> L.)

The monocyclic phase of Stemphylium vesicarium is part of its life cycle and a possible factor for forecasting and the integrated control of purple spot on asparagus. The purpose of the study was to model the flight, germination and germ tube growth of ascospores as basis for the development of a forecasting system. During 2014–2016, the flight period was determined by spore traps. The ascospores flew between March and early July, but most were released in early May. The cumulative percentage of trapped ascospores depending on the daily summed temperature (base 5 °C) on rainy days starting from February 1st was described best by a Chapman Richards function. The germination and germ tube length of ascospores depending on leaf wetness duration and temperature were investigated in laboratory trials. Ascospores germinated rapidly in a wide temperature range. The fitted Chapman Richards function with a temperature-dependent capacity and rate described germination adequately with a calculated optimal temperature of 31.0 °C. The germ tube length was modelled by a combined generalised beta-linear function and it was optimal at 30.4 °C with a narrow temperature range of 25–35 °C for values close to the optimum length. Therefore, the infection process is restricted more severely by the germ tube length than by germination. The ascospore flight is often finished before the end of the harvest, so fungicide treatments during the monocyclic phase might be ineffective in many production sites in Germany. The situation could be different for shorter harvest periods and in non-harvested young plants.     

Rational arrangement of a network for disease survey on a regional scale*

The forecasting and warning system of Emilia‐Romagna region (Italy) produces warnings for crop protection against diseases, using information from weather stations, biological surveys on a network of observation fields and simulation models. The network of field observations is crucial for the efficiency of the service but, unfortunately, the human and economic resources available for their management are usually less than needed. Therefore, the number of observation fields is insufficient to cover the entire territory uniformly, so that their geographical distribution increases in importance. In this work, a method for rational arrangement of observation fields on a regional scale is proposed. It uses models simulating crop growth and disease outbreak, both using meteorological data available on a 5‐km mesh, to draw maps showing homogeneous areas within the territory. For the main pathogens of winter wheat (Erysiphe graminis, Puccinia striiformis, Puccinia recondita and Fusarium subsp.), disease risk is calculated when host plants are susceptible to infection, and both static and dynamic maps are drawn. The use of maps is discussed in arranging observation fields and in timing field surveys.