Untersuchungen zur Übertragung von Clavibacter michiganensis ssp. sepedonicus auf gesunde Kartoffelknollen

Zusammenfassung In den Jahren 1999 bis 2003 wurde in Freiland-, Klimakammer- und Lagerungsversuchen überprüft, ob ein Risiko für die Übertragung des Erregers der Bakteriellen Ringfäule der Kartoffel (Clavibacter michiganensis ssp. sepedonicus) besteht, wenn (a) gesunde Kartoffelknollen in Kontakt mit Maschinen und Geräten kommen, die mit dem Erreger kontaminiert sind (indirekter Kontakt) und (b) gesunde Kartoffelknollen direkt in Kontakt mit infizierten Knollen kommen (direkter Kontakt). Nach indirektem Kontakt konnte nur beim nachfolgenden Anbau der kontaminierten Knollen in der Klimakammer Befall in Kraut und Knollen festgestellt werden. Im Freiland konnte der Erreger, auch bei wiederholtem Nachbau der geernteten Knollen, nicht nachgewiesen werden. Nach direktem Kontakt und nachfolgendem Anbau der kontaminierten Knollen in der Klimakammer und im Freiland, wurde der Erreger in allen Fällen in den geerntete Knollen nachgewiesen. Befall im Kraut wurde nur in dem Klimakammerversuch und in einem Freilandversuch ermittelt. Wurden durch direkten Kontakt kontaminierte Knollen eingelagert, konnte der Erreger in allen untersuchten Knollen festgestellt werden. Insgesamt besteht ein hohes Risiko, dass gesunde Knollen infiziert werden, wenn oberflächliche Kontaminationen mit dem Erreger erfolgen. Die Wahrscheinlichkeit von Infektionen steigt mit zunehmender Kontaminationsstärke.     

Überleben von Ralstonia solanacearum Biovar 2 (Rasse 3), dem Erreger der Schleimkrankheit der Kartoffel, in Boden und auf verschiedenen Materialien (Mikrokosmos)

Microcosm studies were carried out to test the survival of Ralstonia solanacearum biovar 2 (race 3) in soil at the permanent wilting point (wp) water content and at field capacity (fc) water content and on various material. Soils were placed at permanent ?5°C, 4°C, 15°C and 20°C and weekly fluctuating ?10/0/+10°C and the material at 5, 15 °C, 20°C with relative humidity (rh) uncontrolled or at constant 10% or 90%. In soil, survival was clearly dependent on temperature independent of water content. At 20°C Ralstonia solanacearum could be reisolated up to 364 days, at 15°C up to 290 days, at 4°C up to 209 days and at fluctuating temperatures (?10/0/+10°C) only up to 18 days. The lower the temperature, the more the population declined. At 15°C and 20°C appr. 10⁷ cfu/g soil were detected after 100 days, whereas at ?5°C only 10² cfu/g soil were detected after only 18 days. The pathogen was longer detectable in sandy-clay loam than in lighter sandy soil. It could be longer reisolated at wilting point and the populations did not decline as rapidly as at field capacity. Ralstonia solanacearum could best survive on material surfaces like rubber, plastic and varnished metal with maximum survival of 40 days at 5°C and 10% rh. In general there is a low risk of Ralstonia solanacearum overwintering under European climatic conditions when the fields are cleared of plant debris and the soil is frozen. Contamined material surfaces pose the risk of pathogen transmission to healthy tubers.     

Besteht das Risiko der Verschleppung der Bakteriellen Ringfäule der Kartoffel durch den Krautschläger?

In 2001 and 2002, two field trials were performed by the Plant Protection Service (PPS) of the Landwirtschaftskammer Weser-Ems in Oldenburg and the Institute for Plant Protection of the Bavarian State Research Center for Agriculture (LfL) in Freising respectively to examine the transmission of the bacterial ring rot pathogen of potato (Clavibacter michiganensis ssp. sepedonicus) by haulm cutting. In the experiment conducted by the PPS in Oldenburg a lawn-trimmer was used to simulate haulm cutting, before a bacterial suspension was sprayed on the ends of the cut haulms. Two cultivars (early and late) were tested and also the effect of an additional chemical measure for haulm destruction on the transmission of the pathogen was determined. In the trial performed at the LfL in Freising plots with infected plants for the contamination of the haulm cutter were treated immediately prior to plots with healthy plants. Infections of stems (re-growth) and tubers of the plants were determined by polymerase chain reaction (PCR) and indirect immunofluorescence antibody staining (IFAS). In the trials conducted with the haulm cutter, ring rot could be detected in the re-growth of 60% of the plants derived from healthy tubers 4 weeks after haulm cutting. It was confirmed in a bioassay, that the isolated pathogens were viable and virulent. Although the ring rot pathogen was transmitted to a great extent to the leaf material, no infection of progeny tubers occurred in a total of 450 tested plants. However in general a migration of the transmitted pathogen to the tubers cannot be excluded. Therefore further on it is advisable to clean and disinfect the haulm cutter before each use.     

Untersuchungen zur Übertragung von Clavibacter michiganensis ssp. sepedonicus, dem Erreger der Bakteriellen Ringfäule, in das Kraut von Kartoffelpflanzen

From 1999 to 2001, field trials were carried out to find out weather there is a risk of the causal agent of Bacterial Ring Rot of potato (Clavibacter michiganensis ssp. sepedonicus) to be transmitted to the leaves of healthy potato plants via contaminated machinery and equipment during the vegetation period and if so weather the bacteria are transported into the newly formed tubers. Two methods were chosen. Firstly, a sharp-edged metal bar contaminated with a bacterial suspension was drawn through the leaves of potato plants up to 6 times during the vegetation period. Secondly, a suspension of the pathogen was directly injected into the stems of potato plants. The harvested tubers were tested in all trials, leaves were additionally tested in the trial with the contaminated metal bar. The pathogen was not found in any trial. Therefore the risk for the transmission of the Ringrot agent to the leaves of potato plants with contaminated machinery might be very low.     

SIMBLIGHT1 – a new model to predict first occurrence of potato late blight*

Prediction of the first occurrence of potato late blight (Phytophthora infestans) given by the SIMPHYT1 model, which has been used for about 20 years, has not been found satisfactory in years with high soil moisture. Consequently, a new model, SIMBLIGHT1, has been developed. As input parameters SIMBLIGHT1 requires temperature, relative humidity and information on soil moisture, crop prevalence and cultivar susceptibility. SIMBLIGHT1 calculates a cumulative risk index for several groups of emergence dates and signals the start of the epidemic once a given threshold is overridden. Model validation and comparison of SIMBLIGHT1 with SIMPHYT1 were performed with field data from 11 years. Results were promising and SIMBLIGHT1 gave better results than SIMPHYT1 when soils of potato fields were waterlogged. Efforts are currently being made to improve SIMBLIGHT1 and in the long term this model will replace SIMPHYT1.     

Impact of Climate Change on the Phenological Development of Winter Wheat,Sugar Beet and Winter Oilseed Rape in Lower Saxony,Germany

Journal of Plant Diseases and Protection - There is a general agreement that climate change, in the medium and long term perspective, may affect agricultural crops. As part of the KLIFF project...     

Verbreitung der Bakteriellen Ringfäule der Kartoffel (Clavibacter michiganensis ssp. sepedonicus) durch kontaminierte Lagerkisten

In field trials performed by the Institute for Plant Protection of the Bavarian State Research Center for Agriculture (LfL) in Freising in 2001 and 2002, it was studied, whether Clavibacter michiganensis ssp. sepedonicus (Cms), the bacterial ring rot pathogen of potato, could be transmitted to seed potatoes by the use of contaminated crates. Healthy seed tubers were brought into contact with Cms before planting by (i) storage in freshly contaminated crates at 8°C for 4 weeks, (ii) storage at unregulated cellar temperature (between 1 and 15°C) for 8 months in crates, which were already contaminated and empty at filling time for 5 months and (iii) storage in freshly contaminated crates at 4°C for 5 months. Infections of stems and tubers of the plants were determined by polymerase chain reaction (PCR) and indirect immunofluorescence antibody staining (IFAS). Storage of healthy tubers in contaminated crates produced infected plants in all three treatments: PCR results of the tubers were positive in 2 (ii) to 9% (i) of the plants.     

Untersuchungen der Zuckerrübe als Wirtspflanze für Clavibacter michiganensis ssp. sepedonicus, dem Erreger der bakteriellen Ringfäule der Kartoffel

Studies were carried out to test the sugar beet as a host for Clavibacter michiganensis ssp. sepedonicus (Cms), the causal agent of bacterial ring rot of potato. For that purpose field trails and greenhouse experiments were performed. At the field trails sugar beet was cultivated on plots, which were contaminated with Cms infected soil. Subsequently the plots were used for the cultivation of potatoes. Both, the harvested sugar beets and the potatoes, were tested in polymerase-chain reaction (PCR). Both, the sugar beets and the potatoes were tested negative for Cms. In the greenhouse sugar beet was treated with Cms by cultivation in Cms contaminated soil, by direct inoculation into the plant or by indirect inoculation by watering with contaminated suspensions. In most experiments Cms could not be detected in sugar beet after 18 weeks, so it did not remain viable in the plant. But in one experiment after direct inoculation Cms was detected and reisolated in sugar beet. Additionally, no infection of sugar beet was observed via contaminated soil.