A modified technique for leaf disk inoculation of sunflower with zoosporangia of the downy mildew pathogen Plasmopara halstedii was developed. Infection with low concentrations of inoculum was obtained down to the level of single sporangia. No significant difference in the infection rate was seen between disks from cotyledons and true leaves. This makes leaf disk inoculation particularly suitable for infections at low sporangium density and for the investigation on plant tissue which cannot be infected with whole seedling inoculation. The technique seems, however, to be inappropriate for pathotype characterization using differential host lines.
A technique was developed to select vital zoospores of Plasmopara haistedii after zoosporogenesis for the infection of sunflower leaf disks. Successful infections were performed with samples containing several zoospores originated from a single sporangium as well as with samples containing only one single zoospore. Infections were indicated by spontaneous sporulation at the surface of inoculated sunflower leaf discs and were secured by transfer to whole seedlings. Using this method it was possible to generate unithallic infections and genetically homogenous strains of sunflower downy mildew.
ZusammenfassungEinzelsporeninfektion von Sonnenblumen mit Plasmopara haistedii Es wurde ein Verfahren zur selektiven Gewinnung einzelner, frisch geschltipfter Zoosporen von Plasmopara haistedii ftir die Infektion von Blattscheiben der Sonnenblume entwickelt. Erfolgreiche Infektionen wurden einerseits mit Proben erhalten, die mehrere, gemeinsam entstandene Zoosporen aus einem einzelnen Sporangium enthielten, ais auch mit solchen, in denen sich nur eine einzige Zoospore befand. Die Infektionen zeigten sich durch spontane Sporulation an der Oberflache inokulierter Blattscheiben und wurden danach auf Sonnenblumenkeimlinge ubertragen. Die Methode erlaubt die Erzeugung unithallischer Infektionen und die Herstellung genetisch einheitlicher Stamme und von Plasmopara haistedii.
A comparison betweeen the electropherograms of the spelt and wheat cultivars showed specific differences in the gliadin band patterns which provided the possibility of a clear classification into spelt or wheat. A special nomenclature was developed to be able to improve the presentation of the gliadin band pattern of spelt, which is different from that of wheat. This nomenclature, however, has not yet been applied to other cereals. The gliadin band patterns were presented in a schematic form. As a parameter for comparison, idealized band patterns of both wheat and spelt were developed by comparing the proportions of the bands of all available types. When comparing the gliadin band patterns of the spelt cross-breeds with their corresponding parental generations, it was noted that the same parental bands were not always transmitted and that the cross-breeds showed differences in the intensity, mobility, occurrence, and the splitting of single bands. In general it can be said that the band pattern of the daughter generation - even in the examined F(5) and F(6) generations - is more similar to the band pattern of the mother than to that of the father, which proves a maternal effect.
A new method, based on leaf disc inoculation, was developed for the screening of metalaxyl tolerance in field isolates of Plasmopara halstedii. High‐pressure liquid chromatography (HPLC) was used to determine the fungicide concentration in the inoculation medium and in the incubated leaf tissue over the test period. These measurements revealed that the fungicide concentration inside the leaf tissue within 24 h had adjusted to the concentration in the outer medium and remained constant for the time of cultivation over a period of more than 11 days. In contrast to whole seedling tests with application of the fungicide via seed dressing, the leaf disc method allows precise quantification of the effective fungicide concentration at the site of infection and is less space and time consuming. Metalaxyl tolerance of P. halstedii isolates was gradually determined according to the sporulation of the pathogen on sunflower leaf discs in the presence of increasing fungicide concentrations. Isolates collected in South Germany showed no tolerance and sporulation was prohibited when tests were carried out at 0.02 μg (a.i.)/ml of metalaxyl or more. In contrast, a tolerant French isolate developed sporangia on leaf discs incubated in a metalaxyl solution of 100 μg (a.i.)/ml.
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