Browsing by Subject "Oomycetes"

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    Verbreitung, Diversität und Übertragung des Mykovirus PhV und seine Auswirkung auf Plasmopara halstedii, den Falschen Mehltauerreger der Sonnenblume
    (2015) Grasse, Wolfgang; Spring, Otmar
    The Plasmopara halstedii Virus (PhV) is a ss(+)RNA virus with two segments. It occurs only in its host Plasmopara halstedii, the downy mildew pathogen of the sunflower. The two RNA strands encode for an RNA depending RNA Polymerase (RdRp) and a coat protein (CP), respectively. So far the phylogenetic analysis has shown similarities of the RdRp with the family of Nodaviruses while the CP seems to belong to the family of Tombusviruses. Phylogentic comparison based on both sequences now suggest a new clade, containing PhV and the Sclerophthora macrospora Virus A, which is basal to both mentioned virus families. Studies about diversity and the occurrence of PhV have shown that the virus existed in samples from 17 countries from five continents which were collected over the past 40 years. Its presence in more than 90% of these samples was documented. No correlation was found between the geographic origin and age of the samples, and presence or absence of PhV sequences. The calculated genetic diversity among all samples was surprisingly low. For 22 fully sequenced samples from 13 countries, only 18 SNP positions were reported. Genetic distances were extremely low with means of 0.001 for the RdRp and 0.002 for the CP. Investigations of the influence of PhV on the aggressiveness and pathogenicity of P. halstedii have shown a hypovirulent effect of the virus. In this study, isogenic strains of the Oomycete were infected with PhV and used for a series of bioassays on sunflowers. The production of sporangia was lowered by ca. 30% in case of virus presence and the latent period, i.e. the day of the first observed sporulation, was delayed by one day. The potential for systemic infections of the sunflower was also lowered by one third when PhV was present. Experiments to generate PhV by means of active cDNA clones in P. halstedii were performed with two different vectors and three transformation methods. It was shown that elctroporation techniques were useful to transport plasmids into the zoospores of P. halstedii and that the T7 promotor was able to start the transcription. The following generation of sporangia, however, lacked these sequences. This indicates that there was a transient transformation which produced PhV RNA sequences, but these sequences were unable to rebuild the virus itself.