Characterization of an oomycotic virus in Plasmopara halstedii, the downy mildew pathogen of sunflower

• Applicant: Professor Dr. Otmar Spring
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: from 2007 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 55704388

Plasmopara halstedii, the downy mildew pathogen of sunflower, is one of the few Oomycetes identified to host virions. Characterization of the P. halstedii virus is still fragmentary; the viral nucleotide sequences are lacking, the virus distribution has not been studied sufficiently and its impact on the pathogenicity of P. halstedii is unknown. Since P. halstedii is an obligat biotrophic oomycete, P. halstedii and its virus has to be propagated in vital sunflower cultures. We were able to detect the virus in P. halstedii and isolate sufficient virion amounts for phenotypic and genotypic characterization. The virions are isometric (37 nm in diameter) and consist of one coat protein (36 kDa) and two segments of single-stranded RNA (3.0 and 1.6 kb). The objective of this proposal is to reveal the viral nucleotide sequence of both segments and to provide molecular biological tools to study the virus in detail. Based on the viral nucleotide sequence, virus specific primers will be developed. This tool will allow a more sensitive detection for the virus presence or absence in P. halstedii isolates. It will also enable us to provide a broader overview on the distribution of the virus in isolates of different geographic origins and pathotypes. This information will be needed for future studies on the impact of the virus on the pathogenicity of P. halstedii. The viral sequences of representative P. halstedii isolates will then be compared among themselves and also with other viruses. The results might offer a basis to clarify the taxonomic relationships of the P. halstedii virus.

• DFG Programme: Research Grants