The disease complex Beet necrotic yellow vein virus and Beet soil borne mosaic virus on Beta vulgaris , Analysis of viral molecular biology, interactions and resistance stability in Beta vulgaris (Molecular Benyvirus-Interactions and Evolution in Sugarbee

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Beet necrotic yellow vein virus (BNYVV) and Beet soil borne mosaic virus (BSBMV) are members of the genus Benyvirus with relatively high sequence homology. Both species induce virus diseases in sugar beet (Beta vulgaris) with variable symptom expression and tissue specific colonization. BNYVV induces rhizomania, whereas BSBMV produces leaf mosaic symptoms. In contrast to BNYVV that is limited to roots, BSBMV is able to infect sugar beet systemically. Whereas BNYVV is controlled by natural resistance genes, no similar traits are known to act against BSBMV. The molecular basis for this remains unknown. Natural BNYVV sources have limited durability due to the occurrence of resistance breaking variants. Under natural conditions, both viruses occur in sugar beet in mixed infections. Knowledge about possible antagonistic interactions is quite limited. So far, no information is available about commonly colonized tissue or exclusion, the formation of reassortants as well as recombinants, which is expected to have an influence on virus evolution. The establishment of fluorescently labeled infectious clones of both viruses during preliminary work now permits for the first time to perform molecular virological experiments answering these questions. At first the molecular causes for viral symptom expression, host specific long distance movement and systemic colonization in sugar beet shall be revealed in microscopical studies by use of virus mutants and fluorescently labeled viruses. More the interaction of both species in mixed infections will be analysed. This includes investigations of tissue-specific colonization, detection of a possible synergism, antagonism or cross protection as well the analysis of putatively formed interspecies reassortants and recombinants. In addition it is aimed to establish a better understanding of the host-pathogen interaction depending on virus species and plant resistance traits. We plan to decipher the molecular causes of species specific leaf and root symptoms as well as the specific control of BNYVV by natural resistance mechanisms. In the field of BNYVV resistance stability of natural resistance, methods to quantify the selection pressure on the virus population to select resistance breaking isolates shall be developed. The results obtained will help to generate a fundamental and deepened understanding of viral etiology, evolution and interaction of Benyviruses and on a long term perspective will permit a focused and improved resistance management.