Mueller, D. G.
Fakultaet fuer Biologie der Universitaet, D-78457 Konstanz, Germany.
Many brown algal species are infected by viruses with genomes of double stranded DNA. We maintain clonal cultures of healthy and infected isolates comprising seven species from five genera: Ectocarpus, Feldmannia, Hincksia, Pilayella and Myriotrichia. All viruses are distinct taxonomic entities, and highly host specific with few exceptions. Our brown algal viruses are systemic and latently present in every cell of an infected host. They become virulent in the reproductive structures and render the host sterile. A fragment of the Ectocarpus virus genome coding for a coat protein is used as a virus specific indicator to detect infected plants with a PCR amplification technique. With this method 42 out of 97 clonal isolates from all oceans and continents were found to contain viral DNA in a cryptic state. In an epidemiological study we followed an Atlantic and a Pacific Ectocarpus population over 26 months. Between 60 and 100% of the Ectocarpus plants in both habitats contain viral DNA. Furthermore, two different virus genotypes were found to co-exist in the Canary Island habitat. Easiness of infection, vertical passage to daughter generations by vegetative and sexual reproduction, and virus elimination by Mendelian segregation in the host´s meiosis suggest a highly dynamic interaction between host and pathogen, including the possibility of lateral gene transfer.