FACTORS AFFECTING THE SPREAD OF DOUBLE-STRANDED-RNA VIRUSES IN ASPERGILLUS-NIDULANS

Viruses are common in asexual Aspergilli but not in sexual Aspergilli. We found no viruses in 112 isolates of the sexual Aspergillus nidulan s. We have investigated factors that could play a role in preventing t he spread of mycoviruses through populations of A. nidulans. Experimen ts were performed with A. nidulans strains infected with viruses origi nating from A, niger. Horizontal virus transmission was restricted but not prevented by somatic incompatibility. Viruses were transmitted ve rtically via conidiospores but not via ascospores. Competition experim ents revealed no effect of virus infection on host fitness. Outcrossin g was found to limit the spread of viruses significantly more than sel fing. It is concluded that the exclusion of viruses from sexual Asperg illi could be due to the formation of new somatic incompatibility grou ps by sexual recombination.