Abstract
Mutants of vesicular stomatitis virus have previously been isolated whose replication is not affected by the presence of defective interfering (DI) particles. We describe here reconstruction experiments in BHK-21 cells which show that DI particle-resistant viruses are strongly selected over wild-type virus in the presence of DI particles. This occurs both during undiluted lytic passage and persistent infection. This selection is evident even when the mutant virus is added initially at very low levels relative to wild-type virus. This indicates that DI particles can be important selective factors affecting viral evolution.