A simplified plaque reduction assay for antiviral agents from plants. Demonstration of frequent occurrence of antiviral activity in higher plants

An improved plaque reduction assay for antiviral activity was developed and used to examine extracts from sixty-one higher plants. Substantial antiviral activity was observed in ca. 20%, which is higher than might be expected given the limited metabolic differences between viruses and their hosts. The frequent antiviral activity may represent phytoalexins elaborated to protect against plant viruses.