Plant virus inhibitors from marine algae

Methanolic extracts from 30 species of marine algae were assayed for antiviral activity against Potato virus X (PVX) in local lesion assays, using Chenopodium quinoa L. as host. Extracts from six algal species (Fucus gardneri Silva, Alaria marginata Postels & Ruprecht, Ralfsia sp. (Berkeley), Codium fragile (Suringar) Hariot, Fragilaria oceanica Cleve, and Egregia menziesii (Turner) J.E. Areschoug) inhibited PVX infectivity by more than 80%. Most extracts with antiviral activity came from algae that belong to the phylum Heterokontophyta. Fractionation of a crude extract from F. gardneri resulted in identification of the polysaccharide alginate as an antiviral component. Alginate inhibited PVX infectivity by 95%, and the mode of action may be via aggregation of virus particles. The present study is the first to investigate New World algae for compounds with activity against plant viruses and the first report that extracts of F. gardneri, Ralfsia sp., and Fragilaria oceanica are sources of antiviral activity.