Inhibition of tomato ringspot virus by flavonoids

When applied in a mixed inoculum with tomato ringspot nepovirus (TomRSV), flavonoids and related compounds inhibited infectivity in Chenopodium quinoa. Compounds that showed strong anti-viral activity were: quercetin, quercetin 3-methyl ether, quercetin 7-methyl ether, quercetin 3,7,3'4'-tetramethyl ether, galangin 3-methyl ether, morin, robinin, quercetin 3,7,4'-trimethyl ether, quercetin 7,4'-dimethyl ether, 7,4'-di-O-benzolquercetin, 7-hydroxy-3,4'-dimethyl flavone, 6,3'-dihydroxy-4'-methyl aurone and fisetin 4'-methyl ether. Quercetin applied at a concentration of 5 mu g ml(-1) caused 70% inhibition of local lesion development. When quercetin was applied to leaves prior to inoculation, there was only slight induced resistance to infection. Quercetin at 5 mu g ml(-1) did not affect virus multiplication in protoplasts prepared from cucumber cotyledons and transfected with viral-RNA. In meristematic tip cultures, quercetin reduced virus titre by up to 89% over a period of 36 weeks whereas ribavirin caused a 25% reduction over the same period. It is proposed that flavonoids interfere with an early event in the virus life cycle resulting in decreased infectivity and titre in tissue culture. Copyright (C) 1996 Elsevier Science Ltd