INHIBITION OF TOMATO RINGSPOT VIRUS BY FLAVONOIDS

When applied in a mixed inoculum with tomato ringspot nepovirus (TomRS V), flavonoids and related compounds inhibited infectivity in Chenopod ium quinoa. Compounds that showed strong anti-viral activity were: que rcetin, quercetin 3-methyl ether, quercetin 7-methyl ether, quercetin 3,7,3'4'-tetramethyl ether, galangin 3-methyl ether, morin, robinin, q uercetin 3,7,4'-trimethyl ether, quercetin 7,4'-dimethyl ether, 7,4'-d i-O-benzolquercetin, 7-hydroxy-3,4'-dimethyl flavone, 6,3'-dihydroxy-4 '-methyl aurone and fisetin 4'-methyl ether. Quercetin applied at a co ncentration of 5 mu g ml(-1) caused 70% inhibition of local lesion dev elopment. When quercetin was applied to leaves prior to inoculation, t here was only slight induced resistance to infection. Quercetin at 5 m u g ml(-1) did not affect virus multiplication in protoplasts prepared from cucumber cotyledons and transfected with viral-RNA. In meristema tic tip cultures, quercetin reduced virus titre by up to 89% over a pe riod of 36 weeks whereas ribavirin caused a 25% reduction over the sam e 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