Dual role for ethylene in susceptibility of tomato to Verticillium wilt

Ethylene has been observed to both inhibit and promote the symptoms of Vert icillium wilt (caused by Verticillium dahliae) in tomato. To test the hypot hesis that ethylene has different effects at different stages in the infect ion process, ethylene levels were manipulated in V. dahliae-infected tomato plants by the application of an ethylene synthesis inhibitor aminoethoxyvi nylglycine (AVG) and/or ethylene's biosynthetic precursor 1-aminocyclopropa ne-1-carboxylate (ACC) and the effects on disease severity were examined. S tatistically significant reductions in disease severity were consistently o btained for AVG-treated plants that had ACC added at the time of inoculatio n. A model is therefore proposed in which post-infection ethylene enhances Verticillium wilt development in tomato whereas its presence at the time of infection inhibits disease development.