Dual Role for Ethylene in Susceptibility of Tomato to Verticillium Wilt

Ethylene has been observed to both inhibit and promote the symptoms of Verticillium wilt (caused by Verticillium dahliae) in tomato. To test the hypothesis that ethylene has di€erent e€ects at di€erent stages in the infection process, ethylene levels were manipulated in V. dahliae- infected tomato plants by the application of an ethylene synthesis inhibitor aminoethoxyvinylglycine (AVG) and/or ethyleneʹs biosynthetic precursor 1-aminocyclo- propane-1-carboxylate (ACC) and the e€ects on disease severity were examined. Statistically signi®cant reduc- tions in disease severity were consistently obtained for AVG-treated plants that had ACC added at the time of inoculation. A model is therefore proposed in which post-infection ethylene enhances Verticillium wilt devel- opment in tomato whereas its presence at the time of infection inhibits disease development.