Ethylene is Involved but Plays a Limited Role in Tomato Chlorotic Dwarf Viroid-Induced Symptom Development in Tomato

Abstract

To investigate whether ethylene is involved in tomato plants in response to the invasion of viroid, tomato cv. Pearson and its ethylene-insensitive mutant Never ripe ( Nr) was challenged with Tomato chlorotic dwarf viroid (TCDVd). Both Pearson and Nr plants developed various symptoms including dwarf, bunch, reduced leaf size, leaf chlorosis, and necrosis at 3-wk-post-inoculation and thereafter even though the stunting in Nr was not as severe as in Pearson plants. The sizes of fruits were also significantly reduced in the viroid-infected plants. Treatments of Pearson with ethephon, an ethylenereleasing compound, mimicked TCDVd in induction of stunting and pathogenesis-related (PR) genes in the plants. Pretreatment of Pearson plants prior to TCDVd-inoculation or ethephon application with silver thiosulfate (STS), an ethylene action inhibitor, partially suppressed the viroid- or ethephon-induced symptoms as well as PR gene expression. In addition, Nr and STS-treated Pearson exhibited a slightly lower viroid titre in comparison to the control Pearson plants. These results suggest that ethylene is involved but plays a limited role in TCDVd-induced symptom development.