λ-Carrageenan Suppresses Tomato Chlorotic Dwarf Viroid (TCDVd) Replication and Symptom Expression in Tomatoes

The effect of carrageenans on tomato chlorotic dwarf viroid (TCDVd) replication and symptom expression was studied. Three-week-old tomato plants were spray-treated with iota(l)-, lambda()-, and kappa()-carrageenan at 1 gL(-1) and inoculated with TCDVd after 48 h. The -carrageenan significantly suppressed viroid symptom expression after eight weeks of inoculation, only 28% plants showed distinctive bunchy-top symptoms as compared to the 82% in the control group. Viroid concentration was reduced in the infected shoot cuttings incubated in -carrageenan amended growth medium. Proteome analysis revealed that 16 tomato proteins were differentially expressed in the -carrageenan treated plants. Jasmonic acid related genes, allene oxide synthase (AOS) and lipoxygenase (LOX), were up-regulated in -carrageenan treatment during viroid infection. Taken together, our results suggest that -carrageenan induced tomato defense against TCDVd, which was partly jasmonic acid(JA) dependent, and that it could be explored in plant protection against viroid infection.