Induction of resistance in the control of phytoplasma diseases.

Phytoplasma are wall-less prokaryotes that can induce severe diseases in many plants, for which no effective means of control are at present available. However, plants infected by phytoplasma can undergo spontaneous symptom remission, or recovery, a known long-term phenomenon. A strategy to reduce the number of symptomatic plants might thus arise from stimulation of plant defence systems to induce recovery. Several experimental trials have been carried out on different phytoplasma-infected plants, which have shown that it is possible to induce recovery by abiotic stress, treatment with resistance inducers or antimicrobial molecules, and application of mycorrhiza and rhizobacteria. Moreover, several recent findings have indicated the importance of endophytic fungi and bacteria in this recovery phenomenon. Examples of different approaches for control of phytoplasma infection are reported here, and some of the possible mechanisms of action involved are discussed.