Viroid Elimination by Thermotherapy, Cold Therapy, Tissue Culture, In Vitro Micrografting, or Cryotherapy

Viroids cannot be controlled by therapeutic treatments in fields, orchards, vineyards, or palm plantations. Hence, the elimination of viroids from infected plants has been a challenging issue and different approaches have been studied to produce viroid-free planting material. This chapter describes viroid elimination by thermotherapy, cold therapy, tissue culture, in vitro micrografting, or cryotherapy to obtain viroid-free materials. Elevated temperatures do not inactivate or eliminate most viroids from their host plants, whereas cold therapy can be effective depending on the host–viroid system. Meristem culture and shoot-tip micrografting are good methods to obtain viroid-free plants: the eradication rate depends on the size of the shoot, the viroid or its variant, and the host and its variety. The combination of thermotherapy plus shoot-tip culture is more effective for viroid elimination. Cryotherapy of shoot tips, an innovative technique for pathogen eradication based on cryopreservation, did not result in viroid elimination. Further experiments on other host–viroid systems and on combination of cold therapy and cryotherapy are under evaluation.