A viroid is an infectious agent that can cause disease in its host. Although they function similarly to viruses, unlike viruses, viroids lack lipids and proteins.
Discovered in 1978, viroids infect plants. On the other hand, no viroids that affect animals (including humans) have been discovered. As they have no metabolic activity outside the cells they infect, neither viroids nor viruses are living beings. It is important to mention that, thanks to the autocatalysis of genetic material, viroids are able to infect their hosts.
Viroids are composed of a short chain of ribonucleic acid (RNA), which can be either rod-shaped or circular. Experts, who have already discovered about three hundred viroids, consider them the least complex infectious organisms in terms of structure and genes. There are many issues about viroids that are still unknown. It is not known, for example, how they manage to replicate, although it is observed that they usually lodge in the nucleus of cells. Nor have viroids been found to code for proteins or their RNA to act as messenger RNA. Capable of infecting herbaceous or woody plants of the dicotyledonous and monocot families, viroids affect higher plants. High temperatures and light contribute to its replication and manifestation of the symptoms of the infection, which can affect tomatoes, potatoes and citrus fruits, just to name a few possibilities. It is important to emphasize that there are many possible hosts for viroids; Likewise, there are several diseases associated with viroids, some of which are mentioned below: * Coconut palm cadang-cadang: is a disease found mainly in coconut palm. Globally, it tends to appear mainly in the central region of the Philippines. This disturbance was discovered in 1927 and since then it has caused the death of several million palm trees on the island, as the annual number of victims is estimated to be around one million. As far as the trade impact is concerned, this viroid directly harms coconut oil manufacturers. As symptoms appear slowly, over up to fifteen years, it is not easy to diagnose this disease in time; * Citrus fruit exocortis: in general terms, we can say that this disease is noticed when cracks and vertical scales appear on the fruit’s skin, in addition to dwarfism and yellow spots. To avoid exocortis, it is necessary to properly control the crops, something that farmers guarantee is not difficult to achieve . Among the species most affected by this disease are some varieties of grapefruit, lemon and lime. The mentioned symptoms can be seen below the point where the rootstock and scion meet;
* Potato fusiform tuber : although the symptoms vary according to the type of potato, environmental conditions, years of infection and the strain of the viroid, it is possible to name some general signs, such as a stunted appearance , an accentuated dwarfism, withered leaves, darkened, rough and slightly curled. This disease is especially serious given the importance of potatoes in the industry. In the context of viroids, we now find the concept of prion, an infectious agent that is composed of a protein with the ability to generate aberrant molecular aggregates. Among the degenerative diseases that can be produced are Creutzfeldt-Jakob, bovine spongiform encephalopathy and tembladera.