Disease Caused by Viruses
Viruses causes disease in human, animals and plants, disease in human: small pox, AIDS (HIV), hepatitis, poliomyelitis, diseases in animals foot and mouth diseases (FMD), plants: Yellowing, Mosaic, Yellow mosaic, Yellow vein mosaic, Mottling Chlorosis, bunchy top, sterility mosaic etc.
Viroid:
1. T.O diener 1971 coined the term viriod.
2. Viroids are sub-microscopic, a cellular, infectious, self replicating, low molecular weight , naked ribonucleic acid (RNA).
3. Viroids are naked nucleic acid without coat protein. It is a smallest known agents of infectious disease with low molecular weight ribonucleic acid ( RNA) that can infect plant cell, relicate themselves and cause disease.
4. Genome of the viriod naked, single stranded ( RNA) with 250-400 nucleotide, either linear or mostly circular. Viroids are smaller in size than viruses i.e 50 nm or 1.1 to 1.3 X 103 molecular weight.
5. Viroids are notable to synthesis protein and replicase enzyme required for replication.
6. Viroids replicate by direct RNA, copying in which all components required for viroid multiplication including RNA polymerase are provided by the host.
7. Viroids are transmitted by sap transmitted by vegetative propagation, through pollen and seeds.
Disease Caused for Viroids:
Potato spindle tuber, Citrus exocortis, Coconut cadang, tomato bunchy top.