ABSTRACT
Diagnosis is the rst requirement when confronted with a disease caused by an unknown pathogen, and this is especially crucial for diseases thought to be caused by viruses. ere are about 80 recognized genera of plant viruses (see Appendix III.6) and the diagnostic features of most of these are known but at the speci c level there is still more to be learnt. Combinations of physical, biological, biochemical and serological properties can normally ensure the proper detection and identi cation of a virus. e principal property is the physical one, the shape and size of the virus particle and particles may be enveloped or non-enveloped. e shape ranges bullet, bacilliform, short or long rods, exuous laments and isometric or even other variable shape. Diagnosis involves two processes: identification and detection.. There are various methods to identify a virus but detection can be done by sophisticated laboratory-based tests. Identification implies the presence of a virus and detection signi es the quantitative aspect of its presence as well. Recently Astier et al (2007) reviewed the diagnostic methods for plant viruses and provided very useful information in this context. In this chapter, an attempt has been made for precise identi cation and detection of viruses emphasizing more on practical points of view.
