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     Viruses are a unique group of infectious agents whose distinctiveness resides in their simple, acellular organization and pattern of reproduction. A complete virus particle or virion consists of one or more molecule of DNA or RNA enclosed in a coat of protein, and sometimes also in other layers. These additional layers may be very complex and contain carbohydrates, lipids, and additional proteins. Viruses can exist in two phases: extracellular and intracellular. Virions, the extracellular phase, possess few if any enzymes and cannot reproduce independent of living cells. In the intracellular phase, viruses exist primarily as replicating nucleic acids that induce host metabolism to synthesize virion components, eventually complete virus practical or virions are relised. In summary, viruses differ from living cells in at least three ways: (1) their simple, acellular organization: (2) the presence of either DNA or RNA, but not both, in almost all virions (human cytomegalovirus has a DNA genome and four mRNAs): and (3) their inability to reproduce independent of cells and carry out cell division as prokaryotes and eukaryotes do, although some bacterial such as Chlamydia and rickettsia are obligately intracellular parasites like viruses, they do not meet the first two criteria. Although it has long been recognized that viruses can infect plants and causes a variety of diseases, plant viruses generally have not been as well studied as bacteriophages and animal viruses.



     This is mainly because they are often difficult to cultivate and purify. Some viruses, such as tobacco mosaic virus (TMV), can be grown in isolated protoplasts of plant cells just as phase and some animal viruses are cultivated in cell suspensions. However, many cannot grow in protoplast culture and must be inoculated into whole plants or tissue transmission: some of these can be grown in monolayer of cell cultures derived from aphides, leafhoppers, or other insects.








     The word virus comes from Latin witch mean “liquid poison”. Virus was discovered by rusi scientist D. Ivanowski, in 1892, witch first denoted cause of tobacco mosaic disease of tobacco plant and called this tobacco mosaic virus. In 1935 Stanley first separated virus by crystallization method. Since to till today many type of virus discover. Witch different in size and shape witch each other but re obligate parasite. Study of virus called “virology”. They express parasitic specificity. They contain genetic material DNA or RNA. They capable to replicate to genetic material. They also have antigenic characters. They replicate or produce only live cells. They sensitivity to chemicals, rays, stimulators, temperature etc. they have characters of mutation. They not have cell division. They be in active form out of parasitic cell. They are autocatalytic and no have functional autonomy. They maybe crystallized. There outer capsid made of protein that responsible for cellular specificity. They have only one nucleic acid maybe DNA or RNA, that occur as single molecule that maybe single strand or double strand. There culture not is able artificially. They no have cell wall, centriole, cell structures and cytoplasm. They is in micro beads and filtered by bacterial filter easily.








     Viruses range from the structurally simple and small parvoviruses and picornavirus to the large and complex poxvirus and herpes viruses. Their names may describe viral characteristics, the disease they are associated with. Or even the tissue or geographical local where they were first identified,. Names such as picornavirus (pico, “small”, rna, “ribonucleic acid”) or toga virus (toga, Greek for “mantle,” referring to a membrane envelope surrounding the virus) describe the structure of the virus, whereas the name papovavirus describe the members of its family (papilloma, polyoma, and racuolating viruses). The name retrovirus (retro, “reserve”) refers to the virus directed synthesis of DNA from an RNA template, whereas the poxviruses are named for the diseases smallpox, caused by one of its member’s. the adenoviruses (adenoids0 and the repviruses (respitatory,enteric, orphan) re named for the body site from which they were first isolated. Reoviruses was discovered before it was associated with a specific disease, and thus it was designated an “orphan” virus. Coxsackievirus, are naviruses, and bunya viruses are named after African places where they were first isolated.








     Virology is a major field of biotechnology witch is completed in a deep description. There are many several points to study virology in briefly.-


   Brief outline on discovery of virus, nomenclature, classification, (LHT system; classification as per vll report of the international committee on taxonomy of viruses), distinctive properties of viruses: morphology and ultra structure, capsids and their arrangements; envope and their composition, viral genome their types and structure virus related agents. Bateriophage structural organization, replication, step growth curve, eclipse phase, phage production, burst size, brief detail of mu, lambda, 174, m13 etc. cultivation of viruses in embryonat3ed egg, experimental animal and cell cultures, primary, and secondary cell culture, suspension cell culture, assay of viruses, physical or chemical methods,, brief account of assay of viruses using serological techniques, infectivity assay (plaque, method, end point method,. Effect of virus on plant appearance, histology, physiology, and cytology, common virus’s disease, paddy tomato and sugarcane, viruses of cynobacteria. Algae, fungi, replication of plant viruses, virus’s free plants.




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