Agri PDF

 Viroid Viroids are small ,single standard ,circular molecule of infectors RNA.  Viroids lack protein coat . Viroid was low-molecular-weight . New infectious agent that was smaller than virus. Cause potato spindle Tuber disease. It was found to be free RNA. Viroid was first time discovered by T.O.Deiner 1971 in potato spindle Tuber disease. Example :- Cadang-cadnag disease of coconut, Citrus exocortis.

 Viruses The name virus means venom or poisonous fluid was given by  pasture.D.J.Ivanowsky   (1892) recognise mosaic disease of  tobacco. Father of plant virology Beijirinck . Characteristic of virus Virus are  non cellular  organisms. Viruses are  obligate parasite.  Submicroscopic They have either RNA or DNA virus . No virus both contain DNA and RNA. they are inert outside their specific host. They contain nucleici acid, capable of protein synthesis. Virus infect plants have single stranded RNA. But in cauliflower mosaic virus double stranded DNA is present. Virus affect animals  have either single or double stranded RNA or double stranded DNA. Virus have outer layer  capsid . Capsid is protein coat made of a small units  called  capsomeres . Central core + capsid are collectively known as nucleocapsid. These capsomeres arrange in helical or polyhedral geometrical forms. Bacteriophage or bacterial virus  Virus that ...

 Bacteria of Morphology, Structure, Types , flagella. Bacteria Father of bacteriology is Louis Pasteur. Father of bacteriological technique  is Robert koch-given Koch postulates. Anton von leeuwenhoek first time seen bacteria and protozoa under a self-made microscope and regard them  as Animalcules.  F.J .Cohn coined the term bacteria.  Morphology of bacteria  Coccus - spherical shaped. Diplococcus - cocci from paired cells . Tetracoccus - four cells arranged in a cube.  Streptococcus - chain of cocci.  Sarcina - division in three planes produces eight cells arranged in a  cube.  Staphylococcus - grape-like cluster. Bacillus - rod or capsule. Vibrio - comma shaped. Spirillum - rigid, wavy shaped.  Spirochaete - cork-screw shaped. Star-like - star-shaped bacteria. Types of bacteria Stalked bacteria: e.g. Caulobacter, Gallionella. Budding bacteria: e.g. football shaped, network of cells Myxobacteria: e.g. gliding bacteria, lack rigid ...

 Prions Modern medicine certain infectious neurological disease. Transmitted by an agent consists of abnormally folded protein. Most notable disease caused by prions are Bovine spongiform encephalopathy (BSE) commonly called mad cow disease in cattle. It analogous variant Cr -jacob disease in human.