Abstract

                                In the beginning of this century the plant pathologist was familiar with only two kinds of organisms which cause plant diseases viz., fungi and bacteria. But in recent times he has to be familiar with another entity which goes by the name of virus. Virus diseases are those caused by an infective principle which is ultra microscopic in character and is capable of multiplying within the tissue of its host. The presence of this principle is indicated by the manifestation of typical symptoms on the host. Virus diseases attack man, his domestic animals and plants. Small pox, measles, mumps, chicken pox, herpes, yellow fever, cattle plague, swine fever, rabies, foot and mouth diseases of cattle are but a few examples of virus diseases among animals and man. The number of virus diseases attacking crop plants is large and every day new diseases hitherto not observed or ascribed to other causes are brought to light by workers all over the world. Of these may be mentioned the diseases affecting sugarcane, tobacco, potato, the sugar beet and the sandal wood tree.

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