BP Singh

Symptoms Cause,d by Plant VirusesD.B. ParakhIntroductionViruses constitute the most serious pathological problems ofthe living world. In agriculture, they were' recognised as ' growthreducingfactors' for a long time. They are, therefore, the subjectof intensive research. Present knowledge about viruses is that theyare infectious agents (often cause disease), invisible with lightmicroscope (sub-microscopic), small enough to pass through abacteria-proof filter, lacking a metabolism of their own anddependent on living host cells for multiplication~ Virusesconstitute small packages of genetic information of either nucleicacid (ribonucleic acid, RNA or de-oxy ribonucleic acid! DNA)encapsidated together or separately and enclosed in a coat of oneor more than one types of protein. Few viruses have a lipoprotein,besides its nucleic acid and protein.Plant-virus interactions'1There is an intimate relationship between a virus and its hostplant. The process of multiplication of virus in its host cellsdisorganizes the host's physiology and results in 'disease'.. Thevirus is then a pathogen causing disease. Once the plant isdiseased, the virus multiplication leads. to visible deviations orsymptoms. A symptom is defined as any perceptible change inthe plant or its functions, indicating a disturbance in the normalcourse of the physiological process. The science of the stuc4f ofsymptoms is called symptomatology. Different kinds of symptoms