BP Singh

162 D.B. Parakh4. Malformations: Virus infections som.etimes may also lead todeformed plants or organs called malformations. Malformation isa pathological defor.mation that is caused by disturbance ofharmonious tissue development. It differs from stunting anddwarfing which are due to general growth reduction. Malform.ationsare of many types. When growth correlation is more directlydisturbed by virus infection, the malformations are primary.Secondary malformations become evident only after the plant hasdeveloped other symptoms that lead to the malformations.5. Anatomical and Cytological deviations : As virus activitystarts in: the host's cells, its structure (anatomy) and function(physiology) are altered. Cells decrease in size (hypotrophy) orriumber reduced (hypoplasia) or may increase in size (hypertrophy)and number (hyperplasia). Hyperplasia is also called as proliferationwhen cells multiply excessively.Inclusion bodies are the product of host-virus interaction.here, a large number of virus particles get arranged in a particularsequence and shape, which is now known to be characteristic foreach protein group of plant viruses in presence of protein.Inclusion bodies may occur either in cytoplasm or nucleus. Theseare easily stained and detected even in light microscope thusleading to detection of viruses in host tissue.6. Water deficiency symptoms: These are caused because ofshortage of water, due to excessive transpiration or obstruction ofwater supply through vascular tissue causing wilting or moreseriously, withering. This is irreversible desiccation of tissuewhich causes its death. Etching symptoms are caused due todesiccation of superficial tissue as in tobacco etch disease.Constraints in identifying viral disease based on symptoms1. Symptomless carriers : In some diseases, the wrus infects itshost and multiplies within, but causes no vi~ible externalsymptoms. Such hosts are described as symptomless virus carriersand the virus infecting it as latent virus, e.g., potato infected withlatent mosaic virus.2. Masked symptoms : There are instances when the plants areinfected with virus but do not show distingUishable symptoms dueto absence of favourable environmental co~ditions. Such maskedsymptoms are seen in potato infected by potato mild mosaic virus