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» Introductory Plant Pathology
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Current Category » Crop Disease and Management

Properties of Plant Virus

1. Biological Properties:

Each virus produces its own protein, its function is to protect RNA from host enzymes (Ribonuclease), heat, ultra violet light and chemical protein has no infectivity.

Infectiousness of Virus:

1. Viruses are infectious and highly contagious, infectivity depends on virus synthesis.
2. After the entry of pathogen in host through natural opening or wounds or pollen grains, virus comes in contact with with inoculation.
3. This is done by Host, since viruses do not produce enzymes. They lack the Lipman Enzymatic system for the conversion of high energy into potential energy required for biological activity.
4. So they have to depend on hosts. This is a major difference between the host parasite relationship in viral diseases and those of other pathogen.
5.  The naked RNA induces host cell to form enzyme RNA polymerase. These enzyme in presence of viral RNA and nucleotides produce additional RNA. The new viral RNA induces host cell to produce specific protein molecule required for its coat.

2. Physiological Properties of Virus:

i) Dilution End Point (DEP):

Dilution of Juices containing the virus may or may not be affected the infectivity. Tobacco mosaic virus is reported to remain infectious even in a  dilution of 1:1000000 (6) Cucumber mosaic virus retains, Virulence at 1: 1000 Potatorugose mosaic virus causes poor infection when diluted to 1:10 or 1: 100.

ii) Thermal End Point (TEP):      

Effect temperature, no of viruses can be inactivated by Thermo therpy. Tomato mosaic virus is destroyed by treating virus containing Juice at 85 to 90 degree centigrade for 10 minutes, lower temp. Seems to have no effect on the viability of plant viruses.

iii) Longevity in Vitro (LIV):

Retention of infectivity in storage Storability of Juice), if the Juice from mosaic infected tobacco plant is kept; the virus can remain viable for a few hours to several months. TMV in dried leaves or in Juice dried on filter paper remains infective for many years.

3. Chemical Properties:

i) Host Range:

Host range is useful in distinguishing the viruses from one another. The viruses are inoculated into indicator an plant which develops typical symptoms, local lesions, ring spot systemic symptoms etc.

Ex: EMV and TMV incite symptoms on tobacco but EMV affects cucumber systematically where as TMV does not.

ii) Mutability and Strains:

The presence of genetic material in the form of RNA in plant viruses ensure that new strains of the viruses may develop probably by mutation of RNA. In tobacco mosaic virus alone, there are more than 50 strains.

iii) Serological Reactions:

If a virus containing juice is injected into body of a rabbit, the rabbits form antibodies, which will react with viral proteins to give precipitation. The reactions are specific. i. e the antibodies obtained by inoculation of strain A, of a virus will precipitate , the juice containing the same specific type of virus.

Current Category » Crop Disease and Management