Important Plant Pathogenic Organism – Virus
1. Virus are ultra microscopic, nucleoproteinous, self replicating, filterable , a cellular organisms , smaller than bacteria.
2. Their size ranges from 20 to 300 nm (1nm= 1/1000 µm).
3. They can be seen with the electron microscope, scanning microscope or transmission microscope.
4. Shape varies from rod shaped, spherical, polyhedral, bacillifrom or pleomorphic.
5. The single virus particle is called as viron. Each viron or virus particles is chemical composed of nucleic acid and protein.
6. Nucleic acid in virus particle is either RNA or DNA but never both. The percentage of nucleic acid is 5-40% and that of protein is 60-95%.
7. RNA may be single or double stranded and DNA is mostly double stranded.
8. The protecting protein coat of viron or virus particles is known as capsid. Smaller sub units of proteins called as capsomers and nucleic acid protected or enveloped with the capsid is called nucleocasid.
9. They are obligate , intra –cellular parasites, requires living hosts to complete their life cycle, therefore can not be grown on artificial media in laboratory.
10. They can multiply or reproductive within living hosts or cells by the process of replication of genome (RNA or DNA).
11. They do not have any cytoplasma, cytoplasmic organells and plasma membrane.