Plant virus (disease) by swapnil anand.pptx

A short description of plant viruses and the disease caused by them

1. Under the guidance of: Prof. Anupam Dixit Prof. H. K. Kehri Dr. Satadru Pramanik Presented by: Swapnil Anand M.Sc 3 rd Sem DEPARTMENT OF BOTANY Topic: Plant Virus

2. DEFINITION A virus is an infectious agent, s ub microscopic entity consisting of a single nucleic acid (DNA or RNA) surrounded by a protein coat and capable of replication only within the living cells of, animals, plants or bacteria.

3. HISTORY The name virus was given by Pasteur to the causative agents of infectious diseases. Virus is first discovered by Ivanowsk i . Adolph Mayer (1885), a Dutch scientist, and D. J Ivanowsky (1892), a Russian scientist, recognized certain microbes as causative agent of mosaic disease of tobacco. M. W. Beijerinck , a Dutch bacteriologist, demonstrated in 1898 that viruses differ from other cellular organisms. The structure of virus was studied by Wendell M. Stanley , an organic chemist, 1935. Infected tobacco leaf

4. GENERAL CHARACTERISTICS: Viruses display a wide diversity of shapes and size, called morphologies . 1. Size – Virus are very small in size, varying over a wide range from 20 – 350 nm in length & 15 – 20 nm in diameter. Smallpox virus, one of the largest viruses, is about 200 nm in diameter; poliovirus, one of the smallest, is only 28 nm in diameter.

5. 2. Nucleic Acid I:  ds DNA viruses   (e.g.  Adenoviruses ,  Herpesviruses ,  Poxviruses ) II:  ssDNA viruses   (e.g.  Parvoviruses ) III:  dsRNA viruses  (e.g.  Reoviruses ) IV:  ssRNA viruses   (e.g.  Picornaviruses ,  Togaviruses ) V:  ssRNA viruses   (e.g.  Orthomyxoviruses ,  Rhabdoviruses ) VI:  ssRNA -RT viruses   (e.g.  Retroviruses ) VII:  dsDNA -RT viruses   (e.g.  Hepadnaviruses )

6. Bacterial viruses: They contain either ssDNA , dsDNA , ssRNA , or dsRNA . Most of the Bacteriophage possess only DNA. Plant Viruses: They generally Contain dsDNA , ssRNA . Animal viruses: They contain dsDNA , ssRNA or dsRNA . They do not possess ssDNA

7. Structure of Viruses A complete virus particle is called a VIRION . Virions range in size from about 10 to 300 or 400 nm in diameter. All virions contain a nucleocapsid which is composed of a nucleic acid, either DNA or RNA, held within a protein coat called the capsid , which protects viral genetic material and aids in its transfer between host cells .

8. Virion structure of HIV virus

9. Genome The viral genome, in the center of the virion , controls the viral heredity and variation, responsible for the infectivity. The genome of a virus can be either DNA or RNA. DNA-double stranded (ds): linear or circular Single stranded ( ss ) : linear or circular RNA- ss : segmented or non-segmented ds: linear (only reovirus family)

10. Capsid Nearly all viruses form a protein sheath , or capsid, around their nucleic acid core. Each capsid is constructed from identical subunits called capsomeres made of protein. Many animal viruses form an envelope around the capsid rich in proteins, lipids, and glycoprotein molecules . Functions: a . Protect the viral nucleic acid. b . Participate in the viral infection. c . Share the antigenicity .

11. Envelope A lipid-containing membrane that surrounds some viral particles. Envelope is a Lipid bilayer membrane , form when viral glycoproteins and oligosaccharides associate with the plasma membrane of the host cell . Some envelopes have spikes which is made of Glycoproteins (proteins bound to carbohydrates) that stick out from the envelope. Spikes often are important for attachment to host cells. spikes

12. Not all viruses have the envelope and viruses can be divided into 2 kinds: enveloped virus and naked virus.

13. Morphological types of viruses In general, there are following morphological virus types : HELICAL VIRUSES – Composed of single types of capsomere stacked around a central axis. Single – stranded RNA but ssDNA in some cases. Ex – tobacco mosaic virus

14. ICOSAHEDRAL VIRUSES An icosahedron is a polyhedron having 20 triangular faces and 12 corners. The capsomeres of each face form an equilateral triangle. An example of a polyhedral virus is the adenovirus. Another is the poliovirus.

15. COMPLEX VIRUSES 17 Some viruses have complicated structure and are called complex viruses. They may possess tails and other structures (e.g., bacteriophages ) or have complex, multilayered walls surrounding the nucleic acid (e.g., poxviruses such as vaccinia ) These type of viruses have been grouped in two major types- Without identifiable capsids (bacteriophages) With capsids ( vaccinia )

16. VIRUS CLASSIFICATION The classification of virus is based on Latin binomial nomenclature. Holmes (1948) included viruses under the order virales which was further divided into three groups- Phaginae (attacks bacteria), Phytophaginae (attacks plants) & Zoophaginae (attacks animals). Andre Lwoff, Horne and Poul Tournier (1962) proposed LHT system of classification of virus based on physical & chemical characters like nucleic acid, symmetry, presence of envelope, diameter of capsid , number of capsomers .

17. The Baltimore classification system Given by Nobel prize winner David Baltimore, it was based on genetic contents and replication strategies of viruses. According to the Baltimore classification, viruses are divided into the following seven classes: dsDNA viruses ssDNA viruses dsRNA viruses (+) sense ssRNA viruses (codes directly for protein) (-) sense ssRNA viruses ssRNA reverse transcribing viruses dsDNA reverse transcribing viruses where " ds " represents "double strand" and " ss " denotes "single strand".

18. REPRODUCTION IN VIRUS There are two major life cycles of viruses : 1 . The Lytic cycle 2. The Lysogenic cycle Lytic cycle The virulent phage replicates by a process called the Lytic cycle. At the end of it the bacterial cell gets destroyed and thus the name. This process can be divided into several distinct phases-

19. Lysogenic cycle Some of the viruses undergo a lysogenic cycle. In this the viral genome gets incorporated in the host chromosome at a particular place. The term lysogeny refers to a process where the prophage DNA remains associated with the host cell genome till it can be induced to get separated to act as a virulent phage .

20. symptoms External Internal local systemic cytoplasm nucleous Symptoms of plant viral diseases

21. External Symptoms Localized – symptoms occur at the point of inoculation only; do not spread, includes Local lesions. Systemic - symptoms are not limited to point of inoculation, includes Chlorosis , stunting, etc.

22. Local symptoms : - Chlorotic Local Lesions : Infect cell loose chlorophylls and other pigments. Ex -TMV on Cowpea host Necrotic Local Lesions : Infect cell die Ex.- Nicotina glutinosa host

23. 2. Systemic symptoms :- Variegation ( colour breaking ): Discoloration in patches on leaves Sharpness of boundaries Distribution and discoloration of lamina

24. Mosaic : Mosaic are characterized by light green, yellow or white areas intermingled with normal green of leaves of fruit or of whitish areas are intermingled with the area of the normal colour of flowers or fruits depending upon intensity or pattern of discoloration mosaic type symptoms may be described as follows:- Vein clearing: BCMV(bean common mosaic virus) Vein banding: Beat curly top

25. Malformation Change in leaf form , any deviation from normal shape. This includes uneven growth of leaf lamina , leaves become curled, brittle(crinkling) and shows depressions (puckering) upward and downward curling , leaf roll, vein distortion, galls/ tumors.

26. Leaf roll disease

27. Internal symptoms: These include inclusion bodies. Inclusions are microscopic bodies produced by some of the viruses. These are produced in cytoplasm or nucleic acid. (A) Cytoplasm: Amorphous or amoeboid also called as X-bodies produced by spherical or oval viruses Ex-Cucumber Mosaic Virus

28. (B) Nucleus: Ex.- Tobacco etch virus

29. Reference Microbiology: Lansing M.Prescott ; John P. Haley ;Donald A. Klein. 5th Edition Microbiology : Fundamentals and Applications by S.S Purohit Plant Pathology: George N. Agrios . b iologydiscussion.com

30. THANK YOU