Virus and viral diseases in plants

viral diseases in plants

1. VIRUS and viral diseases in plants DR BHAGYASHREE KHAMARI Assistant Professor (Plant Pathology) Institute of Agricultural Sciences SIKSHA “O” ANUSANDHAN (DEEMD TO BE UNIVERSITY) BHUBANESWAR

2. More than 2000 viruses are known so far. 1/4th of them cause plant disease E.g. Tobacco mosaic virus (TMV) Cucumber mosaic virus (CMV) Cauliflower mosaic virus ( CaMV ) Potato Virus X (PVX) Bhindi yellow vein mosaic virus ( YvMV ) Bunchy top Virus Lettuce big vein mosaic virus Viral diseases in Plants

3. Mosaic Leaf curl Vein banding Leaf roll Bunchy top Vein clearing

4. Biological status of Virus Replicate Mutate Transmit Acellular Obligate Donot multiply its own Crystalize Living Non-living Molecule Contagium vivum fluidum ( Beijernick : Father of virology) Poisonous fluid

5. Characteristics of plant virus 1. Ultramicroscopic 2. O bligate parasite 3. Can pass through bacteria proof filter paper 4. Mainly composed of nucleic acid ( DNA or RNA ) and protein coat 5. Acellular 6 . Do not divide and produce any kind of reproductive structures. 7. Do not have the molecular machinery to replicate without a host . 8 . Can transmit by insects, fungi, nematode, grafting, injury, dodder, seeds.

6. Viruses do not capture or store free energy F unctionally inactive outside the host . Common viral symptoms: Mosaic, leaf curl, leaf roll, vein bending, vein clearing, yellows Virus seldom kill plants, but virus disease during vulnerable stage cause crop failure .

7. Composition of virus Nucleic acid Protein Envelope Spikes/ P eplomers

8. Also Known as capsid Subunits of capsid is known as capsomere . I t protects and gives shape to virus P rovides basis for serological determination of viruses Protein may be coat protein or movement protein Protein

9. Nucleic acid Nucleic acid may be DNA or RNA ,never both It is responsible for virulence of virus Nucleic acid may be single stranded or double stranded . Most of the plant viruses are RNA virus Amount of NA varies from virus to virus

10. ssDNA dsDNA dsRNA ssRNA

11. It protects and transmit virus. It is made up of lipoprotein. lipid is host origin where as protein is viral origin. Virus with envelope are known as enveloped virus. Without envelope is known as naked virus. Animal viruses are enveloped virus. Envelope

12. Spikes or peplomers It is a pointed structure on surface of virus. It is used for adherence virus particle on the host surface. It is made up of glycoprotein .

13. Other compositions of virus Polyamines Enzymes W ater Various amount of ions  

14. Structure of virus Filamentous or Helical Rigid rod : Tobacco mosaic virus Flexious rod: Potato Virus X 2. Polyhedral Icosahedral : e.g. Cucumber mosaic virus Spherical : e.g. Tobacco Necrosis virus 3 . Baciliform : Bullet shaped e.g. Alfalfa mosaic virus 4. Complex structure e.g. Bacteriophage

15. Bacilliform

16. transmission of plant viruses. 1 . Insect Transmission 2. Transmission by Vegetative Propagation 3. Transmission by Mechanical Means 4. Transmission by Cuscutta 5. Soil Transmission 6. Seed transmission 7. Transmission by Fungi 8. Transmission by Nematode Vectors.

17. Transmission by Mechanical Means: ( i) By contact of infected and healthy leaves brought about by wind . ( ii) By rubbing the juice of the diseased plants over the surface of the leaves of healthy plants. ( iv) Agricultural implements used for cutting the plant materials and pruning will spread the disease. (v) C ontact between the roots of diseased and healthy plants . E.g. Tobacco mosaic virus

18. Transmission of Virus by seed: Externally seed borne : E xternal contamination of the seed with virus particles (TMV, PVX) Internally seed borne (BCMV, CMV, BYMV, ULCV) due to infection of the living tissues of the embryo. The embryo become infected by two routes Directly from mother plant By pollens

19. Transmission by Cuscutta : Dodder ( Cuscutta ) serves as a transmitting agent and an effective bridge between the infected host and the healthy plants by establishing intimate biological contact through its haustoria . E.g. Tomato spotted wilt virus

20. Transmission through vegetative propagation If either of stock or scion or mother plant of vegetatively propagating material such as tubers, bulbs, roots, buds are infected by virus then the newly grown plant will be virus infected.

21. Transmission by soil : Few viruses are transmitted through the soil are known as soil borne viruses. e.g. Potato mosaic virus, Oat mosaic, Wheat mosaic, etc ..

22. Insect Transmission: Majority of plant virus are transmitted through insects. The insect obtains virus through its mouth parts at the time of feeding on the diseased plant and then inoculated in the healthy plant by means of the mouth part. Most of the insect vectors are sucking insects. The virus may remain active in the body of the vector for many days. E.g. Aphids, Leafhoppers, Flee beetles, Scale insects, thirps and White flies.

23. Transmission by Fungi : Few Fungal genera such as Olpidium , Spongospora , Synchytrium transmit viral disease. e.g. Olpidium brassicae transmits lettuce big vein mosaic virus

24. Transmission by nematodes It feeds on epidermal cells of root and puncture frequently near root tips and acquire virus from infected plants. It is divided into two groups NEPO virus (Nematode transmitted polyhedral virus): Xiphinema , Longidorous NETU virus (Nematode transmitted tubular virus) : Trichodorous and Paratrichodorous E.g. Grapevine fan leaf virus is transmitted by Xiphinema index.

25. Replication of plant virus Attachment Penetration Uncoating Genome replication Assembly Maturation Release

26. 1. Attachment of virus to the Host

27. 2. Penetration and uncoating of virus

28. Ribosomes Proteins 3. Genome replication

29. 4. Viral assembly and maturation

30. 5. Release of virus from host

31. Replication of Plant Virus

32. Management of plant virus 1. Manage the population of vectors Spray M ethyl parathion or D imethoate @ 2 ml per litre of water. 2. Collect seed or planting materials from healthy source. 3. Use resistant varieties. 4. Use sterilized agricultural tools. 5. Advance technologies for management of disease Gene silencing (RNA interference), Genetic engineering, Tissue culture etc.

33. Thank you