2.  INTRODUCTION.
 FEATURES.
 HISTORY.
 VIROIDS.
 PRIONS.
 CHEMICAL
COMPOSITION OF
PLANT VIRUS.
 ARCHITECHTURE
OF PLANT VIRUS.
 TOBACCO MOSAIC
VIRUS.
 CAULIFLOWER
MOSAIC VIRUS.
 TOMATO YELLOW
LEAF CURL VIRUS.
 TRANSMISSION.
 SYMPTOMS.
 PROTECTION.
 CONCLUSIONS.

4.  Plant viruses are viruses that affect plants.
 Plant viruses are pathogenic to higher
plants.
 These are normally insects , but some
fungi.
 Plant viruses are harmless to human and
other animals.

5.  Outside protein coat.
 Consists of a single nucleic acid.
 Non-living and Non-cellular structures.
 Non-cellular sub microscopic entity.
 Most viruses infect only SPECIFIC host
cells.
 May be transmitted in pollen.

6.  Beijerinck (1897) coined the Latin name
“VIRUS” meaning Poison.He studied
filtered plant juices and found they caused
healthy plants to become sick.
 Wendell Stanley (1935) crystallized sap
from sick Tobacco plants. He discovered
viruses were made of nucleic acid and
protein.

7.  Small , circular RNA molecules.
 Infect plants.
 Have no protein coat.
 Potato famine in Ireland.
 Resemble introns cut out of eukaryotic.
 Consist solely of small single-stranded
RNA molecule.
 Define group of pathogens much smaller
and distinctly different from viruses.

8.  Prions are “Infectious Proteins”.
 They have no DNA or RNA.
 Causes neurons to rapidly degeneration.
 Mad Cow Disease (Bovine Spongiform
Encephalitis : BSE) is an example.
 Inherited and transmissible diseases.

9.  Protein (capsid) -
Capsomere.
 Nucleic acids –
DNA : - ssDNA , dsDNA.
RNA : - +ve strand RNA , -ve strand RNA ,
ssRNA , dsRNA.

10. PROTEINS : -
 60% - 95% of the virion.
 Protein protects virus genome from –
Degradation.
Facilitates movement through the host.
Transmission from one host to another.
 Repeating subunits , identical for each
virus type but varies from virus to virus and
even from strain to strain.

11. NUCLEIC ACID : -
 Nucleic acid represents the genetic
material , indispensable for replication.
 Nucleic acid is 5 – 40% of the virion.
ssRNA : - About 540 plant viruses.eg. TMV.
dsRNA : - About 40 pv. eg. Wound tumour
virus.
ssDNA : - About 50.eg. Beet curly top virus.
dsDNA : - About 30. eg. Cauliflower mosaic
virus.

12. ISOMETRIC : -
 Apparently spherical and (depending on the
species) from about 18 nm in diameter
upwards.
 Eg. –Tobacco necrosis virus.
 Genus – Necrovirus , with particles 26 nm in
diameter.
 Geminate – Twinned isometric particles.
ROD – SHAPED : -
 Rigid rod. Eg. TMV.
 Flexuous rod. Eg. Potato virus Y.

13. CLASSIFICATION : -
 Family – Virgaviridae.
 Genus – Tobamovirus.
 Species – Tobacco mosaic virus.

15.  STRUCTURE : -
 Rigid helical rods.
 ssRNA.
 Extremely stable structure.
 95% protein and ~5% nucleic acid(RNA).
 2130 copies of single 17kDa coat protein.
 Simple regulatory elements.
 300 nm long and 18 nm dia.
 Rod-like appearance.
 There are three RNA nucleotides monomer.

16. CLASSIFICATION : -
 Family – Caulimoviridae.
 Genus – Caulimovirus.
 Species – Cauliflower mosaic virus.

18. STRUCTURE : -
 CaMV is an icosahedral virus.
 Diameter 52 nm.
 Genome is circular dsDNA.
 Capsid multilayered.
 Arrangement of capsomere not clear.
 The outermost layer is made up of a total
of 420 coat protein subunits.

19. CLASSIFICATION : -
 Family – Geminiviridae.
 Genus – Begomovirus.
 Species – Tomato yellow leaf curl virus.

21. STRUCTURE : -
 TYLCV has a characteristic twinned
morphology.
 The TYLCV capsid , like that of other
geminiviruses , consists of two joined ,
incomplete icosahedra.
 TYLCV has a single 2787 nucleotides
covalently closed genomic circular ssDNA.

22. There are two types of plant virus transmission
–
 Horizontal transmission.
 Vertical transmission.
 Horizontal transmission :- It is by vectors ,
human pruning shears and tools and other
direct , external contamination.
 Vertical transmission :- It occurs when a plant
gets it from its parent plant. Either through
asexual propagation (cuttings) or in sexual
reproduction via infected seeds.
-

23. Mechanical Transmission :-
 Occure when plant come in contact with
other plant and leaves rub together.
 By the action of humans.

24. Nematode Transmission :-
 Two ssRNA virus genera , Nepovirus and
Tobravirus , have nematode vectors.
NEPOVIRUSES – Comoviridae family.
TOBRAVIRUSES – Family not yet
assigned.

26. Seed Transmission :-
It occurs in two ways –
 Externally seed borne – Due to external
contamination of the seed with virus
particles (TMV , PVX).
 Internally seed borne – Due to infection of
the living tissues of the embryo.

28.  Mosaic.
 Mottle.
 Yellowing.
 Chlorosis.
 Vein clearing.
 Vein banding.
 Necrosis.
 Wilt.
 Ringspot.
 Stunting.

29.  Discard virus infected plants.
 Purchase virus-free plants.
 Remove all crop debris from benches and
the greenhouse structure.
 Remove all weeds since these may
harbor both viruses and insects.
 Maintain strict insect and mite control.

30.  Plant viruses and viroids are unusual
groups of plant pathogens that infect and
cause disease in many crop plants.
 Because these pathogens depend on the
normal cellular machinery of their plant
host for reproduction , it is difficult to
eliminate them without damaging the host
plant.

31. THANK
YOU