4. Plant viruses are viruses that affect plants.
Plant viruses are pathogenic to higher
These are normally insects , but some
Plant viruses are harmless to human and
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
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
7. Small , circular RNA molecules.
Have no protein coat.
Potato famine in Ireland.
Resemble introns cut out of eukaryotic.
Consist solely of small single-stranded
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.
10. PROTEINS : -
60% - 95% of the virion.
Protein protects virus genome from –
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
ssDNA : - About 50.eg. Beet curly top virus.
dsDNA : - About 30. eg. Cauliflower mosaic
12. ISOMETRIC : -
Apparently spherical and (depending on the
species) from about 18 nm in diameter
Eg. –Tobacco necrosis virus.
Genus – Necrovirus , with particles 26 nm in
Geminate – Twinned isometric particles.
ROD – SHAPED : -
Rigid rod. Eg. TMV.
Flexuous rod. Eg. Potato virus Y.
15. STRUCTURE : -
Rigid helical rods.
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.
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.
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
The TYLCV capsid , like that of other
geminiviruses , consists of two joined ,
TYLCV has a single 2787 nucleotides
covalently closed genomic circular ssDNA.
22. There are two types of plant virus 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.
24. Nematode Transmission :-
Two ssRNA virus genera , Nepovirus and
Tobravirus , have nematode vectors.
NEPOVIRUSES – Comoviridae family.
TOBRAVIRUSES – Family not yet
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.
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