• History of plant virology….
• Types of plant viruses....
• Tymo-virus group (cucumber mosaic virus)
• Rice Tungro-virus….
• Transmission of Plant viruses….
• External symptoms….
• Internal symptoms….
• Diagnosis of the viral disease….
In this presentation we are here to discuss about the types of diseases
caused to plants due to the action of some or the other kind of
microorganism which leads either to the death of the plant or to the
reduce in the production of outcomes….
• Microorganisms are those organisms which cannot be seen through
naked eyes .They are both beneficial and harmful to the humans of the
• Microorganisms consists of-
5. • In 1879, Adolf Mayer was the first to study the disease of tobacco..
• 1892,Dmitri Ivanowski determined that the cause of TM(tobacco mosaic) was a
toxin produced by the bacteria..
• In 1935,W.M.Stanley found a crystalline protein sediment causing disease to
• In 1936,F.C.Bawden showed that this crystal had proteins as well as RNA..
• In 1939,Von G. A. Kausche saw the particles of TMV in electron microscope..
• Later on through, crystallography, ELISA test and the other modern techniques
helped to collect much more information about the diseases caused by the
7. • Most of viruses have RNA as their genetic materi
majority of them have rod shaped ssRNA..
• They are in bacilli form or bullet form or
• There are many families of plant viruses
-Tobravirus (Tobacco rattle ) ;(Tobacco Mosaic )
8. • The vectors which do the transmission mainly belong to the order
HEMIPTERA and some to the order ORTHOPTERA and
10. Cucumber Mosaic
• Belongs to the genus Cucumovirus in the
family Bromoviridae ..
• This group consists of several genera like
Alfamovirus , Anulavirus , Bromovirus ,
Cucumovirus , Ilarvirus , Oleavirus..
• It occurs in several countries like INDIA..
• Affects several of plants of about 20
• Occurs mainly in the members of
Cucurbitaceae , tomato , potato , carrot ,
spinach , etc..
11. Symptoms of
• When a plant is being affected byCMV then the
following changes are seen in the plant-
-Leaf mottling ,crinkling and curling of edges occur
-Petioles and internodes are shortened , resulting
in stunned appearance of the plant..
-The symptoms differs with the other plants .For
example, some plants which get affected earlier
than season then they don’t flower nicely , and if
some of the plants are being affected on after or
later in season then they produce small sized
-Fruits get white and yellow patches..
-Older leaves get dry..
12. Structure of CMV..
• Virions have a capsid which is non-enveloped..
• The arrangement of capsomeres is not obvious..
• They have more than one particle component..
• The genome encodes both structural and non-structural protein..
• It has different types of virion due to the presence of 3 genomic and 1
13. Genome of CMV..
• Is segmented , tripartite linear(+) sense
• Genomic nucleic acid is infectious..
• Minor species of non-genomic nucleic acid
are also found in virions ..
• Virions may also contain sub-genomic RNA
and sattelite RNA..
14. Replication of
• Viral replication is cytoplasmic ; does
not depend on the helper virus..
• Molecular receptors play a role in
recognition of virions..
• Virus un-coats the capsid and releases
the genomic RNA into the cytoplasm..
• Sub-genomic RNA4 is translated to
produce capsid proteins..
• New virions are assembled after
completion of protein synthesis...
• The virions are released by the lysis
of the infected cells..
• New genomic RNAs are synthesized by
using the(-) sense RNAs as templates..
• The protein 1a and 2a promote both
replication of genome and internal
15. Cytopathology of CMV…
• Inclusions are found in the cytoplasm of infected host cells..
• Inclusion contains many matureVirions..
• They appear as solid hollow structures..
• These inclusions are of different shapes..
16. Transmission of
•It is transmitted
through SAP and by
insect vectors too
such as Aphis
• It does not persist in
• Tungro word stands for the yellow-orange color..
• This disease mostly affects the rice in the South and South East Asian
• It is an important disease affecting rice..
• It causes a loss of about US $ 1.5 billion..
19. Casual Agents of RTV…
• This disease is caused due to the joint
infection of two distinct viruses rice tungro
spherical waikavirus (RTSV) and rice tungro
bacilliform badnavirus (RTBV)..
• RTVB is rod shaped non-enveloped particle of
• It has circular dsDNA genome..
• Replication is nuclear and its genome does
not integrate with the host genome..
20. Symptoms of RTV…
• The infected plants are stunted and show
mottling and yellow-orange discoloration of
• They produce poor panicles with empty
glumes that impart dark brown color..
• The infected plants bear reduced tillering..
• Hence there is a comparison between RTSV
and RTBV given ahead:
21. Comparision between RTSV and
• This virus mainly causes the typical
• This virus alone causes no symptom
except mild stunning..
22. • Thus, the typicalTungro symptoms are intensified by RTSV..
• The symptoms develop in a synergistic manner..
• Virion of RTBV is in bacilliform , elongated ,
• A virion has a genomes which is monopartite ,
double stranded DNA , open circular..
• 1 discontinuity in transcribed strand and other 3
in non-transcribed strand..
• Waikavirus belongs to the family
• Virion of RTSV is non-enveloped , isometric ,
24. Replication of
• Badnavirus replicates in
cytoplasm/nucleus of infected cell..
• Virions interact with a cellular
receptor present in cell wall of host
• Genomes are en-capsicated with
capsid protein releasing the new
• Waikavirus replicates within the
• Virion penetrates the host cell , un-
coats , releases the viral genomic
RNA into cytoplasm..
25. Transmission of
• Both RTBV and RTSV are
transmitted by aphids and
• RTBV is transmitted by
leafhopper from the host and
cause disease only RTSV is
also present in the infected
26. Transmission of plant viruses…
• Plant viruses are obligate parasites which require cellular machinery of living host
for their multiplication , propagation and survival..
• Some of the ways of plant virus transmission have been described-
• Vegetative andGraft
• Insect vector