2. Plant viruses are viruses that affect plants.
Pathogenic to higher plants.
•. Harmless to human and other animals.
•Reduce plant crop yield and quality of crops.
• Some may be able to multiply within the bodies
Of aphids and nematodes.
3. HISTORY
• Beijernick ( 1897) coined the latin
name “VIRUS” meaning Poison. He
studied 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 acids and proteins.
6. 1) Geminiviridae:
• one of the family of plant virus.
• Currently over 360 species in this
family, divided among 9 genera.
• Diseases associated with this family
include bright yellow mosaic , yellow
mosaic, yellow mottle, leaf curling,
stunting, streaks, reduced yields.
• Ss circular dna diverge in both
directions from a virion strand origin of
replication (AMBISENSE).
7. Continued…
According to Baltimore Classification , they are
considered Class II Viruses.
It is the largest known family of Single Stranded
DNA viruses.
@1
8. VIRUS CLASSIFICATION:
• Group – Group II (ssDNA)
• Order - Unassigned
• Family - Geminiviridae
• Genera – Becurtovirus Grablovirus
Begomovirus Mastrevirus
Capulavirus Topocuvirus
curtovirus Turncurtovirus
Eragrovirus
9.
10. STRUCTURE:
• have Circular single-stranded DNA.
• Genome is either in two segments.
• The non-segmented genome is 2500-3000
nucleotides long, and the segmented
genome is 4800-5600 nucleotides long.
• The genome encodes for both structural and
non-structural proteins.
• In geminivirus, both segments must be
transmitted to the host for a full systemic
infection to occur.
11.
12. VIRION STRUCTURE:
• Geminivirus are non-enveloped,
icosahedral virions that consists
of a capsid.
• The capsid is germinate, or
twinned, and consists of 22
Capsomers.
• The capsid is 30nm long and has
a diameter of 18-20nm.
13. SYMPTOMS:
• the time of infection, the virus
strains and the presence of mixed
infections.
• Common symptoms are stunting,
curling, and twisting of leaves.
• Short internodes and stunted
appearance , no apical growth
caused by early infection.
14.
15. * Yellowing of the infected
plants , very small , down-curled
tips and margins of the youngest
leaves, chlorosis and stunting.
SOURCE:
-not by seed or mechanical.
-whitefly ,leafhopper,
16. REPLICATION:
• Geminivirus encodes only a few
proteins, thus they need to dependent
host cell factors for replication.
• These factors are DNA polymerase
and repair polymerase to amplify their
genome.
• Replicate by a rolling circle mechanism
like bacteriophages such as M13, and
many plasmids.
17.
18. Contin…
• Replication takes place inside the
Nucleus of the host cell.
• 1st step: single strand circular DNA is
converted to a double stranded circular
intermediate. In this step Cellular DNA
repair enzymes produce complementary
negative strand for template.
• 2nd step: virus strand cleave at the site of
origin by viral Rep protein to initate
replication.
19.
20. Continued..
• The ss DNA is packaged into germinate particles in
the nucleus.
• These viruses can introduced into differentiated
plant cells, by mouth of vector.
• These cells generally lack the host enzymes
necessary for DNA replication, making it difficult for
the virus to replicate.
• To overcome this block GEM viruses can induce
plant cells to reenter the cell cycle from a quiescent
state so that virus can replicate.
