1. PPATH 221: Plant Virology WELCOME K. M. Golam Dastogeer Lecturer
Department of PLANT PATHOLOGY
BANGLADESH AGRICULTURAL university
WELCOME
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2. Definition of a Virus
Highly infectuous, submicroscopic and obligate intercellular parasite consisting of one or more molecules of nucleic acid surrounded by a protein coat and capable of replication only within the living cells.

3. Properties
Do not have cells or cellular organells like mitochondria, nucleus, ribosomes etc.
Exists as particle
Not visible under light microscope but can be viewed by electron microscope
Composed of one type of nucleic acid either RNA or DNA and protein
The necleic acid is the infectuou part and protein the protective part

4. Properties
Unable to grow by bunary fission but can multiplicate by means of replication using host ribosome
Neither living nor dead, rather they form bridge between them
Not self motile, therefore depend on vectos for transmission
Can not penetrate host cell by themselves but can enter into host cells through wound or vectors

6. Is virus living or non living?
(I) Living characters of viruses:
(a) They multiply within host cells.
(b) They possess genetic material, either DNA or RNA.
(c) There are definite races or strains.
(d) They exhibit mutations.
(e) they can be transmitted from diseased host to healthy one

7. (II) Non-living Characters of Viruses:
Following characters of viruses assign them as non-living:
(a) They can be crystallized.
(b) Outside the cell, they behave like inert chemicals.
(c) They do not show growth, development, nutrition, reproduction, etc.
(d) No physiological activity
(e) Do not reepire or excrete
(f) They can be precipitated.
Because of the above reasons, viruses form unique bridge between living and non-living things.

11. Single-stranded RNA (ssRNA): about 540 plant viruses e.g. TMV
Double-stranded RNA (dsRNA): ab. 40 pv e.g. Wound tumour virus
Single-stranded DNA (ssDNA): ab. 50 e.g. Beet curly top virus
Double-stranded DNA (dsDNA): ab. 30 e.g. Cauliflower mosaic virus

12. Architechture of plant virus
1. Isometric: apparently spherical and (depending on the species) from about 18nm in diameter upwards. The example here shows Tobacco necrosis virus, genus Necrovirus with particles 26 nm in diameter.
Geminate: twinned isometric particles e.g. viruses in the family Geminiviridae 

13. 2. Rod-shaped: 2.1. Rigid rod: eg. TMV
2.2. Flexuous rod (filamentous): e.g. Potato virus Y 

18. Transmission There are two types of plant virus transmission :
horizontal transmission
Horizontal transmission is by vectors, human pruning shears and tools, and other direct, external contamination.
Vertical transmission
Vertical transmission occurs when a plant gets it from its parent plant. Either through asexual propagation (cuttings) or in sexual reproduction via infected seeds.
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26. persistent transmission: (syn
persistent transmission: (syn. circulative transmission) a type of virus transmission in which the virus is acquired and transmitted by the vector after relatively long feeding times and remains transmissible for a prolonged period.

28. Nematode transmission
Two single-stranded RNA virus genera, Nepovirus (NEPO) and Tobravirus (TOBRA), have nematode vectors
Nepoviruses: Comoviridae family
Tobraviruses: family not yet assigned

29. Seed Transmission: Seed transmission occurs in two ways
Externally seed borne
due to external 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.

30. Prion = a small infectious particle consisting of protein and lack nucleic acid.
Viroid = an infectious RNA particle, smaller than a virus, lacking a capsid, that causes various plant diseases
Virusoid (satellite nucleic acids) = same as viroid; small, ssRNA molecule, usually 500 to 2000 nucleotides in length, lacking a capsid, lack genes required for the replication  virusoid require a helper (satellite) virus to replicate, causes various plant diseases.

31. Methods of detection Based on biological properties mechanical, graft,
1. Symptomatology
2. Transmission tests
mechanical, graft,
and vector transmission
3. Physical properties
thermal inactivation point, dilution end point, and
longevity in vitro)
4. Microscopy
Electron microscopy

32. based on viral coat protein
Precipitation and agglutination tests
Immunosorbent electron microscopy
Enzyme-linked immunosorbent assay (ELISA)
double antibody sandwich (DAS)ELISA
triple antibody sandwich (TAS) ELISA

33. based on virus nucleic acid
Nucleic acid hybridization assays
The dot- or spot-blot hybridization assay
Polymerase chain reaction
real-time quantitative PCR assay
Microarrays for rapid identification of plant viruses.

34. The steps of a "sandwich" ELISA
A surface is prepared to which a known quantity of capture antibody is bound.
Any nonspecific binding sites on the surface are blocked.
The antigen-containing sample is applied to the plate.
The plate is washed to remove unbound antigen.
A specific antibody is added, and binds to antigen (hence the 'sandwich': the Ag is stuck between two antibodies)
Enzyme-linked secondary antibodies are applied as detection antibodies that also bind specifically to the antibody's Fc region (nonspecific).
The plate is washed to remove the unbound antibody-enzyme conjugates.
A chemical is added to be converted by the enzyme into a color or fluorescent or electrochemical signal.
The absorbency or fluorescence or electrochemical signal (e.g., current) of the plate wells is measured to determine the presence and quantity of antigen.

36. Symptoms of plant virus diseases
Symptoms around the site of virus inoculation are denoted local symptoms.
When virus spreads from the site of inoculation and causes symptoms in other parts of the plant, this is referred to as systemic symptoms. 

38. Mottling: abnormal coloration
Mosaic If a mottle is light and creates a mosaic

40. Chlorosis: reduced amount of chorophyll resulting in light color.
Vein clearing:
eins become light and more distinct

41. Leaf spots

42. Leaf morphological change
Leaf rolling and curling: Rolling is folding of leaves along their mid axes resulting in a more or less tube-like structure.  When the folding is more irregular or does not result in a tube-like structure it is usually referred to as leaf curling.

43. Leaf distortion: deviations from normal leaf shape
Rugose Rugose means : "rough leaves".  This term covers both crinkling (leaves looking edged or wrinkled) and leaf puckering (blister-like irregularities formed on the leaf) 

44. Enation Abnormal outgrowth of vascular tissue in leaves or on the stem
Pea enation mosaic virus (PEMV)

45. Blistering

46. Variegation

47. Shoe string
Crown gall/ tumor
Rosette: cluster leaves

48. BANANA BUNCHY TOP

49. Microsoft Engineering Excellence
THANKS For Your Kind Attention
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