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8/6/2019 Important Viral Diseases and Their Management Strategies
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Important Viral DiseasesAnd their Management
Strategies
Dr. A. Samad
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What Is Virus ?
Very small entity(not visible even undernormal light microscope), obligateparasite,reproduce only inside living cells
Strictly intracellular
Genome is an element of nucleic acid(DNA orRNA) encased in a protective protein orlipoprotein shell.
Unable to divide by binary fission & cannot be
grown
Reproduce from their sole nucleic acid
Make use of ribosomes of host cell forreplication
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Background/History
First recorded symptom: Colour breaking of tulip
flower;1776.
Severe disease in Tobacco crops in Holland;1870
First paperpublished in 1886. Start of Virology. Contagium vivum fluidum(Infectious living fluid),
Tobacco disease, sterile solution: Beijernick;1898
Crystallized the virus(TMV): Stanley;1935
Ruska observed TMV under electron microscope:
1939
New era of virology started: 1939
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SYMPTOMATOLOGY
Local and/orsystemic
Characteristic symptoms Only the Yellowing makes the confusion
Can be symptomless also
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Tulip flowers
Tulip flowers
showing mosaic in
the petals due toinfection with tulip
breakingvirus (TBV).
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Pelargonium
Pelargonium (Pelargonium zonale) with white
streaking of petals due to infection with pelargonium
flower break virus(PFBV).
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Rose yellowing
Bright yellow line pattern due to
Prunus necrotic ringspot virus
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Cucumber
Cucumber with papaya ringspot virus
&
watermelon mosaic virus 2
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Cucumber
Left:Cucumissativusinfected with cucumber green mottle
mosaic virus (CGMMV)
Middle:with cucumber mosaic virus (CMV)
Right:healthy.
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Tomato
Tomato infected with Tomato Yellow Leaf Curl
Virus
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Pepper
Pepper infected with Pepper Huasteco Virus
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Lettuce
Yellowing in outer leaves of head lettuce with beet
western yellows virus(BWY
V)
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Carrot
Leaf chlorosis and reddening in carrot with carrotred leaf virus
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Pea
Pea(Pisum sativum) infected withbean leaf roll virus
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Wheat
Right: Leaf of wheat
(Triticum sativum)
infected with Festucaleafstreak
virus(FLSV).
Left: Healthy leaf.
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Soybean
Leaf from soybean (Glycine max) infected with soybean
mosaic virus(SMV).
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Mentha
Mentha gracilis infected with TMV
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Poppy
Opium poppy(Papaver somniferum) infected withpotyvirus
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Henbane
Egyptian henbane(Hyoscyamus muticus) infected with TMV
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Henbane
Egyptian henbane(Hyoscyamus muticus) infected with CMV
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GoldenYellow Mosaic Disease on Mucuna prurience
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Deformation,curling, mosaic and stunt growth on Mentha sp.
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Green mosaic,curling and poor growth on Mentha sp.
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Golden Mosaic, puckering and poor inflorescence on Preiwinkle.
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Green peach aphid (Myzus persicae)
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Whiteflies Bemesia tabaci
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Pathogen detection
Different methods for the detection of plantpathogens have been developed and are applied,depending on the pathogen to be detected, thetime frame, equipment and financial resources
available. These aspects are very important for thechoice of a test system.
Diagnosis of causal virus is difficult because
cannot be cultured
Cannot be viewed under compound microscope
Symptoms are of limited value in identification
Therefore more than one technique has to be
applied for correct identification of the virus
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Methods for virus detection
Internationally approved and recognizeddetection systems includesoUse of indicator hosts in greenhouse and field
indexing
oelectron microscopyoserologicalo molecular laboratory assays
molecular hybridizationNucleic Acid hybridization(DNA/ RNA
probes)
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Indicator hosts
Play a major role in primary identification
Easy, Very helpful & Cheap
Local lesions
Systemic
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Differential Hosts
Necrotic lesions on
O.basilicumTombus
virus
Necrotic lesions on
G.globosaCarla virus
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Systemic host
N.tobacum cv.White burley with mosaic by TMV
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Isolation & Purification
Base for identification & characterizationof the virus
Aim at separation of the virus from hostconstituents with out affecting thestructure & infectivity
No two viruses are exactly alike &
perhaps there are as many purificationprocedures as there as viruses.
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Purification
Common steps are:
Culturing of biologically pure virus in a host
Host should contain less interferingcompounds, support high concentration of
virus Extract to a liquid medium with minimum
loss of infectivity
Clarify the extract to remove as much as host
materials as possible Concentrate the virus in the clarified extract
by differential centrifugation or chemicalprecipitation
Further purification
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Local lesion host
Chenopodium amaranticolorshowing necrotic lesions
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Electron microscopy
Morphology of the purified virus Ultra structural studies of the infected tissue
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Electron microscopy of virus from poppy
Purified Potyvirus Pin wheels & C.I. in theinfected cell
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Electron Microscopy of TMV from Mentha
Purified TMV
Ultra structure of the
infected cell Immunosorbent
Electron microscopy
(ISEM) of the virus
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Serology
Plant viruses are generally identified by
particle morphology host range and the serological properties of the coat
protein.
Cross-reactivity of antisera raised
against viruses from different groups hasfrequently been used foridentificationand for the establishment oftaxonomicrelationships.
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Agar Diffusion Technique
Double diffusion test
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ELISA
(EnzymeL
inked Immunosorbent Assay) Developed for the detection ofplant viruses
almost 30 years ago.
Used routinely for large scale testing of plants forthe presence of many viruses.
It is rapid, inexpensive and convenient.
Can only be applied for those viruses where
specific antisera are commercially available.
Level of titre in the sample is also a limiting factor
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Molecular Lab. Assay
Molecular techniques:SDS-Polyacrylamide gel electrophoresis (SDS-PAGE)
Western blotting
DNA/RNA analysisSequencing of protein(s)
Polymerase Chain Reaction (PCR)
Restriction Fragment Length polymorphism (RFLP)
Nucleic acid hybridization:DNA/RNA Probes
Micro arrays
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Western blotRNA-analysis
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Managementofthe Pathogen/Disease
Cover crops/barriers
Roguing/Field sanitation
Area of Field
Planting and Harvesting time
Heat Therapy
Apical Meristem Tissue Culture
Control of vectors (insecticides, miticides etc.)
Bio-inoculants
Resistant/tolerant varieties
Use of Certified materials
Transgenic plants
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Current Status
Advancement of molecular techniquesgenerated enormous information on thenature & biochemical components of
viruses. Based on these large database,ICTV approved the arrangement of theplant viruses into
Families: 14
Genera : 47
Species : 299
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Geminiviridae
Bean golden mosaic virus
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Tombusviridae
Tomato bushy stunt virus
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Closteroviridae
Beet yellows virus
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Furovirus
Wheat mosaic virus(Soil borne)
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Comoviridae
Tobacco ringspot virus
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Tobravirus
Tobacco rattle virus
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Bunyaviridae
Tospovirus
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