important viral diseases and their management strategies

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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important viral diseases and their management strategies

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