pp-202 plant virology

7/23/2019 PP-202 Plant Virology

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INTRODUCTION TO PLANT VIRUSES

Virus:

Virus is set of one or more nucleic acid template molecules normally

encased in coats of protein or lip-protein and organize its own

replication only within specific host cells

Virion:

A complete mature viral particle is called virion

Prion:Smaller infectious protein particles encoded by a chromosomal gene

of the host cells

Viroids: Small, low-molecular-weight ribonucleic acids (RNAs) that

can infect plant cells, replicate themselves and cause disease. OR

Naked, single-stranded circular molecule of infectious RNA calledviroid

Virusoids:

The extra-small circular RNA component of some isometric RNA

viruses


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Importance of Plant Viruses

Plant virusesare viruses that multiply by using

the material synthesized by the host to

manufacture new virus particles and cause

infection Beneficial Aspects:

Used as color breaking agent in ornamental

plants. Ornamental plants become attractive e.g.

Tulip mosaic virus

Used as a vector in genetic engineering, CuMV

Viruses used as a cross protection
http://www.owleyes.org/nursing-encyclopedia/viruseshttp://www.owleyes.org/nursing-encyclopedia/viruses


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Harmful Aspects

Causes harmful diseases in humans, animals,

and plants

Cause reduction in the growth of the plants.

Reduction in yield and ultimately failure of thecrop

Affect the quality and quantity of the production

Make the plants more vulnerable to otherorganisms (Insects) e.g. TMV, SCMV, CLCuV,

CTV


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COTTON LEAF CURL DISEASE

CLCuV, ssDNA

Genus: Begomovirus, Family: Geminiviridae

Occurrence & Importance:

First reported in Nigeria in 1912

In 1959 from Philippines

In 1967 in Pakistan near Multan

Epidemic form in 1993-95 in Pakistan

Most serious disease of cotton

Cause losses from 22.38-68.50%


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Symptoms

Thickening of veins

Color of infected plants become dark

green

Upward or downward curling of leaves

Leaf enation

Twisted leaf petioles Stunting of plants


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Symptoms


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Symptoms


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DiseaseCycle

Not seed or soil-borne

Over winter on alternate hosts (tomato,tobacco, beans, lehli, okra, datura etc

Transmitted by whitefly (Bemisia tabaci)

30 Min. feeding on infected plants

24 hours latent period

30 Min. inoculation feeding period

Retention period: through out life ofwhitefly


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Epidemiology

Minimum temp. 27-28 0C

Maximum temp. 38-40 0C

Relative humidity: 56-60% Susceptible host on large area

Less rainfall or no rainfall

Abundance of whitefly population


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Management

Tolerant varieties, NIBGE-2, NIAB-111,

PB-899, CIM-446, MNH-786

Destruction of alternate hosts

Uproot & burry first observed infected

plants

Control insect vector (Imidacloprid, polo)Use of nutrients also help to reduce the

disease incidence


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BANANA BUNCHY TOP DISEASE

(BBTV), ssDNA VIRUS

(Genus Babuvi rus, Family Nanovir idae)

Most important disease of banana crop

Occur in all banana producing countries

(Fiji, Indonesia, Malaysia, Australia, Sri-

lanka, Pakistan, India)

Infected plants produce no fruits


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Symptoms

Dark green streaks seen on petioles &veins of new leaves looking against light

Leaves arise in clusters

Margins of leaves become chlorotic &rolled upward

Top of plant become narrow, upright &

closer appearing bunchy Plants show stunted growth

Inflorescence fails to emerge


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Disease cycle

Vector: Black banana aphid (Pentalonia

nigronervosa)

Also transmitted through propagative

materials (rhizomes, suckers, tissue-

cultured meristem)

Aphid feed 17 hrs to become infective

Maxi. Vector concentration at base of stem


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Disease cycle


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Epidemiology

18-20 0C temperature

41-84% Relative Humidity


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Management

Quarantine measures

Use of virus free propagative material

Locating new plantation away from old

Destroying all volunteer banana plants

Uprooting & burning of infected plants

Control vector with insecticidal soap water spray

or insecticides (Prentox Diazinon AG500) Cultivate resistant varieties (Gross Michel)


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Potato Leaf Roll Disease

(PLRV), ssRNA

Genus: Polerovirus, Family: Luteoviridae

Occur world wide

Most destructive virus of potato

Yield losses more than 50%


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Symptoms

Appear mostly on lower leaves

Leaflets roll upwards

Margins & tips of leaves become yellow Leaves become leathery & brittle

Plants stunted & have upright growth

No. of tubers/plant & size is reduced Phloem necrosis occur in tubers


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Disease cycle

More than 10 species of aphid act as

vector (Myzus persicae)

Infected tubers are primary source of

infection

Aphid feed for several hrs (48-54 hrs)

Alternate hosts are Datura stramonium


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Epidemiology

15-20 0C temperature

40-65% Relative Humidity


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Management

Obtain certified seed

Plant early in the season

Pulled out sick plants as soon as locatedDetop plants in last week of December

Apply systemic insecticides (aldicarb,

carbofuran)


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Tobacco Mosaic Virus(TMV)ss-RNA

Genus:Tobamov irus, Family:Virgaviridae

First virus ever discovered in history

Known to occur in all the tobacco growing

countries of the world

55% reduction in yield has been reported

Sub stranded produce fetch low price in

the market
http://en.wikipedia.org/wiki/Virgaviridaehttp://en.wikipedia.org/wiki/Virgaviridae


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Symptoms

Leaves show mild veins clearing

Mottle and mosaic pattern

Light discoloration along the veins ofyoung leaves

Wrinkling, crinkling, twisting margins and

narrowing of leaf lets

Dwarfing of entire plant


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Disease cycleand epidemiology

Survive in herbaceous and woody plants

Tomato, Potato, pepper grown indoor are source

of infection

Virus present in plant debris, soil, cloths andeven manufactured tobacco cigarette and cigar

Contact with the wounded plants

No insect vector, Mechanical transmission Wide host range of 500 species of flowering

plants

Temp. 28-32 C, RH 44-56%


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Management

Use clean and healthy seed in the nursery

All workers should disinfect their hands

RougingCrop rotation maize and wheat, avoiding

tomato and pepper

Healthy leaves harvest first than infectedone

Field sanitation practices

S M i Vi Di


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Sugarcane Mosaic Virus Disease

(SCMV) ss-RNA

Family: Potyviridae Genus: Potyvirus

First recorded in Java in 1892, in Punjab in

1926-27

Occur in every sugarcane growing

country

Estimated yield losses vary greatly uponcultivar and environmental conditions


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SYMPTOMS

Contrasting shades of green, islands of normal

green or yellowish chlorotic areas on the leaf

blade

leaf reddening or necrosis Chlorotic areas most evident at base of the leaf

Chlorotic areas may also be present on the leaf

sheath, but rarely on the stalk Young, rapidly growing plants are more

susceptible to infection


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Disease cycleand epidemiology

There are three principal modes of spread

of SCMV:

(1) by aphid vectors,

(2) by infected seed cane and

(3) by mechanical inoculation.

Only aphid vectors and infected seed caneare important in the field.

Temp. 35-38 C, RH 68-78%


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Management

Resistant varieties is the most effective method

of mosaic control

Management practices targeting insect vectors Control of mosaic through heat treatment only

practical in quarantine situations

Some plants recover from mosaic by nutritional

application


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Citrus Tristeza Virus (CTV)

or Quick decline,ss-RNA

Family: Closteroviridae Genus: Closterovirus

Biggest threats to citrus production in globe

More than 30 virus, virus-like diseases of citrus

known in the world, of which CTV is the mostdestructive.

The first tristeza disaster was reported in 1930's

in Argentina, where 90% of the citrus wasplanted on sour orange rootstock


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Symptoms

Yellowing of leaves

Dieback of the phloem in the sour orange

rootstock below the bud union

Rootstock being girdled 'Slow decline' where trees decline in a period of

years

Stunting where the virus does not kill the tree,but the tree does not grow

Deep pits are present under depressed areas of

the bark


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Disease cycle

Vectors of CTV are black or brown citrus aphid

(Toxoptera citricida)

Due to the aphid introduction, CTV rate of

spread has increased dramaticallyAdditionally, growers have aided in the spread of

the virus with the propagation of trees using

infected bud-wood.

Temperature, 20-27 0C RH, 55-70%


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Management

Exclude any introduction of severe strains

Need for mild strain protection in the future

Strict control by quarantine must be continued

Rootstocks that offer resistance to tristeza

decline include the citranges (C-35, Carrizo,

Troyer), Citrumelos (Swingle), mandarins


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THANKS

Dr. Safdar Ali

Dr. Luqman Amrao

pp-202 plant virology

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