Biotic Stress

8/4/2019 Biotic Stress

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Unit-VPlant Genetic Engineering forProductivity and Performance

Biotic Stress


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Introduction

Plants have to exploit their immediateenvironment to maximum productivity.

They are unable to move from one place toother.

Best way of dealing with many stresses isthrough physiological or morphologicalchanges.


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Introduction

Higher plants are subjected to various adverseenvironmental conditions through out their life timesuch as

-Drought or Low Soil Moisture-Cold

-Temperature

-Prolonged periods of cloudiness

-High wind velocities-Soil salinity

-Air Pollution, Snow etc..


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Introduction

All these types of environmental conditions maycause damage/injury to plants.

Resulting from reduction in growth to death.

Generally stresses are of two types

Biotic stress Abiotic stress


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Biotic stress

Biotic stress is caused by biological organismssuch as

Insects

Herb (Another plant)

Bacteria

Virus


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Insect-Plant Interaction
http://kolya.typepad.com/photos/uncategorized/okra5.jpghttp://kolya.typepad.com/photos/uncategorized/okra2.jpg


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HERBS-CROP


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Bacterial stem rot of tomato (Erwinia carotovora subsp. carotovora)can occur on staked or trellised tomatoes when plants are pruned.


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Citrus canker


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Viral Infection on Plants


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Insect Resistance


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Natural pest resistance

Natural pest resistance mechanismsoccurring in higher plants can be classifiedinto

1). Preformed resistance mechanisms

2). Inducible resistance mechanisms.

P f d i


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1. Preformed resistance

mechanisms

Structural, Morphologic, and Chemical factors

In entomology, it has long been known that

innate morphological and anatomical featuressuch as leaf and flower color, presence oftrichomes, and even the texture of cuticle maycause certain insects to avoid a plant, thusconstituting resistance mechanisms.


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Preformed resistance mechanisms

Anatomical features may also discourageinsect feeding.

These include the degree of secondarywall thickening and other aspects of basicplant structure.


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Plants typically contain significant amountsof preformed chemicals produced viasecondary metabolism.

These include phenolics of varyingstructural sophistication, terpenoids, andsteroids.


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Some preformed compounds are directlytoxic, while others exist as conjugatessuch as glycosides that are not directlytoxic but become toxic following disruption

of the conjugate.


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Plant glycosides are often hydrolyzed followinginsect damage and releases vacuolarglycosidases.

The aglycones thus produced may be quite toxicto the invader as well as neighboring plant cells.

Since the toxic response is local, however, onlya small portion of the plant is affected


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1.1 ) INDUCIBLE RESISTANCEMECHANISMS

Inducible resistance mechanisms are active, energy-requiring systems.

Specific recognition of an invader that ultimately leads to

the production of proteins or metabolites that areantagonistic to the invader.

These resistance mechanisms have been most studiedin regard to plant pathogens, but the same or similar

mechanisms clearly function against insect pests.

Such active resistance mechanisms are usually referredto collectively as the hypersensitive response (HR).


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Biotechnological approach forInsect Resistance


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Development of Disease resistant Plants

by Bacillus thuringiensisapproach


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Crop damage

It is estimated that 13% of the crop is lostdue to pests world over.

63%

Weeds

pests

Diseases

37% lost due to Weeds, pests and diseases


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Crop damage

Adult insects in general feed on plants anddamages crops.

Most of the problem are due to insect larvae.

The major classes of insects that cause cropdamage are

1. Lepidoptera-Butterflies and moths2. Diptera-Flies and Mosquitoes

3. Orthoptera-Grasashoppers, crickets

4. Homoptera-Aphids


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Lepidoptera-Butterflies and moths


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Diptera-Flies and Mosquitoes


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Orthoptera- Grasshoppers, crickets

H t A hid


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Homoptera-Aphids
http://images.google.co.in/imgres?imgurl=http://animaldiversity.ummz.umich.edu/site/resources/phil_myers/homoptera/aphids1564.jpg/large.jpg&imgrefurl=http://animaldiversity.ummz.umich.edu/site/resources/phil_myers/homoptera/aphids1564.jpg/view_large.html&h=600&w=511&sz=85&hl=en&start=16&tbnid=lPhDz4MHYz00LM:&tbnh=133&tbnw=113&prev=/images%3Fq%3DHomoptera-Aphids%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DGhttp://images.google.co.in/imgres?imgurl=http://www.cnr.berkeley.edu/citybugs/search/ident_images/IDed/Homoptera/2185_Homoptera_aphids.jpg&imgrefurl=http://www.cnr.berkeley.edu/citybugs/search/Specifics/aphidspecifics.htm&h=668&w=500&sz=52&hl=en&start=9&tbnid=Xq_WFD9VNXiBlM:&tbnh=138&tbnw=103&prev=/images%3Fq%3DHomoptera-Aphids%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DGhttp://images.google.co.in/imgres?imgurl=http://animaldiversity.ummz.umich.edu/site/resources/phil_myers/homoptera/aphids1549.jpg/large.jpg&imgrefurl=http://animaldiversity.ummz.umich.edu/site/resources/phil_myers/homoptera/aphids1549.jpg/view_large.html&h=600&w=736&sz=132&hl=en&start=11&tbnid=OpiYDgLo8AJSfM:&tbnh=115&tbnw=141&prev=/images%3Fq%3DHomoptera-Aphids%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DGhttp://images.google.co.in/imgres?imgurl=http://pest.ca.uky.edu/EXT/master_gardener/entbasics/homoptera/aphids.jpg&imgrefurl=http://pest.ca.uky.edu/EXT/master_gardener/entbasics/homoptera/homoptera.shtml&h=270&w=360&sz=98&hl=en&start=10&tbnid=3jmpSxLu636N4M:&tbnh=91&tbnw=121&prev=/images%3Fq%3DHomoptera-Aphids%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG


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Crop damage

Insects cause a number of diseases which

cause massive crop damage.

To control these diseases, pesticides,insecticides are enormously used.


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Insect resistance: The Bacillus

thuringiensisapproach

Bacillus thuringiensiswas discovered by

Ishiwaki (1901) in diseased silkworms


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Taxonomy of B. thuringiensis


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Bacillus thuringiensis


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BT Toxins

Bt has two classes of toxins; cytolysins(Cyt) and crystal delta-endotoxins (Cry).

While Cyt proteins are toxic towards theinsect orders Coleoptera (beetles) andDiptera (flies).

Cry proteins selectively targetLepidopterans (moths and butterflies).


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Mode of action

The insecticidal activity of Bacillus is because ofparasporal crystal which is synthesized duringthe sporulation.

No significant role for the bacterium has beenidentified.

The parasporal crystal comprises approximately20-30% of dry weight of the sporulated culture andusually consists of 95% protein and 5%carbohydrate


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Mode of action

During sporulation, it synthesizes a cytoplasmicinclusion containing one or more proteins thatare toxic to insect larvae.

Upon completion of sporulation the parentbacterium lyses to release the spore and theinclusion. In these inclusions, the toxins exist

as inactive protoxins.

When the inclusions are ingested by insect

larvae, the alkaline pH solubilizes the crystal.


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Once it has been solubilised in the insect gut,the protoxin is cleaved by a gut protease toproduce an active toxin of about 60kD.

This toxin is termed delta-endotoxin. It binds

to the midgut epithelial cells, creating pores inthe cell membranes and leading to loss of ions.

As a result, the gut is rapidly immobilized, theepithelial cells lyse, the larva stops feeding.


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Mode of action

It has been indicated that the activatedtoxin binds to insect-specific receptorsexposed on the surface of the plasma

membrane of midgut epithelial cells andthen inserts into the membrane tocreate transmembrane pores that cause

cell swelling and lysis and eventuallydeath of the insect.


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Mode of action

Due to their high specificity for theseunique receptors on the membrane of thegut epithelial cells, these toxins (delta-

endotoxins) are harmless to non-targetinsects and the end-user.


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http://www.greenpeace.org/india/photosvideos/photos/out-of-the-frying-pan-the


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GeneCrystalshape

Proteinsize(kDa)

Insect activity

cry I [several subgroups:A(a), A(b), A(c), B, C, D, E,F, G]

bipyramidal 130-138 lepidoptera larvae

cry II [subgroups A, B, C] cuboidal 69-71 lepidoptera anddiptera

cry III [subgroups A, B, C] flat/irregular 73-74 coleoptera

cry IV [subgroups A, B, C,D]

bipyramidal 73-134 diptera

cry V-IX various 35-129 various

Bt toxins and their classification


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INSECTICIDE RESISTANCE:How Does it Occur?STEP ONE: Mixed population to start with

Repeated spraying, lack of insecticide rotation

Huge reproductive capacity & short life cycle

R

R

R

RS S

S

S SS

SS


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INSECTICIDE RESISTANCE:How Does it Occur?

STEP TWO: susceptible individuals are killed.

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R

RS S

S

S SS

SS


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INSECTICIDE RESISTANCE:How Does it Occur?

STEP THREE: resistant individuals reproduce giving rise to a

resistant strain within the species.

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

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RR

R

Biotic Stress

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