Host plant resistance in maize

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Welcome1


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HOST PLANT RESISTANCE IN MAIZE

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(Ent-608, Advanced Host Plant Resistance)

Presented by,Navik, O. S.

Reg. No. 146Department of Agril. Entomology

Course teacher,

Dr. A.L. NarangalkarHead,

Department of Agril Entomology


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Introduction

Maize suffers damage from a large number of insect

Insects are a particularly acute problem in tropical regions.

Genetic differences in the host plant response of maize

varieties through biochemical and biophysical basis of

resistance against insect

Transgenic maize

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Resistance?

Resistance is a relative property, based on the comparative reaction

of resistant and susceptible plants, grown under similar conditions, to

the pest insect.

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Host plant resistance of Maize based on

1. Allelochemical

2. Morphological Mechanisms

I. Allelochemical

Benzoxazinoids

Phenolic Acids and Cell Wall Components

II. Defense-Related Proteins

Maize Proteinase Inhibitor and Cysteine Proteinase

Maize Ribosome-inactivating Proteins

III. Genetics of Insect Resistance in Maize

Maysin

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Benzoxazinoids

Natural benzoxazinoids were discovered in 1960 in rye when

resistance against fungi was investigated.

It is predominantly found in genera of the Gramineae.

In maize, it is the methoxy derivative, DIMBOA that present.

DIMBOA-glucoside content in corn seedlings can reach

concentrations up to 10mmolesper kg of fresh weight.

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DIMBOA is an enzyme inhibitor of chymotrypsin, aphid

cholinesterase and plasma membrane H + -ATPase.

The first brood of the European corn borer (Ostrinia nubilalis)

(ECB) is controlled by high levels of the benzoxazinoid DIMBOA in

seedlings andyoung plants

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(McMullen et al.,2009)


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2. Phenolic Acids and Cell Wall Components

These compounds are implicated in two defense concepts,

Act as deterrent and strengthen the cell wall as mechanical barrier by

producing ferulic and coumaric.

E.g. ECB

maize weevil (Sitophilus zeamais),

pink stalk borer (Sesamia nonagrioide)

The phenolic acid esters chlorogenic acid and the C-glycosyl flavonemaysin have been implicated as antibiosis to corn earworm (Helicoverpa

zea).

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2. Maize Ribosome-inactivating Proteins

Maize Ripis a Opaque-2-regulated protein associated with endospermdevelopment.

Maize opaque-2 line shows increased insect susceptibility with

deficiency of RIP suggestions that RIP can play a defensive role

against insects.

The activated RIP protein is relatively stable to digestion by

caterpillar.

This finding provides support for the assumption that maize RIP plays

a role in resistance to maize-feeding insects.

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(McMullen et al.,2009)


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Genetics of Insect Resistance in Maize

Maysin

The level of maysin in maize silks in 23-day-old silks is generally in the

range of 0.20.8% silk fresh weight and a very impressive accumulation

for a secondary metabolite helpful to control the Corn earworm.

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II. Plant Morphology

Several types of morphological defenses in maize varieties deter insectfeeding and oviposition.

The increased leaf, stem silica content and tight husked maize ears

contribute to European corn borer resistance in maize.

Maize varieties with reduced trichome density and delayed development

ofpubescence have been shown to be less preferred for oviposition by

corn earworm and are resistant to larval feeding.

Some maize verities have higher hemicellulose and crude fiber content

than susceptible inbred lines.

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Morphological defenses of insect resistant maize

Defense Insect(s) affectedDense surface waxes Southwestern corn borer, Fall armyworm

High fiber, dense European corn borer

Vascular bundles Fall armyworm

High hemicellulose, Southwestern corn borer

Thick cuticle Sugarcane borer

Low trichome density Corn earworm

Silica European corn borer

Tight husks Corn earworm, Maize weevil

(CIMMYT,2005)13


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CryIA(b)Gene in Transgenic Maize Confers

Resistance to European corn borer

For control of European corn borer introduced a truncated form of the

cryIA(b) gene obtained from Bacillus thuringiensis into an elite line of

maize which expressing a endotoxin.

The expression of the cryIA(b) gene was targeted to the pollen, pith

andgreen tissues by using appropriate tissue specific promoters.

The resulting transgenic maize plants were evaluated for resistance to

European corn borer (ECB), Ostrinia nubilalis, under field conditions.

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Transformation Technology

For maize transformation ballistic and protoplast transformation methods used

successful recovery of fertile transformed maize plants.

In the ballistic method - microscopic tungsten particles coated with foreign

DNA are forcefully propelled through the cell wall into the cytoplasm and

nuclei of cells.

In the protoplast method, the cell walls are first removed. Then the cell

membrane becomes readily permeable to foreign DNA. Movement of foreign

DNA through the cell membrane is facilitated either by applying an

electrical current (electroporation) or adding Polyethylene Glycol (PEG).

Foreign DNA in solution surrounding the cells passes through the cell

membrane, with some of it being incorporated into the nuclei of cells.

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Plant transformation method - Ballistic method and Protoplast method

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Host plant resistance in maize