PRESENTED BY ERESHCOLLEGE OF AGRICULTURE RAICHUR

Structural defence

mechanism in plants

1.Pre-existing

2. Post infectional

The first line of defence in plants is present on

its surface

Pre-existing structural defence

mechanism

First layer in the host to defence

The structures of epidermal

cells&cellwalls

The size,location and shape ,no.of

stomata and lenticels,hydathodes

structures

1.waxes:

synhesized by epidermal cells

Complex mixture of long chain acyl lipids.

Extremely hydrophobic

Wax forms outer coating of the cuticle

Often crystallizes in pattern of rods or tubes or

plates

It prevents germination of fungal spores and

bactria

No parasite is known to produce enzymes that

can degrade the cuticular waxes

2.Cuticle and epidermal cells

The cuticle is composed of insoluble membranes

Covered with

1.insoluble waxes

2.cutin embeded

3.cutin+wax blended

Thick cuticle and tough outer wall of epidermal cell resistance to direct penetration of pathogen

Eg:Barbery-Puccinia graminis tritici-resistence is attributed to the tough outer epidermal cells

Pyricularia grisea-leaf blast of paddy-the entry is through the guard cells and motor

3.Sclerenchyma cells

o Composed of walls thickened with

lignin

o Have brittle cells helps in mechanical

support to plants

o These cells effectively blocks spread

of fungal and bacterial pathogen that

cause angular leaf spots

o Eg: some wheat varieties resistant to

stem rust –stem contain high

sclerenchyma cells

4.Natural openings

1.stomata:

The minute pores in the epidermis of

leaf through which exchange of gases

takes place

The structures of stomata provides

resistance to penetration of pathogen

Eg: citrus variety szinkum –resistant to

citrus canker

Cultivar Hope-resistant to wheat rust

2.lenticels

Lenticels are airy cells in the bark of

stems and roots

The shape and internal structure of

lenticels can increase or decrease the

incidence of fruit diseases

Lenticels of small size restrict entry of

pathogen

3.Hydathodes:Early entry points of bacterial pathogen

Eg: xanthomonas campestris

pv.campestris

4.Nectarithodes:Present tip of infloroscence

Eg: Erwinia amylovora-fire blight of

apple

2.Post –infectional defence

mechnism

Present within but produced after

infection

1.histological barriers

2.cellular barriers

Histological barriers

A)cork layer: stronger rough surface of the host

A layer of meristamatic cells which form on the surface of the host

Toxical material spread stops infection

Stops flow of water & nutrients towards infection part

Eg:scab of gauva and citrus canker

Rhizopus rot of sweet potato

b.Abscission layer

Means fall off or shred off

Gap formed b/w infected cell and healthy cell at the site of infection .

It surrounds point of locus of infection.

Gradually infected area shrivels , dyes carrying with it the pathogen

Abscission layer-amputativeresistance

Ex. Xanthomonas pruni and closterosporium carpophylum on peach leaves

c.Tyloses

Over growth of adjacent lining

paravascular cells which protrudes into

xylem vessels through pits

Tyloses are selective permeable to water

and nutrients

It blocks further spread of pathogen

Eg: Fusarium oxysporum f.sp. batatas-

wilt of sweet potato

Cellular defence mechanisms

Hyphal sheathing :the hyphae

penetrating the cell wall and growing

into the cell lumen are enveloped by a

cellulosic sheath

Inward stretching of the host cellwall

around the haustorium

Eg:Botrytis cinera