Post on 18-Jul-2015
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