This document discusses structural and post-infection defense mechanisms in plants. Pre-existing structural defenses include waxes, cuticles, epidermal and sclerenchyma cells that form physical barriers against pathogens. Post-infection defenses are produced after infection, including histological barriers like cork layers and abscission layers that isolate the infection, and cellular defenses where invading hyphae are enveloped by the plant cell. Together these defenses provide plants with multilayered protection against fungal, bacterial and viral pathogens.

1. PRESENTED BY ERESH
COLLEGE OF
AGRICULTURE RAICHUR

2. Structural defence
mechanism in plants
1.Pre-existing
2. Post infectional
The first line of defence in plants is present on
its surface

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 2.Post –infectional defence
mechnism
 Present within but produced after
infection
 1.histological barriers
 2.cellular barriers

11. 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

12. 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-amputative
resistance
 Ex. Xanthomonas pruni and
closterosporium carpophylum on
peach leaves

13. 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

14. 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