Plants have evolved several defense mechanisms to resist exploitation by pathogens. These include constitutive defenses that are always present and induced defenses that are activated after exposure to a pathogen. A successful plant disease requires an interaction between the host plant, pathogen, and the plant's resistance. Plants defend themselves through basal resistance, which involves both constitutive and induced defenses that act as barriers to infection and disease development.

1. PlantDefence
Mechanisms
By- Krishna Dhakar
M.Sc. Botany
IV Semester

2. Introduction
• Adjustment is probably, one of the most important
virtue of a system that ensures it survival, be it host or
parasite.
• On planet earth, the green plants (autotrophs)
constitute the only biological system capable of
converting solar energy (electro-magnetic radiations)
into chemical energy.
• Plants as a biological system resist this exploitation, at
all levels and by all means. The co evolution, forced by
co-existence with pathogen, has led to development of
defence mechanism in plants.
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3. Cont…Introduction
 Consequently, the plants have evolved several different
mechanisms by which they defend themselves.
 These defence mechanisms in plants are termed as “BASAL
RESISTANCE”.
 This term referring to two distinct aspects of plant-pathogen
interaction.
Constitutive defense.
Induced defense.
 Each plant species is affected by approximately 100 different
kinds of fungi, bacteria, mollicutes, viruses and nematodes.
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4. Cont…Introduction
 For the development of the disease in
plants, there must be a successful
interaction between three components.
HOST
PATHOGEN
RESISTANCE
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oHOST: -
oPATHOGEN: -
oRESISTANCE: -
A living organism from which other
organism derive its food.
Any agent (living organism or
virus) which can cause disease.
The ability of an organism to
exclude or overcome
completely or in some degree,
the effect of a pathogens, or
other damaging factor.
Cont…Introduction

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7. • Besides these the potential for any
pathogen to cause disease also
depends upon.
1. Host-microbe
compatibility/incompatibility.
2. Host receptors and sites for
toxins
3. Essential nutrients and growth
factors.
4. Recognition factors.
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Cont…Introduction

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