Page 1
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 1
Discipline: Botany
Paper: Plant Physiology
Lesson: Plant Defense against Pathogens-I
Lesson Developer: Anita Thakur
Department/College: Department of Botany,
University of Delhi
Page 2
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 1
Discipline: Botany
Paper: Plant Physiology
Lesson: Plant Defense against Pathogens-I
Lesson Developer: Anita Thakur
Department/College: Department of Botany,
University of Delhi
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 2
Table of contents
Plant Defense against Pathogens-I
• Introduction
• What study plant pathogen interaction
• Plant disease
• Types of plant-microbe relationships
• Constitutive and inducible defenses
• Plant pathogens and their strategies of pathogenesis
• Plant pathogens
• Types of plant pathogens and their modes of entry in host
plants
• Plant defense systems
• Structural defenses
• Chemical defenses
• Enzymes and Proteins
• Summary
• Exercise/Practice
• Glossary
• References/bibliography/ further reading
Page 3
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 1
Discipline: Botany
Paper: Plant Physiology
Lesson: Plant Defense against Pathogens-I
Lesson Developer: Anita Thakur
Department/College: Department of Botany,
University of Delhi
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 2
Table of contents
Plant Defense against Pathogens-I
• Introduction
• What study plant pathogen interaction
• Plant disease
• Types of plant-microbe relationships
• Constitutive and inducible defenses
• Plant pathogens and their strategies of pathogenesis
• Plant pathogens
• Types of plant pathogens and their modes of entry in host
plants
• Plant defense systems
• Structural defenses
• Chemical defenses
• Enzymes and Proteins
• Summary
• Exercise/Practice
• Glossary
• References/bibliography/ further reading
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 3
Learning outcomes
The student will be able to
• Understand the basic concepts of plant-pathogen interaction
• Learn the types of host-pathogen interactions
• Understand the concepts of disease, injury, and the signs and symptoms of plant
pathogenic agents
• Explain the various defense mechanisms adopted by plants
• Describe terms like pathogenicity, non-host, non-pathogen, host range.
• Differentiate between constitutive and induced defenses
• Explain the various structural barriers present in plants which help in plant defense
against pathogens
• Become familiar with chemical compounds secreted by plants which play role in
defense
Page 4
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 1
Discipline: Botany
Paper: Plant Physiology
Lesson: Plant Defense against Pathogens-I
Lesson Developer: Anita Thakur
Department/College: Department of Botany,
University of Delhi
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 2
Table of contents
Plant Defense against Pathogens-I
• Introduction
• What study plant pathogen interaction
• Plant disease
• Types of plant-microbe relationships
• Constitutive and inducible defenses
• Plant pathogens and their strategies of pathogenesis
• Plant pathogens
• Types of plant pathogens and their modes of entry in host
plants
• Plant defense systems
• Structural defenses
• Chemical defenses
• Enzymes and Proteins
• Summary
• Exercise/Practice
• Glossary
• References/bibliography/ further reading
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 3
Learning outcomes
The student will be able to
• Understand the basic concepts of plant-pathogen interaction
• Learn the types of host-pathogen interactions
• Understand the concepts of disease, injury, and the signs and symptoms of plant
pathogenic agents
• Explain the various defense mechanisms adopted by plants
• Describe terms like pathogenicity, non-host, non-pathogen, host range.
• Differentiate between constitutive and induced defenses
• Explain the various structural barriers present in plants which help in plant defense
against pathogens
• Become familiar with chemical compounds secreted by plants which play role in
defense
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 4
Introduction
Why study plant-pathogen interaction?
Plants are continuously confronted with a wide range of potential pathogens in their
environment. Under favorable conditions, plant pathogenic microorganisms such as fungi,
bacteria and viruses, can multiply and spread rapidly through plant populations to cause
severe outbreaks of disease. Although plants are immobile and lack an immune system in
comparison to animals, each plant cell possesses both a preformed (constitutive) and an
inducible defense capacity. Since plants are the primary producers in an ecosystem and are
a rich source of nutrients and energy for other organisms, including humans, the health of
plants is of vital importance. Disease is one of the major factors that affect plant growth and
productivity by limiting the quality, quantity and availability of staple foods. Major diseases
of crop plants caused by plant pathogens are a considerable threat to global food security.
The coevolution of plant pathogens and their hosts has resulted in highly adapted microbial
invasion strategies and counter-defense mechanisms in plants. Plants have developed an
array of structural, and chemical defenses to protect themselves from extensive damage
caused by pathogens. Understanding how plants defend themselves against disease-causing
organisms is of fundamental importance, in order to develop highly disease-resistant plant
species and protect our food supply. A detailed study of the mechanisms by which plant and
pathogenic organisms interact provides sustainable practice methods and solutions for the
control of plant disease in agricultural crops. Uncontrolled plant diseases may result in lower
crop yield and higher food prices or in poor quality of food, which is unfit for consumption.
Some plant diseases may eliminate entire plant species while others affect the beauty and
landscape of our environment. Plant-pathogen interaction studies help in elucidating the
signaling mechanisms by which plant cells cope with a stress situation. Also investigations
on plant-pathogen interactions help us in determining how organisms from different
kingdoms communicate with each other.
Plant pathology is the study of all aspects of plant diseases, including causal agents, their
diagnosis, mechanisms by which disease is induced, physiological effects, methods of
preventing or controlling the disease and reducing the damage caused.
Page 5
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 1
Discipline: Botany
Paper: Plant Physiology
Lesson: Plant Defense against Pathogens-I
Lesson Developer: Anita Thakur
Department/College: Department of Botany,
University of Delhi
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 2
Table of contents
Plant Defense against Pathogens-I
• Introduction
• What study plant pathogen interaction
• Plant disease
• Types of plant-microbe relationships
• Constitutive and inducible defenses
• Plant pathogens and their strategies of pathogenesis
• Plant pathogens
• Types of plant pathogens and their modes of entry in host
plants
• Plant defense systems
• Structural defenses
• Chemical defenses
• Enzymes and Proteins
• Summary
• Exercise/Practice
• Glossary
• References/bibliography/ further reading
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 3
Learning outcomes
The student will be able to
• Understand the basic concepts of plant-pathogen interaction
• Learn the types of host-pathogen interactions
• Understand the concepts of disease, injury, and the signs and symptoms of plant
pathogenic agents
• Explain the various defense mechanisms adopted by plants
• Describe terms like pathogenicity, non-host, non-pathogen, host range.
• Differentiate between constitutive and induced defenses
• Explain the various structural barriers present in plants which help in plant defense
against pathogens
• Become familiar with chemical compounds secreted by plants which play role in
defense
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 4
Introduction
Why study plant-pathogen interaction?
Plants are continuously confronted with a wide range of potential pathogens in their
environment. Under favorable conditions, plant pathogenic microorganisms such as fungi,
bacteria and viruses, can multiply and spread rapidly through plant populations to cause
severe outbreaks of disease. Although plants are immobile and lack an immune system in
comparison to animals, each plant cell possesses both a preformed (constitutive) and an
inducible defense capacity. Since plants are the primary producers in an ecosystem and are
a rich source of nutrients and energy for other organisms, including humans, the health of
plants is of vital importance. Disease is one of the major factors that affect plant growth and
productivity by limiting the quality, quantity and availability of staple foods. Major diseases
of crop plants caused by plant pathogens are a considerable threat to global food security.
The coevolution of plant pathogens and their hosts has resulted in highly adapted microbial
invasion strategies and counter-defense mechanisms in plants. Plants have developed an
array of structural, and chemical defenses to protect themselves from extensive damage
caused by pathogens. Understanding how plants defend themselves against disease-causing
organisms is of fundamental importance, in order to develop highly disease-resistant plant
species and protect our food supply. A detailed study of the mechanisms by which plant and
pathogenic organisms interact provides sustainable practice methods and solutions for the
control of plant disease in agricultural crops. Uncontrolled plant diseases may result in lower
crop yield and higher food prices or in poor quality of food, which is unfit for consumption.
Some plant diseases may eliminate entire plant species while others affect the beauty and
landscape of our environment. Plant-pathogen interaction studies help in elucidating the
signaling mechanisms by which plant cells cope with a stress situation. Also investigations
on plant-pathogen interactions help us in determining how organisms from different
kingdoms communicate with each other.
Plant pathology is the study of all aspects of plant diseases, including causal agents, their
diagnosis, mechanisms by which disease is induced, physiological effects, methods of
preventing or controlling the disease and reducing the damage caused.
Plant defense against pathogens I
Institute of Lifelong Learning, University of Delhi 5
Plant disease
Plants are considered healthy when they can carry out their physiological functions to the
best of their genetic potential. Disease, in a broad sense, is any physiological abnormality or
significant dysfunction of normal physiological processes in plants, caused by a
microorganism or an abiotic factor. When a plant, or any of its plant parts, is not able to
carry out the essential functions because of interactions with pathogenic microbes,
parasites, or adverse environmental factors, then the plant is said to be diseased.
Figure: Possible disease symptoms in a plant
Source: ILLL
In a diseased plant, the activities of the cells are disrupted, altered, or inhibited, and the
cells malfunction or die. At first the affliction is invisible and localized to one or a few cells.
Soon, the reaction spreads and the alterations in the affected plant parts become visible.
These visible changes are referred to as symptoms of the disease. Symptoms are the
internal or external adverse changes in a plant or plant part, produced as a result of
infection caused by an organism or any unfavorable environmental condition. Signs are
physical indications of the presence of a disease-causing agent. The visible and measurable
effects or alterations exhibited by a plant suffering from disease are a measure of the extent
of disease in the plant. Disease in plants, thus, can be defined as a series of adverse
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