Course Content
Introduction
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Some facts to remember
Types of pathogen dispersal
Facts about Pathology
Glossary
Types of disease
Disease and their causative agent
Necrosis
Asexual and Sexual fruiting bodies
Reproduction in fungi
Method of sexual reproduction @GPS2
Flagella arrangement
Gram positive and negative bacteria
Various Nematodes
Deficiency symptom
Chemicals in plant disease control
Some facts about Mushroom
Disease and their causative agent in various fruits
Viral disease in fruits and their vectors
Disease and their causative agent in various vegetables
Viral disease in vegetables and their vectors
Disease of Agronomical crops
Vectors and their disease transmission
Viral disease and their transmission agent
Plant growth regulators effects on plant disease
Toxins
Principle of plant disease control (PPD)
Disease and their fungal vectors
Indirect penetration
Plant growth regulators (PGRs) and its relation with pathology
Plant growth regulators (PGRs) and its relation with pathology
Defense mechanism in Plants
Difference between compound interest disease and simple interest disease
Soil solarization and sterilization
Copper fungicide
Types of resistance
Integrated plant disease management (IPDM)
Difference between Zoospore and Zygospore
Disease forecasting of late blight
Agricultural Pathology Essentials: Rahul’s Quick Guide for Master’s Prep

Defense mechanism in Plants

  1. Structural defense mechanism

A. Preexisting structural defense mechanism

i) Waxes

ii) Cuticle and epidermal cells: In lin seed, cuticle acts as barrier against Malampsora lini.

iii) Sclerenchyma cells: blocks pathogen that causes angular leaf spots.

iv) Structure of natural openings:

a) Stomata:

Stem rust of wheat can enter its host only when stomata is open.

 

b) Lenticels:

  • Small and suberized lenticels offer resistance to potato scab (Streptomyses scabies)

 

B. Post-infectional structural defense mechanism/ induced structural barriers

I. Histological

a) Cork layer:

  • Induces formation of large number of cork layers when infected by pathogen.

 

b) Abscission layer:

  • Infected area shrivels, dies and sloughs off.
  • Xanthomonas pruni on peach leaves.

 

c) Tyloses:

  • No tyloses formed after pathogen invasion.

 

II. Cellular defense structures

a) Hyphal sheathing:

  • Cellulosic sheath formed by extension of cell wall, become infected with phenolic substances and prevents further spread of the pathogen.
  • Eg: Observed in flax infected with Fusarium oxysporum sp. lini.
  1. Biochemical defense mechanism:

A. Preexisting:

a) Inhibitor released by plant in its environment.

  • Tomato leaves secretes exudates which are inhibitory to Botrytis cinerea.
  • Resistant varieties of apple secrete waxes that prevents germination of Podosphaera leucotricha (powdery mildew of apples).
  • Root exudates of marigold contain α-terthinyl inhibitory to

 

b) Inhibitors before infection

  • Chlorogenic acid in potato inhibits common scab bacteria, Streptomyces scabes and wilt pathogen Verticillium alboatrum.
  • Glucanases and chitinases breaks cell wall of the pathogen.

 

B. Post infectional or induced defense mechanism

a) Phytoalexins

  • First used by Muller and Borger (1940).
  • Produced by plants after stimulation by phytopathogenic microorganism or mechanical injury.
  • Not produced during compatible biotrophic infections.

 

b) Hypersensitive response (HR)

  • First used by Stakwan (1915) for rust fungus, Puccinia graminis
  • Refers to localized induced cell death.
  • Pathogen produced signal molecules known as elicitors

 

c) Plantibodies

  • Encodedby animal genes but produced in and by the plant.
  • Plantibodies against antichoke mottle crinkle virus.
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