Pathogenesis Process described in detail.

1. DSE – BOT 8102T – PLANT MICROBE INTERACTION(PMIs)
TOPIC – PATHOGENESIS
Submitted to – Dr. PRAVEEN GEHLOT Submitted by – KARISHMA
Class – M.Sc. BOTANY 1ST SEM.

2. CONTENT :-
1.Pathogenesis Introduction & Defenition
2.Parasitism & Pathogenecity
3.Disease Cycle & Development
4.Events in Disease Cycle -
a) Inoculation
b) Penetration
c) Perception and Recognition between Host and the pathogen
d) Infection
e) Invasion
f) Growth and Reproduction of the pathogen,
g) Dissemination of the pathogen, and
h) Survival of the pathogen.
In some diseases there may be several infection cycles
within one diseases cycle.

3. PATHOGENESIS INTRODUCTION & DEFENITION :-
Pathogenesis :- is the chain of events that led to development of
disease in the host (or) sequence of progress in disease
development from the initial contact between the pathogen and
host to the completion of the syndrome.
1. It can include factors which contribute not only to the onset of
the disease or disorders, but also to it’s progression and
maintenance.
2. This process which involves Inoculation, Penetration,
Establishment of infection, Colonization (Invasion), growth
and reproduction of the pathogen, Dissemination of the
pathogen, and Survival of the pathogen is called
pathogenesis.

4. Parasitism -
■The removal of food by a parasite from its host.
In some cases, both the plant & the microbe benefit
from the association called symbiosis.
Pathogenicity -
■The ability of the parasite to interfere with one or more
of the essential functions of the host, causing disease.
■ Parasitism plays an important role, but not the
most important role in pathogenicity.

5. Disease Cycle
Pathogenesis/ Disease Cycle – a series of events
that occur in succession during a pathogenic
relationship of a pathogen and host that leads
to disease.
The study of disease cycle generate information
about -
- Source of perpetuation of pathogen
- Mode of spread
- Help in formulation of control measures
A pathogen's life cycle may follow events similar
to the disease cycle.

6. Disease Development
-Disease triangle
-Disease tetrahedron

8. Inoculation -
• It is the process by which the pathogen come in
contact with its host.
- Inoculum: any part of pathogen that can cause disease
(may consist of single unit of the pathogen or whole of
the pathogen).

9. Penetration
The process by which the pathogen enter its host
Varies in different pathogens.
The penetration process is divided into -
• Pre-penetration process
• Penetration
• Post penetration process
Penetration Process Types
• Direct penetration
• Indirect penetration
— Fungi may penetrate in either way
— Bacteria mostly enter through wounds and some time by
natural openings
— Viruses, viroids, phytoplasma etc.
by mechanical means (wounds) and by vector.

12. PERCEPTION -
Perception
means how
pathogen and
host recognize
each other. It
may
take place
directly or
indirectly.

13. Recognition Between Host & The Pathogen
 It is assumed that when a pathogen comes in contact
with the host cell, an early events takes place that
trigger a fairly rapid response in each organism which
either allows or impedes further growth of the pathogen
and development of the disease.
 The nature of early events is not known with certainty
in any host-pathogen combination;
— however, it may be one of the many biochemical
substances structures and pathways.
— These may include specific host signal compound or
structures or either of them may induce specific action or
formation of specific products by the other organism.

14. Infection -
 Establishment of organic relationship of the pathogen
with susceptible cells of the host plant is called
infection.
 Infection process is affected by various factors -
— Resistance & susceptibility of the host
— Aggressiveness & virulence of the pathogen
— Environmental factors
— Host nutrition & pH
— Incubation period ( depends upon host-
pathogen combination, stage of host and
environment etc.

15.  Infection is of
different types –
1. Localized infection
2. Systemic infection
3. Latent infection

16.  Invasion and reproduction are the two concurrent
stages that occur during infection as pathogen
invade different cells, grow & multiply.
INVASION
 Pathogens enters to variable extents inside the host.
 Different pathogens invade their host as:-
— Ectoparasite e.g. powdery mildew
— Endoparasites e.g. wilts, viruses etc.
Sub-cuticular pathogens (Apple scab- Venturia
inequalis)
Sub-epidermal pathogens (wheat rust )
Vascular pathogens (Pseudomonas solanacearum)
— Ecto-endo parasites e.g. potato canker
(Corticium solani).

18. Growth & Reproduction
 Different pathogens grow intercellulary & intracellularly inside
their host.
 Growth & reproduction rate depends upon invasion behaviour
of the pathogen.
 Method of reproduction -
— Asexual
— Sexual
— Replication in case of majority of sub-microscopic pathogens.
 Growth and reproduction of the pathogen is affected by -
─ Pathogen aggressiveness
─ Susceptibility of the host tissue
─ And environmental factors.

19. Dissemination of
The Pathogen-
 Transfer of
inoculum -
a.) Passive - wind,
water, insects, man,
animals, machinery
b.) Active - move on
own power
bacteria (some)
Pythium(Zoospores)
Fungi- spores
expelled forcibly

20. Pathogen Survival -
1. In infected crop debris
2. In seed
3. In soil
4. On growing plants
5. Infected material on host plants
6. In propagating material
7. Alternate host
8. Collateral host
9. As dormant-structures e.g. sclerotia.

21. Refrences –
1. Fungal Pathogenesis in Plants and Crops (2nd edition) by P. Vidhyasekaran
2. Plant Diseases (9th edition) by R.S. Singh
3. Class notes by Dr. Praveen Gehlot
4. http//wikipedia.com/pathogenesis
5. http//googlescholer.com/pathogenesis etc.