A brief Power Point Presentation on disease cycle for students about their academics on professional level. Content for this compilation (Power Point Presentation) was collected from Different sources: Internet, books, social media, research papers, websites etc. and acknowledged all these sources to provide such a helpful content. This Presentation was prepared and presented during Bachelors In Agriculture (Session 2014-2018) at "University College of Agriculture and Environmental Sciences, Baghdad-ul-Jadeed Campus, The Islamia University of Bahawalpur (Pakistan)" as an Assignment on the topic of "The Disease Cycle" with the collaboration of Student fellows Muhammad Amir Shehzad and Muhammad Farhan. I hope, content might be helpful for student on academic level. Best Regards Muhammad Raza Ullah Tariq

2.  Muhammad Raza Ullah Tariq
 Muhammad Amir Shehzad
 Muhammad Farhan
Presented BY:
Session: 2014-2018
Semester: 4th
Section: B
University College Of Agriculture And Environmental Sciences
The Islamia University Of Bahawalpur
Pakistan

3. The Disease Cycle

4. Disease
Any disturbance in the physiological functions of living organism.
Disease Cycle
In every infectious disease a series of more or less distinct events
occurs in succession and leads to the development and
perpetuation of the disease and the pathogen. This chain of events
is called disease cycle.

5. Stages Involved
In
The Development Of Disease

6. 1. Inoculation
2. Penetration
3. Infection
4. Growth And Reproduction
5. Dissemination

8. Inoculation
It is the initial contact of a pathogen with a site of plant where
infection is possible.
Inoculum
The pathogen that lands on the host or
Any part of pathogen that can initiate infection.

9. Types of Inoculum
Primary inoculum
Survives during dormant period and causes the first infection.
Secondary inoculum
Produced from primary infections.

10. Landing or arrival of inoculum
Most pathogen carried to the host plant by wind ,insects and water.
Only a small number actually land on susceptible plants.
Vector born pathogen are much more efficient since the vectors have
an attraction for plants.
Examples:
Germination of spores and seeds(fungus)
Hatching of nematode eggs.
Attachment of pathogen to host(virus and bacteria).
Recognition between host and pathogen(pathogen recognizes the
host).

11. Penetration
Initial invasion of host by a pathogen.
 Direct penetration
 Penetration through natural openings
 Penetration through wounds

12. 1 Direct penetration
Direct with haustoria
Direct subcuticular only
Direct intercellular mycelium
Direct intercellular mycelium with haustoria
Direct with appresorium (A), penetration peg (PP) and
intracellular mycelium (IM)

18.  The most common type of penetration by fungi and nematodes and
the only type by parasitic plants
 Fungi uses a fine hyphae produced by a spore or mycelium or
penetration peg produced by an appressorium
 This is formed at the point of contact by the host

19.  The penetration is through mechanical force and softening of the
cell walls by an enzyme.
 Most fungi form an appressorium at the end of the germ tube.
 Then the penetration peg emerges from the flat surface of the
appressorium and pierces the cuticle and the cell wall.

20.  The peg grows into the fine hyphae then reaches in normal diameter
once it is inside the cell.
 A s in the case of apple scab, the fungus penetrates only the cuticle and
stays between the cuticle and the cell wall.
 Parasitic plants also penetrate in the same way.

21. 2 Penetration through Natural
openings
 Through stomata
 Through lenticels (opening on fruits, stems and tubers-filled with loosely
connected cells which allow the passage of air)
 Hydathodes (permanently open pores at the margins and tips of leaves)

23. 3 Penetration through wounds
 Through various types of wounds and injuries
 Natural cracks between main and lateral roots
 Openings made by fungus

24. Infection
Establishment of pathogen with vulnerable cells or tissues of the
host and obtain the nutrients from them.
Successful infection will produce symptoms.

25. Incubation period
The time interval between inoculation and appearance of
disease symptoms.
Latent infection
The state in which a host is infected by the pathogen but
does not show any symptoms.

26. Growth and Reproduction
The pathogen will grow and multiply within the infected host.
 Fungi- spores
 Viruses- replicated by the cell
 Nematodes- reproduce by means of eggs

27. Dissemination of pathogen
 While airborne-spores touch with wet surfaces-get
trapped-air movement stops/ rains- washed out
 From the air- brought down by rain drops
 Winds also helps spreading by blowing away rain
splash droplets containing pathogens.
Pathogens are disseminated by several ways:
 By Air

28.  Transmitted by insects when they feed from plant to plant.
 Nematodes can also transmit viruses internally.
 By Water
Pathogens in the soil-dissemination by rain/ irrigation water that moves
on the surface/ through soil.
By insects , nematodes & other vectors

29.  Through handling of diseased and healthy plants
 Tools (pruning shears)
 Transporting contaminated soil on their feet/ equipment's
 Contaminated container
 Using infected seeds/ nursery stock.
By seeds and transplanting process
 Transported to other fields
 Are sold and transported to other areas
By human

30. DEMO

32. Thank you
for
Attention