This document discusses types of plant disease epidemics. It defines an epidemic as a disease occurring year after year at a moderate to severe level or an increase in disease within a population. Epidemiology is the study of disease in populations. The main types of epidemics discussed are monocyclic, polycyclic, and polyetic. Monocyclic diseases have one infection cycle per season, while polycyclic diseases can have multiple cycles from secondary infections. Polyetic diseases take multiple years to produce inoculum and may not cause new infections every year. Examples of each type are provided.

2. Course tittle:
Epidemiology and Forecasting of Plant Diseases
PAT 507 (2+1)
Presentation on : Types of Epidemics
Presented by :
ARUNKUMAR
PALB8315
UNIVERSITY OF AGRICULTURAL SCIENCES,
BENGALURU
COLLEGE OF AGRICULTURE, GKVK

3. EPIDEMIC
Epidemic: A disease which is more or less constantly
occurring year after year in a moderate to severe form
(OR)
Increase of disease in population
(OR)
A similar definition of an epidemic is the dynamics of change
in plant disease in time and space.
Epidemiology: Study of disease in populations

4. TYPES OF EPIDEMICS
Monocyclic
Polycyclic
Polyetic

6. Monocyclic diseases :
 Pathogen completes just one cycle per season
 Primary inoculum is the only inoculum available for entire
season
 No secondary inoculum and infection

7. Monocyclic disease

8.  Pathogen has low birth rate and death rate
 No or low dispersal rate
 Soil borne diseases are typically monocyclic
Cotton wilt
Tomato wilt
 Amount of disease may slowly increase from year to
year

9.  Also known as “simple interest” diseases
 Equation : Xt = QRT
 Graphically, disease caused by monocyclic
pathogens looks like a saturation curve

10. Monocyclic disease

11. Examples
Fusarium wilt of tomato Smut of wheat Ergot of bajra

12. Polycyclic disease :
Pathogen completes several infection cycles per
season
Primary inoculum consists of sexual spores or
sclerotia
Once after primary infection, large amount of
asexual spores will be produced at each
infection cycle, which can cause new infection

13. Polycyclic disease

14.  Pathogen has high birth rate and death rate
 High dispersal rate
 Air borne diseases are typically polycyclic
Powdery mildew
Wheat rust

15.  Also known as “compound interest” diseases
 Equation : X = X0 e rt
 Graphically, disease caused by polycyclic pathogens
looks like a sigmoid curve

17. Life Cycle of Puccinia graminis tritici

18. Examples
Paddy blast Late blight of potato Black stemrust of
wheat

20. Bimodal polycyclic diseases:
It affects two different growth stages of the
crop
Examples :
Blossom and fruit infection of Pear
Blast of Ragi i.e Nursery and Tillering

21. Polyetic disease :
 Some pathogens take several years to produce the
inoculum
 May not cause new infections in a year
 Amount of inoculum does not increase greatly within a
year
 Inoculum may increase steadily from year to year and
cause severe outbreaks

22. Also, known as “multiyear disease”
It is monocyclic disease over years
Pathogen survives on perennial hosts like
trees

23. Polyetic disease

24. Branch death, or flagging,
at multiple locations in
the crown of a diseased
elm
Dutch elm
disease
Ophistoma ulmi
Vector : Bark elm
Beetle

25. Examples
Dutch elm disease Pear decline Citrus tristeza

26. Conclusion

27. References :
Wikipedia
https://www.apsnet.org/edcenter/advanced/
topics
Plant disease Epidemiology
Subhashini sinha
Manjula varma