This document discusses different criteria for classifying plant diseases. It describes classification based on mode of perpetuation (soil-borne, air-borne, seed-borne), infectious nature (infectious vs. non-infectious), number of pathogen generations (single-cycle, multi-cycle, polyetic), extent of plant parts affected (localized, systematic), cause of disease (biotic, abiotic, mesobiotic), occurrence and geographic distribution (epidemic, endemic, sporadic, pandemic), plant part affected, crop affected, and symptoms produced. For each criteria, examples are provided such as damping off for soil-borne diseases and powdery mildew for air-borne diseases. The key points of classification

1. Muhammad Saeed Siddiqui
Department of Botany
GPGC No 1 Abbottabad
Roll No: BOT-19-27

2. By
Muhammad Saeed Siddiqui

3. Classification on the basis of different
criteria:
1. Mode of perpetuation and primary infection.
2. Infectious nature.
3. Production and spread of the inoculums or number of
pathogen generations.
4. Extents of plant parts affected.
5. Causes of the disease.
6. Occurrence and geographic distribution.
7. Plant part affected.
8. Crop plants affected.
9. Symptoms produced on host plants.

4. On the basis of Mode of perpetuation and
primary infection:
It is of three types
1. Soil borne diseases
2. Air borne diseases
3. Seed borne diseases

5. Soil borne diseases
• The pathogen survive in the soil or on the infected plant
debris lying in the soil either as their resting spore or as
mycelia strand.
• They all attack the root system of host plants.
• E.g Damping off (Pythium sp.), seedling blight (phytophthora,
Fusarium sp.)

6. Air borne diseases
• Some pathogen infect the host plant through
air and bring primary and secondary infection.
• E.g. Rusts, powdery mildews
Seed borne diseases
• Some pathogen survive as dormant mycelium
or other propagative structures in the seeds of
host plants.
• E.g. Loose smut of wheat (internally seed
borne)

7. On the basis of infectious nature
• 1) infectious plant diseases:
• These disease are caused by living agents, the pathogen. All
the pathogens are parasitic on plants . These are
characterized by the ability of the pathogen to grow and
multiply rapidly.
• e.g. Powdery mildew, Rusts
• 2) Non-infectious diseases:
• These disease do not spread from plant to plant (non
infectious). These are caused by abiotic factors ( Physiological
disorder, lack of nutrients).
• e.g. black heart of potato (lack of oxygen)

8. On the basis of production and spread of the
inoculum or number of pathogen generation
1. Single cycle or monocyclic disease:
• The increase of disease is mathematically analogous to
simple interest money.
• Those disease which have only generation in one cropping
season.
• E.g. loose smut of wheat

9. On the basis of production and spread of the
inoculum or number of pathogen generation
2. Multiple cyclic or polycyclic disease:
• The increase in disease is mathematically analogous to
compound interest of money.
• Those disease which have more than one generation in a
cropping season.
• E.g. late blight of potato

10. On the basis of production and spread of the
inoculum or number of pathogen generation
3. Polyetic diseases:
• These are also polycyclic diseases but they complete their
disease cycle in more than one year.
• e.g. Cedar apple rust

11. On the basis of extent of plant parts
affected
1. Localized:
If they affect only specific organ
or parts of the plants.
e.g. Root rot, leaf spot
2. Systematic:
If entire plant is affected.
e.g. downy mildew,
Damping off

12. On the basis of cause of the disease
Three types of diseases on the basis of the cause
1. Biotic disease
Fungal disease, bacterial disease, phytoplasma disease,
phanerogamic disease, nematode disease.
2. Mesobiotic disease
Disease caused by virus or viroid.
3. Abiotic disease
By abnormal environmental condition

13. On the basis of occurrence and
geographic distriution
1. Epidemic disease:
• A disease usually occurs widely but periodically in a
destructive form is reffered as epidemic or epiphytotic
disease.
• e.g. late blight of potato – Irish famine (1845)

14. On the basis of occurrence and
geographic distriution
2. Endemic:
• Constantly present in a moderate to severe from and is
confined to a particular country or ditrict.
• e.g. club root of cabbage in Nilgiris, black wart of potato and
onion smut

15. On the basis of occurrence and
geographic distriution
3. Sporodic disease
• Occur at very irregular intervals and locations and in
relativity fewer instances.
• e.g. udbatta disease of rice, angular leaf spot of cocumber

16. On the basis of occurrence and
geographic distriution
4. Pandemic disease
• An epidemic occuring worldwide, or over a very wide area,
crossing international boundaries and usually affecing a
large number of population.
• e.g. Wheat rust UG99

17. On the basis of organ and plant part
affected
• Fruit disease e.g Apple scab
• Root disease e.g. Root rot of papaya
• Leaf disease e.g. Leaf spot of cotton
• Seedling disease e.g. damping off of seedling

18. On the basis of crop plant affected
• Cereal disease e.g. wheat, barley and oat
• Pulses disease e.g. ascochyta blight of chickpea
• Millet disease e.g. green ear disease of bajra
• Vegetable disease e.g. early blight of tomato
• Fruit disease e.g. apple scab
• Ornamenatal plant disease e.g. chrysanthimum stunt
• Forests plant diseases e.g. sudden oak death

19. On the basis of symptoms produced
on host plants
1. Downy mildew
• Symptoms appears as yellow to white patches on the uper
surface of leaves.
• This disease is caused by family peronosporaceae (Fungus).
• e.g. DMD of grapevine

20. On the basis of symptoms produced
on host plants
2. Powdery mildew
• Symptoms appears as white powdery mass on upper surface
of leaves, inflorescence.
• E.g. mango powdery mildew, Pea PMD

21. On the basis of symptoms produced
on host plants
3. Leaf curls
• Curling, thickening and distoration of leaves.
• E.g. peach leaf curl (Fungus), Tomato leaf curl (Virus)

22. On the basis of symptoms produced
on host plants
4. Galls
• Enlarged parts of plant organs, usually caused by excessive
multiplication or enlargement of plant cells.
• E.g. clubroot – enlarged root, bacterial gall by
agarobacterium

23. On the basis of symptoms produced
on host plants
5. Scab
• A roughened, crust-like diseased area on the surface of a
plant organ.
• E.g. apple scab and pear scab

24. On the basis of symptoms produced
on host plants
6. Dieback
• Progressive death of shoots and twigs generally starting at
the tip of infected plant part.
• E.g. shoot dieback of apple

25. On the basis of symptoms produced
on host plants
7. Anthracnose
8. Damping off
9. Rots
10. Leaf spot
11. Blight
12. Spot blotch
13. Rusts
14. Canker
15. Smut
16. Wilt

26. Thanks for your
attention
Submitted to Professor
Sarfaraz sb of department of
Government Postgraduate
College No 1 Abbottabad