CLASSIFICATION OF PLANT DISEASE BY SOMBIR KASHYAP MDU ROHTAK HARYANA PLANT PATHOLOGY

1. • SUBMITTED BY
• SOMBIR KASHYAP
• MSC FINAL
• 5077
• SUBMITTED TO
• DR SUNDER SINGH
ARYA
• PROFESSOR
DEPARTMENT OF
BOTANY MDU ROHTAK

2. DEFINITION
Plant disease – an impairment of the normal state of a
plant that interrupts or modifies its vital functions.
Or
“ A malfunctioning process that is caused by continuous
irritation and produce symptoms’’.
The organisms that cause disease are called pathogen.
E.g. bacteria, fungi, viruses and protozoa etc.
The study of disease condition is called pathology, also
known as phytopathology

3. Difference between healthy and diseased plant
HEALTHY PLANT
• Normal physiological
functions including
• Normal cell division,
differentiation and
development
• Absorption of water and
minerals from the soil and
translocation
• Photosynthesis
• Reproduction
SICK /DISEASED PLANT
• A plant would not have
all of these functions

4. CLASSIFICATION ON THE BASIS OF CAUSE
• Infectious disease – a disease that is caused by
a pathogen that can spread from a diseased
plant to healthy plant.
Disease is caused by living organisms.
It is also known as parasitic and biotic disease
E.g. fungi, bacteria, virus, phytoplasma,
nematodes, higher parasitic plants etc.
Such as Pectobacterium atrosepticum (a
potato pathogen)

5. • Non-infectious disease – disease that is caused by non-living
organisms.
 Could not be spread to other healthy plant
 Such as factors
 Unfavourable environment e.g. frost injury, physiological wilt.
 Too low/high temperature
 Lack/excess of soil moisture
 Air pollution
 Nutrient deficiency- e.g. khaira disease in rice due deficiency of
Zinc
 Mineral toxicity
 Soil acidity or alkalinity

6. ON THE BASIS OF OCCURRENCE AND
GEOGRAPHIC DISTRIBUTION
• Endemic – when a disease more or less constantly prevalent from year to year.
 These diseases are natural to one country or part of the earth.
 E.g. wart disease in potato in Darjeeling
• Epidemic – such a disease occurs periodically but in severe state involving major
area of crop.
 It may be constantly present in the locality.
 This is because the environmental conditions favourable for rapid disease
development occur only periodically.
 E.g. rust, late blight, mildews.
• Pandemic –
 E.g. late blight of potato
• Sporadic – these diseases occur at very irregular intervals and locations and in
relatively few instances.
 A given disease may be endemic in one region and epidemic in another.
 E.g. leaf blight, wilt.

7. On the basis of natural perpetuation and mode of
infection
• Soil borne – pathogen survive in soil or on infested
plant debris lying in soil either as their resting spores or
as mycelial strands and rhizomorphs.
 E.g. Root rot , wilt and seedling blight
• Air borne – the micro-organisms are spread through air
and attack the plants causing disease
 E.g. blight, rust, powdery mildew.
• Seed borne – the micro-organisms are carried along
with seeds
 E.g. damping off

8. On the basis of symptoms
• Rust – caused by Basidiomycetes of the order Uredinales
 Mostly attack on leaves and stems
 Appear as numerous rusty, orange, yellow, or even white-
coloured spots that ruptured epidermis
 Some form local spots, swelling and even galls
 E.g. stem rust of wheat caused by Puccinia graminis,
yellow or stripe rust of wheat , rye, and barley is caused P.
striiformis, leaf rust of wheat and rye by P. triticina , leaf
rust of barley , crown rust of oats , corn rust , sugarcane
rust , sorghum rust ,coffee leaf rust ( Hemileia vastatrix ) ,
cedar apple rust ( Gymnosporangium juniperi ) etc

9. Rust on wheat leaf, stripe,stem

10. Rust on sugarcane leaf

11. Coffee leaf rust

12. • Smuts – caused by a fungus of the order Ustilaginales.
 Many types of plant affected , but smuts are important in
cereals and other grasses.
 They produce a mass of black , powdery spores and no
grains are formed.
 The symptoms include the formation of masses of lack soot
like spores and infected plant shows some degrees of
distortions.
 E.g. loose smut of wheat and barley caused by Ustilago
nuda tritici
 It is world wide in distribution
 In India, occurs in all states where wheat is grown, losses
may be up to 40 per cent in some area.

13. Smut in wheat and barley

14.  Karnal bunt of wheat –Mitra reported in 1930 and by 1985 also reported
from W.B.,Gujrat, Bihar, M.P.
 Pathogen- Tilletia indica
 The disease is usually noticed only when the partly smutted and broken
kernels are seen in threshold grain.
 Although infected wheat is not toxic to humans or animals, wheat grain
containing more than 3% bunted kernels is generally considered unfit for
human consumption.
 Because the smut causes an unpleasant odour , colour and taste in wheat
product.
 All the spikes on a plant are not infected , and within a spike only a few
spikelets are attacked .
 it becomes evident when the grains have developed.
 Grains have been partially, rarely wholly , converted into bunt balls
enclosed by the pericarp.

15. Karnal bunt in wheat

16. • Rots – diseases that infect underground plant parts.
 They can be caused by fungi, bacteria or soil-borne nematodes.
 Infections lead to disintegration of underground tissues are difficult
to manage because they are not visible.
 E.g.
 Rhizoctonia and Phytophthora are root rots.
 These two fungi attack the root system of many different plants.
 Bacteria can only enter the host tissue through wounds.
 Crown and collar rots occur at the soil line where the plant
emerges.

17. crown rot infection on Beta vulgaris

18. • Wilt – a wilt disease is any number of disease
that affect the vascular system of plants.
Bacterial wilt of Cucurbits is caused by the
bacteria Erwinia tracheiphila.
Bacteria spread through the xylem vessels
from the area of infection to the main stem
and the entire plant wilts and dies.
E.g. wilt disease in potato, tomato.

19. bacterial wilt symptoms displayed by a
muskmelon plant

20. Wilt in tomato

21. • Canker – a canker is a dead area in bark or
cortex of woody stems.
They are often large areas with definite
margin.
Dead bark splits and falls away.
An example is citrus canker (bacterial)

22. Citrus canker

23. • Powdery mildew – it is a fungal disease of foliage ,
stems, flowers and fruit where a superficial fungal
growth covers the surface of the plant.
 E.g. grapes, cucumbers, grasses, soyabean etc.
 Symptoms white, powdery spreading patches of fungus
on upper or lower surfaces, flowers and fruit.
 Sometimes tissue become stunted or distorted.
 Disease seldom kill their hosts but utilize their
nutrients, reduce photosynthesis , increase respiration
and transpiration and reduce yields by as much as 20
to 40%.

24. Powdery mildew of grape and soyabean leaves

25. Powdery mildew of cucurbits

26. • Downy mildew – it is caused by family
Peronosporaceae.
Many ornamental and edible plants including
peas, onions, lettuce, grapevines are affected.
Main symptoms are discoloured areas on upper
leaf surfaces; white, grey or purple mould below.
Timing is mainly summer and autumn,
particularly in wet conditions.
E.g. rose and lettuce.

27. Downy mildew on rose and lettuce

28. On the basis of organ they attack
Root disease –
Shoot disease –
Fruit disease –
Foliage disease –

29. On the basis of host plant
Cereal disease –
Vegetable disease –
Fruit disease –
Forest disease –
Ornamental disease –

30. On the basis of extent to which plant disease
associated with plant
Localised – these disease are limited to a
definite area of varying extents of an organ, or
only to a particular part of the plant.
Systematic – pathogen spreads throughout
the entire plant to varying extents and is
associated with almost every stage of plants
life cycle.

31. Based on pathogen generations
Monocyclic disease – those diseases which
have only generation in one cropping season
e.g. loose smut of wheat.
Polycyclic disease – those diseases which have
more than one generation in a cropping
season e.g. late blight of potato

32. • References
• George N. Agrios , Plant pathology 5th edition
• R.S. Mehrotra , Plant pathology 2nd edition