Plant pathology is the study of plant diseases caused by pathogens like viruses, bacteria, and fungi. For a disease to develop, there must be a susceptible host plant, a pathogen, and favorable environmental conditions. To diagnose a disease, the causal organism is isolated from infected plant tissues and inoculated onto healthy plants to observe if it causes the same symptoms. Pathogens interfere with important plant functions like photosynthesis, respiration, membrane permeability, and nutrient transport. They do this by damaging chloroplasts, increasing respiration rates, degrading membranes, growing in vascular tissues, and altering permeability and transpiration. This affects the plant's ability to carry out functions like carbon fixation and water and nutrient translocation.

1. PLANT PATHOLOGY

2. Topic
 How a plant disease is diagnosed ?
 Describe the effect of pathogen on plants.

3. What is disease?
Disease is defined as a pathological
condition or physiological deviation
from normal functioning.

4. What is plant pathology ?
Plant pathology is the study of plant
diseases.
It is also known as phytopathology

5. Disease triangle
 During the development of a disease three
elements are required.
 Pathogen (disease causing virus, bacteria,
fungi)
 Susceptible host (plant)
 Favourable environmental conditions.

6. Disease triangle
When one of the element is not in
favourable condition disease will not
develop

7. Diagnosis of plant disease
For the diagnosis of disease Sir Koch gave the
principles
 Causal organism must be present on the disease
part of the plant
 That organism or inoculum should be cultured in a
culture medium and should observe the
morphological characters in that colonies formed by
pathogen in culture medium

8. Disease diagnosis
 From that culture, take inoculation of colonies
of pathogen and then inoculated to healthy
plant of the same species and symptoms of
disease should be noted and compare the
symptoms with effected plants. If the
symptoms are similar on the first and second
plant then that organism will be the
pathogen.

9. Disease diagnosis
 Inoculum should be taken from second
healthy plant and should be grown in culture
medium and again characters should be
studied.

10. Effect of plant pathogens
 Main pathogens are:
 Virus
 Bacteria
 Fungi

11. Effect of plant pathogens
The most important physiological functions
which are affected by pathogens are
 Photosynthesis
 Respiration
 Permeability of cell membrane
 Translocation of water and nutrients
 Transcription and translation

12. Photosynthesis
Pathogens interfere by
Cause chlorosis (yellowing of leaves) necrosis
(death of tissues).
Reduced growth.
Chlorophyll is reduced.
Photosynthesis is reduced.

13. Influence of viral infection.
 Reduce chloroplast amount.
 Reduction in chlorophyll content.
 Chloroplast abnormalities.

14. Influence of bacterial infection.
 Disorientation of chloroplasts.
 Suppression of carbon dioxide fixation.

15. Effect of fungal infection.
 Reduce chloroplast content.
 Loss of chlorophyll.
 Inhibit electron transport.

16. Respiration
 Respiration increases during pathogen attack
 The rate continues to rise during
multiplication and sporulation of the
pathogen.
 Changes metabolism.

17. Effect of virus
 Non hypersensitive hosts.
Slightly increase in respiration rate of
inoculated leaves.
►Hypersensitive hosts.
a much more considerable increase in
respiration rate than systemic hosts.

18. Effect of bacteria
 Resistant tissues:
Immediate increase in oxygen
consumption.
►Susceptible tissues:
They do not reflect an increase in
respiration until about 30 hours of
inoculation.

19. Effect of fungi
 Respiration rate is increased in diseased
plants
 In early stage of disease, synthetic processes
induce high rates of respiration.
 In the late stages injury and decomposition of
tissues lead to increase respiration.

20. Membrane permeability
 Pathogens change the permeability by :
Mechanical injury
Enzymatic degradation
Toxins
Occur when host pathogen interaction is
compatible.

21. Translocation of water and nutrients
 Pathogens affect the function of root
(absorb less water )
►Growth in xylem vessels interfering with
translocation.

22. Conti..
 Interfere with water economy of plant by
causing excessive transpiration
 For example. Fusarium crown rot

23. Effect of virus
 Leads to a reduction in transpiration rate
 Reduced leaf stomata
 Accumulation of carbohydrates in leaf tissue
 Phloem necrosis, gummosis(release of gum)and
tylosis(abnormality in trachaeids)

24. Effect of bacteria
 Enter the vascular systems, both xylem and
phloem, through wounds

25. Effect of fungi
 Water absorption decreases
 Vascular diseases
Decrease the water flow
►Polysaccharides (e.g. tylosis) produced by
fusarium – obstruction of normal water
translocation

26. Effect in translocation of water and
inorganic nutrients
 Root damage
 Damping –Off fungi:
cause injury to roots
 Root rot fungi, bacteria:
inhibit root hair production

27. Conti..
 Most Nematodes and some Viruses:
alter permeability of root cells.
►Xylem gets destroyed
►Rot or canker pathogens
►Gall formation

28. Conti…
 Xylem get clogged
 Pathogen secretions

29. Effect in translocation of phloem
 Obligate fungal parasite
 Respiration increases
 Photosynthesis decreases

30. Effect of viruses
 Death of phloem
 Inhibit enzymes that break down starch into
smaller molecules

31. Transcription and translation
 Effect on Transcription
Change composition , structure or function of
chromatin associated with cell DNA
Increase in the activity of enzymes that break
down RNA

32. Conti
 Effect on translation
Need high energy
Increased production of phenolics
Resistant plants have high protein synthesis

33. Thank you