The document discusses how various plant pathogens like viruses, bacteria, and fungi can interfere with key physiological functions in plants such as photosynthesis, respiration, membrane permeability, translocation of water and nutrients, and transcription and translation. Pathogens are shown to reduce chloroplast function, chlorophyll content, and carbon fixation, while increasing respiration rates. They also impact membrane permeability, block translocation through vascular systems, and alter transcription and translation processes in the plant.

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2. INTRODUCTION
 Main pathogens are
 Virus
 Bacteria
 Fungi
 Physiological functions
 Photosynthesis
 Respiration
 Permeability of cell membrane
 Translocation of water and nutrients
 Transcription and translation
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3. PHOTOSYNTHESIS
 Interfere by chlorosis, necrosis, and reduced
growth and yield
 Reduce amount of photosynthetic surface
 Produce toxins that inhibit enzymes involved
 Stomata remains unpartially closed
 chlorophyll is reduced
 photosynthesis stops
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4. Influence of virus infection
 Reduce chloroplast amount
 Reduction in chlorophyll content
 Chloroplast abnormalities
 Reduction in photochemical activity
 Reduction in sucrose content
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5. Influence of bacterial infection
 Decrease in chloroplast storma
 Disorientation of chloroplasts
 Destroy of chloroplast integrity - HR
 Suppression of CO2 fixation
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6. EFFECT OF FUNGAL INFECTION
 Reduce chloroplast RNA content
 Loss of chlorophyll
 Inhibit photophosphorylation coupling
mechanism
 Inhibit electron transport
 Suppress CO2 fixation
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7. RESPIRATION
 Respiration increases during pathogen attack
 Rate Continues to Rise during Multiplication and
Sporulation of the Pathogen
 Declines to Normal or below-Normal Levels
 Rate Increases more Rapidly in Resistant Varieties
 Increased Respiration Depletes Plant’s Reserves
 Changes Metabolism
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8. Effect of viruses
 Non hypersensitive hosts
 Slightly increase in respiration rate of
inoculated leaves
 Hypersensitive hosts
 A much more considerable increase in
respiration activity than systemic hosts
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9. EFFECT OF BACTERIA
 Resistant tissue :Immediate increase in O2
consumption
 Susceptible tissue : Do not reflect an increase in
respiration until about 30 hours after inoculation
eg : pepper – Xanthomonas vesicatoria
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10. Effect of fungi
 Respiration rate is usually increased in diseased
plants
 In the early stage of disease, synthetic processes
induce high rates of respiration
 In the late stages injury and decomposition of
tissues lead to increase respiration.
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11. MEMBRANE PERMEABILITY
 Pathogens change the permeability by
 Mechanical injury
 Enzymatic degradation
 Toxins
 First detectable responses of cells
 Leakage of electrolytes
 Occur when host-pathogen interaction is
incompatible
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12. TRANSLOCATION OF WATER AND
NUTRIENTS
 Affect the function of root
- absorb less water
 Growth in xylem vessels interfering with
translocation
 Interfere with water economy of plant by causing
excessive transpiration
 Eg :Fusarium crown rot 1/1/2017
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13. EFFECT OF VIRUS
 Leads to a reduction in transpiration rate
 reduced leaf stomata aperture
 Accumulation of carbohydrates in leaf
tissue
 Accompanied by phloem necrosis and/or
gummosis, particularly in the later stage of
disease
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14. EFFECT OF BACTERIA
 Enter the vascular systems, both xylem
and phloem, through wounds
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Infection of Ralstonia
solanacearum on tomato
Infection of Xanthomonas spp. on
banana

15. EFFECT OF FUNGI
 Water absorption decreases
 Vascular wilt diseases
Decrease the water flow
 Polysaccharides (eg: tyloses) produced by
Fusarium - obstruction of normal water
translocation
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16. 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
Most Nematodes & Some Viruses
: Alter permeability of root cells 1/1/2017
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17. Cont…………..
 Xylem gets destroyed
Rot or Canker Pathogens
Gall Formation
 Xylem gets clogged
Growth of Vascular Wilt Pathogens
Pathogen Secretions
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18. Effect in translocation of phloem
 Obligate fungal parasites
Respiration increase
 Photosynthesis decrease
Photosynthetic Products Accumulate in Invaded
Areas
 Nutrients from Uninfected Areas are translocated
toward the Infected Areas
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19. CONT……………
 Viruses
Death of phloem
Inhibit Enzymes that Break Down Starch
into Smaller, Translocatable Molecules
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20. 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
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21. Cont…………
 EFFECT ON TRANSLATION
 Higher energy needs
Increased Production of Phenolics
Resistant plants have high Protein synthesis
in first few minutes of infection
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22. SUMMARY
 Main pathogens are bacteria, fungi and virus
 Pathogens mainly affect the following physiological
functions in plants
 Photosynthesis
 Respiration
 Permeability of cell membrane
 Translocation of water and nutrients
 Transcription and translation 1/1/2017
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