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1EFFECT OF PLANT PATHOGENS

IN PHYSIOLOGICAL

FUNCTION

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2INTRODUCTION

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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3PHOTOSYNTHESIS

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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4Influence of virus infection

Reduce chloroplast amount Reduction in chlorophyll content Chloroplast abnormalities Reduction in photochemical activity Reduction in sucrose content

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5Influence of bacterial infection

Decrease in chloroplast storma Disorientation of chloroplasts Destroy of chloroplast integrity -

HR Suppression of CO2 fixation

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6EFFECT OF FUNGAL INFECTION

Reduce chloroplast RNA content Loss of chlorophyll Inhibit photophosphorylation

coupling mechanism Inhibit electron transport Suppress CO2 fixation

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7RESPIRATION

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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8Effect 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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9EFFECT 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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10Effect 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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11MEMBRANE 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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12TRANSLOCATION 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

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13EFFECT 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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14EFFECT OF BACTERIA

Enter the vascular systems, both xylem and phloem, through wounds

Infection of Ralstonia solanacearum on tomato Infection of Xanthomonas spp.

on banana

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15EFFECT 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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16EFFECT IN TRANSLOCATION OF WATER AND INORGANIC NUTRIENTS

Root damageDamping-Off Fungi : Cause injury to

rootsRoot-Rot Fungi, Bacteria

: Inhibit root hair production

Most Nematodes & Some Viruses

: Alter permeability of root cells

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17Cont…………..

Xylem gets destroyedRot or Canker Pathogens Gall Formation

Xylem gets cloggedGrowth of Vascular Wilt Pathogens Pathogen Secretions

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18Effect in translocation of phloem

Obligate fungal parasitesRespiration increase Photosynthesis decreasePhotosynthetic Products Accumulate in

Invaded Areas Nutrients from Uninfected Areas are

translocated toward the Infected Areas

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19CONT……………

VirusesDeath of phloemInhibit Enzymes that Break Down

Starch into Smaller, Translocatable Molecules

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20TRANSCRIPTION AND TRANSLATION

Effect on transcriptionChange Composition, Structure or Function

of Chromatin Associated with Cell DNA Increase in the activity of Enzymes that

Break Down RNA

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21Cont…………

EFFECT ON TRANSLATION Higher energy needsIncreased Production of Phenolics Resistant plants have high Protein

synthesis in first few minutes of infection

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22SUMMARY

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

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