Different techniques for detection of plant pathogens.
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Transcript of Different techniques for detection of plant pathogens.
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Different techniques for detection of plant pathogens
Zohaib ul Hassan Plant pathology ([email protected])
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Plant pathogen“An entity that can incite the disease in plant”. Disturb the normal physiological functioning of
plant. Take its nutrient from plant.
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Plant pathology It is the branch of Agriculture , which deals with
The study of plant diseases. It includes: importance, occurrence, symptoms,
cause, etiology, disease cycle and management of diseases.
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Major plant pathogensFungiBacteriaNematodes viruses
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ISOLATION & DETECTION TECHNIQUES FOR PLANT PATHOGENS
Koch,s postulates: (1881-1882)I. AssociationII. Isolation , PurificationIII.Re-inoculation
Compare the symptoms of diseased and healthy plants.
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Modification's in postulatesE.F. Smith : (1903)Re-isolation , was added by E.F. Smith.For obligate parasites some modifications
also done.1.Study of bio-chemical properties for the particular virus.2.Study of intrinsic properties.
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TECHNIQUES USED FOR DETECTION OF PATHOGENS
Histopathological: ( on the basis of infected tissues) , mostly done in cases of fungi, bacteria and nematodes.
Serological (interaction between antigen and antibody)
Molecular techniques ( Nucleic acid based methods)
Serological and NA based techniques are mostly used for viruses.
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HISTOPATHOLOGICAL TECHNIQUES SymptomologyVisual observation through naked eye.All plant pathogens can detect through
characteristics symptoms, which they have produced in different plant parts.
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Symptomology (fungal diseases)
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FUNGAL DISEASESPOWDERY MILDEW: WILT:
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Identification of BacteriaOn the basis of symptoms. (ooze production is the
characteristics symptom of plant pathogenic bacteria)
Characteristics symptom of bacteria.
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SYMPTOMS OF VIRUSDwarfing & stuntingMosaicChlorosisNecrosisRing spotEnation or TumorVariegation
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CULTURE GROWTH/ COLONY MORPHOLOGYFor Bacteria and Fungi.Growth on culture media will give the
information about the pathogen. e.g. Xanthomonas axonopodis pv. citri gives
yellowish colour growth , when streaked on growth media,
(nutrient agar).In fungi: Rhizopus spp. Gives the cottony
growth on PDA , while Geotrichum candidum gives the condensed growth.
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Geotrichum spp. Rhizopus spp.
xanthomonas
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MOUNTSTemporary & Permanent.
Used for fungi, nematodes, bacteria.
Can detect the pathogen to observe it under microscope or stereoscope.
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MICROSCOPYTo detect the pathogen on the basis of
morphology.
In case of fungi: reproductive structures, vegetative structures, spores can be seen under microscope. From which we can identify the fungus up to genera level.
We can detect the nematodes after preparing slide from suspension, and visualized it under microscope.
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MICROSCOPY
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STAININGBacterial cells, fungi and nematodes can be
colored with a stain.Provide contrast with the background or to make
cellular organelles visible.SIMPLE STAINS: methylene blue, basic fuchsin,
and crystal violet.
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BACTERIAL STAINNING
Staining a bacterial smear. (a) Pass the slide, smear side up, through a flame three times. (b) Flood the smear with a stain and let stand one minute. (c) Rinse the slide gently with water, making sure the stream of water does not strike the smear directly. (d) Carefully blot the slide dry.
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Gram StainThe Gram stain separates almost all bacteria into
two large groups: the Gram-positive bacteria, which stain blue, and the Gram-negative bacteria, which stain pink.
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Gram staining
Gram-positive bacteria Gram-negative bacteria.
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Differentiation on basis of bio-chemical properties
A more precise method is to determine whether or not the bacteria utilize a particular biochemical pathway.
Many bacteria use carbohydrates as energy sources.
Starch hydrolysis. Some bacteria do not hydrolyze starch (left), while others do (right), leaving a clear ring in the agar around the bacterial culture.
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Biochemical propertiesAbility of different bacteria toferment the carbohydrate dextrose.Some bacteria produce acids as end products of dextrose fermentation(center). Others produce both acid and gaseous end products (left). Some cannot ferment dextrose at all (right).