plant pathology.ppt

plant pathology

1. DISCOVER . LEARN.
EMPOWER
Experiment no.1 :To Acquaint with various
laboratory equipment's and microscopy
University Institute Of
Agricultural Sciences
BSc Hons Agriculture
Subject Name :Fundamentals of plant
pathology
Code : AGP-110

2. Course Introduction
Thestudentswillbeacquaintedwiththehistory,importance,symptoms,
etiology,epidemiology,ecologyandmanagementofcommonlyoccurring
diseasesoffieldcrops.Studentswillalsobeabletosurvey,sample
collectionbaseduponsymptomology,isolation,purificationand
microscopicidentificationofdifferentplantpathogenscausingdiseasesin
majorfieldcrops.Purificationofpathogeniccultureswouldbehelpfulin
pathogenicitytests.
Objectives
To understand the basic horticultural disease s and their management.
To impart the knowledge to identify the diseases through symptoms.
SubjectOutcome
The students will be able to strengthen their understanding of different
horticultural diseases.
The students will be able to gain knowledge about management of different
diseases

3. An introduction to PlantPathology
What is PlantPathology?
Objectives of PlantPathology
Disease &Disorder
PlantPathogens
Classification ofdiseases
Terminology

4. What is PlantPathology?
Phytopathology(Phyton:plant)Greek-Pathos
(suffering)+Logos(study)=Thestudyofthe
sufferingplant
Plantpathologyisthatbranchofagricultural,
botanicalorbiologicalscienceswhichdeals
withthestudyof:
cause of the disease
Resulting losses and
Control of plant diseases

5. Objectives of Plantpathology
1.Studyoforigin,causesorreasons.Studyofliving,non-
livingandothercausesofdiseaseordisorderinplants-
Etiology:
2.Studyofmechanismofdiseasedevelopmenti.e.
processesofinfectionandcolonizationofthehostbythe
pathogen.Thisphaseinvolvescomplexhost-pathogen
interactions-Pathogenesis
3.studytheinteractionbetweenthecausalagentandthe
diseasedplantsinrelationtoenvironmentalconditions.
Generallyatthepopulationlevel-Epidemiology
4.Developmentofmanagementsystemsofthediseases
landreductionoflossescausedbythem-Control/
Management.

6. What is health?
The ability to carry out normal physiological
functions at a acceptable level consistent to
genetic potential.
Normal physiological functionsinclude:
–Normal call division, differentiation, anddevelopment,
–Absorption of water and minerals from the soil andtranslocation;
–Photosynthesis and translocation ofphotosynthates;
–Utilization and storage ofphotosynthates;
–Metabolism of metabolites andsynthates;
–Reproduction;
–Storage of reserves for overwintering orreproduction.

7. Plant pathology is both science
(of Learning and understanding
the nature of disease )
and
Art (of diagnosing and
controlling the disease)

8. plantishealthy,ornormal,whenit
cancarryoutitsphysiological
functionstothebestofitsgenetic
potential.
Any deviation-Disease
Thekindsofcellsandtissuesthat
becomeaffecteddeterminethetype
ofphysiologicalfunctionthatwill
be
Forexample,infectionofrootsmay
causerootstorotandmakethem
unabletoabsorbwaterand
nutrientsfromthesoil;
infectionofxylemvessels,interferes
withthetranslocationofwaterand
mineralstothecrownoftheplant;
infectionofthefoliage,(leafspots,
blights,rusts,mildews,mosaics
etc.),interfereswithphotosynthesis
The Concept of Disease in
Plants

9. WhatisaDisease
Stakman&Harrar(1957)defineddiseaseas
physiologicaldisorderorstructuralabnormalitythat
isdeleterioustotheplantoritspartorproduct,that
reducestheeconomicvalueoftheplante.g.,wilt,
potatoblight,Loosesmutofwheat,karnalbuntof
wheat

10. Disease
Disease –
the process in which a pathogen interferes with one or more
essential plant cell functions
Marshall Ward (1901): disease represents a condition in which
functions of the plant are not properly discharged.
Diseaseisaharmfuldeviationfromnormalfunctioningof
physiologicalprocesses.(BritishMycologicalSociety,1950)
Horsfall&Diamond(1957):Diseasecanbedefinedasa
physiologicaldisorderorstructuralabnormalitythatis
deleteriousorharmfultoetheplantoritspartorproductthat
reducesitseconomicvalue.
Disease can be defined as the result of interaction between host,
pathogen and environment

11. How Pathogens affectPlants
There are many ways in which plant disease pathogens can
affect plants
–By utilizing host cell contents
–Bykillinghostorbyinterferingwithits
metabolic processes through their enzymes, toxins etc.
–Byweakeningthehostduet continuous
lossof the nutrients.
–By interfering with the translocation of the food, minerals
land water.
–They can suppress the chlorophyll content.
–They can reduce the leaf area.
–They can curb the movement of solutes and water through the stems.
–They sometimes reduce the water-absorbing capacity of the roots.
–They suppress the translocation of photosynthates away from the
leaves.
–They sometimes promotewastefuluse of
the productsof photosynthesis as in the formation of galls.

12. DiseaseTriangle
Host
Environment
Disease
Pathogen
Conditi
ons for disease
 Host should besusceptible
 Pathogen should bevirulent
 Environment should be favourable for thedisease
TIME

13. Environment
Host Pathogen
Time
HumanActivity
DiseaseTetra-hedron

14. Classification of plantdiseases
Based on type of
symptoms
–Blights
–Rusts
–Smuts
–Rots
–wilts
Based on type of
crop
–Cereal diseases
–Vegetable diseases
–Fruit
Based on type of organ
affected
–Fruit diseases
–Root diseases
Based on cause:
–Infectious diseases
–Non-infectious
diseases

15. Plant DiseaseAgents
Livingorganisms-including
fungi,bacteria,virusesand
nematodes
Nonlivingagents-including
unbalancedsoilfertility,
toxicchemicals,airpollution,
frost,drought,sunburn,wind
andhail

16. Infectious Plant Disease
Causes
Fungi
Bacteria
Viruses
Viroids
Virusoids
Protozoa
Nematodes
Algae
ParasiticPlants

17. Non-infectious diseases
(due to abiotic factors
Environmental stress/excess
–Temperature e.g. high orlow
–Moisture e.g. excess-rotting orStress-wilt/drying
–Air
–Light e.g.etiolation
Nutritionalimbalance
–Excess
–Deficiency e.g. N deficiency, Zndeficiency

18. Disorder:
Abnormalphysiologicalchangeduetonon-parasitic
agentorisanon-parasiticphysiological
malfunctioningduetoeitherexcessordeficiencyin
environmentalfactorsornutrients.
e.g.Physiologicalwilt,sunscald,Nutrientdeficiency)
Disorder
IronDeficiency

19. Scope & Importance of
plant diseases

20. Scopes & Importance of PlantDiseases
Plantpathologydealswithdifferentaspectsofplant
diseasesandhaswidescopethanhumanpathology
whichonlydealwithonlyoneaspect
Inrecentyearsplantpathologistshavebegunto
specializeinparticularaspect.Thefieldinwhich
notableadvanceshavebeenmadeare:
–Interactionbetweenhostandpathogenat
chemical, molecular and genetic level
–Plant virology, chemistry of fungitoxicity
–Disease forecasting

21. Onpracticalaspectsmuchadvanceshave
beenmadeinplantprotectionchemicals;
breedingfordiseaseresistance
Increasedpopulationemphasizesthe
applicationofallpossiblemeanstomeetthe
foodrequirements
–Expansion of crop area
–Improved methods of cultivation
–Increased use of fertilizers
–Improved varieties
–Increased irrigation
–Crop protection

22. Importance of PlantDiseases
Late blight of potato-1841-51 (Irishfamine)
Coffee rust 1867-1870(Srilanka)
Downy mildew of grapes (1880s)(France)
Bengal Famine 1942(India)
Bacterial Blight of Rice 1963(Bihar)
Southern corn leaf blight -1970(USA)

23. Estimated annual lossesworldwide
Diseases 14.1%
Insects 10.2%
Weeds 12.2%
Total av.looses 36.5%
Losses are more in developing world
and
less in develop world

24. Losses
caused by
Plant
Diseases

26. Terminology
Parasite
Pathogenicity
Symptom
Syndrome
Host
Collateralhost
Susceptibility
Pathogen
Pathogenesis
Sign
Hypersensitivity
Alternatehost
Resistance
Tolerance

27. Parasite
Anorganismthatlivesonorinanother
organismandobtainsfoodfromthesecond
organism
Pathogenicity-istheabilityofapathogento
causethediseasebyinterferingwithoneor
moreoftheessentialplantcellfunctions.

28. What isPathogen?
Any entity that can cause disease in a host
eg. Fungus,Bacteria, virus,Phytoplasma,
Viroids, RLO’s, Parasitic Plants, Nematodes

29. symptom andSign
Symptom–aretheexpressionofthediseasecausedby
themanifestationofthephysiologicalreactionoftheplant
duetoharmfulactivityofthepathogen
Sign-physicalevidenceofthepresenceofdisease
agent(e.g., mold or fungal spores, bacterial ooze)

30. Syndrome
Definedassequentialappearanceofdisease
symptomsonaplantduringthedevelopment
ofthedisease
orsumtotalofsymptomsexhibitedbya
disease
Fleck or necrotic spot Blight
Fungal growth Death of of organ or plant

31. FacultativeParasite:
usuallygrowsandcompleteslifecycleondead
material,butcandosoonlivingtissue.Sclerotinia
FacultativeSaprophyte:
usuallygrowsandcompleteslifecycleonliving
tissue,butcandosoondeadmaterial.
Phytophthorainfestans
Necrotrophs–killtheirhostbeforefeedingonthecells
orthecell’scontentsandliveondeadtissue.Rhizoctonia
Biotrophs–donotkillplantcells.Theypenetratethe
cellwallandestablishacontinuousrelationshipor
movefromcelltocell.e.g.Rusts,powderymildew,

32. harbouranotherorganismisHost:anyorganismthat
called host
Alternatehost:isthehostthathelpinthecompletionof
thelifecycleofthepathogenanditssurvival,belongto
diff.family
Collateralhost:hostofthesamefamilyandhelpinthe
survivalofthepathogen
Infection:Establishmentoforganicrelationshipbetween
hostandpathogen
Pathogenesis:Chainofeventsthattakesplaceduringthe
developmentofdisease(inoculationtosurvivalofthe
pathogen)

33. Susceptibility: Inability of the host to resist the attack of
the pathogen

Tolerance:isa typeofdefence
thatminimisescrop losses with out restricting
the disease development.
Resistance: Ability of the host to resist the attack of the
pathogen
–Horizontal resistance
–Vertical resistance
Hypersensitivity: is the quick death of the host tissue in
the vicinity of the pathogen
Diseaseescape:itisabilityofthesusceptiblehostto
avoidthedamagingdiseasestresse.g.unfavorable
environment/growthhabit

34. Virulence:Itisdefinedasthedegreeof
pathogenecityofaparticularisolateorraceof
thepathogen.
Aggressiveness:itisthecapacityofthe
pathogentoinvadeandcolonizethehostandto
reproduceonorinit.
Predisposition:itisthesetofconditionsthat
makestheplantvulnerabletotheattackofthe
pathogen

35. Terms describing microbial
habitats related to plants:
Epiphytic = organisms growing on the surface ofphotosynthetic
organisms
Endophyitc= organisms growing inside thehost
Phylloplane = leafsurface
Phyllosphere = area surrounding the leaf and impacted byit

Rhizoplane = rootsurface
Rhizosphere = area surrounding the root and impacted byit

36. Plant Pathology-Today &Future
Molecular Plant Pathology
–Discovery of WM Stanley in 1935 about proteinaceous nature of the
TMV can be considered as beginning
of the molecular Plant
\Pathology, though two years later, Bawden and Pierie showed the presence
of small amount of RNA with it.
–Gierrer & Schramm in 1956 –RNA as infectious not protein and also
replicate.
–1941, Beadle & Tatum showed that one gene code for one enzyme
–1942, HH Flor-Gene for Gene hypothesis
–1953,Watson& Crick-DNA in a double
helixform– a major
discovery
–Inmid1960s,TMVstudieshelpedinelucidationofthegenticcode
showingthatspecificbasetripletofDNA(andRNA)codefora
certainaminoacid.

37. In1970s,studyonAgrobacteriumtumefaciensT-DNAcontainTi-
Plasmidhavingmanygenes,ofwhichtwocodeforgrowthhormones
leadingtotumourformation.Latertheseplasmidswereusedas
vectortotransfergenestootherorganismsincludingplants.
Laterviruseswerealsousedasvectorsingeneticengineering.
In1984,Albersheimetal.,identifiedamoleculelatercalledelicitor,
inthecellwallofthePhytophthoramegaspermathatactaselicitorof
thedefenceresponseinitssoybeanhost.
In1984,Staskawiczetal.,isolatedfirstavirulencegenefrom
bacteriumPseudomonassyringaepv.glycines
Thesestudieshelpinunderstandingofthehostpathogeninteraction
andresistancephenomenon.
In1986,hrpinitiallycalledbacterialhypersensitiveresponseprotein
,andthoughttohaveroleinhypersensitivereactionofbacterial
infectionbutlaterfoundtohaveroleintransportofproteinin
pathogenicbacteriaandalsothetransportofbacteriaintoplant
cells.
Plant Pathology-Today &Future

38. In1986,Beachyetal.,transformedthetobaccoplants(Transgenic)
bytransferringthecpgeneofTMVandimpartresistancetoTMV
infection-suchresistancecalledaspathogenderivedresistance.
In1989,DickmanandKolattukudi,transformedafungusby
insertingcutinaseenzymecodinggene,facilitatingdirectpenetration
ofitshostthusprovingtheroleofcutinaseenzymeindirect
penetration.
In1991,Broglieetal.,showedthatplantstransformedwithcutinase
geneexhibitenhancedresistancetofungihavingchitinintheircell
wall.
In1990,Cheimetal.,producedaresistanttransgenictobaccowith
genecodingforstilbenesynthetase,aenzymethatsynthesise
phytoalexin.
In1992,JohalandBriggs,isolatedthefirstresistancegene(HM-
(avr9) inCladosporium
1)from corn against Cochliobolus carbonum
De Wit isolated the first avirulence gene
fulvum infecting tomato.
Plant Pathology-Today &Future

39. Similarly,advanceswerealsomadeinthediagnosticand
detectiontechniqueshelpinginaccurateandquickdetection
andidentificationofthepathogens.
–ELISA
–Monoclonal antibodies,
–DNA probes
–PCR based methods
–RFLP
–RT-PCR
–IC/RT-PCR
In management of diseases
–Cp mediated resistance
–SAR
–Gene silencing
Plant Pathology-Today &Future

40. Acknowledgements
Igratefullyacknowledgetheuseofsomevery
importantphotographsgivenintextbook“Plant
Pathology”byGNAgrios.Thisbookservesas
oneoftheimportantandessentialsourceof
learningofthedisciplineofplantpathology.
Ialsoacknowledgethescientistswhospent
valuabletimeingeneratinginformationon
variousaspectsofplantpathologyanddisplayed
thesameoninternetforusebyteachersand
researchers