Role of toxins in pathogenesis

Explained in detail about role of toxins in plant disease and their functions in hots plants with examples, will be very easy to understand

1. ROLE OF TOXINS IN
PATHOGENESIS
N. H. SHANKAR REDDY
2
nd
, Ph.D. Plant Pathology
Annamalai University

2. Toxin–Anycompound(lowmolecularweight)producedbythe
microorganismswhichistoxictoplants.
•Toxinsareextremelypoisonousandeffectiveinverylow
concentrations.
•Toxinsinjurehostcelleitherbyaffectingosmoticrelationsorby
affectingenzymaticreactionsgoingonintheplantcells.
•Mosttoxinshaveadirectorindirecteffectontherespirationofthe
plant.
•Toxinswhichdirectlyactonlivinghostprotoplastandkillthecells
oftheplant.

3. Wheeler and Luke (1963) classified toxins into 3 categories
Phytotoxins,
Vivotoxinsand
Pathotoxins

4. Phytotoxins-
•Compoundproducedbythemicroorganismwhichistoxic
toplantsiscalledphytotoxinProducefeworno
symptoms
•Phytotoxinshasnoroleinpathogenicity
•Eg–Alternaricacid,Cochliobolin

5. Vivotoxins-
•DiamondandWaggoner(1953)coinedtheterm“vivotoxin”and
definedassubstanceproducedintheinfectedplantsbythe
pathogenand/oritshostwhichfunctionsintheproductionof
diseasebutisnotitselftheinitialincitingagentofthedisease.
•Itproducesmajorityofthesymptomswhichdeterminesthe
virulence
•Vivotoxinisusuallynonspecific
•Eg–Fusaricacid

6. Pathotoxins
•Toxinsproducedbytheplantpathogenswhichplays
majorroleindiseaseproductionanddevelopment
•Pathotoxinmainlydeterminesthepathogenicityand
producecharacteristicssymptomsofthedisease
•Eg–Pyricularin,tentoxin,tabtoxinandvictorin

7. Host specific –
Hostspecifictoxin(HST)isametaboliteproducedbythe
pathogenwhichisselectivelytoxictosusceptiblehostonly,
littleornontoxictothenonsuceptablehosts.
Hostnon-specific
Toxinsproducedthepathogennotonlydiseaseshostplant,
butalsoaffects/targetsnonhostplantsandotherspeciesof
plants

8. Host specific Host non specific
Name of the toxin Produced by the pathogen
HV –toxin/ VictorinHelminthosporiumvictoriae
HC –toxin H. carbonum/ Cochliobolus
carbonum
HS –toxin H. sacchari(eye spot of
sugarcane)
HM-T toxin H. maydisrace T
ACL –toxin Alternariacitri
AL toxin A. lycopersici
AK –toxin A. kikuchiana
AM –toxin A. mali
PC –toxin Periconiacircinata
PM –toxin Phyllostictamaydis
Name of the toxin Produced by the pathogen
Alternaricacid, Zinniol,
Alternariol
Alternaria
Fumaricacid Rhizopusspp
Oxalic acid Aspergillus,Sclerotiumand
Sclerotiniaispp
Thaxtomins Streptomyces
Syringomycin,
Syringotoxin, Tagetoxin
Pseudomonassyringaepv.
syringae
Phaseolotoxin Pseudomonassyringaepv.
phaseolicola
Tab toxin (wild fire toxin)Pseudomonassyringaepv.
tabaci
Ten toxin Alternariatenuis
Ophiobolin Cochiliobolus spp,
Helminthospporiumoryzae