Chromista

Classification of chromista and description about important diseases especially Pythium and Phytophthora and their general characters and life cycles will give us an detail description and idea about diseases comes under this group

1. CHROMISTA
N.H. SHANKAR REDDY
2
nd
Ph.D. Plant Pathology
Annamalai University

3. Oomycota
GeneracharactersofOomycota
•OtherwisecalledasEggfungi/pseudofungi
•Cellwalliscomposedofcellulose+hydroxyproline
•Oomycotafungicanreproducebymeansofbothsexualandasexualreproduction
•Asexualreproductionbymeansofmotilespores(zoospores)withtwoflagellaand
sexualreproductionisbygametangialcontact(malegametes,antheridiumand
femalegametes,oogoium)resultingtheformationofthickwalledrestingspore
(oospore).
•Asexualspores–zoospores
•Sexualspores–oospores
•Thespecialfeature,zoosporesisofbiflagellatewithanteriorlongtinseland
posteriorshortwhiplash
•Thegametesarenon-flagellate.Thefusionofgametesresultsintheformationof
thick-walledoospores
•Eg–Lateblightofpotato-Phytophthorainfestans
• Grapesdownymildew–Plasmoparaviticola

4. Life cycle of damping off of vegetables –
Pythium aphanidermatum
Systemic classification :-
Domain –Eukarya
Kingdom –Chromista
Phylum –Oomycota
Class –Oomycetes
Order –Pythiales
Family –Pythiaceae
Genus –Pythium
Species –aphanidermatum

5. Symptoms
•Preemergencedampingoff–seeds
andradiclesrotsbeforethe
seedlingemergenceoutofthesoil
•Postemergencedampingoff–
newlyemergingseedlingsarekilled
atgroundlevelafteremergefrom
thesoil

6. Asexual reproduction –
•Myceliumconsistsofcoenocytichyphae,hyphaeisbothintercellular
andintracellular.Nohaustoriaareproduced
•Pythiumproducessimplebranchedandglobosezoosporangia
(producesatterminalorintercalary)
•Germinationiseitherzoosporesongermtube,sporangiosporeconsists
ofsporangiawithbubblelikevesicle,thesporangialprotoplastmoves
rapidlythroughtubeintovesicleandappearsremainsdelimitationof
zoosporestakesplace
•Zoosporearereleasedinarockingmotionandbouncesonthevesicle
•Thereniformzoosporesarebiflagellatewithanteriortinseland
posteriorwhiplashtype,sporescomeinrestandencystandgerminate
byproducinggermtube

7. Sexual reproduction
•Sexualreproductionisoogmousandtakesplacebygametangialcontact
•Themalesexorganisantheridiumandfemaleisoogonium
•Uponthegametangialcontact,afertilizationtubedevelopsand
penetratestheoogonialwallandentertheperiplasm
•Inthemeantimemeiosistakesplaceonlyfunctionalnucleiremains,
otherdisintegrate.
•Nowmalenucleipassestofemalenuclei(oosphere)through
fertilizationtube,whichformszygote
•Theoosporedevelopathickwallarounditselfandgerminatebyusing
germinationtube(iffavourableconditionsoccursitgerminates,
otherwiseitundergoesrestingperiod)

9. Life cycle of Phytophthora infestans
Systemic Clasification
Domain –Eukarya
Kingdom –Chromista
Phylum –Oomycota
Class –Oomycetes
Order –Pernosporales
Family –Pernosporaceae
Genus –Phytophthora
Species –infestans

10. •Symptoms–‘Phytophthotra’means
plantdestroyer,watersoakedlight
brownlesionsdevelopontheleavesand
laterenlargesandcovertheentireleaf,
petioleandstem.Rottenportionemits
characteristicodour

11. Asexuallifecycle
•Sporangiaareborneaerialsympodiallybranchedsporangiophore
arisedirectlyfrominternalmycelium
•Hyphaeisinterandintracellularprofuselybranchedandproduced
fingerlikehaustoria
•Thesporangiophoresarewithcharacteristicswellingsatthenodesof
indeterminategrowth
•Onfallingsuitablehostthesporangiagerminate(<15oC)favours
thezoosporeproduction,hightemperaturefavoursthegermtube
formation(>20oC)

12. Sexuallifecycle
•Sexualreproductiontakesplacemeansofantheridiaandoogonia
ofoppositematingtypes
•Oogoniapenetratesandgothroughtheantheridiaandforma
globosestructureabovetheantheridiaiscalledamphigynous
antheridia
•Migrationofantheridiumnucleusintooogonialwallby
fertilizationtube
•Thefertilizedeggsecretesaheavywallarounditselfandbecome
oospore
•Oosporegerminatesbymeansofgermtubeandproduceszoospore
andproducednewthalli.

14. Difference between Pythiumand Phytophthora
Particulars Pythium Phytophthora
Meaning PythiumwhichmeansDecay Phytophthorawhichmeans Plant
destroyer
Family Pythiaceae Pernosporaceae
Order Pythiales Pernosporales
Symptoms Rootingofroots,slowgrowth,stunting Rottingofrootsandstem,stunting,
discolourationandwilting
Parasitism Facultativeparasite Facultativesaprophyte
HaustoriaandappresoriaAbsent Present
Sporangiophores Sporangiophores are not well-
distinguishedfromhyphae
Sporangiophoresarewelldistinguished
fromhyphaehavingsympodialbranches
(zigzag)
Differentiation of
zoospores
Zoosporesaredifferentiatedinthevesicle
andreleaseupontheruptureofvesicle
Zoosporearedifferentiatedinsidethe
sporangiaandreleasedinan
disappearingvesicleatthesporangia
apexaftermaturation
TypeofAntheridia Antheridiaisofparagynoustype Antheridiaisofamphigynoustype
Baitingtechnique Mustardisusedforbaitingtechnique Appleisusedforbaitingtechnique
Examples Pytiumaphanidermatum(dampingof
vegetables),Pythiumdebaryanum
Phytophthorainfestans(lateblightof
potato)