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OOMYCETES IOOMYCETES I

INTRODUCTION &INTRODUCTION &SAPROLEGNIALESSAPROLEGNIALES

OOMYCETES IOOMYCETES I

INTRODUCTION &INTRODUCTION &SAPROLEGNIALESSAPROLEGNIALES

IB 371IB 371 GENERAL MYCOLOGYGENERAL MYCOLOGY

LECTURE 13LECTURE 13

THURSDAY, OCTOBER 9, 2003THURSDAY, OCTOBER 9, 2003

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OOMYCETES

DEFINING CHARACTERISTICS

OOMYCETES

DEFINING CHARACTERISTICS

Vegetative thallus filamentous, coenocytic,Vegetative thallus filamentous, coenocytic,in some groups unicellularin some groups unicellular

Cell walls lacking chitin (except for a fewCell walls lacking chitin (except for a fewtaxa), made of glucans & cellulosetaxa), made of glucans & cellulose

Asexual reproduction by biflagellateAsexual reproduction by biflagellatezoosporeszoospores

Sexual reproduction by oogonia (female) &Sexual reproduction by oogonia (female) &antheridia (male)antheridia (male) -- no motile gametesno motile gametes

Sexual spore is the oosporeSexual spore is the oospore

Diploid life cycleDiploid life cycle

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OOMYCETES

DEFINING CHARACTERISTICS

OOMYCETES

DEFINING CHARACTERISTICS

Sexual reproduction is oogamous

Female gamete (oosphere) produced by

an oogonium

Depending on taxon, there may be one

to many oospheres per oogonium

Male gamete is produced by

antheridium and transferred to the

oogonium by gametangial contact and

migration of male nuclei

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Oogonium and antheridium (From Tom Volk)Oogonium and antheridium (From Tom Volk)

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OOMYCETES

DEFINING CHARACTERISTICS

OOMYCETES

DEFINING CHARACTERISTICS

Asexual reproduction is by zoospores

Zoospores have flagella that are

anisokont (unequal) and heterokont(different) (straminipilous)

The anteriorly directed flagellum bears

two rows of tubular tripartite hairs The posteriorly directed flagellum is a

whiplash type

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FromFromLowerLower

Fungi in theFungi in the

LaboratoryLaboratory

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DIPLOID

LIFE

CYCLE

(From

Alexopoulos

et al.)

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OOMYCETESOOMYCETESOOMYCETESOOMYCETES

Phylogenetically unrelated to thePhylogenetically unrelated to the

fungi but similar in morphology &fungi but similar in morphology &

physiologyphysiology

Now in Chromophyta with brownNow in Chromophyta with brown

algaealgae

9 orders, 25 families, 95 genera9 orders, 25 families, 95 genera

Between 500Between 500--800 species800 species

Called Peronosporomycetes by DickCalled Peronosporomycetes by Dick

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ORDERS OF OOMYCETESORDERS OF OOMYCETES

TO BE COVEREDTO BE COVERED

ORDERS OF OOMYCETESORDERS OF OOMYCETES

TO BE COVEREDTO BE COVERED

SaprolegnialesSaprolegniales

LeptomitalesLeptomitales

LagenidialesLagenidiales(Salilagenidiales)(Salilagenidiales)

PeronosporalesPeronosporales

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SAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALES

Found in water and soil.Found in water and soil.

Captured by baiting soil and waterCaptured by baiting soil and watersamples with hemp seeds or deadsamples with hemp seeds or dead

flies.flies.

Saprobic on both dead plants andSaprobic on both dead plants andanimals.animals.

A few species are parasitic on fish.A few species are parasitic on fish.

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SAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALES

Thallus isThallus is filamentousfilamentous..

Hyphae is hyaline, broad &Hyphae is hyaline, broad & coenocyticcoenocytic..

Asexual reproduction is byAsexual reproduction is by biflagellatebiflagellatezoosporeszoospores formed in large, cylindricalformed in large, cylindrical

sporangiasporangia..

Sexual reproduction is bySexual reproduction is by oogoniaoogonia

containing severalcontaining several oospheresoospheres that receivethat receive

nuclei directly fromnuclei directly from antheridiaantheridia..

A fertilized oosphere is called anA fertilized oosphere is called an oosporeoospore..

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FromFrom Introductory MycologyIntroductory Mycologyby J. Websterby J. Webster

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ZOOSPORESZOOSPORES

PrimaryPrimary oval with two flagella atoval with two flagella at

apex, one is tinsel and the other isapex, one is tinsel and the other is

whiplash.whiplash.

SecondarySecondary kidney shaped with twokidney shaped with two

lateral flagella, one anteriorlylateral flagella, one anteriorly

directed tinsel and one posteriorlydirected tinsel and one posteriorly

directed whiplashdirected whiplash

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From

Introductory

Mycology

by

J. Webster

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ZOOSPORESZOOSPORES

MonomorphicMonomorphic having only one typehaving only one type

of zoospore.of zoospore.

DimorphicDimorphic having both types ofhaving both types of

zoospores.zoospores.

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ZOOSPORESZOOSPORES

MonoplaneticMonoplanetic having only one swimminghaving only one swimmingperiod followed by encystment.period followed by encystment.

DiplaneticDiplanetic having one swimming periodhaving one swimming periodfollowed by encystment, emergence and afollowed by encystment, emergence and asecond swimming period followed bysecond swimming period followed byencystment.encystment.

PolyplaneticPolyplanetic Having multiple swimming andHaving multiple swimming andencystment periods.encystment periods.

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SAPROLEGNIALESSAPROLEGNIALES

SaprolegniaDimorphic, diplanetic with

swimming periods of equal duration.

Achlya Dimorphic, diplanetic but primaryzoospores encyst just outside the

sporangium.

Dictyuchus Monomorphic, polyplanetic, noprimary spores are liberated. Primary spore

encysts in the sporangium, each cyst releases

a secondary zoospore that can swim and

encyst repeatedly.

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From Money & Webster Trans. Br. Mycol. Soc 88: 341-

348 (1987)

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Sporangium ofSporangium ofDictyuchus sp.Dictyuchus sp.

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Secondary zoospores ofSecondary zoospores ofDictyuchusDictyuchus sp. emergingsp. emerging

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Primary zoospore cyst walls ofPrimary zoospore cyst walls ofDictyuchusDictyuchus sp.sp.

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SAPROLEGNIALESSAPROLEGNIALES

Thraustotheca Monomorphic,

monoplanetic, primary zoospores

encyst within sporangium, secondaryzoospores swim only once.

Geolegnia Aplanetic, both swimming

periods have been repressed,aplanospores germinate directly from

sporangia.

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SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

Most species are monoecious andMost species are monoecious and

selfself--fertile.fertile.

A few species are selfA few species are self--sterile andsterile andheterothallic (Achlya ambisexualis,heterothallic (Achlya ambisexualis,

Achlya bisexualis).Achlya bisexualis).

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SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

Hormone A (antheridiol)Hormone A (antheridiol) -- produced by theproduced by the

vegetative hyphae of female, causes thevegetative hyphae of female, causes the

vegetative hyphae of the male strain to formvegetative hyphae of the male strain to form

antheridial branches and grow toward theantheridial branches and grow toward theoogonia along a concentration gradientoogonia along a concentration gradient

(chemotropic).(chemotropic).

Hormone B (oogonial)Hormone B (oogonial) -- produced by theproduced by theantheridial branches, causes femaleantheridial branches, causes female

vegetative hyphae to produce oogonialvegetative hyphae to produce oogonial

initials.initials.

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Sexual reproduction in Achlya sp.

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FromFrom

Lower Fungi inLower Fungi in

the Laboratorythe Laboratory

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LEPTOMITALESLEPTOMITALESLEPTOMITALESLEPTOMITALES

Small group of about 30 species.

Differs from Saprolegniales in having

hyphae that is constricted at regularintervals.

Cytoplasm of coenocytic hyphae

contains conspicuous granules.

Oogonia contain a single oosphere

(except in Apodachlyella completa)

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From Lower Fungi in the Laboratory

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FromFrom

LowerLower

Fungi inFungi inthethe

LaboratoryLaboratory