OOMYCETES IOOMYCETES IINTRODUCTION &INTRODUCTION &

SAPROLEGNIALESSAPROLEGNIALES

OOMYCETES IOOMYCETES IINTRODUCTION &INTRODUCTION &

SAPROLEGNIALESSAPROLEGNIALES

IB 371 – GENERAL MYCOLOGYIB 371 – GENERAL MYCOLOGY

LECTURE 13LECTURE 13

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

OOMYCETESDEFINING CHARACTERISTICS

OOMYCETESDEFINING CHARACTERISTICS

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

• Cell walls lacking chitin (except for a few Cell walls lacking chitin (except for a few taxa), made of glucans & cellulosetaxa), made of glucans & cellulose

• Asexual reproduction by biflagellate Asexual reproduction by biflagellate zoosporeszoospores

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

• Sexual spore is the oosporeSexual spore is the oospore

• Diploid life cycleDiploid life cycle

OOMYCETESDEFINING CHARACTERISTICS

OOMYCETESDEFINING 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

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

OOMYCETESDEFINING CHARACTERISTICS

OOMYCETESDEFINING 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

From From Lower Lower Fungi in the Fungi in the LaboratoryLaboratory

DIPLOID

LIFE

CYCLE

(From Alexopoulos et al.)

OOMYCETESOOMYCETESOOMYCETESOOMYCETES

• Phylogenetically unrelated to the Phylogenetically unrelated to the fungi but similar in morphology & fungi but similar in morphology & physiologyphysiology

• Now in Chromophyta with brown Now in Chromophyta with brown algaealgae

• 9 orders, 25 families, 95 genera9 orders, 25 families, 95 genera• Between 500-800 speciesBetween 500-800 species• Called Peronosporomycetes by Dick Called Peronosporomycetes by Dick

ORDERS OF OOMYCETES ORDERS OF OOMYCETES TO BE COVEREDTO BE COVERED

ORDERS OF OOMYCETES ORDERS OF OOMYCETES TO BE COVEREDTO BE COVERED

• SaprolegnialesSaprolegniales

• LeptomitalesLeptomitales

• Lagenidiales Lagenidiales (Salilagenidiales)(Salilagenidiales)

• PeronosporalesPeronosporales

SAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALES

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

• Captured by baiting soil and water Captured by baiting soil and water samples with hemp seeds or dead samples with hemp seeds or dead flies.flies.

• Saprobic on both dead plants and Saprobic on both dead plants and animals.animals.

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

SAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALESSAPROLEGNIALES

• Thallus is Thallus is filamentousfilamentous..

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

• Asexual reproduction is by Asexual reproduction is by biflagellatebiflagellate zoosporeszoospores formed in large, cylindrical formed in large, cylindrical sporangiasporangia..

• Sexual reproduction is by Sexual reproduction is by oogoniaoogonia containing several containing several oospheresoospheres that receive that receive nuclei directly from nuclei directly from antheridiaantheridia..

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

From From Introductory MycologyIntroductory Mycology by J. Webster by J. Webster

ZOOSPORESZOOSPORES

• PrimaryPrimary – oval with two flagella at – oval with two flagella at apex, one is tinsel and the other is apex, one is tinsel and the other is whiplash.whiplash.

• SecondarySecondary – kidney shaped with two – kidney shaped with two lateral flagella, one anteriorly lateral flagella, one anteriorly directed tinsel and one posteriorly directed tinsel and one posteriorly directed whiplashdirected whiplash

From

Introductory

Mycology

by

J. Webster

ZOOSPORESZOOSPORES

• Monomorphic Monomorphic – having only one type – having only one type of zoospore.of zoospore.

• DimorphicDimorphic – having both types of – having both types of zoospores.zoospores.

ZOOSPORESZOOSPORES

• Monoplanetic Monoplanetic – having only one swimming – having only one swimming period followed by encystment. period followed by encystment.

• DiplaneticDiplanetic – having one swimming period – having one swimming period followed by encystment, emergence and a followed by encystment, emergence and a second swimming period followed by second swimming period followed by encystment.encystment.

• PolyplaneticPolyplanetic – Having multiple swimming and – Having multiple swimming and encystment periods.encystment periods.

SAPROLEGNIALESSAPROLEGNIALES

• Saprolegnia – Dimorphic, diplanetic with swimming periods of equal duration.

• Achlya – Dimorphic, diplanetic but primary zoospores encyst just outside the sporangium.

• Dictyuchus – Monomorphic, polyplanetic, no primary spores are liberated. Primary spore encysts in the sporangium, each cyst releases a secondary zoospore that can swim and encyst repeatedly.

From Money & Webster Trans. Br. Mycol. Soc 88: 341-348 (1987)

Sporangium of Sporangium of Dictyuchus sp.Dictyuchus sp.

Secondary zoospores of Secondary zoospores of DictyuchusDictyuchus sp. emerging sp. emerging

Primary zoospore cyst walls of Primary zoospore cyst walls of DictyuchusDictyuchus sp. sp.

SAPROLEGNIALESSAPROLEGNIALES

• Thraustotheca – Monomorphic, monoplanetic, primary zoospores encyst within sporangium, secondary zoospores swim only once.

• Geolegnia – Aplanetic, both swimming periods have been repressed, aplanospores germinate directly from sporangia.

SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

• Most species are monoecious and Most species are monoecious and self-fertile.self-fertile.

• A few species are self-sterile and A few species are self-sterile and heterothallic (Achlya ambisexualis, heterothallic (Achlya ambisexualis, Achlya bisexualis).Achlya bisexualis).

SEXUAL REPRODUCTIONSEXUAL REPRODUCTION

• Hormone A (antheridiol)Hormone A (antheridiol) - produced by the - produced by the vegetative hyphae of female, causes the vegetative hyphae of female, causes the vegetative hyphae of the male strain to form vegetative hyphae of the male strain to form antheridial branches and grow toward the antheridial branches and grow toward the oogonia along a concentration gradient oogonia along a concentration gradient (chemotropic). (chemotropic).

• Hormone B (oogonial)Hormone B (oogonial) - produced by the - produced by the antheridial branches, causes female antheridial branches, causes female vegetative hyphae to produce oogonial vegetative hyphae to produce oogonial initials. initials.

Sexual reproduction in Achlya sp.

FromFrom

Lower Fungi inLower Fungi in

the Laboratorythe Laboratory

LEPTOMITALESLEPTOMITALESLEPTOMITALESLEPTOMITALES

• Small group of about 30 species.• Differs from Saprolegniales in having

hyphae that is constricted at regular intervals.

• Cytoplasm of coenocytic hyphae contains conspicuous granules.

• Oogonia contain a single oosphere (except in Apodachlyella completa)

From Lower Fungi in the Laboratory

FromFrom

Lower Lower Fungi in Fungi in the the LaboratoryLaboratory