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The Basics of  Mycology & The Fungi

For educational purposes; quote cited references when available--

 

 

 

◄Introduction                                                                                                                                                                                                                                     Ascomycota►

 

                                                                                                  Page 2

 

True Fungi (Eumycophyta) 1

Zygomycota (Phycomycetes) -- Zygote fungi

Biflagellatae: 

(Contact)

 

Sample Examinations

 

 CLICK on illustrations to enlarge:

 

Biflagellatae

 

          The principal orders in the Biflagellatae are Lagenidiales, Saprolegniales, Leptomitales and Peronosporales, in a presumed increasing order of evolution.  This is the last group in the fungi whtat possess flagellated cells at all.  Spores may be either of two kinds:  pear shaped or reniform (kidney-shaped).  When a tinsel flagellum is present it is always to the anterior portion of the spore.  Flagellated cells in the Biflagellatae are always zoospores, and there are no flagellated gametes.

 

 

          In the order Lagenidiales Olpidiopsis vexans is a typical representative species.  It is a simple, holocarpic, biflagellated form with no mycelium.  It parasitizes water molds causing a hypertrophy of the mycelium.  Two principal families are Olpidiopsidaceae and Lagenidiaceae.

 

 

          The entire thallus forms zoosporangia.

 

 

          Zoospores escape and reinfest a water mold

 

 

          The gametangia are differentiated into male and female and copulation occurs, the contents of the male empties into the female.

 

 

          Resting spores are released after decompositon of the host and later zoospores are produced.

 

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          Another example of Lagenidiales is Myzocytium proliferum.  This species parasitizes algae of the genus Spirogyra.  A zoospore lands on a filament, germinates into a mycelium, which then septates.

 

 

          The chloroplast or spiral of the alga collapses after infection.  The segments each round off and form gametangia.  This is a holocarpic organism.

 

 

          An exit papilla is formed on each sporangium and zoospores fill into a balloon-like vesicle in the immature stage.  Later on maturing the vesicle bursts and the zoospores are scattered.

 

 

          Any two of the sporangia will function as gametangia and one will empty its cellular contents into the other.

 

 

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          The final example in the Lagenidiales is Lagenidium, which is an aquatic fungus that may occur in wet soil.  Many species in the genus are parasite and some are saprophytes.  One species parasitizes the eggs of blue crab and lives on algae.  It possesses a branched mycelium and is holocarpic.  During the asexual stage of life cycle a zoospore lands on an alga and sends out a branched mycelium.

 

          Septation occurs, which is wider spread than in Myzocytium, and there is no rounding away of the individual cells.

 

 

          A sporangium develops on the outside of the host from the cells of the mycelium.

 

 

          During the sexual phase one of the septate sections of the myceliar cells rounds off into a female gametangium and a male cell near to it sends out a fertilization tube.  After transfer of protoplasm to the female a resting sporangium is formed.

 

 

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          Please see following plates for life cycles in the Lagenidiales:

 

Zygomycota:  Biflagellatae:  Lagenidiales

 

Plate 30 = Life Cycle -- Lagenidiales:  Olpidiopsis vexans

Plate 31 = Life Cycle – Lagenidiales: Myzocytium proliferum

Plate 32 = Example Structures -- Lagenidiales:  Lagenidium callinectes

Plate 33 = Life Cycle – Lagenidiales: Lagenidium spp.

Plate 34 = Life Cycle – Saprolegniales: Saprolegnia sp-1

Plate 81 = Life Cycle -- Lagenidium rabenhorstii.

 

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            The order Saprolegniales  or water molds, are more typical of the Biflagellatae.  Hyphae are coarse (50 microns diam.) and very conspicuous.  They attack a great variety of animal matter in the water, but they are mainly saprophytes.  Some, such as Saprolegnia parasitica and Achlya flagellata,  are parasites that attack fish and fish eggs.  Other species are root and algae parasites, e.g., Aphanomyces enteiches.  Different authorities have variously drawn the limits of this order, which varies from only one to three families, etc.  Only one family, the Saprolegniaceae, will be presented here.

 

          The Genus Saprolegnia is a typical representative of this order.  The species occur in great abundance in fresh water with most being primarily saprophytic and a few parasitic on fish.  The life cycle includes a branching mycelium that emanates from the host (hemp seed) and forms zoosporangia on the tips of hyphae.

 

 

          In the asexual phase progressive cleavage delimits zoospores in the sporangium, which is followed by internal proliferations.

 

 

          The zoospores are pear-shaped; they swim in water and form a wall when on the host.  The zoospores resume swimming but this time their shape has become reniform.  In Diplanaticism there are two types of zoospores produced, which have two swarming periods.

 

 

          Occasionally a hypha will swell up and the irregular-shaped tips (gemmae) break off and give rise to a new mycelium.  The organism possesses a minor reproductive system.

 

 

          In the sexual phase gametangia form on the ends of the hyphae and are called Oogonia.  Oospheres (eggs) are delimited inside.

 

 

          Antheridia may form on another hypha or the same one.  These send fertilization tubes through the wall of the oogonium and directly to each oosphere within.

 

 

          Each oosphere develops into an oőspore after fertilization.

 

 

          The oöspores can germinate and the tip may develop into a sporangium.  If oospores develop without fertilization they are called aboöspores (developed parthenogenically).

 

Review of the Saprolegniales

 

          The Asexual stage has a well-developed mycelium, which consists of coarse, sparsely branching hyphae.  Gemmae, zoosporangia are present and pear-shaped zoospores are biflagellated at the apex and  primary while the reniform zoospores are secondary.  In the Sexual stage there is an oogonium with oospheres (eggs).  There are an antheridium, a fertilization tube and oosphores that give rise to a hypha, which produces sporangia and send out zoospores.

 

Variation in the Order Saprolegniales

 

          There are three types:  Diplanetic, Monoplanetic and Aplanetic (= two, one or no motile zoospores).  Example of the different types follows with some genera having both types:

 

          Diplanetic:  In Achlya there is no inner proliferation of sporangia, and the sporangium arises from new growth below the old one (later proliferation). 

 

 

          In Isoachlya there is both a lateral and internal proliferation.  In Aphanomyces, Aplanes, Thraustotheca and Dictyuchus there is no proliferation.  Saprolegnia and Isoachlya are also diplanetic.  In Achlya and Aphanomyces there is encystment in groups at the mouth of the sporangium, and the reniform type follows and is the one that swims.  In Aphanomyces, which is pathogenic on peas, the sporangium differs from Achlya.

 

 

          Monoplanetic:  In Thraustotheca the sporangia are bulbous, the sporangia never open and the primary zoospores encyst right in the sporangium.  A breakdown of the zoosporangial wall releases encysted primary zoospores and these give rise to the reniform type.

 

 

In Dictyuchus after the sporangia are formed, the zoospores become tightly packed inside in an angular arrangement.  Reniform spores emerge from a hole in the side.  A deciduous sporangium is present.

 

 

          Aplanetic:  Aplanes has no swimming zoospores and in Geolegnia there is an encystment of primary zoospores in the sporangia.  A germ tube is sent out directly through the wall of the sporangium from each zoospore.

 

 

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Sexual Phase Differences in the Saprolegniales

 

          In the Genera Aphanomyces, Dictyuchus and Geolegnia there is a single oosphere in one oogonium and the whole protoplast of the oogonium is used up in the production of the oosphere.  Water lies between the oogonial wall and the oosphere.

 

 

          The majority of species are monoecious where both reproductive structures are borne on the same mycelium.  However, some species, as in Achlya, are dioecious.  In the diagram below when cultures I and II are separate no sexual structures are formed.  But when fluid of I (female) is placed into II (male) it will cause the male thallus to produce antheridia (Hormone A involved).

 

 

          The male produces another Hormone B, which causes the female to produce oogonia.  Once the female has oogonia it produces Hormone C that causes the male to develop an attraction.  The male then produces Hormone D, which causes delimitation of oospheres.

 

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          Please see the following plates for life cycles in the Saprolegniales:

 

Zygomycota:  Biflagellatae:  Saprolegniales

 

Plate 35 = Example Structures – Saprolegniales:  Saprolegnia sp2. 

Plate 36  = Genera of Saprolegniaceae: Saprolegnia, Isoachlya, Achlya, Aphanomyces, Aplanes, Thaustotheca,

                      Dictyuchus

Plate 82 = Mature sporangium of Saprolegnia sp.

Plate 83 = Dictyuchus sp.:  Sporangium & zoospores.

Plate 84 = Gemmae of Saprolegnia spp.

Plate 85 = Saprolegnia litoralis:  Terminal oogonium & Intercalary oogonium.

Plate 86 = Life Cycle -- Saprolegnia sp.

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          All species in the order Leptomitales are saprophytic and aquatic.  They flourish in highly polluted waters.  Most are relatively unimportant save for their breaking-down action.  They possess a well developed mycelium, which is coenocytic but always constricted.  Plugs of celluin may be in the constrictions.

 

 

          Some species, cush as Rhipidium and Sapromyces, may have an arbusculate mycelium.  The following discussion on representative genera will reveal the characteristics of this order.

 

          The Genus Leptomitus has constrictions that occur at the branch points of the mycelium.

 

 

          The genus cannot use sugar as a carbon source, but instead uses organic acids and thus they are adapted to polluted waters.  There is no sexual stage known.  The tip of a mycelium branch may turn into a sporangium, and septation may or may not occur before the sporangium.

 

 

The species are also diplanetic (first pear-shaped followed by reniform), and there is no proliferation although the next cell may function as a sporangium.

 

 

          The Genus Rhipidium has conspicuous swellings in the sporangium and a tendency towards globular sporangia.

 

 

The zoospores are delimited in a sporangium of the reniform type.  No pear-shaped are ever formed in the sporangium (this in contrast to the Genus Thraustotheca).

 

          In the Genus Sapromyces there is a single oosphere produced, and the protoplast is differentiated into two areas:  an oosphere and a periplasm.  The periplasm is left as an area between the oogonium wall and the oosphere.  An antheridium is produced on the same thallus and gametangial copulation takes place.  There is an arbusculate mycelium.

 

 

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          Please see the following for examples of Leptomitales:

 

Zygomycota:  Biflagellatae:  Leptomitales

 

Plate 87 = Leptomitales:  Apodachlya pyrifera & Rhipidium americanum.

 

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          The order Peronosporales   is the most advanced order in the Biflagellatae. They are mostly terrestrial species, although some are aquatic or semi-aquatic.  They are primarily parasites on higher plants, a considerable portion of which are obligate parasites, such as Phytophthora that causes Downy mildews and Pythium causing White rusts.  The probable evolutionary sequence of families from lower to higher is Pythiaceae (damping-off fungi), Albuginaceae (white rusts) and Peronosporaceae (downy mildews).

 

          Key characteristics of the group is a well-developed coenocytic mycelium, and all produce globular oogonia and a single oosphere and periplasm.  Fertilization results in an oospore that is normally sculptured, the latter formed from the collapsed portion of periplasm.  The antheridia emit a fertilization tube that persists.  Sporangia are short and wide and detachable in higher forms.  Detachable zoosporangia produce either conidia or sporangia, while the hyphae that bear these produce either conidiophores or sporangiophores.

 

 

          Zoospores are cut out usually after detachment and they are released shortly afterwards (= indirect germination).  Under different climatic conditions the zoospores may not be cut out in the conidia and the latter simply germinate via a germ tube (= direct germination).  These behaviors are characteristic of highly evolved fungi and is shown in the Peronosporaceae.

 

          The order is mainly distinctions of this order are the coenocytic mycelium that occurs mostly inside host tissue.  In the vegetative state sporangia are present but conidia are in the more advanced forms.  The zoospores that are produced from sporangia are all reniform and in the more advanced forms the sporangia germinate directly to form a new mycelium.  Sexual reproduction is remarkably uniform in the group.  The oogonium always contains one oosphere that is accompanied by periplasm.  The antheridium produces a fertilization tube that gives rise to an oospore, which in turn gives rise to zoospores in similar ways.

 

Key Families of Peronosporales

 

           The Pythiaceae are the most primitive family in the order. Some lowly members thrive in aquatic habitats and they often appear on hemp seed bait put out to trap organisms belonging to the Saprolegniales.  The higher forms tend to be terrestrial.  They are never obligatory parasitic but rather facultatively saprophytic or parasitic.  The Genus Pythium, causing “Damping-off” and many other plant diseases, is abundant in soil and in some waters.  They are low grade parasites that kill tissue rapidly and then go on to live on the dead tissue either intra- or intercellularly.  They destroy the hypocotyl region of seedlings or some may cause root rots.  Because the sexual stage is so uniform, vegetative features are the primary basis of separation of families

 

          Zoosporangia are produced from unspecialized hyphae and zoospores develop from the vesicle that emanates from the sporangium.

 

 

 

          Proliferations when they occur are often lateral, but they may be internal as well by going through the old sporangium.

 

 

      

          The sexual stages are typical for the order.  There is an oogonium with periplasm and an antheridium on the same or different hyphae.  After fertilization the oospore is formed.  The outer layer of the spore is of decomposed periplasm.  The oospore may bear sporangiospores directly or a hypha may bear a sporangium on its end, which in turn produces zoospores.

 

          Phytophthora infestans causes “Late Blight of Potato and Tomato.”  It is a facultative saprophyte.  In 1840 this species caused disease in epidemic proportions in Europe, but was especially serious in Ireland.  It probably did not show up earlier because of the mode of shipping where high temperatures over a prolonged period in the holds of ships sterilized the potato tubers.  By 1880 Bordeaux Mixture afforded partial control.

 

          During the life cycle [see Plate 38] the fungus may invade the potato tuber in addition to aerial portions.  Mycelium grows on rotted tissues as a saprophyte.  The fungus is carried over in the tuber and sporulation is on the young shoots.

 

          In the vegetative cycle mycelium produces conidiophores, which emerge through stomata and are coarse with diagnostic swellings at points where the conidia were attached.  The conidia may do one of two things:  either they may form zoospores through indirect germination, or they may germinate directly without production of zoospores (direct germination).  The direct penetration is through the cuticle whereas the indirect penetration is through the stomata.

 

 

          In the sexual cycle mating is controlled by a compatibility factor: a heterothallic form or possibly a facultative homothallic form.  It is not known if there are male strains and female strains in the oogonia and antheridia.  The antheridium is borne at the base of the oogonium and is “collar-like.”  It is believed that the oogonium punctures the antheridium and grows right through it.

 

 

          The life cycle of another species, Pythium debaryanum, is shown in Plate 37.

 

 

          The Albuginaceae, or “White Rusts” are generally not as important as the other groups in the Peronosporales. Only a single genus, Albugo, occurs.

 

          Albugo candida shows up as white spots or blotches on plant leaves, which are caused by conidial pustules [see Plate 39].  Plants are killed very slowly and infection of inflorescences are serious.  Sepals and petals turn green and become hypertrophied.  During asexual reproduction the mycelium grows in intercellular spaces where it is coenocytic and sends out haustoria.  Conidiophores are borne very close together just under the epidermis.

 

 

          The conidia are catenulate.

 

 

          Pressure from underneath breaks the epidermis and spores form disjunctures followed by being released through wind and rain primarily.

 

 

          The conidia, functioning as sporangia, form zoospores that penetrate indirectly.  Sometimes in cases of low moisture and high temperature germination may be direct where a germ tube is produced from the conidium.  Albugo is, therefore, most prevalent in spring and autumn.

 

          During sexual reproduction the mycelium, which produces conidiophores, forms multinucleate oogonia in intercellular spaces.  A single oosphere is formed with only one nucleus.  Other nuclei disintegrate in the periplasm.  The nucleus from the antheridium fuses with that of the oosphere.  The oospore that is formed differentiates into a 3-layered wall.

 

 

          Many oil droplets occur in the center, which fuse to form one large oil droplet that is in a half-moon shape.  The diploid nucleus divides to form many nuclei.  The fertilization tube becomes conspicuous and holds the oospore in position inside the empty oogonium.  A rest period will occur.  Later the oospore wall cracks open and a balloon-like vesicle emerges and delimits zoospores.  The number of zoospores produced is more than the number of nuclei before the rest period.  Hence, it is believed that two nuclear divisions occur during the resting phase.

 

          The Peronosporaceae, or “Downy Mildews” are all obligate parasites on angiosperms, causing great economic damage.  They differ from the white rusts in that the vegetative reproductive stage has distinctive branching conidiophores, which grow out through the stomata (determinate).  There are haustoria and intercellular mycelia with nuclei.  Detachable sporangia occur that are commonly called conidia.  These may germinate directly or give rise to zoospores.  The sporangia are determinate in growth.

 

          Plasmopara viticola causing “Downy Mildew of Grape.” Is a fungus of wild grapes native to America [see Plate 40].  It is relatively unimportant on the native American grapes, but in 1875 it was introduced into Europe where it proved to be highly pathogenic on European grapes and practically ruined the wine industry.  In the 1880’s Bordeaux Mixture (CuSO4 + CaO) was discovered accidentally as a remedy for Downy Mildew.  Vineyards that had been treated with this mixture did not show a prevalence of Downy Mildew.  The mixture proved useful against other fungi as well.

 

          The pathogen, P. viticola, forms mycelium in intercellular spaces with haustoria.  It is rather coarse and irregular in shape and the haustoria are larger than in Albugo.

 

 

          Conidiophores grow out through the stomata.  They are tree-like and monopodial (= single branch at a node).

 

 

          The tips of the sterigmata are rather blunt.  The conidia readily fall off and are carried away by rain.  They are determinate in growth.  Emergence is always through live host tissue and the area may commonly be chlorotic.  Conidia may function as zoosporangia or germinate directly.  The sexual stage is similar to Albugo the only difference being that the oospore germinates with a germ tube that bears a single conidium at its apex.

 

 

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          Considering other generaa in the Peronosporaceae the largest and most complicated haustoria are found in the Genus Peronospora.

 

 

          Almost all obligate parasites that have mycelium also have haustoria.  This does not indicate that all haustoria-producing fungi are also obligate parasites.  Under favorable conditions the conidia release zoospores in Plasmopara, but in Bremia there is a greater tendency to germinate directly.  Peronospora always germinates directly.  The genera can also be distinguished by that occurrence of conidia on distinctive conidiophores.

 

 

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          A review of the differences among the three families of Peronosporales is as follows:

 

          Pythiaceae.  Phytophthora possess haustoria while Pythium does not.  There are no obligate parasites and conidiophores grow out through the stomata.  They have indeterminate growth.

 

          Albuginaceae.  Albugo are obligate parasites on angiosperms.  They have knob-like haustoria without nuclei.  Conidiophores are club-shaped and are tightly packed in the subepidermal layer.  Conidia may germinate directly or produce zoospores.  There is a single oosphere, periplasm and antheridium.

 

          Peronosporaceae are all obligate parasites on angiosperms and differ from Albuginaceae in that the vegetative reproductive stage has distinctive branching conidiophores that grow out through the stomata.  The haustoria and intercellular mycelium do not have nuclei, and the detachable sporangia may germinate directly or give rise to zoospores. The sporangiophores are always determinate in growth.

 

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          Please see the following plates for life cycles and structures in the Peronosporales:

 

Zygomycota:  Biflagellatae:  Peronosporales

 

Plate 37 = Life Cycle – Biflagellatae: Peronosporales: Pythiaceae:  Pythium debaryanum

Plate 38 = Life Cycle – Biflagellatae: Peronosporales: Pythiaceae:  Phytophthora infestans

Plate 39 = Life Cycle – Biflagellatae: Peronosporales: Albuginaceae:  Albugo  candida

Plate 40 = Life Cycle – Biflagellatae: Peronosporales: Peronosporaceae:  Plasmopara viticola

Plate 41 = Example Structures – Biflagellatae: Peronosporales: Pythiaceae:  Phytophthora infestans

Plate 42 = Example Structures – Biflagellatae: Peronosporales: Albuginaceae:  Albugo spp.

Plate 43 = Example Structures – Biflagellatae: Peronosporales: Peronosporaceae:  Plasmophora, Bremia &

                     Basidiophora.

Plate 88 = Peronosporaceae haustoria:  Peronospora ficariae, Plasmopara pygmaea & Peronospora parasitica.

Plate 89 = Life Cycle -- Pythium debaryanum.

Plate 90 = Life Cycle -- Phytophthora infestans.

Plate 91 = Sporangiophors in 5 genera of Peronosporaceae.

Plate 92 = Life Cycle -- Plasmopara viticola.

Plate 93 = Life Cycle -- Albugo candida.

Plate 94 = Oospores of 6 species of Albugo.

 

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Aflagellatae

 

          Three principal orders in the Aflagellatae are Mucorales, Entomophthorales and Zoopagales. 

 

          The Mucorales are for the most part saprophytic organisms.  Some species are extremely common and constitute a prominent element in the “mold” population.  Their spores by often being abundant in the air readily contaminate any exposed objects.  These spores may germinate and give rise to mycelia on suitable substrates.  The order plays a significant role in the decomposition of organic waste.  However, they also cause extensive damage through spoilage of food and they are a nuisance as laboratory contaminants.  A few species act as low-grade parasites and may occasionally cause destructive rots of living plant structures.  Rhizopus causes a soft rot of vegetables and fruits after harvest, especially sweet potatoes, white potatoes, strawberries, plums, etc.  Uncommonly lung and ear infections in humans by some species have been reported.  Some mucors are parasites on other mucors and various members of the order may be found as soil inhabitants, and certain ones called “coprophilous” are ordinarily encountered growing on dung.  Among the latter the most spectacular is Pilobolus.

 

          Many species form a conspicuous cottony mycelium, which is coenocytic when young but as age progresses often develops numerous crosswalls.  There are very interesting specialization of vegetative hyphae in some genera, e.g., Absidia and Rhizopus.  During vegetative reproduction sporangia may be formed on sporangiophores that may be branched or unbranched.  Non-motile spores (sporangiospores) are borne in such sporangial sacs.  Some species bear diminutive deciduous sporangia called sporangiola.  The merosporangium represents a peculiar sporangial type.  Some of the higher evolved species do not produce sporangia at all but rather bear conidia that are believed to be derived from monosporous sporangia.  Chlamydospores are frequently encountered and in some species these are very abundant.  During sexual reproduction zygospores appear following the union of gametangia that are frequently of almost equal size, although in a few cases the size difference may be pronounced.  Many species are heterothallic.

 

          The Genus Rhizopus, which includes the black bread molds, serves as a typical example of the order.  These fungi decompose soil and organic matter and some are low-grade pathogens but may incite destructive rots of fruits and vegetables.  Some species are animal pathogens causing eye and ear infections.  The mycelium grows rapidly and is coenocytic, coarse, cottony and profusely branching The hyphae have crosswalls in older mycelia and septa almost always yield multinucleate cells.  There are no septal pores, which is different from higher true fungi.

 

          Stolons and a system of rhizoids form at the point of contact with the substrate.

 

 

          During vegetative reproduction there is growth at the junctures of rhizoids, which are sporangiophores, that later bear sporangia.

 

 

          A membrane is formed by the fusion of vacuoles and later a fully formed wall is laid down.  The basal portion of the sporangium is now the columella, and progressive cleavage delimits aplanospores, which are wind disseminated.

 

 

          During sexual reproduction a very thick-walled structure the zygospore is formed by the fusion of two gametangia.

 

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          The life cycle of Rhizopus nigricans further serves to characterize the genus [see Plate 44].  Zygospore formation is rarely seen in this species because of heterothallism, which involves Plus and Minus strains. Progametangia meet and change into gametangia and suspensors.

 

 

          Fusion occurs to produce a thick-walled, dark-colored zygospore.

 

 

          Commonly one of the suspensors swells up markedly.

 

 

          Occasionally the gametangia will develop thick walls without fusion.  These are azygospores that function similarly as zygospores.

 

 

          The zygospores eventually germinate but they are rarely seen to do so.  A hypha grows out of the zygospore that terminates in a columellate or “germ sporangium.”  The columella will remain after the sporangium is shed.

 

 

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Families and Genera of Mucorales

[Also see <Mucorales Key>]

 

          Five families are discussed as representative of the Mucorales:  Mucoraceae, Pilobolaceae, Piptocephalodaceae, Thaminidiaceae, Cunninghamellaceae.

 

          Mucoraceae. -- In the Genus Rhizopus stolons and rhizoids occur at the point where the stolon touches the substrate.  Sporangiophores arise at the junctions with rhizoids.

 

 

          Some species like Rhizopus nigricans are heterothallic while other species may show homothallism.  There is a well-developed columella at the apex of a sporangiophore, and the wall of the sporangium is quite delicate.

 

          Absidia is one of the principal genera of the Mucorales encountered in the soil.  The mycelium is more delicate than Rhizopus and stolons and rhizoids have patterns that differ from Rhizopus.  Rhizoids are inconspicuous and attached at the apex of an extension.  Sporangiophores arise on the arch, singly or in small groups.  The pear-shaped sporangia are quite delicate.

 

 

          During the sexual stage of Absidia appendages are formed on the suspensors (either one or both suspensors bear appendages).  They are called “coiled appendages” and emanate from one or both suspensors to form a basket-like structure.

 

          In Circinella’s vegetative stage sporangiophores are long with short side branches that curl.  Curling is called “circinate

 

 

          Sporangia are columellate and are borne on the “curl.”  Some species have a mate to the circinate structure.  The sexual stage of Circinella is similar to Rhizopus.

        

 

          Mucor is the largest genus in the Mucorales.  The species have a rapidly growing mycelium and all are saprophytes and very common in the soil.  There are homo- and heterothallic species.  The vegetative stage is similar to Rhizopus but the sporangiophores are taller.  There are no stolons or rhizoids (Absidia and Rhizopus are the only two genera producing these structures in the Mucorales).  Sporangiophores may arise anywhere and may be branched or unbranched.

 

          Syzygites (Sporodinia) are parasites of fleshy fungi (gill and pore fungi).  They are rapidly growing, have a slightly yellowish mycelium, which forms sporangiophores in abundance.  The sporangiophores are dichotomously branched.

 

 

          The sporangia have columellae and each sporangium contains a few sporangiospores.  The sporangiospores stick on the outside of the columella after disintegration of the sporangial wall.  These species are homothallic.  Gametangia develop on specialized hyphae called zygophores (= stiffened hyphae).

 

 

          In Phycomyces the sexual stage is distinctive but very rare.  Suspensors form outgrowths, as in the case of Absidia.  These are spine-like structures.

 

 

          There are particularly large sporangiophores coming from undifferentiated hyphae.  They are strong and coarse and yellowish-green when young.  The sporangium is columellate and the whole structure is sensitively phototropic.

 

 

          Up to this point all of the Mucorales have had a well-developed columella.

 

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          Pilobolaceae. -- Pilobolus is a coprophilous genus where the mycelium grows rapidly on dung and produces characteristic sporangiophores.  There is a bulbous cell at the base of a sporangiophore called a Trophocyst or “Basal Bulb”.  A subsporangial vesicle occurs at the base of the sporangium, and a columella exists in the sporangium.  A cap is produced, which is coal black.

 

 

          There is a forcible discharge of the sporangium where the sporangia are shot off.  The sporangium lands with cap up; it flattens out into a cushion and adheres to the substrate by a sticky substance.  In a phototropic response the sporangium points eastward toward the rising sun.  This orientation is quick and remarkable.  Spores land on the grass after being discharged from the dung.  Herbaceous animals may ingest the sporangia and the spores are modified in the digestive tract to later germinate in the dung.

 

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          Piptocephalodaceae. -- Syncephalis parasitizes other Mucorales, which is rare for parasites to be found in the same order as the host.  The mycelium grows closely attached to the host and sends out haustoria.  They are high-type parasites and probably obligate.  The sporangiophores are highly distinctive as is also the case with the sporangia.  Rhizoids and haustoria anchor the sporangiophore to the host hypha.  A vesicle appears at the apex of the sporangiophore and finger-like structures grow out of the vesicle.

 

 

          There is no columella and spores are arranged in a single row.  The sporangia here are called merosporangia.

 

          In the Genus Piptocephalis dichotomous branching of the sporangiophore occurs giving a broom-like effect.

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          Thamnidiaceae. -- The Genus Thamnidium has unbranched sporangiophores with columellate sporangia.

 

 

          A different kind of sporangium originates from another profusely branched sporangiophore, which is called a sporangiola.  These do not possess a columella and are deciduous.  There are few sporangiospores in the sporangiola.

 

 

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          Cunninghamellaceae. —Cunninghamella is a common saprophytic form in the soil and decaying debris.  There is nothing peculiar about the sexual stage.  A vesicle is produced on sporangium-like structures and sterigmata emanate from the vesicle and conidia are formed on them.  Terminal portions release conidia first.  In some species the conidia bear spines.  Essentially each conidium is a one-spored sporangiolum.  The wall of the spore is contiguous with that of the conidium or sporangium.

 

 

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          Please see the following plates for life cycles and structures in the Mucorales:

 

Zygomycota:  Aflagellatae:  Mucorales

 

Plate 44 = Life Cycle – Aflagellatae: Mucorales: Rhizopus nigricans

Plate 45 = Example Structures – Aflagellatae: Mucorales:  Absidia, Circinella,  Cunninghamella, Mucor,

                     Philobolus, Phycomyces, Rhizopus,  Syncephalis, Syzygites, Thamnidium

Plate 46 = Aflagellateae: Mucorales:  Distinction of Genera in The Mucorales:  Absidia, Circinella,

                     Cunninghamella, Mucor, Philobolus, Phycomyces, Rhizopus, Syncephalis, Sygygites, Thamnidium

Plate 95 = Stages of evolution of sporangium to a conidium.

Plate 96 = Life Cycle -- Rhizopus nigricans.

Plate 97 = Zygospores of Mucorales.

Plate 98 = Zygophore & Sporangiophore formation:  Sporodinia grandis.

Plate 99 = Sporangial apparatus:  Philobolus longipes.

 

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          Entomophthorales  are represented here by six genera:  Entomophthora, Massospora, Completoria, Ancylistes, Conidiobolus and Basidiobolus.  The distinction among three of these genera may be viewed in Plate 49 This order is more advanced than the Mucorales.  Aflagellate forms produce conidia, which in most cases are forceably discharged (except in the Genus Massospora).  Spores are not formed until the conidia are discharged.  The majority of species are parasitic on insects but they are not obligate parasites and might best be considered facultative saprophytes.  The mycelium is irregularly septate (cells irregular in length), and septa occur in young hyphae.  Hyphal bodies form when cells of the mycelium disarticulate and pull apart.  Sexual resting spores, or zygospores occur, and vegetative resting spores are called chlamydospores.

 

          The Genus Basidiobolus is coprophilous on the dung of amphibians and reptiles.  The mycelium is rapid in development, and the septate hyphae may form hyphal bodies.  Conidiophores arise from cells of the mycelium and there is a forcible discharge of the conidia.

 

 

          Upon discharge the conidia land on vegetation where beetles may ingest them.  Later frogs and snakes may consume the beetles.  The conidia give rise to internally formed spores tht function as sporangia.  The wall of a sporangium breaks down releasing sporangiospores in the dung.  During the sexual stage, large thick-walled zygospores are formed in abundance at intervals along the hyphae.  The genus is readily distinguished by the presence of two msall projections (-= "beaks" or "rabbit ears.") 

 

 

These "beaks" form when two processes extend from adjacent cells in the mycelium.  A crosswall forms across each process and fusion results in a manner not unlike earlier organisms studied.  The fusion takes place inside the gametangium which in this case is the hyphal cell.

 

 

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          In the Genus Entomophthora all species are parasites on insects, and infection is always fatal.  As epidemics occur frequently the genus is thought to be important in the natural control of insects.  This is the most important genus in the order as it attacks many kinds of insects.  Once infection is accomplished, an insect rarely survives attack by one of these fungi.. 

 

          The mycelium of Entomophthora develops throughout the insect body.  The hyphae are coarse, irregularly septate and may form irregularly shaped hyphal bodies.

 

 

 

          Conidiophores grow out to the outside of the insect after death to form a "halo" around the dead fly on the window pane or other surface.

 

 

          The conidium has a small beak and is forcibly discharged.  It then sticks to surrounding objects, which may include another fly.  If the conidium fails to land on an insect it will produce another conidium that is again forcibly discharged, and this may be repeated several times until vigor is lost.

 

 

          Every conidiophore takes its origin from a hyphal body in some species.  It may produce characteristic conidia.  Germination of conidia is direct.

 

 

          Chlamydospores are present in some species and form when a hyphal body may simply round up to form a thick wall and become a resting spore.

 

 

          During Zygospore formation the entire hyphal cell acts as a gametangium.

 

 

          Hyphal bodies may also behave as gametangia.

 

 

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          The Genus Massospora also contains entomophagous forms, one species attacking the 17-year Locust.  It differs from Entomophthora in that it does not forcibly dicharge conidia [see Plate 49].  Conidia are found inside the insect's posterior portions.  Posterior segments drop off the insect and the conidia are diseminated during the final movements of the insect before death.

 

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         Please see the following plates for life cycles and structures in the Entomophthorales:

 

Zygomycota:  Aflagellatae:  Entomophthorales

 

Plate 47 = Life Cycle – Aflagellatae:  Entomophthorales: Basidiobolus sp.

Plate 48 = Life Cycle – Aflagellatae: Entomophthorales: Entomophthora sp.

Plate 49 = Example Structures: Aflagellatae, Entomophthorales:  Basidiobolus,  Entomophthora, Massospora

Plate 100 = Structures of Entomophthora muscae.

Plate 101 = Structures of Entomophthora sepulchralis.

 

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          Zoopagales  is one of the most highly specialized and advanced groups in the Zygomycota.  They parasitize amoebae, nematodes and insect larvae in the soil.  The mycelium is fine and septate and conidia are produced in all of the species.  Zygospores are present also.  They may serve to regulate the populations of the small forms of animal life in the soil.

 

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Bibliography

 

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