Classification of fungi

Evolutionary tendencies in fungi
 Fungi are a highly diverse group of heterotrophic eukaryotes
characterized by the absence of phagotrophy and the presence of a
chitinous cell wall.
 While unicellular fungi are far from rare, part of the evolutionary
success of the group resides in their ability to grow indefinitely as a
cylindrical multinucleated cell (hypha).
 Armed with these morphological traits and with an extremely high
metabolical diversity, fungi have conquered numerous ecological niches
and have shaped a whole world of interactions with other living
organisms.
 The kingdom Fungi is a highly diverse clade of eukaryotes found in
virtually all environments, particularly in terrestrial ecosystems
 Fungi play key roles in nutrient cycling, can act as predators, pathogens
and parasites of myriad other organisms, and can be found living in
symbiotic associations with plants, algae, animals and other organisms.
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EARLY FUNGAL EVOLUTION
 Inferring the potential lifestyle of the last common fungal ancestor (LCFA) is
challenging. The sister group to Fungi, the Nucleariida, are amoeboid
protozoans that are common in marine environments, according to
metagenomic studies
 This, together with the age of the group, which pre‐dates fossil evidence of
terrestrial biota in most molecular dating analyses
 points to a likely marine origin for fungi. However, all known extant fungal
lineages are apparently primarily continental, either truly terrestrial or
associated with non‐marine water bodies.
 Marine fungi do exist, but even zoosporic lineages seem to be much more
diverse in non‐marine environments
 Ancestral fungi must have been primarily aquatic, however, as all terrestrial
fungi form a clearly monophyletic clade with a single inferred loss of the
flagellum
 Thus, either Fungi originated in continental water bodies, or we are missing
key marine lineages. The early‐branching lineages Aphelida, Rozellida and
Chytridiomycota seem to show high diversity in marine environments, based
on environmental studies
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 Ecologically speaking, the parasitoid lifestyle unites the Opisthosporidia,
Chytridiomycota and Blastocladiomycota; although other lifestyles are
known for these groups. This suggests that the ancestor of all fungi was
probably a parasitoid of microalgae, with phagotrophic capabilities,
showed both amoeboid and flagellar motility, and possessed chitin cell
walls, at least in some life stages
 These characteristics are similar to modern Aphelidea, with Rozella and
many chytrids sharing most of these traits, too. This suite of adaptations
separates Fungi from the remaining Holomycota clades (Nucleariida
and Fonticulida), that are amoeboid free‐living predatory protists.
 This important division provides ancestral phenotypic qualities to define
the fungal kingdom, which is otherwise devoid of unifying traits
 Future comparative genomic analyses between zoosporic fungi and
their amoeboid sister lineages are likely to provide new insights on this
period of fungal evolution.
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TERRESTRIALIZATION IN FUNGI
 The most definitory evolutionary novelty within Fungi is the adaptation to land
environments (terrestrialization), which involved the development of hyphal growth and
the loss of the flagellum
 The development of the hypha likely reflects either the necessity to infect much larger
organisms or to increase the surface of influence within a saprotrophic lifestyle
 The ability to secrete digestive enzymes and to express abundant membrane transporters
preferentially at the hyphal tips, can be understood as a direct consequence of an
ancestral pillaging lifestyle of organisms that had to break into other living structures to
obtain nutrients.
 The hypha of most filamentous fungi is organized around an organelle called the
Spitzenkörper
 The SPK is composed of a collection of vesicles originating in the Golgi apparatus that
contain the enzymes, lipids and polysaccharides required for the synthesis of membranes
and the cell wall.
 The presence of the SPK in these lineages suggests that the common ancestor of all
terrestrial fungi
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Classification of fungi
 The classification of fungi presents several difficulties. As the knowledge
increases, the classification is bound to change
 Many mycologists present their classification
 Classification of Fungi by Ainsworth G. C.
 Ainsworth G. C. (1966, 71, 73) proposed a more natural system of
classification of fungi. This classification is based on morphology, especially
of reproductive structure.
 He includes fungi along with slime molds under the kingdom Mycota
 Myxomycota i.e., slime molds and Eumycota or true fungi. Divisions are
subsequently divided into subdivision, class, subclass, order, family and
then to genus.
 According to his classification, division ends in mycota, subdivision in
mycotina, class in mycetes, subclass in mycetidae order in ales and family
in aceae.
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A schematic outline of Ainsworth’s (1973) classification is given:
Kingdom: Mycota
Important features:
 Free-living, parasitic or mutualistic symbionts, devoid of chlorophyll.
 Cell wall composition is very variable, majority contain chitin and glucan
 Reserve food materials are oil, mannitol and glycogen.
 Except some unicellular members, majority are filamentous.
A. Division. Myxomycota:
 Wall-less organisms possess either a Plasmodium (a mass of naked
multinucleate protoplasm having amoeboid movement) or a
pseudoplasmodium (an aggregation of separate amoeboid cells). Both
are of slimy consistency, hence slime molds.
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1. Class. Acrasiomycetes (cellular slime molds)
2. Class. Hydromyxomycetes (net slime molds)
3. Class. Myxomycetes (true slime molds)
4. Class. Plasmodiophoromycetes (endo- parasitic slime molds).
B. Division Eumycota (True fungi, all with walls):
 Subdivision Mastigomycotina (motile cells – zoospores present, perfect state
spore-oospore).
1. Class. Chitridiomycetes (unicellular, zoospore with single whiplash flagellum).
2. Class. Hyphochytridiomycetes (unicellular, zoospore with single tinsel flagellum).
3. Class. Oomycetes (aseptate mycelium, zoospores with two flagella).
 Subdivision. Zygomycotina (mycelium aseptate, perfect state spore-zygospore).
1. Class. Zygomycetes (mycelium immersed in the host tissue).
2. Class. Trichomycetes (mycelium not immersed in the host tissue).
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 Subdivision. Ascomycotina (yeasts or septate mycelium, perfect
state spore- ascospores formed in ascus, usually within
ascocarp).
1. Class. Hemiascomycetes (no ascocarp, asci naked).
2. Class. Loculoascomycetes (fruit body an ascostroma, asci
bitunicate i.e., 2-walled).
3. Class. Plectomycetes (fruit body cleistothecium, asci unitunicate
i.e., 1-walled).
4. Class. Laboulbeniomycetes (fruit body perithecium, asci
unitunicate, exoparasite ofarthopods).
5. Class. Pyrenomycetes (fruit body perithecium, asci unitunicate,
not parasitic on arthopods.
6. Class. Discomycetes (fruit body apothecium, asci unitunicate)
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 Subdivision. Basidiomycotina (yeast or septate mycelium, perfect state
spore – basidiospore formed on a basidium).
1. Class. Teliomycetes. Basidiocarp lacking, teliospores grouped in sori or
scattered within the host tissue, parasitic on vascular plant.
2. Class. Hymenomycetes. Basidio- carp present. Hymenium is completely
or partly exposed at maturity. Basidiospore ballistospores.
3. Class. Casteromycetes. Basidiocarp present. Hymenium enclosed in
basidiocarp. Basidiospore not ballistospores.
 Subdivision. Deuteromycotina or Fungi imperfecti. Yeast or septate
mycelium. Perfect state unknown.
1. Class. Blastomycetes. Budding (Yeast or Yeast like) cells with or without
pseudomycelium. True mycelium lacking or not well-developed.
2. Class. Hyphomycetes. Mycelia sterile or bearing asexual spore directly or
on conidiophore, in various aggregation.
3. Class. Coelomycetes. Mycelial; asexual spore formed in pycnidium or
acervulus.
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Salient features of Division and Subdivision of
Fungal Kingdom:
Myxomycota
Characters
 The division Myxomycota includes the organisms like cellular slime molds,
the plasmodial slime molds and the net slime molds.
 Martin (1960) also treated slime molds as Myxomycetes under fungi and
which according to him has a protozoan ancestry
 The Myxomycota differs from true fungi because their vegetative body
consists of only protoplast bounded by membrane and devoid of cell wall
and also for their phagotrophic mode of nutrition.
 Presence of trophic phase which may be of myxamoeba (simple uninucleate
amoeboid cell), a pseudoplasmodium (aggregation of uninucleate amoeboid
cells) or the plasmodium (a free-living multinucleate mass of protoplasm).
 The mode of nutrition is phagotrophic.
 The vegetative part consists of protoplast covered by plasma membrane and
devoid of cell wall (cell wall is present on the spore if produced by them).
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 They resemble the primitive fungi in their mode of reproduction by
producing spores within sporangia
 They are either holocarpic or eucarpic.
 They exhibit variable colouration.
Class: Acrasiomycetes
Characters
 Acrasiomycetes are commonly known as cellular or amoeboid slime molds,
and are found profusely in the upper layer of humus in deciduous forests
and also in cultivated lands.
 Somatic phase commonly consists of amoeboid cells or myxamoebae.(lobes
of cellular material possess pseudopodia)
 Myxamoebae aggregate to form a pseudoplasmodium, which develops fruit
body.
 Lack of flagellated cells, except in Pocheina rosea.
 Spore wall contains cellulose.
 Plsmodium is characteristics of vegetative phase of slime molds
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 Fruit bodies may be sorocarps (in Dictyostelium) or
sporocarp (in Protostelium)
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Class: Hydromyxomycetes
Characters
 This group shows uncertain affinities. The thallus forms net
plasmodium and are commonly aquatic and saprobic, but
rarely parasitic.
 The thallus consists of uninucleate spindle shaped cells, forming
extensive filaments.
 The filaments are tubular and form net-like structure
 Reproduction by cyst formation, zoospore formation
 The class consists of two orders Hydro- myxales and
Labyrinthulales
 excluded Hydromyxales from fungi and included it in
Protozoans. The members of Labyrinthulales are parasitic on
higher plants and also on marine algae
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Class: Myxomycetes
Characters
 This group is commonly known as true slime molds or plasmodial slime
molds
 They are commonly found in damp places, especially on old wood and other
decomposing plant parts.
 The vegetative body is a free-living plasmodium.
 They feed on yeast cells, protozoa, fungal spores and other substances.
 Reproduction takes place by asexual and sexual means
 Asexual reproduction takes place by fragmentation of plasmodium or binary
fission in myxamoebae.
 Sexual reproduction takes place by fusion between flagellated zoospores or
myxamoeba to form zygote, from which multinucleate plasmodium develops
by mitotic divisions.
 They develop different types of fructification. These are sporangium,
aethalium and plasmodiocarp
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Class: Plasmodiophoromycetes
Characters
 This group is commonly known as endo- parasitic slime molds.
 They are obligate parasites, grow on algae, aquatic fungi and higher plants
(commonly in the roots).
 Members of this class are obligate (i.e., biotrophic) parasites of fresh water
algae, aquatic fungi and higher plants (commonly in the roots).
 Somatic body consists of a naked holocarpic plasmodium.
 Plasmodia are of two types in their life cycle: sporangiogenous plasmodium
(form sporangia) and cytogenous plasmodium (gives rise to cysts i.e., resting
spores).
 Zoospores biflagellate, having unequal flagella of whiplash type(single ),
situated in opposite direction, the shorter one in anterior and longer one in
posterior side.
 he class consists of a single order Plasmodiophorales with a single family
Plasmo- diophoraceae
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Contd..
 The class consists of 16 genera and 45 species. Some like
Plasmodiophora brassicae causes club-root of crucifer;
Spongospora subterranea causes powdery scab of potato.
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Division: Eumycota
Characters
 The members of the division Eumycota are called true fungi. It is a very large
group consists of approximately 75,000 known species, but this number should
be much more as more species are regularly being added in the list due to the
discovery of new species from different corners of the world.
 The thalli of Eumycota usually do not posses Plasmodia or pseudoplasmodia.
Members are unicellular or filamentous with definite cell wall.
 The plant body is thalloid and commonly consists of profusely branched
filament, the mycelium, except a few unicellular members (Saccharomyces
etc.). In filamentous body, unit branch of the mycelium is called hypha
 The mycelial plant body may be aseptate i.e., coenocytic (lower fungi,
Mastigomycotina and Zygomycotina) or septate (higher fungi, Ascomycotina,
Basidiomycotina and Deuteromycotina).
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 Septa, when present, are perforated. The pores are of different types:
micropore (Geotrichum), simple pore (most of the Ascomycotina and
Deuteromycotina) or dolipore (Basidiomycotina except rusts and smuts).
 The hyphal wall is made up of fungal cellulose i.e., chitin; but in some
lower fungi (members of Oomycetes), cell wall composed of cellulose
or glucan.
 The cells are haploid, dikaryotic or diploid. Diploid phase is ephemeral
(short lived). The dikaryotic phase persists for longer period in higher
fungi (members of Basidiomycotina).
 Reproduction takes place by all the three means: vegetative, asexual
and sexual. (Sexual reproduction is absent in Deuteromycotina).
 Spores are either motile (Mastigomycotina) or non-motile (in rest
members).
 Parasitic members cause diseases having both harmful and useful
activities.
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Subdivision Mastigomycotina (Zoosporic Fungi):
Characters
 The Mastigomycotina are zoosporic fungi, adapted mostly in aquatic
habitat.
 Three types of zoospores are common in this group.
 These are:
(a) Laterally biflagellate,
(b) Posteriorly uniflagellate, and
(c) Anteriorly uniflagellate type having “9 + 2” arrangement of component
fibrils.
 Members of this group vary from unicellular plant body (with or without
rhizoid) to filamentous coenocytic mycelium.
 Sexual reproduction takes place by gametic copulation, gametangial
copulation and gametangial contact.
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Contd..
Class:Chytridiomycetes
Characters
 The vegetative body is unicellular or chain of cells attached with the substratum by
rhizoids.
 Cell wall is mainly made up of chitin and glucans.
 The plant body is normally haploid, except Allomyces.
 Asexual reproduction takes place by zoospores produced in zoosporangium; zoospores
are uniflagellate, flagellum whiplash type and posteriorly placed.
 Sexual reproduction takes place by piano- gametes developed in gametangia. The fused
gametes form zygote. After resting period, it undergoes meiosis and forms new haploid
thallus.
 Members of this group are mostly aquatic. Some of them are terrestrial and parasitic.
 Important parasitic members are Synchytrium endobioticum causes wart disease of
potato; Olpidium brassicae, in roots of Crucifers; Urophlyctis alfalfae causes crown wart of
alfalfa (Medicago); and Physoderma maydis causes brown spot of maize.
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Class:Oomycetes
Characters
 The members are mostly aquatic, either free- living or parasitic on water molds, algae
and small animals
 Some are terrestrial and few are parasitic on higher plants. The class Oomycetes is
characterised by oogamous type of sexual reproduction.
 Members of this class are generally aquatic, but some are terrestrial, grows
saprophyticaily on soil or parasitically on shoots of higher plants.
 The plant body ranges from unicellular, holocarpic, endobiotic parasites to well-
developed coenocytic and branched mycelium.
 The cell wall is composed mainly of cellulose glucan and devoid of chitin.
 Asexual reproduction takes place by biflagellate zoospore without cell wall. The
zoospores may be either pear-shaped with anteriorly placed flagella (primary) or
reniform with laterally placed flagella (secondary).
 Members of Oomycetes are generally eucarpic, except Lagenidiales those are holocarpic.
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Contd..
Some important parasitic members of this group are:
 Pythium. Different species of Pythium cause foot rot, fruit
rot, rhizome rot and damping off
 Phytophthora. Different species of Phytophthora cause stem
and leaf blight, foot rot, leaf rot, corm rot, fruit rot etc.
 Plasmopara. P
. viticola causes downy mildew of grape vine.
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Class: Hyphochytridiomycetes
Characters
 They are aquatic, fresh water and marine fungi
 Thallus is holocarpic or eucarpic, mono or polycentric
 Zoospore bear a single , anterior tinsel flagellum with mastigonemes
 Their cell wall contain chitin or chitin with cellulose
 The zoospores either completely differentiated in the sporangium, or
the undifferentiated protoplasm is extruded through the sporangial
orifice and the zoospore differentiated outside the sporangium
 Strikingly similar to Chytridiomycetes but differ from them in structure
and anterior flagellation of the zoospores
 Only one order Hyphochytriales
 There are 6 genera and 21 species, which are parasitic or saprobic in
nature
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Subdivision: Zygomycotina
Characters
 The thallus is normally haploid, consisting of coenocytic
mycelium and its cell wall contains chitin and chitosan.
 The mycelium contains cell organelles like other fungi,
except typical golgi bodies and centriole.
 Asexual reproduction takes place by aplanospores.
 Sexual reproduction takes place by gametangial copulation,
resulting in the formation of zygospore.
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Contd..
Class:Zygomycetes
Characters
 The class Zygomycetes includes those members in which the resting
spore (zogospore) develops by the fusion of two gametangia
 They do not have motile cells (zoospores) in any stage of their life-
cycle.
 The members are saprobes or weak parasites on plants to specialized
parasites on animals. A few occur on dung thus coprophilous in nature.
 The thallus usually consists of well developed, branched, filamentous,
and coenocytic mycelium
 some members possess very much reduced septate mycelium. In some
cases, the coenocytic mycelium produces rhizoids and adheres to hard
surfaces with their help.
 The cell wall is mainly composed of chitosan-chitin
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Contd..
 The asexual reproduction takes place usually by means of non-
motile sporangiospores, called aplanospores, but some also
reproduce by chlamydospores
 The sexual reproduction takes place by means of gametangial
copulation, resulting in the formation of thick-walled
zygospores
 The zygospore germinates by producing a germ
sporangiophore that terminally bears a germ sporangium
 Many members of Zygomycetes (especially those of order
Mucorales) grow rapidly and are often the first species that
participate in the decay of vegetable matter by utilizing the
simplest carbohydrates (sugars)
 The common member of this class is Rhizopus the bread-
mould fungus,
 Mucor another member of this class
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Contd..
Class: Trichomycetes
Characters
 The motile cells are lacking. The asexual spores are produced exogenously at the
tips of special hyphae (conidiophores) and are called the conidia.
 that grow in the guts of arthropods living in aquatic habitats.
 The Trichomycetes are filamentous fungi that live in the digestive tract of
arthropods, including a great variety of insect families
 Their hosts include terrestrial, marine and freshwater arthropods, most commonly
midges (Chironomidae), mosquitoes (Culicidae), black flies (Simuliidae), beetles
(Coleoptera), stoneflies (Plecoptera), and mayflies (Ephemeroptera), as well as
several millipedes (Diplopoda) and crustaceans.
 Trichomycetes develop nonseptate (in the Amoebidiales and Eccrinales) or
irregularly septate (in the Harpellales and Asellariales) vegetative mycelia and
asexual sporangia.
 Further, most genera of the Harpellales produce zygospores and it is this character
which was used to include all the Trichomycetes among the zygomycete fungi.
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 Harpellales and Asellariales. These are true fungi having
hyphal thalli with cell walls containing chitin fibrils and being
regularly septate with incomplete septa having a plugged
central pore
 The unique trichospores, for which the class is named, are
the asexual spores.
 Harpellales produce branched or unbranched thalli, and
either the entire thallus or lateral branches of it become
regularly septate at maturity to form a series of uninucleate
generative cells. From the apical region of each generative
cell a single unisporous merosporangium is produced; this
is the trichospore
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Contd..
Subdivision: Ascomycotina
Characters
 Most of the members are terrestrial, although a large number lives in fresh
and marine waters.
 The majority of ascomycetes are saprophytic, some are parasites of insects
and other animals, and some are responsible for causing destructive plant
diseases.
 The members vary in their form and structure. Yeasts and other a few
members (e.g. Taphrina) are unicellular, but almost all other members of this
group have a well-developed, profusely branched, and septate mycelium
 In unicellular forms, the cell wall is composed of glucans and mannans,
whereas in septate forms it consists of chitin and glucans.
 Asexual reproduction takes place by various types of non-motile spores, such
as oidia, chlamydospores, and conidia. In unicellular forms, fission,
fragmentation, and budding are the most common methods of propagation.
 They are homothallic or heterothallic
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Contd..
Class: Hemiascomycetes
Characters
 The class is characterized by the lack of ascocarp, vegetative
phase comprising of unicellular thallus or poorly developed
mycelium.
 . It is divided into three orders: 1. Asci developing
parthenogenetically from a single cell or directly from a zygote
formed by population of 2 cells – Endomycetales
 Asci developing from ascogenous cells, forming a palisade like
layer - Taphrinales . Asci developing in a compound spore sac
(synascus), produced singly from thick walled chlamydospores –
Protomycetales
 Included in this group are yeasts, extremely simple single-celled
fungi that convert their one and only cell into an ascus.
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Contd..
Class: Plectomycetes
Characters
 The ascocarp wall is a tissue enclosing the hymenium; it usually
is called the excipulum in discoid fungi (discomycetes) and
the peridium in flask fungi
 The ascocarp wall sometimes is composed of a loose mass of
hyphae
 In most genera the walls are differentiated into several layers
comprised of a number of possible tissue types
 Plectomycetes having mostly brightly-coloured to almost
colourless ascomata and ascospores
 The majority have phialidic asexual stages belonging to the
genera Aspergillus and Penicillium or, less commonly, to
Paecilomyces or even simpler types
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Contd..
Class: Pyrenomycetes
Characters
 Pyrenomycetes* are fungi with perithecia, small flask-shaped
fruit-bodies that contain asci and they constitute a large part of
the sac-fungi or Ascomycota.
 This species rich group of mainly decomposers, plant, animal
and fungal parasites are ecologically important
 Pyrenomycetes are ascomycetes with perithecia; pear-shaped
fruitbodies usually smaller than 1 mm with an apical pore.
 Many pyrenomycetes also have a stroma, a much larger
structure embedding the perithecia in fungal tissue.
 The sexual spores are produced in perithecia embedded in the
stroma. The openings (ostioles) of the perithecia are placed on
top of small papilla which protrude from the surface
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Contd..
Class:Discomycetes
Characters
 The most distinctive feature is the cup or saucer-shaped usually fleshy
ascocarp which is botanically known as the apothecium
 The apothecia vary in colour through a wide range and may be red,
yellow, orange, brown, black or even colourless.
 The ascocarps invariably are open. The asci are club shaped or
cylindrical in form and are arranged in columnar disposition (a
palisade-like layer) on the surface or in open cavities.
 In habit the Discomycetes are mostly saprobes found growing in high
humidity of soil, humus, dead logs of wood and dung.
 The conidial stage appears to be non-existent in most cases. Gradual
and progressive reduction in sexuality is another feature of this sub-
series.
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Contd..
Class:Laboulbeniomycetes
Characters
 The Laboulbeniomycetes form a distinct and unusual group of fungi. All are
parasitic on insects and related arthropods but remain on the outside of the
animal in much the same way a tick or leech would.
 The feature all Laboulbeniomycetes have in common is the ascospore
 The spore is long and narrow and has a dark attachment on the upper end
 The ascospores are not forcibly discharged from the ascus but instead collect
inside the perithecium and then are pushed up out of the ostiole.
 They collect at the ostiole in a cluster or in a chain, attachment pad up, and
adhere to a mite or insect when it comes in contact with them. They adhere
to the animal by the attachment pad and then penetrate its cuticle with an
absorption cell called a haustorium. Once the haustorium is in place the
spore can begin to develop into its final form.
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Contd..
Class: Loculoascomycetes
Characters
 The characteristic feature of this group is that the ascus is
bitunicate and fissitunicate; it has two separable walls
 The outer wall (ectotunica or ectoascus) does not stretch
readily, but ruptures laterally or at its apex to allow the
stretching of the thinner inner layer, the endotunica or
endoascus
 The fruit body with asci is regarded as an ascostroma, and each
cavity in which asci develop is termed a locule.
 An ascostroma is a locule that forms in a stroma where the asci
are borne.
 This differs from a perithecium that is formed within a stroma in
that a perithecial wall is formed by the perithecium that delimits
it from the stroma. Such a wall layer is absent in the
Loculoascomycetes.
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Contd..
Subdivision: Basidiomycotina
Characters
 The somatic phase consists of a well-developed, septate, filamentous
mycelium which passes chiefly through two stages.
 Primary mycelium:It is formed by the germination of a basidiospore and
contains a single haploid (n) nucleus in each cell. It bears neither sex organs
nor any basidia and basidiospores. It is short-lived.
 Secondary or dikaryotic mycelium:It constitutes the main food absorbing
phase and consists of cells each containing two haploid nuclei (n+n). It is
long-lived and plays prominent role in the life cycle.
 The motile cells are absent in the life cycle.
 Asexual reproduction by spores plays an insignificant role in the life cycle.
The Homobasidiomycetidae do not form any asexual spores. The
Heterobasidiomycetidae form them in the dikaryotic mycelium. The latter
produces uredospore’s and aeciospores in the rusts.
 The sex organs are lacking in the Basidiomycetes. The sexual process is
represented by plasmogamy and karyogamy. Karyogamy is immediately
followed by meiosis.
50

Contd..
 Basidium is the characteristic reproductive organ of
Basidiomycetes in which both karyogamy and meiosis take
place
 Typically the basidium bears four basidiospores exogenously.
The number, however, varies from one to many depending on
the species
 The basidiospore germinates to produce the primary mycelium.
 The Basidiomycetes and Ascomycetes are similar in their habit
as both include parastitic as well as saprophytic species
 The characteristic reproductive organ, basidium of
Basidiomycetes and ascus of Ascomycetes resemble each other
in development and cytology till the initiation of spores.
51

Contd..
Class:Teliomycetes
Characters
 This class includes many economically important plant pathogens commonly
known as rusts and smuts
 Mycelial hyphae septate and the septa are of simple type. Asexual
reproduction is uncommon, through dikaryotic spores of conidial nature
produced in rusts
 The class is characterized by thick walled, dikaryotic resting spores
commonly called as teliospores in rusts and chlamydospores in smuts
 Karyogamy takes place in this part and therefore, is actually a probasidium.
The resting spores on germination produce promycelium (metabasidium)
into which diploid nucleus moves and after meiosis four haploid nuclei are
produced
 These nuclei later, result in the formation of haploid basidiospores
 This class is divided into 2 orders: Uredinales and Ustilaginales
 Uridinales: The members of this order are commonly called as 'rust fungi'
due to the characteristic reddish brown colour of some of their spores.
52

Contd..
Class:Hymenomycetes
Characters
 Hymenomycetes, name often given to an informal grouping
of fungi that are members of the phylum Basidiomycota
 It includes more than 5,000 species characterized by an
exposed spore-bearing layer (hymenium) and basidiospores
that are forcibly discharged
 Included are boletes, canterelles, coral fungi, mushrooms, and
pore fungi.
 A fruiting body, almost totally lacking in some genera, is highly
developed in others.
 Basidia are formed in hymenium
 Basidiospores are discharge explosively therefore called
ballistospores
54

Contd..
Class-Gastromycetes
Characters
 Basidiocarp is present, The basidiocarp remain closed until the spores have
been released from the basidia
 The common name "puffballs", refers to the basidiospores being "puffed"
from the basidiocarp, in some species.
 Unlike the Agaricales and Aphyllophorales, the puff balls do not forcibly
eject their basidiospores.
 A hymenium is not formed in this group of fungi. Basidia and
basidiospores are formed throughout the fertile area of the basidiocarp
called the gleba.
 The part of the basidiocarp that encloses the gleba is referred to as
the peridium.
56

Contd..
Class: Deuteromycotina
Characters
 Deuteromycetes occur mostly as saprophytes on a wide range of substrates, but a large number
of them are parasites on plants and animals (including humans) and cause a variety of diseases
 Leaf- spots, blights, blotch, wilts, rots, anthracnose, etc. are the important diseases of plants, while
diseases like meningitis, candidiasis, skin diseases, nail diseases, dermatomycosis as ringworms,
athlete’s foot, etc. occur in animals (including humans)
 The mycelium is made up of well-developed, profusely branched and septate hypha that possess
multinucleate cells and simple pore septa.
 The hyphae may be inter- or intracellular, and their cell wall chiefly contains chitin-glucan
 Deuteromycetes reproduce only asexually. The asexual reproduction may take place by hyphal
fragments, budding
 arthrospores (flat-ended asexual spores formed by the breaking up of cells from the hypha),
chlamydospores (thick-walled modified cells functioning as resting spores), or most commonly by
conidia or conidiospores (nonmotile spores formed externally on the surface of hyphae or on
specialized hyphal branches called conidiophores).
 Sexual reproduction lacks, but a parasexual cycle or parasexuality generally operates in their life to
fulfil the requirements of sexuality
58

Contd..
Class: Hyphomycetes
Characters
 Deuteromycota, or anamorphic fungi. Hyphomycetes lack
closed fruit bodies, and are often referred to as moulds
 Asexual reproductive structures produced directly on their
substrate without any kind of enclosing tissues
 Each species grows in a particular habit
 Septation [one-celled, two-celled, multicelled with transverse
septa only, or multicelled with both transverse and longitudinal
septa]
 Arrangement of conidia as they are borne on the
conidiogenous cells. Solitary [single, in balls,
acropleurogenous].
59

Contd..
Class: Coelomycetes
Characters
 The members are found both in tropical and temperate regions
 They are commonly found in cultivated and uncultivated soils,
leaf litter organic debris, fresh water and saline water
 They may found on other fungi and lichens. They are also
pathogens of plants, insects and vertebrates.
 Coelomycetes is divided into two orders, Melanconiales and
Sphaeropsidales. In this class conidia are produced either in
acervuli(short fruiting body) or pycnidia(inversely pear shaped
fruiting body) and accordingly the members have been
grouped into two orders:
1 Conidia produced in acervuli –Melanconiales
2 Conidia produced in pycnidia –Sphaeropsidales
60

Contd..
Class: Blastomycetes
Characters
 Members of this form-class are characterized by yeast-like
cells which propagate by budding. A pseudomycelium may
or may not be formed. True mycelium is either lacking or is
not well developed.
 FORM-ORDER SPOROBOLOMYCETALES
 This form-order is characterized by the presence of forcibly
discharged ballistospores. There is only one form-family, the
Sporobolomycetaceae.
 This causes a infection called Blastomycosis is an infection
caused by a fungus called Blastomyces. The fungus lives in
the environment, particularly in moist soil and in
decomposing matter such as wood and leaves.
61

Structure and reproduction
Dictyostelium
Structure
 Dictyostelium are known as cellular slime molds
 Dictyostelium are able to alternate between unicellular and multicelluar
forms. There are no cell walls on these organisms. Individual cells are not
flagellated, and thus are largely non-motile.
 These individual cells eventually aggregate by sliding. The cytoplasm projects
to form a pseudopod, allowing the organism to travel.
 Dictyostelium adapts to changes in environment. In response to elevated
temperatures, Dictyostelium change their fatty acid composition to maintain
membrane fluidity.
Reproduction
 Dictyostelium are both haploid and diploid organisms. Sexual and asexual
reproduction are both options.
 The transition from unicellular organism to multicellular fruiting body makes
up an important part of Dictyostelium life cycles.
62

Contd..
 After aggregation occurs, the amoebae differentiate
between prestalk and prespore cells. These eventually form
the stalk and the spore head
 Prestalk cells form at the top of the organism and form the
tip. This tip controls further development and cell
movement. Finally, a fruiting body forms, with spores at the
top of the stalk
 These spores are dispersed by the wind, and release
amoebae
64

Contd..
Allomyces
Structure
 The hyphal wall consists chiefly of Chitin, B glucan and ash.
 Within it, is the plasma membrane which closely investes the hyphal
cytoplasm
 Embedded in the cytoplasm are the numerous nuclei. Besides the nuclei
there are mitochondria and roughly unique organelles termed the concentric
granules.
 They are found in abundance in each hyphal segment. The concentric
granules move about in a slow random fashion separate from the normal
cytoplasmic streaming.
 concentric granules act as plugs for septal pores and thus prevent
protoplasmic loss of following damage.
 The vegetative thalli in Allomyces are of two types, gametothalli and
sporothalli
 The former are haploid and the latter diploid. In the vegetative phase the
two are indistinguishable
65

Contd..
 Towards maturity the gametothalli bear gametangia and
sporothalli produce sporangia.
 Thus, the two types of thalli can be distinguished only when
they begin to form the reproductive organs.
 Gametothallus: It is concerned with sexual reproduction and
is homothallic
 Sporothallus:It is concerned with asexual reproduction
66

Contd..
Reproduction
 Allomyces in its life cycle exhibits distinct alternation of generations—a
significant feature which sets these fungi
 apart from all other fungi, there occur two distinct but identical individuals in
a single life cycle of Allomyces. One of these is the haploid gametothallus
and the other diploid sporothallus.
 Gametothallus:It is homothallic and at a certain stage of maturity bears
gametangia which are distinguished as male and female.
 Both produce gametes which are motile, uniflagellate and uninucleate.
 The planogametes are unequal in size. The male gamete is about half the
size of the female.
 The gametothallus, male and female gametangia and gametes which are all
haploid structures constitute the gametophyte generation or haplophase.
 Meiozoospores are the pioneer structures of this phase and the
anisoplanogametes, the last. The anisoplanogametes fuse in pairs to form
the diploid zygote.
67

Contd..
Sporothallus:The diploid zygote germinates immediately to produce an
alternate plant in the life cycle.
 It is the diploid sporothallus. At maturity the sporothallus produces two
types of sporangia and not the gametangia.
 These are thin-walled mitosporangia and thick-walled, pitted resting or
resistant meiosporangia. The mitosporangia produce diploid zoosores.
68

Contd..
Pilobolus
Structure
 Pilobolus, also called hat-thrower fungus, a cosmopolitan genus of at
least five species of fungi in the family Pilobolaceae (order Mucorales)
that are known for their explosive spore dispersal.
 The asexual fruiting structure (the sporangiophore) of Pilobolus species
is unique. It consists of a transparent stalk which rises above the
excrement to end in a balloon-like subsporangial vesicle
 On top of this, a single, black sporangium develops. The
sporangiophore has the remarkable ability of orienting itself to point
directly towards a light source
 The shape and transparency of the subsporangial vesicle allow it to act
as a lens, focusing light into carotenoid pigments deposited near the
base of the vesicle, which absorb the photons and allow cells to detect
the light level in the direction of the lens.
70

Contd..
 The developing sporangiophore grows such that the maturing
sporangium is aimed directly at the light.
 Sporangia having a few spores are called sporangiole. The single spore
in the sporangium, by fusion with the wall of the sporangium, might
have given rise to a conidium
Reproduction
 Pilobolus reproduces both asexually and sexually.
 Asexual reproduction takes place by means of sporangiospores. The
modes of development of the sporangia, columella and the formation
of spores agree closely with those of Mucor mucedo, but the structure
of the sporangium represents a special modification of the Mucor type
 The many-spored sporangium, instead of being spherical is somewhat
flattened and the upper half of the sporangial wall is very much
thickened.
 The part of the sporangiophore just below the sporangium enlarges
considerably to form a sub-sporangial vesicle which may be three to
four times the diameter of the flattened sporangium.
72

Contd..
 When the sporangiophore is in a fully turgid condition, the sub-
sporangial vesicle has been found to be sensitive to the
directive influence of light. This stimulus causes curvature of the
lower part of the sporangiophore, and the sporangium is
directed towards the source of light.
 The neck, i.e. the constricted portion between the sporangium
and the sub-sporangial vesicle, undergoes softening and
stretching and finally the turgidity of the vesicle reaches to such
a degree that the neck ruptures and the entire sporangium,
with mature spore, is blown off along with the watery contents
of the vesicle towards the sources of light, without much
scattering of aim, to a distance of several centimeters. Hence, it
is known as pilobousgun.
 he sporangia finally descend on the vegetation, adhere to it
and are taken up by animals. The spores, only after passing out
of their alimentary canals, are capable of germination and give
rise to mycelia of this mould under favourable conditions.
73

Contd..
 Sexual reproduction takes place by the union of two
isogametangia and their coenocytic contents, and
resembles essential features of the sexual reproduction of
Mucor mucedo. But, in this case, the gametangia are
somewhat club-shaped and they meet in such a way that
they resemble a pair of tongs.
 A coenocytic zygospore is formed, by their union, at the
point of contact, and it appears as a bud and occupies, as if,
a terminal position. P
. crystallius is heterothallic, and the
formation of a zygospore is dependent upon the union of
mycelia of two sexual strains, ( + ) and (-).
74

Contd..
Claviceps
Structure
 these organisms belong to a group of fungi that are referred to as ergot
fungi. As such, they can be found growing on a variety of grasses where they
produce alkaloids.
 The intercellular hyphae are hyaline, septate and about 3 µm in dia. Within
the hyphal wall is the plasma membrane.
 The latter encloses granular cytoplasm containing mitochondria, vesicles,
small lipid globules and several nuclei.
Reproduction
 they reproduce both sexually and asexually.
 Sexual reproduction occurs when two compatible mycelia undergo
plasmogamy. This just means that they fuse their cytoplasm together, but
they DO NOT fuse their nuclei quite yet. This means that the cells are in the
dikaryotic, or "N+N" stage;
 Asexual reproduction is takes place by the formation of asexual spores called
conidiospores
75

Contd..
Puccinia
Structure
 Genus Puccinia consists of more than 4000 different species all of which are
plant pathogens
 These are known to cause rusts in both monocotyledons and dicotyledons.
 Major pathogen, P
. graminis (Stem rust) affects cereal crops such as wheat,
barley etc.
 Some other species are- P
. recondita (Brown rust), P
. asparagi (Asparagus
rust), P
. psidii (Guava rust) etc
 The vegetative structure of Puccinia is represented by both mono and
dikaryotic mycelium.
 Generally the dikaryotic mycelium with two nuclei are found in primary host
 Monokaryotic mycelium with single nuclei are found in secondary host
 Mycelium is formed of septate, tubular hyphae.
77

Contd..
 Mycelium is formed of septate, tubular hyphae.
Reproduction
 P
. graminis is a macrocyclic rust. consisting of five stages of growth
 Wheat: Uredo Stage: Formation of single celled, binucleated
uredospores on stalk. Uredospores form germ tube that apply pressure
on epidermis breaking it and forming uredinia.
 Uredospore germinate and forms mycelia
 Telial Stage (Black stage): Teleutospores formation from uredospore in
unfavourable condition of growth. Each cell has single germ pore
and two nuclei. Karyogamy leads to formation of diploid nucleus.
Spores rests until favourable condition
 Basidial Stage: Formation of haploid basidiospores by meiosis.
Ejection of spores that are carried out by wind to secondary host.
Infects barberry forming haploid mycelia
78

Contd..
 Barberry: Pycnidial Stage: Formation of specialised Pycnia or spermatia.
Pycnia produces haploid pycniospores and receptive hyphae. Dispersed
by insects, Pycniospores fertilise receptive hyphae of another plant forming
dikaryotic mycelia.
 Aecial stage: Formation of dikaryotic aeciospores from mycelia. Chain
like aeciospores are carried by wind to infect cereal host.
79

Contd..
Fusarium
Structure
 Fusarium is represented by large number of species which
occur both in temperate and tropical regions of the world.
 Majority of the species are saprophytic, some are mild
facultative parasite while some species are parasitic and
cause serious diseases like wilt or rot of economically
important crops
 Mycelium is branched, sepate, hyaline or coloured, inter-or
intracellular and uninucleate to multinucleate.
 Hyphae invade the tracheids and vessels of xylem, ramify
there, produce toxic substances and block them completely.
As a result the plants wilt and die.
82

Contd..
Reproduction
It takes place by the formation of there kinds of asexual spores
 Micro conidia,
 Macro conidia, and
 Chlamydospores.
 Micro Conidia: The micro conidia and macro conidia are produced in
same sporodochia. These sporodochia develop on the surface of stem,
leaves and other parts of the host plant
 The fungal mycelium collects near the surface of the host tissue as
anpseudoparenchymatous mass. It gets exposed by the rupturing of the
epidermis
 From the fungal hyphae arise many short and cylindrical structures.
These are conidiophores
 Micro conidia are small, unicellular or bi-celled, spherial or oval in
shape.
83

Contd..
 Macro Conidia:
 The macro conidia are long, sickle or crescent shaped, multi-septate (3-
5 septa), pointed at the end and broad in the middle.
 They measure 15-50 µ in length and 3-5 µ in breadth. Both macro
conidia and micro conidia are produced in vast numbers. They are
easily disseminated by wind and after falling on the suitable substratum,
they germinate and infect the host plants
 Chlamydospores: Under relatively starvation and dry conditions, the
mycelial hyphae produce ovoid or spherical thick walled cells. These are
called chlamydospores.
 They occur either single or in chains and may be terminal or intercalary
in position.
 After maturity they get separated from the parent hyphae and act as
resting spores, under favourable conditions they germinate by means of
germ tubes to form a fresh mycelium.
84

Classification of fungi

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