Introduction to botany
Fungi structure and reproduction
The fungi are a group of eukaryotic,
non-vascular organism. Which are of diverse forms, sizes, physiology and reproduces both by sexual (meiotic)
and asexual (mitotic) spores. Examples of fungi :-Mushrooms, yeasts, molds, Penicillium- the first of the wonder
drugs, penicillin, was isolated from this fungus and crop parasites.Fungi are most often associated with the roots of
plant species, and this type of symbiotic associations is known as mycorrhizae.
The study of fungi is known as mycology (Mykes = mushroom + logos = discourse) or mycetology and who study about
fungus is known as mycologist.
General characteristics of Fungi
- Most fungi are eukaryotic,multinucleate, multicellular organisms,
except yeasts which are unicellular.
- Nutrition Fungi are heterotrophic because these lack chlorophyll (green pigment) and thus cannot create their own
food through photosynthesis.Fungi acquire their nutrients from dead organic matter by secretion of
extracellular enzymes followed by absorption. These are either :-
- Saprophytes or Saprobes :-
Most fungi are saprophytes ,obtaining nutrients by absorbing dead organic matter.
- Parasitic :-Some fungi are
parasites, living in or on another organism (called a host) from which they obtain their nutrients. This relationship usually
harms the host. Such parasitic fungi usually have specialized tissues called haustoria that penetrate the host's body for food
- Symbionts :- Some fungi live in a mutually beneficial symbiotic relationship with another organism.
- Lichen (association of fungi + algae)Some fungi are associated with either cynobacteria or green algae and this type of
symbiotic associations is known as lichen.
- Mycorrhizae (fungi + plants) :- Some fungi are most often associated with the roots of
plant species, and this type of symbiotic associations is known as mycorrhizae.Mutualistic association of plant roots and fungi
increase the absorptive surface area of plant roots.
(Fungus gets organic nutrients from plant;
Plant gets minerals from the soil via the fungus).
- Thallus organization (structure):-
- Most of the fungi, are filamentous and the vegetative
(=assimilative) stage is a tubular
branching thread-like filament called a hypha (plural = hyphae).
- The hypha extends by tip growth, and multiplies by
branching, creating a fine network called a mycelium.
- Two of the phyla Zygomycotina and the Chytridiomycotina (also known as lower fungi) vegetative mycelium is without cross
-walls known as non-septate (aseptate) or coenocytes. Complete septa are only found in reproductive structures. In aseptate
mycelium numerous nuclei lie in a common mass of protoplasm.This condition is called coenocytes.
- The other two phyla Ascomycotina and the Basidiomycotina( higher fungi)the hyphae have cross walls that break them up
into cells. A cross wall in fungi is called a septum ( plural septa).The septum has a central pore which enable exchange of
nuclei and most organelles within the cytoplasm between adjacent compartments.
- Septum formation is a simple process.
Wall ingrowth towards the centre of the compartment results in a complete or incomplete blockage of the hypha. Inward growth
may be followed by modification of the outer wall. The septum also increases rigidity of the hypha as it can function as a
structural support to the turgor pressure within the compartment.
- Ultrastructure of fungal thallus:-
- Rigid cell walls are strengthened with chitin, a polymer of
(except oomycetes where cellulose present).
- Food reserves are in the form of glycogen
- Hyphae contain nuclei, mitochondria, ribosomes, golgi and membrane-bound vesicles within a plasma-membrane bound cytoplasm.
The sub-cellular structures are supported and organized by micro-tubules and endoplasmic reticulum. The cytoplasm and most
organelles and inclusions of fungal cytoplasm are typical of eukaryotic organisms. However, chloroplasts or plastids are
- Reproduction :-
- At the time of reproduction when entire cell asin case of unicellular fungus may be converted into
Such a condition is known as holocarpic. But if only a portion of thallus is converted into reproductive structure , it is
called eucarpic.Some fungi are unicellular and are termed as yeasts. These grow by binary fission or budding, creating
new individuals from the parent cell.
- Members of the Ascomycotina produce asexual conidiospores and sexual ascospores
in sac-shaped cells called asci.
- Fungi from the Basidiomycotina rarely produce asexual spores, and produce their
sexual spores from club-shaped basidia in complex fruit bodies
Classification of Fungi
Over 60,000 species of fungi are known. Fungi are classified primarily by their method of reproduction (both sexual and
asexual) and fruiting bodies (asexual or sexual spores surrounded by highly organised protective structures).
In the earliest classification, there were only two recognized kingdoms:- Plants and Animals.This two kingdom system was used
until Whitaker (1969) proposed that organisms be classified into five kingdoms :- Monera (=Bacteria), Protista (=Mostly Algae
and Protozoans), Plantae (=Plants), Mycetae (=Fungi) and Animalia (=Animals).
Fungi belong to Domain-Eukarya and Kingdom -Mycetae (=Fungi) The classification of fungi, as proposed by Ainsworth (1973), is
commonly followed :-
The more recent systems of classification that is based, in part, on molecular research are :-
Division :- Myxomycota (plasmodial slime molds)
The organisms included in this division are commonly known as the plasmodial or acellular slime molds. The exact systemic
position of the Myxomycota is not clear. Olive (1975) classified them in the Kingdom
Protista. Ainsworth (1973) classification is most accepted in which Division Myxomycota belong to Kingdom
Within the Myxomycota, the class Myxomycetes,
the acellular slime molds.
- Vegetative phase is unicellular, without a cell wall, a multinucleate mass of protoplasm called a
- They engulf bacteria, protozoa, and other food particles by phagocytosis.During this mode of ingestion,
particles, usually bacteria, beceome surrounded by the pseudopodia of the myxamoeba. Once the food has been engulfed in this
matter, it is surrounded by a membrane or food vacuole where hydrolytic enzymes are secreted that will digest the food.
vegetative stage in slime molds is morphologically similar to that of an amoeba, because of that known as myxamoeba.
Plasmodium produces one or more sporangia where meiosis takes place.
Class: Myxomycetes There are approximately 71 genera and 500 species of Myxomycetes.
Habitats (Occurrence) :-There are commonly occur in damp places especially on decaying wood, all of which are
terrestrial (found on land).
- Asexual reproduction occurs by binary fission of myxamoeba or fragmentation of the
- Sexual reproduction takes place by the plasmogamy (fusion of compatible gametes) occurs between myxamoebae or swarm cells
(some species are heterothallic).Karyogamy (fusion of nucleus) occurs shortly after plasmogamy to form zygote (2n). Zygote
forms plasmodium – longest lived vegetative stage.
Life Cycle of Myxomycetes:- Bi-phasic life cycle with a haploid and a diploid phase.
The diploid stage is a naked coenocytic protoplast (that is, it consists of a multinucleate mass of
cytoplasm that is enclosed only by a plasma membrane and does not have a cell wall).When the sporangia matured and turned
grey. Normally globose, with a definite, rather
cell wall,unicellular, uninucelate and haploid spores are released by rupture of the sporangial coat.The spore surface may
range from almost smooth to reticulate. Spores of myxomycetes are small (4-20 µm) and are easily picked up by air currents,
arthropods and other animals
On germination a spore produces one or four myxamoebae or flagellate cells known as swarm cells- that have one or two anterior
flagella, all of which are of the whiplash type. In most cases swarm cells possess one long prominent flagellum and a second
shorter, inconspicuous flagellum that is directed backward and appressed to the cell surface.
Myxamoebae and swarm cells can be interconverted. When food is abundant and environmental conditions are favorable, myxamoebae
divide repeatedly, giving rise to a large population of cells. The nuclear divisions are centric and open (the nuclear membrane
breaks down during prophase and is reconstituted after telophase.) Under unfavorable conditions myxamoebae round up and secrete
a galactosamine wall to form microcysts (sclerotia). When favorable conditions return, the microcysts germinate and either a
myxamoeba or swarm cell emerges from each wall.
When free water is available myxamoeba can differentiate into flagellated swarm cells
Swarm cells and myxamoeba may function as gametes (both in homothallic or heterothallic strains).The compatible gametes fuse in
pairs (two swarm cells, two myxamoebae) to form a diploid zygote.As the zygote grows, its nucleus undergoes successive
synchronous mitotic divisions without cytokinesis. And the cell becomes transformed into a multinucleate, amoeboid structure,
Plasmodium:-The plasmodium is a diploid structure.Plasmodium is a naked, multinucleate, motile mass of
protoplasm; no cell wall around it.
However, in most species, the plasmodium is enveloped by a gelatinous slime sheath that contains microfibrils. Just inside the
slime sheath is the plasma membrane that surrounds and confines the cytoplasm
Plasmodia are of various colors. Examples- Physarum polycephalum it is a bright yellow, slimy structure and Didymium iridis
the plasmodium is colorless
In nature plasmodia probably feed on bacteria, spores of fungi and plants, and possibly on protozoa and even on bits of
nonliving organic matter
Growth is accompanied by successive mitotic divisions of the nuclei embedded in the cytoplasm. In growing plasmodia of P.
polycephalum, nuclear division occurs almost simultaneously every 8-10 hours throughout the plasmodium and requires 20 to 40
minutes for completion. There are three types of plasmodia :-
protoplasmodium - microscopic throughout its existence; gives rise to only a single sporangium when it fruits.
aphanoplasmodium - resembles a protoplasmodium in its initial stages, but soon elongates, branches, and becomes a network of
very fine, transparent strands; Stemonitales.
phaneroplasmodium - characteristic of Physarales, also resembles a protoplasmodium at first; it grows larger and becomes more
massive. Its protoplasm is very granular, and the plasmodium is visible even at an early stage of development. The gelified and
fluid portions of the veins are easily distinguishable and the rhythmic, reversible streaming is very conspicuous
Sporulation and Sporophores :-
- Under favorable conditions, the plasmodium will migrate and feed for a period of time
before being converted to one or more sporophores.Sporophores posses brightly coloured sporangia.
- Entire plasmodium of
a myxomycete usually is converted into one or more sporophores so
that the somatic and reproductive
phases seldom coexist in the same individual.
- Sporangium consists of the following parts: -
- Peridium (persistent or evanescent):- The fragile, outer layer of the sporangium is the peridium (pl.=peridia), which may
be persistent or degenerate by the time the sporangium is ready to disperse its spores.
- Hypothallus - The hypothallus is a plasmodial remnant forming the base for one or more fruiting bodies. The hypothallus
connects the stalk or stipe to the substrate. It may be dull or brightly colored, thin and delicate or coarse.The hypothallus
may be composed of calcium carbonate
- Stalk :- Basal portion of sporangium, may or may not be present, may be hollow or filled with material
Stalks formed from secretions of plasmodium and are acellular (in contrast to cellular slime molds
- Columella and Pseudocolumella :-The columella appears as an extension of the stalk into the spore mass, although it may not
resemble the stalk. In a sessile fruiting body, the columella may be an area on the inside of the peridium where it contacts
the substrate or appears as a dome-shaped structure. A pseudocolumella (pseudo=false) is a columella that does not attach to
the stalk. The pseudocolumella is found only in the order Physarales, existing as a lime mass within the spore mass.
Capillitial elements may be attached to the columella or pseudocolumella.
- Capillitium and Pseudocapillitium :-The capillitium consists of threadlike elements inside the sporophores, intermingled
with the spores.Some elements of capillitium may be elastic, allowing for expansion when the peridium opens, while other types
are hygroscopic and capable of dispersing spores by a twisting motion. A pseudocapillitium is present in some aethalia and
pseudoaethalia producing species. Pseudocapillitial elements are highly variable in size and shape, and may appear as bristles,
threads or perforated plates.
General characteristics of Mastigomycotina :-
- One large group of the Mastigomycotina is aquatic. While
another group of the Mastigomycotina are primarily terrestrial, although the organisms still form motile zoospores when open
water is available
- The members of Mastigomycotina produce
flagellated zoospores in their life cycle.
- Most of them are filamentous and have coenocytic mycelium. However, unicellular form are present, and some genera show
the pseudosepta (false cross wall) formation.
- Rhizoids are present in some of unicellular forms.
- They show centric nuclear division. Their centrioles remain functional during nuclear division.
- Live either as saprophytes or parasites.Due to presence of haustoria in a majority of Mastigomycotina , the mode of
nutrition is typically absorptive.
- The sexual reproduction takes place by different methods , oospores formation are common in almost all Mastigomycotina
Three classes are
included in this sub-division, on the basis of zoospore and oospore and comprise 204
genera and 1160 species:-
- Chytridiomycetes produces posteriorly uniflagellate zoospores Chytridiomycetous fungi occur as saprobes on plants and
animal remains in water while other members occur as parasites on algae and aquatic animals.
- Hyphochytridiomycetes :-
Zoospores are anteriorly uniflagellate.The Hyphochytridiomycetes are those aquatic fungi whose thallus is holocarpic or
eucarpic, monocentric or polycentric and their vegetative system is rhizoidal or hypha-like with intercalary swellings.
- Oomycetes :- The Oomycetes contain 74
genera and 580 species, which are mostly aquatic, though some are terrestrial and live as parasites or saprophytes.Includes
classic “water molds” in the Order
Saprolegniales and the “downy mildews” in the
General characteristics of Class :- Oomycetes :-
- Vegetative body is filamentous and coenocytic except
the unicellular Lagenidiales.
- Holocarpic or Eucarpic
- Entire thallus converted into reproductive structures
- Reproductive organs arise from only a portion of the thallus and remainder continues as somatic
Majority of species are eucarpic.
- Cell wall contains cellulose and glucans.Chitin is absent.
- Asexual reproduction is by biflagellate heterokont (different) and anisokont (unequal) zoospores that are produced in
- Zoosporangia- Modified hyphae that are usually terminal and delimited by a septum
- Zoospores are diploid formed by mitosis
- Anteriorly directed flagellum is tinsel type and posteriorly directed is whiplash type .Depending on genera single
type-monomorphic or two types of zoospores are formed-dimorphic . Two types of zoospores are
formed in the life cycle are :-
- Primary zoospores :- First formed, pip-shaped, and the flagella are located anteriorly. Primary zoospore is
released from the zoosporangium, encyst and germinates to form the secondary zoospore.
- Secondary zoospores :- The
secondary zoospore which is reniform or bean-shaped and laterally flagellated.
- Zooporangium and zoospores are the
major dispersal agents for most species.
- Sexual reproduction:- Sexual reproduction is heterogamous (oogamous) by oogonia (female) and antheridia (male). Female
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 into
oogonia and fertilize oospheres
Homothallic– self-fertile or Heterothallic– opposite mating types required for sexual reproduction. A swimming sperm is absent
in the Oomycetes. This type of sexual reproduction is referred to as gametangial copulation. In antheridia and oogonia meiosis
The eggs and sperms are products of meiosis and the only parts of the life cycle that are haploid.
Diploid zygote develops into thick-walled resistant oospore that germinates and give rise to vegatative diploid hyphae that
reproduce asexually by production of zoospores.
The vegetative body is diploid and the life cycle is diplontic.
Class Oomycetes is divided into four orders.
The most economically important group of Oomycetes is the Peronosporales that contain the late blight of potato fungus
Phytophthora infestans and relatives such as Peronospora, Bremia, Plasmopara and others that cause “downy mildews”, the
“damping off” fungi, Pythium spp., and the white rust fungi, Albugo spp.
- Lagenidiales (Salilagenidiales)
- Peronosporales :- This order has
some of the most well known pathogens (fungi cause diseases) cause
diseases to many a crop plants. Peronosporales:- divided into three families :-
- Pythiaceae - Pithium,Phytophthora
- Albuginaceae -Albugo.
- Peronosporales differs from the Saprolegniales in producing
only secondary zoospores in a zoosporangium
- That is differentiated from hyphae (eucarpic) and one oosphere
(egg) per oogonium.
- Zoosporangia often deciduous
- Zoospores often formed in vesicle
- They are aquatic, amphibious, terrestrial and some of the most destructive plant pathogens .
However, although members of Mastigomycotina are
they share no close phylogenetic
relationships to fungi. The combination of cellulose cell wall,
biflatellated zoospores, one flagellum of the tinsel type and the other of the whiplash type, and gametangial copulation are
characteristics that are shared with some members of the algal divisions Phaeophyta and Chrysophyta. This has recently led to
recognition of yet another kingdom, Stramenopila, which includes the divisions Bacillariophyta, Chrysophyta, Phaeophyta,
Hyphochytridiomycota and Oomycota. These divisions are now thought to be derived from a common ancestor .
Sub-division : -Zygomycotina
- Most of the Zygomycotina are present in soil and dung, occurring
mostly as saprophytes; few are parasitic on plants and
animals. About 1000 fungal species belong to Zygomycotina.
- Vegetative ( somatic) body is
- Thallus is usually mycelial, hyphae coenocytic.
- Cell wall is made up of
chitin and chitosan.
- Asexual reproduction occurs most commonly by the formation of nonmotile, unicelled
sporangiospores in uni- or multispored sporangia or merosporangia. In addition, arthrospores, chlamydospores, and yeast cells
can be formed by some species.
- These characteristics are shared with the divisions of
flagellated fungi (Mastigomycotina).
- Spores are dispersed either violently or passively by wind, rain
- Flagellated spores and gametes are absent in this division as well as in the remaining taxa of terrestrial
- Sexual reproduction occurs with the fusion of two multi-nucleate isogametangia or anisogametangia to produce a
zygote. The zygote later develops into a thick-walled zygospore, the diagnostic feature of this division.
Because of this the fungi of the class
zygomycetes are also known as conjugation fungi.
- Two classes are recognized in this division :-
Zygomycetes :- The members of this class are mostly saprobic(saprophytes), though a few may become weakly parasite on
plants.The common examples are black bread moulds or pin moulds (the genera Rhizopus and Mucor).
In the class, Zygomycetes there are three orders:-
Order :- Mucorales
Rhizopus (common bread mold)
- This species is one of the most common members of this class.
- Vegetative thallus is eucarpic, branching, coenocytic (multinucleate) and aseptate (not divided by cross walls into cells
or compartments) mycelium and haploid (n).
- The mycelium of R. stolonifera is differentiated into three different
- Stolons:- The mycelium develop aerially above the substratum is called "stolons".
- Rhizoids:- Stolons produce
rhizoids in a cluster from below into substratum. Branching rhizoids behave as roots, anchoring the fungus into its
substrate, releasing digestive enzymes, and absorbing nutrients for the fungus.
- Sporangiophores: -Sporangia form on
the tips of
sporangiophores, which are erect branches formed directly above the nodes of rhizoids.
Internal structure The hyphae cell wall are made up of chitin lined by a thin plasma membrane. The protoplasm
includes typical cell organelles like nuclei, mitochondria, ribosomes, endoplasmic reticulum etc.
Life cycle of Rhizopus stolonifer
Rhizopus stolonifer Life cycle includes both asexual reproduction and sexual.
- Asexual reproduction :- Asexual reproduction during favourable condition.
- Asexual reproduction takes place by the formation of sporangiophores with terminal uni-to-multispored sporangia.
Sporangiophores arise from mycelium.
- Each sporangium begins as a swelling into which a number of nuclei flow, and it
is eventually cut off from the
sporangiophores (Aplanospores) by the formation of a septum.
- The protoplasm within is cleaved, and a cell wall is in
the sporangium. Which divides sporangium into an outer fertile sporiferous zone and a central sterile columella.The protoplasts
of the sporiferous zone cleave mitotically to form dark-coloured multinucleate
- In this process, nonmotile, single-celled, haploid sporangiospores are formed.
- The sporangium becomes black as it matures, giving the mold its characteristic colour. Each spore, when liberated, can
germinate to produce a new mycelium.
- Sexual reproduction :- R. stolonifer is different from all other fungi because it reproduces by sexual reproduction via
- Sexual reproduction occurs only between different mating strains such fungi are known as
- Which have been traditionally labeled as + and - types. But the mating strains are morphologically
- Two hyphae of opposite strains come closer, hormones cause their hyphal tips to come
together.These hyphae are called zygophores.
- The tip of zygophores develop into gametangia, which become separated
from the rest of the fungal body by the formation of septa.
- The walls between the two touching gametangia dissolve, and
the two multinucleate protoplasts come together.
- The + and - nuclei fuse in pairs to form a young zygospore with
several diploid nuclei.
- The zygospore which can become dormant for several months.
- Meiosis occurs in the
diploid nuclei of zygospore.It results in the segregation of separate '+' and '-' nuclei all the nuclei so formed disintegrate
- After a long period of rest, the wall of the zygosporangium cracks. And produces a sporangium that produces
spores same as the asexually produced sporangium, and the life cycle begins again.
Sub- division :- Ascomycotina(sac fungi) Members of the Ascomycotina are known as the Sac Fungi. The majority of
fungi that lack
morphological evidence of sexual reproduction are
placed here. Examples of sac fungi are yeasts, morels, truffles, and Penicillium. This includes the salmon-coloured bread
mold Neurospora sp., which has played an important role in the development of modern
Important features of Ascomycotina:-
- These fungi posses well-developed, profusely branched mycelium except the
- Hyphae with regular cross-walls called septa and haploid.Which are centrally perforated to allow
cytoplasm, and sometimes nuclei, between compartments.
- The hyphal cells of the vegetative mycelium may be either
uninucleate or multinucleate.
- Cell walls are composed mostly of chitin.
- All produce an ascus (sac-like
structure) that contains haploid (n) ascospores after meiosis
- Plasmogamy is separated from karyogamy in time so that a dikaryotic phase is produced – the ascogenous hyphae
represent the dikaryotic hyphae(or at least in those which produce a teleomorph).
- Sexual life cycle is basically
similar – haploid-dikaryotic life cycle.
- Some species of
Ascomycota can self-fertilize and produce sexual structures from a single genetic strain; others require a combination of + and
Nutrition and Symbioses :-Ascomycotina are heterotrophs and obtain nutrients from dead or living organisms :-
As saprotrophs they can consume almost any carbonaceous substrate such as cellulose (found in plant cell walls), lignin (found
in wood) and recycled dead plant material .
- As parasites, ascomycetes account for most of plant pathogens including
powdery mildews that attack fruits, chestnut blight, and Dutch Elm disease (caused by Ceratocytis ulmi).
- Lichens- Symbiotic association between a sac fungus and a photosynthetic green algae or cyanobacteria
- Mycorrhizae :- Symbiotic association of a sac fungus living on plant roots.
- Endophytes:- Symbiotic association of a sac fungus with the leaves and stems of plants.
Reproduction and life cycle Fungi are Holomorphs.
- Holomorph a fungus that is characterized both by sexual
and asexual reproductive states.
- Teleomorph :-the fungus when reproducing sexually.
- Anamorph :- the fungus when reproducing asexually.
- Asexual reproduction :-
- Yeasts reproduces by budding or fission.
reproduction in the majority of the Ascomycetes occurs by the formation of specialized spores, known as conidia.
Which are formed on tips of modified hyphae called conidiophores.
- Conidia are formed in longitudinal chains on the
- Each conidium contains one or more nuclei.
- Conidia form on the surface of conidiophores in
contrast to spores that form within sporangia in Rhizopus.
- When mature, conidia are released in large numbers and
germinate to produce new organisms.
- Sexual reproduction :-In these fungi sexual reproduction occurs by the formation of multinucleate gametangia called :-
- Male gametangia may be an antheridium or conidium-like structure – spermatium.
- Female gametangium - ascogonium, may have a long projection, the trichogyne
- Asci formation occur on the same mycelia that produce conidia.
- The male nuclei of the antheridium pass into the ascogonium or an ascogonium and a spermatium ,through
- Plasmogamy or the fusion of the two cytoplasms, has now taken place.
- The male nuclei then pair with the genetically different female nuclei within the common cytoplasm but do not fuse.
now begin to grow out of the ascogonium.
- As the hyphae develop, pairs of nuclei migrate into them and simultaneous mitotic
divisions occur in the hyphae and ascogonium -dikaryotic cells.
The pairing of two genetically (+ and -) different types of nuclei followed by
septation results in the formation of a number of dikaryotic cells (i.e. containing two haploid nuclei, one from each strain).
- Sterile haploid hyphae known as peridium envelope the ascogonium to form the multicellular ascoma or
ascogenous hyphae produced inside the developing ascoma.
- Tips of ascogenous hyphae form croziers (hooks) before developing into an ascus.
- Ascoma contains two types of
- Ascogenous hyphae – dikaryotic, form asci through crozier formation.
- Sterile hyphae – haploid, form bulk of ascoma.
- The two nuclei in the terminal cell (ascus) of the dikaryotic hyphae then fuse into
a single diploid nucleus ("karyogamy"). The zygote is only diploid phase in life cycle.
- The ascus then elongates and
the diploid nucleus divides by meiosis, forming 4 haploid nuclei.
- Each haploid nucleus usually divides again by
mitosis, generally resulting in a total of 8 haploid nuclei but this may vary.
- These haploid nuclei are then cut off
in segments of the cytoplasm to form ascospores.
- In most Ascomycotina, the
ascus becomes turgid at maturity and finally bursts, sending its ascospores explosively into the air.
- Within the ascocarp, there is usually a layer containing the asci, and sterile cells known as paraphyses. This layer is
the hymenial layer.
The form of the ascocarp may be one of four types :-
There are four basic types of ascus:-
Unitunicate-operculate ascus has single wall, operculum (lid/) at the top. The operculum pops open when the ascus becomes
mature to release ascospores.
- found in apothecia
- Unitunicate-inoperculate ascus has no operculum but instead contains a special elastic ring at the top. On ripening it
briefly expands and so lets the spores shoot out
- found in perithecia and some apothecia.
- Prototunicate asci are mostly spherical in shape and they have no active
dispersal mechanism at all. The ripe ascus wall simply dissolves so that the spores can escape, or it is broken open by other
influences such as animals. Found in cleistothecia, some perithecia, and hypogeous ascomata.
- Bitunicate ascus is enclosed in a double wall. This consists of a thin brittle outer shell and a thick elastic inner wall.
At maturity the thin outer wall splits, and the thick inner wall absorbs water and expands upward, carrying the ascospores
with it . This 'Jack-in-a-box' design allows the ascus to stretch up into the neck of the ascoma to expel its spores.
Bitunicate asci occur only in pseudothecia.
Section "F" Sub-section "1"
Sub division - Basidiomycotina
Basidiomycotina are mostly terrestrial and saprophytic or parasitic. It includes some 25,000 described species. This
group includes most of the
mushrooms , toadstools, stinkhorns, puffballs, and shelf fungi. And also contains important obligate parasites, two
important plant pathogens the rusts and smuts.
This sub division shares many features in common with the Ascomycotina:-
- Well-developed, branched, regularly septate hyphae.
- Hyphae are initially uninucleate but soon become dikaryotic.
- Presence of yeast stage and presence of macroscopic
fruiting bodies, in some taxa. Few species form blastic conidia.
- Cell walls are usually
- As in the Ascomycota and Zygomycota, the
most important feature is the production of basidiospores (sexual spore).
- The basidiospores that are
typically borne, exogenously, on horn-like sterigmata (singular-sterigma) of basidia (singular- basidium).
General characters of Basidiomycotina :-The mycelium of the Basidiomycotina in most species have three distinct
phases during the life cycle of the fungus:- Primary mycelium :- When it germinates, a basidiospore produces haploid
primary mycelium . Initially the mycelium may be multinucleate, but septa soon form and the mycelium is divided into
monokaryotic (uninucleate) cells. This septate mycelium grows by division of the terminal cell. Dolipore septa with
parenthesome are present in most of the genera.Allows cytoplasmic movement but prevents nuclear migration from one
compartment to the next.
:-Commonly a secondary mycelium forms upon conjugation of two sexually compatible hyphae
( heterokaryotic). The dominant phase of the life cycle in most Basidiomycotina is a dikaryon, in which the two
together in mating exist side-by-side in each cell.
But some times, septa are not formed after a mitosis in the
terminal cell of primary hyphae as a results secondary mycelium is formed. Therefore all subsequent cells of the hyphae are
binucleate (dikaryotic). In both cases, the dikaryotic
(binucleate) mycelium is formed, since karyogamy (the fusion of the gametic nuclei) dose not immediately follow plasmogamy
(fusion of the protoplasts).As the dikaryotic mycelium grows, the cells divide and more septa are formed between the
Each of the new cells in the secondary mycelium has one haploid nucleus from each parent. This is due to clamp connections,
specialized structures unique to the Basidiomycotina.>
These are loop-like hyphae which connect the cytoplasm of
and through which nuclei move during cell division. During cell division, one nucleus divides directly into the
newly formed cell. The other nucleus divides inside the clamp connection and the two daughter nuclei migrate through the clamp
connection in opposite directions to the two daughter cells, reestablishing the dikaryotic condition.
The tertiary mycelium which is also dikaryotic, arises directly from the secondary mycelium forms the fruiting bodies
Reproduction and life-cycle of Basidiomycotina :- Like all fungi, Basidiomycotina can undergo both asexual and
- Asexual Reproduction :- Basidiomycotina reproduce asexually by either budding or asexual spore formation.
- Budding occurs when an outgrowth of the parent cell is separated into a new cell. Any cell in the organism can bud.
- The usual asexual spores formed by these fungi are arthrospores, sometimes called oidia.
- Few species form
conidia. Conidia (asexual spore) formation, takes place at the ends of specialized structures called conidiophores. The septae
of terminal cells become fully defined, dividing a random number of nuclei into individual cells. The cell walls then thicken
into a protective coat. The protected spores break off and are disbursed and germinate.
- Oidia are formed on
specialised, erect hyphal branches known as oidiophores. Oidia can have two functions. They may germinate to form mycelium or
they may function in the mating process. Asexual spores are usually haploid and the hyphae that form after germination are also
- Sexual reproduction :-
- No specialized sex organs form in the Basidiomycotina except in the rusts.
- The sexuality in Basidiomycotina gets progressively subdued.
- The specialized nature of sex organs is lost and the whole process is ultimately confined to copulation between vegetative
- The tertiary mycelium, which is also dikaryotic, arises directly from the secondary mycelium, and
forms the basidiocarp. The spore forming basidia(basidia are not produced by asexual Basidiomycota) are produced by the
terminal cell on millions of dikaryotic hyphae.
- Basidiocarps vary greatly in appearance in different genera, but all
bear basidia which are usually arranged in a layer of hymenium.
The basidia and basidiospores are produced on even sufaces or on hymenophores in form of teeth, tubes or leaf-like structures
(gills) at the inferior side of caps or consoles (crustothecium, pileothecium).
In special parts of the fruit body (hymenia, hymenophores if existing) karyogamy occurs between the two haploid nuclei within a
developing basidium. Then, the diploid nucleus undergoes meiosis to produce four haploid nuclei.
formation on the basidium is exogenic (external) which means that the 4 basidiospores appear on small appendages (sterigma) on
top of each basidium, in contrast to that, ascospore formation is endogenic. Basidia of Hymenomycetidae are formed in
layers called hymenia.
- The hymenia are exposed on special surface enlarging structures
(hymenophores) for spore discharge.
- One of the most important characteristics of Basidiomycotina is the production of
forcibly discharged ballistospores which are propelled into the air from the sterigma.
- Ballistospores are sexual or
asexual, and produced by basidia, hyphae, yeast cells, or even other ballistospores.
- This type of spore discharge
have been evolved very early in the evolutionary history of the Basidiomycotina as it is found in members of the earliest
diverging lineages within the group.
- Ballistospory is associated with forms that disperse their spores directly into
the air. Most aquatic Basidiomycotina and forms that produce spores inside the fruiting body, such as puffballs, have lost
- Basidiocarps is generally divided into 3 parts :-
- Hymenium The typical hymenium consists of parallel arranged fertile elements: young basidia (basidioles), basidiospore
forming basidia in various stages of developement and also sterile elements (cystidia).
- Subhymenium – Below the hymenium a layer of isodiametric cells is present
which is the subhymenium
- Trama – The layer on which the subhymenium and the hymenium is found to be located is the
trama. The trama is the main hyphal structure within the hymenophore (hymenophoral trama) and within the whole fruit body.
Fruit bodies (Basidiocarps) of the different species show a great variety of different shapes :-
Holothecium:- No clear delimination of spore producing and sterile parts in the fruit body which is cushion-like, club-shaped
(clavate), coralliform (coraloid) or irregularily lobed.
- Crustothecium : -A fruit body which is more or less
completely adnate to the substrate.
- Pilothecium :-a fruit body which is differentiated in a stipe and a cap.
Section "F" Sub-section "2"
Rusts (Pucciniales, previously known as Uredinales) shows greatest complexity in their life-cycle. Five different types of
spores are formed on two different hosts in two unrelated host families. Such rusts are heteroecious (requiring 2 hosts) and
macrocyclic. Autoecious rusts complete their life-cycles on one host intead of two.
In order to complete its life history, this species produces the following five spore stages:-
- Spore Stage 0: Spermogonia (sing.=spermogonium) (consists of Receptive hyphae and Spermatia [sing.=spermatium]) :-Generally
, basidiospores infect the alternate host the barberry , the mycelium forms pycnidia, called spermagonia. which are miniature,
flask-shaped, hollow, submicroscopic bodies embedded in host tissue (upper surface of a leaf). This stage, numbered "0",
produces single-celled, minute spores that ooze out in a sweet liquid and that act as nonmotile spermatia, and also protruding
receptive hyphae. Insects and probably other vectors such as rain carry the spermatia from spermagonia to spermagonia, for
crossing between the mating types.
- Spore Stage I: Aeciospores in aecia (sing.=aecium) :-After crossing , the dikaryons are formed and a second spore stage is
formed, numbered "I" and called aecia. The aecia with the dikaryotic aeciospores are formed in dry chains in inverted
cup-shaped bodies embedded in the lower surface of the barberry leaves. These aeciospores then infect the second host genus
and cannot infect the host on which they are formed (in macrocyclic rusts).
- Spore Stage II: Urediospores in uredia (sing.=uredium) :- During the early spring ,the aeciospores infect the wheat
plant. Infection of the wheat occurs in both the stem and leaves. Entry into the host occurs when the spores germinates and
enters the plant through openings called stomata. After germination of spores, the mycelium in the host plant gives rise to
clusters of the uredospores in dry pustules called uredinia.
On the second host a repeating spore stage is formed, numbered "II", As the urediospores develop, they will burst the
epidermis, exposing the characteristic, rusty-colored urediospores on the surface of the plant . The urediospore can infect
other wheat plants throughout the spring and early summer.
- Spore Stage III: Teliospores in telia (sing.=telium) :- During late summer, the uredium gradually converts into the telium
and begin to produce the two-celled, thick-walled teliospores a fourth spore type . The rusty-brown uredium becomes black as
the teliospores are borne.The teliospore stage, with its thick wall is the over winter stage and will remain dormant for the
- Spore Stage IV: Basidiospores on basidia (sing.=basidium) :- Under favorable condition, each cell is capable of germinating
to produce basidia and basidiospores.In the Pucciniales, the basidia are cylindrical and become 3-septate (four celled) after
meiosis, with each of the 4 cells bearing one basidiospore each. The basidospores disperse and start the infection process on
host first again.
On the basis of life cycle patterns, the rusts are of three types :-
- Macrocyclicrusts -Producing all 5 spores
- Demicyclic rusts in which uredial stage absent
- Microcyclic rusts Only two types of spores are formed
-teleutospores and basidiospores)
Sub- division - Deuteromycotina (Fungi Imperfecti)
- The Deuteromycota
are characterized by a
well-developed, septate mycelium, some are siphonaceous.
- Cell walls: Usually chitin and glucan.
- Asexual reproduction is by means of conidia (sing.=conidium) or may be lacking.
- Sexual reproduction is not known;
thus these are the "imperfect Fungi."
- This includes unrelated fungi from the Ascomycotina, Basidiomycotina and even
the Zygomycotina. Members of different fungal division may produce conidial states which are morphologically very similar and
classified in the same genus. Because any such genus may include such unrelated taxa, it is called a "form-genus."
- Many forms of Deuteromycota are pathogenic, affecting man, animals, or plants. Example Alternaria tenuis, Sporobolomyces.
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