Jahnvi’s Biology Classes
We say what we do
Synopsis
Topic- Fungi
Content- :

Introduction

“The only way of finding the limits of the
possible is by going beyond them into
the impossible.”
“ur determination defines ur destiny”
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FUNGI
Mycology : The branch of biology dealing with the study of fungi is called Mycology or Mycetology.
•
Father and Founder of mycology is Pier Antonio Micheli
•
The fungi constitute a unique kingdom of heterotrophic organisms. They show a great diversity
in morphology and habitat. Fungi are achlorophyllous, heterotrophic, spore-producing, non
vascular eukaryotic organisms.
Occurence
The fungi grow in dark, warm and moist places. Fungi are cosmopolitan occur in air, water, soil and
on animals and plants. Majority are terrestrial, few are aquatic, parasitic and symbionts. On the basis
of the place of inhabiting area, these are grouped as
i.
Coprophilous : on dung.
ii.
Corticolous : on bark.
iii.
Epixylic/xylophilous/lignicolous : on wood.
iv.
Keratinophilous : on hairs & horns.
•
When your bread develops a mould or your orange rots it is because of fungi. The common
mushroom you eat and toadstools are also fungi.
•
White spots seen on mustard leaves are due to a parasitic fungus. Some unicellular fungi, e.g.,
yeast are used to make bread and beer.
•
Other fungi cause diseases in plants and animals; wheat rust-causing Puccinia is an important
example. Some are the source of antibiotics, e.g.,
Penicillium.
•
Food is kept in referigerator in order to prevent it from going bad due to bacterial or fungal
infections.
Somatic structure : The basic structural unit of fungi is a tube like structure known as Hypha. The
fungal body is made up of network of hyphal strands, known as Mycelium.
•
Some hyphae are continuous tubes filled with multinucleated cytoplasm - these are called
coenocytic hyphae. Others have septae or cross walls in their hyphae.
•
The cell walls of fungi are composed of chitin and polysaccharides. Chitin is made up of acetyl
glucosamine (NAG).
•
The dictyosomes are uni cisternal.
•
Lomasomes are present which are outgrowths of cell membranes. These helps in increasing the
surface area.
•
Nuclear division is intranuclear in which spindle is formed inside nucleus. It is also known as
closed or karyochorisis (Moore).
•
Ribosomes generally lie freely in cytoplasm. Special vesicles which occur near hyphal tips
contain wall materials and are known as chitosomes.
•
Exceptions are yeast, which are unicellular or acel-lular, all other fungi are filamentous. The
unicellular forms may form pseudomycelium
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Nutrition
Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are
called saprophytes.
•
Nutrition is heterotrophic and absorptive. In saprophytic fungi digestion takes place outside the
body (Extra-cellular or external digestion). Hyphae release hydrolytic enzymes like :
amylases, lipases, cellulases and proteases on organic matter and digested nutrients are
absorbed directly.
•
The saprophytic fungi may be obligate or facultative. It may be symbiotic.
•
The reserve food is glycogen and oil in all the fungi.
•
Those that depend on living plants and animals are called parasites. Parasitic forms may
develop haustoria for absorption of food
Nature of Hyphae
Hyphae can be septate or aseptate Aseptate hyphae when multinucleate are called as coenocytic hyphae (Oomycetes, Zygomycetes).
In septate hyphae, cells have one or two nuclei. The septa are of two types:
i.
Septa with simple pores : Septa have simple central pore (Ascomycen
Deuteromycetes).
ii.
With dolipore septum : Central septal pore possess barrel shaped inflations (Basidiomycetes).
Reproduction
It occurs by three ways i.e., vegetative, asexual and sexual.
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1.
Vegetative: In vegetative reproduction any part of the mycelium directly act as unit of
reproduction. It occurs by multiple ways.
i.
Fragmentation : Mycelium breaks down into small fragments accidentally or by decay.
ii.
Fission : It occurs in unicellular forms where cell divides to produce two daughter cells.
iii.
Budding : An outgrowth develops at one end of cell. It grows into a bud which separates
and
develops new individual.
iv.
Rhizomorphs : These are subterranean, long
distinct
rope like twisted hyphal strands with
growing points like roots and also act as pe-
rennating structure. Under
favourable conditions it will give rise to normal mycelium.
v.
Sclerotia : These perennating structure are hard compact masses of hyphae without any
growing point. Under favourable conditions each sclerotium forms a new mycelium.
2.
Asexual Reproduction : It occurs through the for- mation of spores. Spores produced in
specialized structures developed on the hyphae. These are single celled reproductive and
dispersal units. Spores may be motile, non motile, thick walled or thin walled. There are
different types of spores:
i.
Zoospores : These are motile and are produced by some members of phycomycetes. The
zoospores are of multiple types i.e. uniflagellate with whiplash type flagellum,
uniflagellate with tinsel type flagellum, biflagellate with tinsel & whiplash type
flagellum. These can be biflagellate with two whiplash type flagella.
ii.
Sporangiospores : These are nonmotile spores produced inside sporangia e.g.
Zygomycetes.
iii.
Chlamydospores: These are thick-walled perennating spores.
iv.
Oidia : These are individual cells separated from hyphae under condition of excess water,
sugar and certain salts. Oidia multiply by budding and forms Torula stage, e.g., Rhizopus.
v.
Conidia :These are non motile spores produced in chains exogenously. e.g.,
Ascomycetes, .
deuteromycetes
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3.
Sexual Reproduction : Sexual reproduction involves syngamy and meiosis. The syngamy
involves the fusion of male and female gametes. The fusion of cytoplasm is called
plasmogamy
while that of nuclei is called karyogamy. Then, meiosis occurs in the zygote to
produce haploid spores. The sexually produced spores are oospores, ascospores and basidiospores.
The various
spores are formed inside the distinct structures known as fruiting bodies.
The sexual cycle involves the following three steps:
(i)
Fusion of protoplasms between two motile or non-motile gametes called plasmogamy.
(ii) Fusion of two nuclei called karyogamy.
(iii) Meiosis in zygote resulting in haploid spores
When a fungus reproduce sexually, two haploid hyphae of compitible mating types come together and
fuse. This results in formation of an intermediate stage called dikaryotic stage in which cell contains
two nuclei. Such cells are called dikaryons. Karyogamy occurs just before meiosis. So life cycle has
three phases : haplophase (n), dikaryophase (n + n) and diplophase (2n).
Dikaryotic phase is characteristics feature of ascomycetes, basidiomycetes.
The sexual reproduction is absent in the group of fungi called "fungi imperfecti" or Deuteromycetes.
Sexual reproduction occurs by five methods
i.
Planogametic copulation : It involves the fusion of motile gametes.
ii.
Gametangial contact : Two types of gametangia (sex organs) male-antheridia and femaleoogonia come in contact with each other. Male gametes are transferred to the oogonium
directty through a fertilisatioin tube e.g. oomycetes like Albugo
iii.
Gametangial copulation (conjugation) : It is complete fusion of two gametangia resulting in
the formation of a zygospore e.g., Rhizopus, Mucor.
iv.
Somatogamy : This involves fusion of two somatic cells. Sex organs are absent, e.g.,
Agaricus.
v.
Spermatogamy or spermatisation : Male gametes which are non-motile small cells called
spermatia are carried by wind or water or insects to a small hyphae which acts as a female
sex organ called Trichogyne.
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•
In fungi there is gradual reduction in sexuality from lower fungi to higher fungi.
Behaviour of fungal mycelium
•
Homothallism : The phenomenon in which the two fusing gametes belong to same mycelium
or genetically similar mycelium e.g., Rhizopus sexualis.
•
Heterothallism : The phenomenon in which the two fusing gametes belong to genetically and
physiologically different mycelia but sex organs and thalli are morphologically similar. These
morphologically similar but genetically different types are known as mating types or termed as (
+) & (-) strains.
The phenomenon of heterothallism was discovered by A.F. Blakeslee in Rhizopus stolonifer. It is
advantageous because it results in greater variations. It is a device to prevent inbreeding.
Type of fungus on the basis of its reproductive unit
 Holocarpic : It is a fungus in which whole of the thallus is used in the formation of a
reproductive structure.
 Eucarpic : It is a fungus in which part of the thallus is used in formation of a reproductive
structure.
•
Fungicides:
i.
Bordeaux mixture ; It was first fungicide to be discovered by Millardet against grape vine
downy mildew (Plasmopara viticola). It is a mixture of copper sulphate and lime (calcium
hydroxide). It is also known as Holy water of plant pathology.
ii
Burgundy mixture : It is a mixture of copper sulphate and sodium carbonate.
Classification : The fungi is classified into different classes on the basis of morphology of mycelium,
mode of spore formation & fruiting bodies, sexual reproduction & nature of life cycle
Phycomycetes
•
Members of phycomycetes are found in aquatic habitats and on decaying wood in moist and
damp places or as obligate parasites on plants.
•
The mycelium is aseptate and coenocytic.
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•
Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). These
spores are endogeneously produced in sporangium.
•
Zygospores are formed by fusion of two gametes. These gametes are similar in morphology
(isoga-mous) or dissimilar (anisogamous or oogamous).
Oomycetes
•
This class includes both aquatic and terrestrial fung or some members are obligate parasite on
plants.
Mycelium is coenocytic. Hyphal wall is made up of cellulose or both cellulose and chitin.
Asexual reproduction occurs with the help of zoospores(motile) and aplanospores(non-motile). These
are produced endogeneously inside the sporangia. The another type of spores which are produced
inside the specialised structures called conidiosporangia. They form conidia under dry conditions and
form zoospores in wet conditions.
In aquatic fungi the zoospores produced are biflagellate and heterokontae type with one flagellum
smooth and other is tinsel type and are generally laterally attached.
Sexual reproduction occurs by gametang'ial contact by the formation of conjugation tube. The
fertilized oogonium forms oospore e.g., Albugo, Phytophthora
Common diseases caused by the members of oomycetes
1.
White rust of crucifers (white spots on mustard leaf) : Albugo Candida (Cystopus candidus).
2.
Late blight of Potato : Phytophthora infestans. It was cause of Irish Famine.
3.
Damping off seedlings : Pythium debaryanum
4.
Downy Mildew of cereals and Green Ear disease of Bajra (Pennisetum typhoides)
5.
Downy Mildew of pea/mustard
Zygomycetes (Conjugating fungi)
•
This class includes only terrestrial forms which are mostly saprotrophic, few are parasitic.
•
Mycelium is coenocytic with hyphal wall made up of chitin.
•
Asexual reproduction takes place with the help of non motile spores known as sporangiospores
which are produced inside sporangia. Sporangia are produced at the tips of vertically growing
hyphae called sporangiophores. Motile stages are completely absent.
Sexual reproduction occurs by gametangial copulation or conjugation. It involves fusion of
two gametangia or coenogametes which produces a resting and perennating diploid sporezygospore. At the time of germination, each zygospore undergoes meiosis and forms a germ
sporangium at the tip of hyphae called promycelium. Germ sporangium forms
meiospore called germ spores. Germ spores when released give rise to new mycelium.
Life cycle is haplontic. Somatic (vegetative) phase is haploid and diploid stage is represented by
zygote or zygospore only.
Important members
1.
Life cycle of Rhizopus stolonifer : It is also known as black bread mould or pin mould. Hyphae
are aseptate coenocytic. The vegetative phase is made up two types of hyphae i.e.,
stoloniferous hyphae and rhizoidal hyphae.
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Asexual reproduction: It occurs during favourable conditions. Around 2-5 vertically growing
unbranched hyphae arise from the node. These are called sporangiophore and bear sporangia at the
tip. Each Sporangium has inner sterile dome shaped columella and outer spore bearing part called
sporangiferous zone which has large number of brownish black, multinucleate non-motile thin walledsporangiospores or mito-spores or aplanospores.These spores when released germinate on suitable
substratum to produce new mycelium.
Asexual reproduction also occurs by oidia and chlamydospores. The oidia are produced in sugary,
liquid, acidic medium where they also form torula stage.
Sexual reproduction: It is of conjugation type e.g., Rhizopus stolonifer (heterothallic). The Rhizopus
sexualis is homothalic. Generally Rhizopus species are heterothallic.
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When both ( + ve) and (-ve) type mycelia are growing together in the same medium, they stimulate
each other by producing-phermomone like chemical-trisporic acid because of which mycelia produce
club shaped negatively geotrophic hyphae-Zygophore. These + ve and -ve types of zygophores come
in contact with each other and develop progametangia. Tips of progametangia gets differentiated as
multinucleate, gametangia or coenogametes and are separated from lower part or suspensor by a
septum. At the time of fertilization, common wall between two gametangia dissolves and the two
coenogametes fuses to form diploid dark coloured resting spore called zygospore. The sexual
reproduction is isogamous type. If copulation fails then azygospore or parthenospore are produced
parthenogenously.
Under favourable conditions zygospore undergoes meiosis but only one haploid nucleus survives. Zygospore germinates forms promycelium and bear germ sporangium. Germ spores are uninucleate
and haploid which on germination produces a new mycelium.
Economic Importance
1.
Spoilage of food.
2.
Soft Rot or Soft leak of fruits and vegetables
Ascomycetes or sac Fungi
•
Ascomycetes includes saprophytic, decomposers parasitic and coprophilous forms. These are
multicellular eukaryotic except yeast which is unicellular.
•
Mycelium is branched, septate & haploid. The septa has simple central pore. Pores are having
woronin bodies present around them. Cells may be uninucleate (Penicillium), binucleate or
multinucleate.
•
Cell wall is made up of chitin (Fungus cellulose).
•
Reproduction occurs by fragmentation, asexual and sexual methods.
•
Asexual reproduction : It occurs with the help of conidia which are developed exogenously in
chains at the tip of special mycelium, conidiophore with basipetal arrangement. Conidiophores
may be unbranched (Aspergillus) or branched [Penicillium). Tips of condiophores produce
bottle shaped appendages known as sterigmata. Conidia on germination give rise to new
mycelium. Sexual reprodution : It may occur by somatogamy or by gametangial contact as
in Penicillium. Male gametangium of Penicillium is long tubular known as a antheridium and
female gametangium is club shaped known as ascogonium.
In all ascomycetes (except yeast) at the time of fusion only plasmogamy occurs, karyogamy is
delayed. This results in the formation of a dikaryotic phase. In this phase cells are dikaryotic (n
+ n). Some dikaryotic cells acts as Ascus mother cells and show karyogamy which forms
diploid nucleus. The ascus mother cell with a synkaryon is called young ascus cell. Ascus
cell elongates and undergoes meiosis followed by mitosis. The resulting 8-haploid nuclei are
organised into 8 ascospores (meiospores) in the mature ascus. So sexually produced ascospores
are endogenous in origin. When released ascospores produce haploid mycelium
In most of the species, asci are grouped to form definite complex-fruit bodies known as ascocarps.
•
According to their shape, ascocarps are of 3 types
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i.
Apothecium: These are cup or saucer shaped open structures, e.g., Peziza, Morchella.
ii.
Perithecium : These are flask shaped, with a small opening known as ostiole, e.g., Neurospora, Claviceps.
iii.
Cleistothecium : These are completely closed, e.g., Penicillium, Aspergillus
Important member of class ascomycetes
Yeast (life cycle)
•
Yeast were first described by A.V.
Leeuwenhoek.
•
These
are
unicellular
members
of
ascomycetes and may get organised into
temporary chains or pseudomycelia. Cell
wall is made up of chitin, mannan, glucan,
lipid & proteins.
•
Nutrition
is
saprophytic
sometimes
parasitic also. Yeast secretes enzyme
named zymase. The glycogen is chief
reserve food.
•
Yeast are facultative aerobes
Asexual reproduction : Depending upon the
mode of asexual reproduction, yeast are of three
types.
i.
Budding: It occurs under sugary conditions or favourable conditions, e.g., Saccharomy –
ces cerevisiae.
ii. Fission : e.g., Schizosaccharomyces, octosporous.
iii. Helobial : Both budding and fission, e.g., Saccharomycoides ludwigii
Sexual reproduction : The yeast is of two types.
False yeast : In this sexual reproduction is absent and there is no ascus formation e.g. Candida.
True yeast: In this sexual reproduction is present. The fusing gametes may be iso or anisogamous
type. It is gametic copulation or conjugation. There is no dikaryotic stage. After meiosis, usually
four ascospores are produced inside ascus. Ascocarps are absent.
The yeast's sexual reproduction is the best example of Hologamy.
The fusion of two adjoining sister cells is called adelphogamy. Fusion between mother and
daughter cell is known as pedogamy.
Economic Importance
i. Brewing Industry : Under anaerobic condition sugary solution can be converted into
alcoholic beverages with the help of yeast.
Saccharomyces cerevisiae (Brewer's yeast)
ii.Baking industry : Yeasts when added to flour during kneading produces carbon dioxide and
alcohol. The two evaporate during baking and make dough soft and spongy.
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iii Food : Yeast are added to food to increases vitamin content.
1.
Penicillium (Blue green mould)
It is a source of antibiotic penicillin. It was earlier obtained from P. notatum and now is obtained
from P. chrysogenum. Griseofulvin (antifungal) is obtained from P. griseofulvum; Brefeldin (P.
brefeldianum),
2.
Aspergillus : (Laboratory weed, Guinea Pig of plant kingdom)
Aspergillus flavus grows on stored grains and groundnut and produces a carcinogenic toxin
called Aflatoxin.
It may cause pulmonary disease-Aspergillosus and otomycosis (ear infection) in human
beings.
3.
Neurospora (Red/Pink Bread Mould) : It is also called as Drosophila of Plant kingdom. It is
used extensively in biochemical and genetical work.
4.
Powdery Mildew (Fungal disease resulting in Powdery coating).
Powdery Mildew of cereals like wheat/Barley
Powdery Mildew of Pea or Legumes
5.
Ergot of Rye : Claviceps purpurea : Sclerotia are the source of lysergic acid which is used for
preparing LSD (D-lysergic acid diethylamide) a hallucinogenic drug.
6.
Bakane or Foolish seedling disease of rice : Gibberella fujikori.
7.
Morchella esculenta (morels ): These, are having edible ascocarp.
8.
Tuber aestivum (Truffels) : Its underground asco-carps are edible.
9.
The members like morels and truffels are edible and are considered delicacies
Basidiomycetes (Club Fungi)
These are most advanced fungi and best decomposers of wood. It includes Mushrooms, Bracket fungi,
Puff balls. The grow in soil, on logs, on tree stumps and in the living plant bodies as parasites (e.g.
rusts and smuts).
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•
Mycelium is branched and septate which is having dolipores. Hyphal wall is made up of chitin.
Motile structures are absent.
•
Asexual spores are generally not found but vegetative reproduction by fragmentation is
common.
•
Mycelia are of two types, i.e., primary and secondary mycelia.
•
The primary mycelium is multicellular, monokaryotic and with haploid nuclei. Primary
mycelium may multiply by oidia or conidia like spores, but is generally short lived. So asexual
spores are generally
•
Secondary mycelium is also multicellular but dikaryotic, long lived and profusely branched.
The hyphae develops clamp connections. .
•
This mycelium can perennate in the soil or wood by means of sclerotia or rhizomorphs. It
multiply by different types of spores like chlamydospores, aecidiospores or uredospores etc.
•
Secondary mycelium also produces club shaped structures known as basidia (Basidium
singular). In this basidium occurs karyogamy and meiosis. Basidium usually develops four
meiospores or basid-iospores exogenously at the tip of fine outgrowth called sterigmata.
•
The basidia arranged in the form of fruiting bodies known as basidiocarps. Basidiocarps of
many basidiomycetes are large sized e.g. Mushrooms, puff balls and bracket fungi.
•
Sexual reproduction : Sex organs are absent. Sexual reproduction may be by somatogamy or
spermatisation. Species generally show heteroth-allism. Plasmogamy or somatogamy is brought
about by fusion of two vegetative or somatic cells of different strains or genotypes. At the time
of fusion only plasmogamy occurs and karyogamy is delayed. This results in the formation of a
dikaryon It produces a dikaryotic (n + n) mycelium called secondary mycelium.
Important Members
1.
Mushrooms [Agaricus campestris) Lifecycle :
It is a common mushroom with edible basidiocarp.
Life cycle starts with the germination of
basidiospore
which is haploid. It give rise to
haploid, sep
tate monokaryotic mycelium known as
primary
mycelium. Hyphae of opposite mating
types ( + ve
and -ve) when come in contact show
somatogamy. It produces
dikaryotic
a
mycelium
long
called
mycelium (spawn). This mycelium
form of a ring inside
lived
extensive
secondary
grows in the
soil.
Under favourable conditions, from this mycelium arises
compact masses of hyphae at places called button. The
buttons enlarge and produce basidiocarp, which are
called as Mushrooms. Such mushrooms often lie in
rings called "Fairy rings".
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Each mushroom has a fleshy stalk called stipe and umbrella shaped cap or pileus. In button stage
pileus is connected to stipe by membranous covering called veil or velum. Later on it ruptures and
appears as a ring known as annulus. Under surface of pileus bears 300-600 radiating rows .of
verticalplates called gills or lamellae. The
two sides of gills are lined by thousands of
club
shaped
basidia
alongwith
sterile
paraphyses.
Now each basidium develops four sterigmata
with a basidiospore at top. On germination
each
basidiospore
produce
primary
mycelium.
2.
Toad
stools
:
mushrooms
Poisonous
Amanita
caesarea (Caesar's Mushroom), A.
muscaria. Amanita phalloids (Death
cup).
3.
Puff balls : Lycoperdon, Clavatia.
4.
Bracket fungi: Polyporus, Fomes
Plant diseases :
1. Rusts:
i
Black stem rust of wheat - Puccinia graminis tritici.
ii
Yellow rust of wheat - Puccinia glumarum = P.striiformis.
iii
Brown rust of wheat - P. recondita.
Life cycle of P. graminis tritici:
It is a common rust and is heteroecious (two
hosts : wheat and barberry) in nature. It produces
5 types of spores, i.e..
On wheat plant
Stage-ll : Uredospores (n +n) (can reinfect
wheat)
Stage-Ill : Teleutospores (n + n), bicelled
(cannot reinfect wheat) but give rise
to basidia and basidiospores.
In Soil
Stage-IV : Basidiospores (n)
On barberry plant
Stage-I : Pycnidia (n) are developed on the upper
(Adaxial) surface of barberry leaf and produce
pycniospores.
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Stage-0 : Acedia developed on the lower (abaxial) surface of barberry leaf and produce aeciodospores
(n + n) which are produced after spermatisation or dikaryotisation and so are dikaryotic.
Indian Scientist K.C. Mehta is famous for his work on Black stem rust of wheat in India.
2. Smuts : Smuts are caused by pathogen Ustilago.
Smuts are of two types : Loose and Covered.
i.
Loose smut of wheat : Ustilago tritici.
ii.
Loose smut of Oat: U.avenae.
Spores are exposed from the begining
•
i.
Covered smut of Corn : U.maydis.
ii.
Covered smut of Barley : U.jensenii
Economic importance of Basidiomycetes
i.
These cause plant diseases, e.g., Rusts, Smuts etc.
ii.
Basidiomycets are wood rotters. These cause decomposition of lignin and cellulose.
iii.
These form mycorrhiza, e.g., Amanita, Boletus.
iv.
Some members are edible, e.g., Puffballs, Mushrooms.
v.
Some have hallucinating properties, e.g., Psilocybe (Sacred mushroom) etc.
vi.
Some are poisonous, e.g., Amanita caesarea, A. phalloides, A. muscaria commonly
called Toad stools.
vii.
Clavicin drug obtained from Clavatia
Deuteromycetes (Fungi imperfecta or imperfect fungi)
•
The mycellium is branched, septate
•
Sexual or perfect stage is not known. Only asexual and vegetative phases of these fungi are
known.
•
Asexual reproduction : It occurs generally by means of conidia.
•
When the sexual forms of these fungi were discovered they move into classes they right belong
to. Once perfect (sexual) stages of members of deutereomycetes were discovered, they were often move to ascomycetes and basidiomycetes.
•
Large members of this class are decomposers of litter and help in mineral cycling.
Economic importance:
• Early blight of potato : Alternaria solani.
• Red rot of sugar cane : Colletotrichum falcatum.
• Brown leaf spot of rice : Helminthosporium oryzae. It caused the famous, Bengal famine of
1942-43.
• Wilt disease of potato, tomato, banana, gram, cotton etc.: Fusarium oxysporum. Fusarium
moniliforme. It is imperfect stage of Gibberella fujikuroi.
• Tikka disease of groundnut: Cercosporapersonata.
• False yeast: Many yeast cause skin disease in human beings commonly called as ring worm
diseases: Trichophyton.
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• Predator fungi : Some fungi trap small nematodes and other small animals and obtain
nourishment from them, e.g., Dactylella, Arthrobotrys.
LICHENS
•
Lichens are composite or dual organisms which are formed by symbiotic association between
fungi and algae. Their dual nature was discovered by Schwendener.
•
The branch of science that deals with study of lichens is called lichenology.
•
Theophrastus used term lichen for first time for superficial growth on bark of Olea
europea (Olive) tree
Relationships:
•
Symbiosis : Lichens show a symbiotic relationship
between algae and fungal cells. The fungal
partner is
called as mycobiont (Ascomycetes or Basidiomyctes).
The algal partner is called
phycobiont
(Chlorophyceae and Cyanophyceae). Algae prepare food
for fungi and fungi provide
shelter
and
absorbs
mineral nutrients and water for its parterner.
The algal and fungal partners are autotrophs and
heterotrophs respectively. The algae prepares mannitol. In lichens, this association between algae and
fungus is example of mutualism, popularly called
symbiosis.
•
Helotism : Fungus sends haustoria into algal cells,
prevent the alga to develop pectic covering and
induce alga to secrete organic substance. So, the
fungus is considered as controlled parasite over the
alga. This phenomenon is called as helotism.
•
The bulk of the thallus of lichen is made up of fungus (95%) and the algal part is only 5%.
Habitat:
• Lichens grow on bare rocks, cooled volcanic lava,
sand dunes, roofs, walls, window panes, tree bark,
leaves, in arctic or alpines regions or in humid climate.
Classification :
The lichens are classified on the basis of different parameters.
A.
On the basis of fungal partner:
• Lichens are of two types :
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i.
Ascolichens : In these the fungal member is of as- comycetes and algal partner is mostly member
of green algae (Trebauxia) and rarely blue green algae(Scytonema, Nostoc, Anabaena).
ii. Basidiolichens : Where basidiomycetes member is fungal partner and the algal partner is
generally blue green algae.
Most common lichens are ascolichens which have green algae as the symbiotic partner.
B.
On the basis of growth form :
• Lichens are of three types :
i.
Crustose (Crustaceous) lichens : Present in form of thin or thick crust over rocks, soil, tree
barks, e.g., Graphis, Lecanora.
ii
Foliose (Foliaceous) lichens : These are like dried leaves and are attached to substratum by
special structure called rhizine, e.g., Parmelia, Peltigera.
iii Fruticose (Filamentous) lichens : These are having cylindrical flat or ribbon like upright
generally branched structure attached to the substratum by their basal ends, e.g.,Cladonia,
Usnea, Evernia, Ramalina.
Reproduction in Lichens :
a)
Fragmentation : Occur by breaking of thal - fragment growing into new thallus.
b)
By isidia : These are small papilla like outgrowths, which get detach from parent thallus and
grow into new thalli. These are also photosynthetic in function.
c)
By soredia : These are small sac-like bodies consisiting of one or more algal cells elapsed or
surrounded by fungal hyphae and are formed in pusule like structure called soralium. These
get detached from the thallus, disseminate by the wind and falling upon suitable substratum ,
germinate to form new plant.
Sexual reproduction : It is the function of fungal partner.The male sex organ is called
spermatogonium which contain number of non-motile sperms or sperma-tia while the female sex
organ is called carpogonium which is having lower coiled portion called ascogonium and upper
straight portion called trichogyne
Economic importance :
•
As food and fodder: Cladonia rangifera (Reindeer moss) is used as fodder for reindeer, musk
ox in Tundra region. Cetraria islandica (Iceland moss) is used as food by human in Iceland.
•
Source of dyes : Litmus and orcein are obtained from Rocella tinctoria.
•
Source of medicines : Usnic acid which is obtained from Usnea ( Old man beard)and Cladonia
acts as antibiotic.
Peltigera canina is used against hydrophobia.
•
Usnea is highly inflammable and can cause forest fires.
•
Soil formers : Lichens secrete lichnic acid which break down rocks and thus help in soil
formation.
•
Source of cosmetics and perfumes : Everina and Rarpalina used for manfacturing soaps,
havan samagri and Dhoop etc.
•
Crustoso tichens are pioneer in xerosere.
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•
Lichens are very good pollution indicators (S0 2 pollution).
MYCORRHIZA
•
The mycorrhiza term was given by Frank.
•
Mycorrhiza is a symbiotic association between a fungus and the root of higher plant. Such roots
lack root caps and root hairs. Mycorrhizal roots remain in upper layer of soil where organic
matter is abundant.
•
Mycorrhiza can be divided into 2 groups.
i
Ectomycorrhiza
(Ectotrophic
mycorrhizae)
:
Mostly
fungal
partner
belongs
to
basidiomycetes.
a)
The fungus forms a mantle of hyphae over the surface of roots as well as penetrates the
root cortex but remains in its intercellular spaces producing Hartig's net.
b)
The cortical cells of root secrete nutrients into intercellular spaces to be absorbed by
fungal hyphae.
c)
Examples of ectomycorrhizal fungi are Boletus, Amanita. Rhizopogon. These fungi show
symbiotic association with roots of Pinus and other forest trees.
ii
Endomycorrhiza (endotrophic mycorrhizae) : Mostly fungal partner belongs to zygomycetes.
a)
External mantle is absent. So root hairs are present.
b)
Fungal hyphae pass into intercellular and intracellular spaces in cortical cells. Inside cortical cells, fungus forms swollen vesicles or finely branched masses called arbuscules.
c)
Because of this, endomycorrhiza is called as VAM (Vesicular arbuscular mycorrhiza).
d)
VAM help in absorption of nourishment from cortical cells.
e)
Examples of endomycorrhizal fungi are Rhizoctonia, Endogone, Glomus. These fungi
show symbiotic association with roots of Orchids.
Advantages of Mycorrhizal Association :
•
Pines and birches are known to absorb 2-3 times more of potassium, nitrogen, phosphorus,
copper and zinc in the presence of mycorrhiza.
•
Fungal association increase water availability to the root.
•
These helps in dissolving essential minerals present in organic debris and handing over the
same to the plants.
•
The fungus produces various growth hormones for plants.
•
It secretes antimicrobial substance which protect the young roots from attack of pathogens.
**all the best**
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