1. MYCOLOGY
Welcome to Basidiomycotina: General
Characteristics & Ecology
By
N.Sannigrahi, Associate Professor,
Deptt. Of Botany, Nistarini College, Purulia
West Bengal, India
nandadulal2002prl@gmail.com
3. INTRODUCTION
Basidiomycetes , commonly called club fungi having basidium
and basidiospores in basidiocarp are fairly a large group of
fungi represented by about 1100 genera consisting of 30,000
species and classified under the sub-division Basidiomycotina.
Many of the Basidiomycetes are the familiar larger fleshy fungi
such as mushrooms, toadstools, puffballs, geasters, stinkhorns,
earth stars, bird’s nest fungi, jelly fungi bracket fungi, rusts,
and smuts.
Majority of the Basidiomycetes are saprophytes causing decay
of litter, wood or dung. A few forms are found as symbionts
forming mycorrhizae in trees, whereas some ones are
destructive parasites destroying a wide range of woody and
herbaceous plants. Rusts and smuts are pathogenic to plants
causing important diseases and are restricted to live tissues of
their respective host plants.
4. GENERAL CHARACTERISTICS
(i) Thallus is usually mycelial (some are yeasts called
basidiomycetous yeasts). Hyphae are septate. In some cases, a
number of hyphae lying parallel to one another are joined
together to form thick strands enveloped in a sheath or cortex
and behave as a unit or tissue. This modified hyphal form is
called rhizomorph.
(ii) The mycelium of most of the Basidiomycetes passes
through three distinct stages of development, which are called
primary mycelium (monokaryotic and develops from the
germination of sexual spore called basidiospore), secondary
mycelium (dikaryotic and develops from primary mycelium
after the process of plasmogamy during sexual reproduction),
and tertiary mycelium (represented by well-matured secondary
mycelia that compose the fruiting bodies called basidiomata of
complex Basidiomycetes).
5. GENERAL CHARACTERISTICS
(iii) Septa in hyphae are simple or characteristic dolipore. The
dolipore septum flares sharply and broadly in the middle
portion forming a barrel-shaped structure with open ends,
which is covered by membranous structure called
paranthesome or septal pore ,helps in continuity of protoplasm.
(iv) Cell wall is made up of chitin and glucans.
(v) In all the Basidiomycetes, except the rusts, a specialized
structure called clamp-connection is formed on the secondary
mycelium. Clamp-connection is a device for the perpetuation
of dikaryophase in the secondary mycelia in Basidiomycetes.
(vi) The asexual reproduction takes place by oidia, conidia, or
chlamydospore formation. Out of the several types of spores
developed in the life cycle of rusts and smuts, some (e.g.,
uredospore) function as asexual spores. The higher taxa of this
class lack asexual reproduction.
6. ASEXUAL REPRODUCTION
In terms of structure and ontogeny, three basic kinds of conidia
in Basidiomycetes develop-
Oidia- Small, hyaline, thin walled, unicellular structure;
uninucleate, may develop on monokaryotic or dikaryotic
mycelia but the oidia borne on dikaryotic hyphae are
monokaryotic and develop the process of dikaryotization,
Oidia may be wet type or dry type
Blastic conidia-formed on the conidiophores and liberated by a
blowing out mechanism, can develop on germinating
basidiospores or on monokaryotic mycelia.
Chlamydospores- unicellular spores formed on some
mushrooms and bracket fungi, formed intercalary in position
inside the substratum,
Bulbils are multicellular parenchymatous propagules
composed of thin walled , undifferentiated homogenous cells
7. SEXUAL REPRODUCTION
(vii) No specialized sex organs develop in Basidiomycetes and
sexual reproduction takes place by conjugation of nuclei of two
different strains.
(viii) During sexual reproduction, the dikaryotic cell is formed
by spermatization, somatogamy, clamp- connection, or Buller
phenomenon. Plasmogamy may occur by fusion of cells of two
primary mycelia of opposite strains, two basidiospores of
opposite strains, Buller phenomenon etc.
(ix) Karyogamy does not occur just after plasmogamy because
there exists a prolonged dikaryophase between plasmogamy
and karyogamy. The fusion of nuclei of two different strains
occurs within the basidial mother cell.
(x) Meiosis takes place just after karyogamy resulting in
haploid daughter nuclei that are used in the formation of
basidiospores.
9. SEXUAL REPRODUCTION
The dikaryotic get organized to form fruiting bodies called
basidiocarp where karyogamy and meiosis occur to form
basidiospores. Basidiocarp consists of Stipe ( stalk), Pileus ( Cup)
along with other parts but the structure may varies from species to
species from microscopic to 3ft or more in diameter.
xi) Basidiospores are the characteristic haploid sexual spores of
basidiomycetous fungi, which are produced exogenously on the
surface of basidia after karyogamy and meiosis within nuclei lying
inside basidia. If the sexual spore of a fungus is a basidiospore, the
fungus is a Basidiomycete regardless of any other character. This one
character distinguishes Basidiomycetes from all other fungi.
(xii) Except rusts and smuts, the Basidiomycetes usually produce
fruiting bodies called basidiomata (sing. basidioma), which were
earlier called basidiocarps.
Basidia may be of Holobasidia(Aseptate with rounded apex) or
Phragmobasidia (Septate with incised apex)- Stichobasidial,
Chiastobasidial and Tunning fork types.
11. COMPATIBILITY
Due to lack of sex organs, mycelia of Basidiomycetes are
sexually undifferentiated. But on the basis of mating behaviors,
only 10% are homothallic where the mycelia derived from a
single basidiospore forms fruiting bodies. Three type of
homothallism found in this group according to Roper(1966).
Primary Homothallism- Monokariotic mycelia develop from
the basidiospores are self fertile. Dikariotization occurs through
clump connections.
Secondary Homothallism- Each basidia produces two
heterokaryoytic spores after meiosis and each spore on
germination give rise to dikaryotic mycelia
Unspecified homothallism-where mycelia from a single
basidiospore is able to form basidiocarp without
dikaryotization.
90% members are heterothallic- bipolar (A or a)or tetra polar
9AB, Ab, aB, ab) called bifactorial heterothallism.
12. HETEROTHALLISM
Two types of heterothallism are found to occur-
A. Bipolar heterothallism- Compatibility is governed by one
pair of factors. Due to segregation of two alleles at meiosis, a
single spore carried only one allele A or a. Dikaryons are
formed between monokaryons carrying different alleles of this
pair. A monokaryon carrying ‘A’ factor can not form a dikaryon
with another monokaryon carrying the same allele ‘A’. It is also
called unifactorial heterothallism.
B. Tetra polar heterothallism- It occurs near about 67% of the
heterothallic species Sexual compatibility is governed by two
pairs of factors AaBb located on different chromosome and
segregate independently as par law of Mendelian
segreggation.They produce four types of basidiospores-AB, Ab,
aB and ab. Mating will occur between AB and ab type of
monokaryon. Ab and aB type of monokaryons are also called
bi-factorial heterothallism.
13. ECOLOGY
Experience cosmopolitan in distribution-either saprophytes,
symbionts and parasites
Mostly terrestrial but few are marine,
Saprophytes are corticolous (grow on wood) includes edible
mushrooms and toxigenic group, ectomycorrhizal group,
Some members form rhizomorphs enabling access to fresh
sources of organic nutrients,
Few members are pathogenic of plants and humans like rust
and smuts of rice, wheat and some human beings,
Degrade lignin of the wood and grow in household uncared
woods and deteriorate the quality and strength.
Members play a very important role in decomposition of debris
and release bound elements to nature
Imrove mineral availability and uptake for the host plants .
14. IMPORTANCE
i) Rusts and smuts cause many diseases of cereals and other
economically important plants resulting in great loss in
production that brings famine in certain parts of the world.
(ii) Mushrooms are edible and are enjoyed by mycophagists for
food and flavor. Agaricus, Pleurotus, and Volvoriella are
cultivated on large scale throughout the world. Mushroom
cultivation industry is growing fastly.
(iii) Some mushrooms (called toadstools) such as Amanita spp.
are deadly poisonous, while others such as Psilocybe spp.
produce hallucinogenic chemical substances.
(iv) The polypore cause enormous damage to forest trees as
parasites and to timber as saprophytes.
15. IMPORTANCE
(v) Mycelia of basidiomycetous fungi play significant role in
decomposition of organic matter and recycling of nutrients. It
is because they bear ability to produce various extracellular
enzymes which break down complex chemicals like cellulose
and lignin.
Clavatia contains anticancer drugs- Clavacin having high
degree of importance as chemotherapy agent,
Ectotropic mycorrhizal connection with roots of forest trees is
mutually beneficial as far as forest ecology is concerned.
Many wood fungi play a very destructive roll in the
deterioration of the wood decaying and reduce the quality and
quantity of the valuable timber species.
The fungi group plays a very significant role to form green and
sustainable environment.
16. THANK YOU FOR YOUR
PARTICIPATION
ACKNOWLEDGEMENT
Introduction to Mycology & Mycopathology- Mishra & Dash
Botany for Degree students: Fungi- Vasistha & Sinha
A text book of Botany- Hait, Bhattacharya & Ghosh
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Disclaimer: This presentation has been made as free learning
resources without any financial interest.
