This is an illustrated account for Unit 1 of Coure Course III Mycology and Phytopathology of Bsc Hons Program - Introduction to True fungi including characters, affinities, thallus, cell wall, nutrition and classification

1. BSc Hons Program ;Core Course III :
Mycology and Plant Pathology
Unit 1 -: Introduction to fungi
Dr Rita Som Paul
Associate Professor
Siliguri College
Siliguri

2. General characteristics
• 1. Chlorophyll is absent hence they are non-
photosynthetic
• 2. They are heterotrophic in their mode of
nutrition
• 3. They are eukaryotic but sometimes also called
as mesokaryotic because of their special mode
of division
• 4. The body does not have differentiation into
different specialized parts so it is called as
thallus

3. Affinities with plants
• Both are eukaryotic thus cell structure is similar
ie presence of organelles and membrane-bound
nucleus
• Presence of rigid cell wall around the cell
• Both lack locomotion ie mobility
• Both engage in relationships with other
organisms – mutualistic, symbiosis, parasitism
etc
• External structure is similar in plants and some
macrofungi (mushrooms)

4. Affinities with animals
• Presence of chitin in the cell wall
• Food storage in the form of glycogen
• Formation of centrioles during cell division
• Achlorophyllous
• Heterotrophic
• Microscopic or macroscopic in structure

5. Thallus (no organization into
tissues/organs) structure
• 1. Unicellular thallus. The body consists of a single
cell. No mycelium. The vegetative and reproductive
stages cannot occur in the same thallus. The whole cell
changes into a reproductive structure - holocarpic
fungi. Types :
• With a rigid call wall in the vegetative phase Eg.
Chytrids like Synchitrium spp.
• No rigid cell wall in their vegetative phase. There is
naked multi-nucleate, amoeboid mass of protoplasm,
termed as plasmodium. Eg Slime moulds like
Plasmodiophora spp.

6. Synchitrium (holocarpic)-rigid CW Plasmodiophora(holocarpic)- no
rigid CW

7. Thallus….
• 2. Filamentous thallus. Most have long fine filaments called
hyphae (singular hypha), which on aggregation form
mycelium. During reproduction, some hyphae extend into
air and give rise to reproductive structures- eucarpic fungi.
Two types :
• Possessing aseptate (septation i.e. compartmentalization
into cells) multinucleate (innumerable nuclei present)
mycelium- called as coenocytic mycelium. Eg. Lower fungi
(Mastigomycotina and Zygomyctina) like Rhizopus spp.,
Phytophthora spp., etc.
• Possessing septate mycelium i.e. multicellular filaments
with usually an incomplete septum with a pore that
permits exchange of protoplasm. Eg. Higher fungi like
Agaricus spp., Ascobolus spp., Fusarium spp. etc.

8. Rhizopus (holocarpic fungus)-
coenocytic mycelium
Aspergillus (holocarpic fungus)-
septate mycelium; multicellular

9. Thallus….
• 3. Pseudomycelium. Some fungi have a rigid
cell wall and a single cell in their vegetative
phase, but when they reproduce asexually
they may form false mycelium or
pseudomycelium in the form of short chain-
like filamentous structures. Eg. Saccharomyces
cerevisiae.

11. Cell Wall composition
• Usually Three layers :
• 1.chitin (called as fungal cellulose, polymer of N-acetyl
D-glucosamine) – basic constituent in most Fungi
• 2. Zymosan. (layer of b-1,3-glucan)
• 3. Mannoproteins (mannose-containing glycoproteins)
• Oomycetes or water moulds have the usual cellulose
and glucans in their cell walls. They also have
hydroxyproline (amino acid) in cell walls, not found in
the true fungi.
• Note : A new group of fungi, Cryptomycota , does not
have chitin in their cell wall at all. This a highly diverse
group of unculturable fungi ( Jones et al, 2011).

12. Nutrition
• Fungi depend on external sources for their growth and
development- heterotrophs (hetero – others, trophy –
food). Types :
• 1. Obligate parasites or biotrophs – the fungi that need to
get into a suitable host in order to live and reproduce, but
they may or may not cause a disease. Definitely, they will
cause a discomfort to the plant or animal. These are
seldom fatal, because these fungi depend on their host for
survival and it will not be in their interest to kill the host.
They cannot be cultured on synthetic media. Most of the
obligate fungal parasites that have been discovered , are
pathogens i. e. they do cause disease. Eg. Erysiphe causes
powdery mildew, Puccinia causes rust.

13. Nutrition….
• 2. Facultative parasites – do not need a living
host in order to survive, but they may
occasionally infect a suitable host and live as
parasites. Eg. Fusarium spp, Botrytis cinerea
are the usual residents of soil and infect hosts
under suitable conditions.

14. Nutrition…
• 3. Obligate saprophyte or necrotroph – The
fungi that live only on dead and decaying
matter and never infect a living organism. Eg.
Agaricus spp.

15. Nutrition…
• 4. Facultative saprophyte – These usually
prefer a living host for their development and
reproduction. However, they can survive on
dead organic remains also and can be grown
on artificial media in laboratory. Eg.
Phytophthora infestans.
•

16. Nutrition….
• 5. Symbiont – A fungus enters into a mutually
beneficial relationship. Eg. Lichen – a
partnership with an alga. Mycorrhiza –
partnership of fungi with roots of higher
plants.

17. Taxonomic position and Classification
R. H. Wittaker (1969). According to his five-kingdom
concept, Monera includes unicellular prokaryotes
(bacteria and cyanobacteria), Protista – unicellular
eukaryotes (microalgae and protozoa), Mychota (or
Mycota)– yeast and moulds, Plantae – true plants ,
Animalia – true animals.
In 1996, Lynn Margulis, an eminent evolutionary
biologist, stated that molecular biology, life history and
fossil record evidence support the reunification of
bacteria as Prokaryota while subdivision Eukaryota into
uniquely defined subtaxa : Protoctista (unicellular
eukaryotes), Animalia, Fungi and Plantae.