DIVERSITY OF FUNGI

BIO102: Plant Diversity

OLABISI ONABANJO UNIVERSITY Bup Oyesiku PhD

www.bupoyesiku.net ~ 1 ~ Department of Plant Science

DIVERSITY OF FUNGI

http://www.bupoyesiku.net/




Contents Topic: Diversity of Fungi ............................................................................................................................3

Objectives .............................................................................................................................................3

Reading Assignment ..............................................................................................................................3

Lecture ..................................................................................................................................................3

Introduction ..........................................................................................................................................4

Main Content ........................................................................................................................................4

Background of Fungi ..........................................................................................................................4

Reproduction in Fungi ........................................................................................................................5

Classification of Fungi ........................................................................................................................7

Characteristics of Fungi ......................................................................................................................8

Diversity of Forms in Fungi .................................................................................................................9

Habitats of Fungi.............................................................................................................................. 10

Ecology of Fungi ............................................................................................................................... 10

Economic uses of Fungi .................................................................................................................... 11

Conclusion ............................................................................................................................................... 12

Summary ................................................................................................................................................. 13

References/Further readings/Links .......................................................................................................... 13

Test Yourself Questions (TYQ).................................................................................................................. 14





Topic: Diversity of Fungi

Objectives

In this lecture we will learn the followings:

Awareness and knowledge of the fungi diversity

Acquired skills to identify poisonous members of the Fungi

ecological functions of fungi

Economic values of fungi to our lives

Reading Assignment

In addition to the discussion in this lecture read current textbooks in the main library of

OOU and visit: ilearn.bupoyesiku.net and [email protected]

for the online lecture.

Lecture

Fungi are majorly land plants, and equally important in many different ecosystems as

bacteria. Activities of fungi and bacteria make possible the recycling of dead organisms

in the ecosystems. They are the decomposers of any given ecosystem, without them

there may be no ecosystem. In today’s lecture, we shall be discussing the kingdom

Fungi, which consists of mainly non-photosynthetic organisms. For students aspiring to

major in Mycology, Plant Pathology, as well as those that need the knowledge in various

fields of study, you will gain more knowledge about the unusual diversity of fungi and

their contributions to our ecosystems, particularly their importance to our life.


mailto:[email protected]




Introduction

Fungi belong to the Kingdom Fungi. Mycology (Gr. Mykes = mushroom) is the study of

fungi. A scientist who studies fungi is called mycologist. It is important you know that

fungi contain some fascinating and unusual species. They are neither green plants nor

animals. But share certain characteristics of both plant and animal. The important facts

that made them stand in-between plants and animals are given to their shared

characters. Rigid cell walls made of mixture of polysaccharides (cellulose) as in plants

and chitin similar to exoskeleton of insect. Aside from shared characters with other

organisms, fungi relationship with the environment is very different from that of any given

organism. They are discussed in this lecture because they have traditionally been

grouped with plants. Although no direct evolutionary connection with plants, but fungi

share filamentous multicellular growth forms, except for the yeast that exists in a

unicellular form.

Fungi form the decomposers (saprobic fungi) of terrestrial food web in a typical

ecosystem. It is also important for you to note that continued existence of the whole

world rest solely on activities of fungi and bacteria as the only heterotrophic organisms of

the universe. Another fact is that fungi are equipped with a powerful arsenal of enzymes

that break organic products. Fungi activities (decomposition) like bacteria also consume

oxygen, releases carbon dioxide into the atmosphere and nitrogenous compounds into

the soil that are in turn recycled by plant and humans. The importance of fungi as

commercial pests cannot be overemphasized by their ability to grow under a wide range

of conditions.

Main Content

Background of Fungi

Fungi are primarily terrestrial with only few examples of aquatic members. Traditionally,

the fungi have been observed to include heterotrophic protists. For clarity protists will be

discussed in another lecture because there are few evidences as regard their connection





with fungi and it seems not to be a likely ancestor of fungi. About 100,000 species of

fungi have been so far discovered and described, while double these numbers of species

are out there in the soils waiting to be discovered.

Reproduction in Fungi

The three most important and common modes of reproduction in fungi are as follows:

Vegetative strategy

Asexual strategy

Sexual strategy

Vegetative strategy

Almost all fungi reproduce majorly by vegetative strategies. In fragmentation method the

mycelium breaks up into small fragments. Each fragment in turn develops into a new

mycelium. Other strategies include fission, budding, sclerotia and rhizomorphs (Fig 1.1).

Fission Budding Sclerotia

Fragmentation

Rhizomorphs

Figure1.1 Diversity of fungi vegetative reproduction





Asexual strategy

Asexual reproduction takes place in fungi by production of asexual or sexual spores. hey

Spores may be produced singly or on a special structure/stalks known as sporangia or

conidia. (Fig1.2).

Sexual strategy

A large number of fungi reproduce sexually except for the members of Deuteromycetes

(Imperfecti). Sexual reproduction in fungi involved alternation of generations of haploid

(n) and diploid (2n) phases. The gametes are always haploids and through process of

fusion a diploid sexual spores (zygospores, oospores) are produced. It is important to

note here that gametes taking part in sexual fusion may be morphologically or

physiologically different. Any two gametes taking part in fusion are of opposite sexes

(male and female sex organs) or plus and minus strains. Gametes that are involved in

fusion are found inside a special sac called sporangium. If participating gametes are

equal in size and shape the resulting gametes are therefore isogametes. The

morphologically dissimilar male and female gametes are called the heterogametes. To

further enhance your understanding, sexual reproduction in fungi involves the union of

two compatible nuclei, which takes place once in a life cycle. Fungi are remarkable for

Hypha

Conidia

2

2

2

2

2

2

2

2

2

2

2

2

2

Figure 1.2 Diversity of fungi asexual spores. Conidia of Aspergillus (A), Clamydospores

of Ustilago spp., Conidiophore and conidia of Penicillium(C)

Hypha

Conidiophore

Conidia

A B C





their diversity of sexual process. For your knowledge, basically, sexual reproduction

involves a cycle of plasmogamy, karyogamy and meiosis, which happens in sequence;

first the fusion of the plasma (plasmogamy) of the gametes followed by the fusion of

nuclei (karyogamy) and finally the meiotic division. It is beginning to be clear why fungi

should have a separate kingdom; they have a different mechanism of sexual

reproduction compare to other plants and animals.

Classification of Fungi

Traditionally in the past fungi membership includes protists (molds) but now treated as

separate group (Fig 1.3). Protista (molds) including three divisions, Myxomycota,

Oomycota and Acrasiomycota, which have been separated from fungi; because unlike

fungi they are known to produce motile cells (swarm cells and zoospores) during certain

stage of their life cycles. This attribute of motile cells is never found in most fungi, this

attribute supported the recent separation from fungi.

However, fungi are classified by their reproductive structures. There are three divisions

of fungi, distinguished by reproductive structures.

Division Zygomycota - fusion of plus and minus hyphae lead directly to the formation

of a zygote

Division Ascomycota - fusion of plus and minus strains leads to massive hyphae that

form zygotes in a sac-like structure (ascus). Yeast, a unicellular fungus is mostly

Ascomycetes that play many important commercial and medicinal roles.

Division Basidiomycota - zygotes are produced within reproductive structures called

basidia

Fungi imperfecti have not been observed to reproduce sexually so they have not been

classified into any one of the three divisions. However they have a separate division,

Deuteromycota. Besides the macroscopic fungi division outlined above there are few

microscopic members belonging to the division Phycomycota. Members in this group

include fungi with coenocytic hyphae.





Characteristics of Fungi

Fossil records have shown that the first fungi were believed to be unicellular eukaryotic

organisms with no living copies. The oldest fossils with a resemblance of fungi exist 900

Million Years Ago (MYA).

Other characteristics of fungi include the followings:

All fungi have cell walls with cellulose, hemicellulose and chitin(as in animals)

Almost all fungi have glycogen as the basic storage polysaccharide (as in animals)

FUNGI

Motile

Slime molds

Water molds

Cellular molds

Non-motile

Ascomycetes

Basidiomycetes

Deuteromycetes

Phycomycetes

Zygomycetes

Fig. 1.3. Classification of protista (A) and fungi (B)

B

A





Almost all fungi produce spores as in bryophytes and pteridophytes (cryptogams)

All fungi are non-motile throughout their life cycle (unlike Protista)

Almost all fungi spores are dispersed by wind

All fungi are non-photosynthetic

Modes of feeding in fungi include biotrophic, necrophytic, saprophytic and symbiotic

Diversity of Forms in Fungi

Fungi are traditionally divided into two groups based on absence or presence of cross

walls (septate) partitions. The two groups are coenocytic; filament with no partitions and

non-coenocytic, filament with partitions. In coenocytic hypha filament many nuclei are

contained in an extensive cytoplasm while in non-coenocytic hypha filament nuclei are in

compartments created by the cross walls, which may or may not be perforated (Fig 1.4).

The divisions include Zygomycota, Ascomycota and Basidiomycota). Of the three

divisions only members of Ascomycetes have coenocytic hyphae (or mycelia).

.

B

A

Figure1.4 Typical hyphae filaments in fungi. A=Coenocytic, B=Non-coenocytic





Habitats of Fungi

Fungi grow by mean of filaments called hyphae (singular=hypha) which tangle together to

form a network called mycelia (singular=mycelium) that make up the body of most fungi. It

is important we should know that hyphae of some species of fungi can spread more than

30 acres in forest soil and may be one of the world's longest length living organisms.

Fungi occupy habitats with large quantity of decaying organic matter. They obtain their

food either by living off dead organic materials as saprobes or feed on living materials as

parasites. Saprobic fungi are equipped with modified hyphae called rhizoids, for

attachment to their habitats (substrates). Parasitic fungi have specialized hyphae called

haustoria for absorbing nutrients from the living cells of their host organisms. Others are

pathogenic fungi and mostly the phycomycetes group, which will be discussed in another

lecture.

Ecology of Fungi

Fungi are important key-species in the world ecosystems, occupying the basal portion of

ecological food chain (or web) as decomposers of organic products. Almost all living

plants directly or indirectly depend fungi and bacteria for their nutritional needs. It is

important for you to know that all fungi are heterotrophic except lichenized fungi. Fungi

are mostly in relationship with other organisms. For example in nature, certain vascular

plants form associations called Mycorrhiza between their roots and fungi; these

associations are responsible for production and distribution of the plants nutrients. You

will recollect a similar association between bacteria and the root nodules of vascular

plants, legumes; this alliance fixes nitrogen in nodules of legume roots and enhances soil

fertility balance. Another example is lichens, a symbiotic associations of fungi and algal

or cyanobacteria cells. It is important to know that lichen occupies all inhospitable

environments as you will learn in another lecture. Like bacteria, fungi are known to cause

biodeterioration of synthetic materials. Such as cloths, paper, leather, optical lenses and

almost any materials you can possibly imagine. Nevertheless, it has not been

established anywhere that fungi are effective biomonitor of environmental pollution. But

fungi are specially known for binding soil particles together by their mycelia.





Economic uses of Fungi

From historical stand point, fungi have a great economic value to humans, animals and

plants. It will also be interesting to you to know that the qualities that make fungi

important pests also make them commercially valuable. However, almost all fungi reduce

the nutritional values and palatability of foodstuffs.

Current trend in the use of fungi have step up the interest in the field of pharmaceuticals.

New unknown compounds extracted from soil dwelling fungus Cyclosporine; “wonder”

drug suppresses immune reactions that could arise following organ transplantation. It will

be of utmost interest to you that the discovery of this novel drug makes organ

transplantation successful today. Because it does not have any side effect of the other

drugs used in the past, which often kill bone marrows and cause leukemia.

Androstenol extracted from truffles and added to certain cosmetics designed to attract

potential opposite sex.

Yeasts (unicellular organisms) are used in production of ethanol and carbon dioxide by

fermentation process; play a key role in baking and brewery industries. You should not

be surprised to know that fungi are singularly responsible for the majority of plants

diseases. Of the world’s Basidiomycetes (mushrooms) 95% are deadly to higher

organisms. Learn to distinguish the edible fungi from the poisonous ones before deciding

to pick mushrooms for consumption.

Poisonous mushrooms are roughly identified on the field by presence of a number of

characters (Fig. 1.5).

Fragments of the veil net on the mushroom cap

Cap (yellowish green, brownish or white) with shiny radiating stripes

White or greenish gills with white spores

Larger annular ring (white) compared with that of edible mushrooms

White long stem (with or without) green patches

white cuplike or sheath (volva) surrounding the stem and partially underground

Let these characteristics remain engraved in your mind.





We should be careful because some of these characters are unstable and quickly fade

away from sight. They are not always reliable characters to identify poisonous fungi. A

traditional method of placing a silver spoon in a pan containing cooked mushrooms to

see if it turns black is also not a reliable method of testing poisonous mushrooms. The

only reliable and safe method is the use of Taxonomic key by the experts.

Conclusion

You must have learnt how to recognize fungi in the wild, and their diverse divisions.

Habitats and niches of many of the fungi as emphasized here. Absolute dependence of

natural ecosystems upon the fungi; a need for further research as to discover more

commercial and ecological uses of fungi cannot be overemphasized.

B

C

E

A

D

F

Figure1.5 Field diagnostic characters of poisonous mushrooms. A=Veil,

B=Cap, C=Ring, D=Stem, E=Volva, F=Substrate.





Summary

Having study this lecture, students should:

Have some understanding of types of Fungi

Have a better idea of the characters that separate the fungi from other organisms

Be ready to look around the environment for the common members of mushrooms

Develop skills to identify the poisonous fungi in the wild

Know ecological and economic benefits of fungi

References/Further readings/Links





Test Yourself Questions (TYQ)

Matric No Department Attendance Code Session/Student’s Level

AC___________________

Question TRUE FALSE

1. Fungi are mostly aquatic and terrestrial in nature

X

2. All Fungi are non-photosynthetic organisms

X

3. Protists are true fungi

X

4. Fusion of two nuclear is term karyogamy X

5. Association of vascular plant root with a fungus is Mycorrhiza X

6. Fungi mycelium length is one of the longest living world’s

organism X

7. Fungi are good indicator of pollution

X

8. Sexual reproduction in fungi involve plus and minus hyphae X

9. Existence of the universe only rest upon fungi

X

10. Soil fungus that suppresses immune reactions is Androstenol

X

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