Chapter 4

Characteristics & Classification

of Fungi

Chapter Overview

Explain the major characteristics of fungi

Identify the modification of hypae

Give explanation of the types of fungi

Discuss the reproduction of fungi

Clarify classification of fungi

Characteristics of Plant Pathogenic Fungi

Small - Usually filamentous and branched

Lack chlorophyll

Microscopic

Have cell wall - that contain glucan & chitin but no cellulose

Eukaryotic

The MorphologyThe body of the fungus is called mycelium

The individual branches of mycelium are called hyphaeMycelium (a mass of hyphae)

Each hyphae or mycelium is generally uniform in thickness (0.5 m in diameter)The mycelium consists of many cells containing one or more nuclei per cell

Mycelium

Growth of the mycelium occurs at the tips of the hyphae

The mycelium may be either have a:1. Septa (higher fungi) - Septate hyphae2. No septa (lower fungi)- Aseptate hyphae

Somatic Structure-Modification of Hyphae

A. Rhizoids A short, thin hyphae growing in a root like fashion towards the substrateArise from the node of stolon Absorb water and nourishment from substrate

B. Stolon The hyphae that grow horizontally above substrum and then bend down into the substrum

C. Rhizomorphs Root-like structures, thicker than mycelium

A thick strands of hyphae

Extend from the mycelium through the substrate

They help in spreading the fungus from one root system to another root system.

D. Haustorium (absorptive organs)The lateral branches of hyphae that penetrate into the host cells

And enlarge in the form of knob-like

Obtain nourishment from the protoplasts of the host cells.

Originate on the hyphae of obligate parasites

E. Appressorium

The small swelling formed at the tip of hyphae

Allowed the germ tube to penetrate into the host epidermis

Germ tube – The early growth of mycelium produced by a germinating fungus spores.

F. Chlamydospores

Larger than the standard spores

Formed from the dense of cytoplasm at certain portion of hyphae

Have thick wall

It is the life-stage which survives in unfavourable conditions

G. Sclerotia It is a dark, hard and irregular structure

It is the resting bodies formed from the hyphal aggregation

It is a fungal “survival structure” Formed under unfavorable conditions

Types of Fungi

Saprophyte

Parasite

Symbion

Saprophyte

Live on the dead organic matterHelp decomposeMost of 100,000 species.Obligate saprophyte – only can live as saprophyteFacultative saprophyte – lives as parasite but in certain condition can live as saprophyte

Parasite

Live in the living host

Obligate parasite – only live in the living host/ organism

Facultative parasite – lives as saprophyte but in certain condition can live as parasite.

Symbion

Live with other living organism and both give the advantage to one another Not important in causing disease in plant

Eg: Mycorrhizae – the relationship of fungi and roots will enhance the absorbent of nutrients

Mycorrhizae (fungus-root)

Some Mycorrhizae colonize roots intercellularly (ectomycorrhizae)Some of them colonize roots intracellularly (endomycorrhizae)The mycorrhizae mycelium is much more smaller than the plant roots.Help the plant to absorb nutrients and water from soilAt the same time the mycorrhizae also get the nutrients directly from the plant.

The long, white strands here are

fungal mychorrhizae

Reproduction of Fungi

Three (3) types of reproduction:

Asexual reproduction

Sexual reproduction

Parasexual reproduction

1. Asexual Reproduction

Formation of spores without involving the fusion of nuclei or sex cells.

The most important way of reproduction - produce a lot of sporesCan be group into 4 categories:

Fragmentation

Fission

Budding

Spore Formation

1. Fragmentation - A part of the vegetative hypha separated and develops into a new individual mycelium

2. Fission - The somatic cells splitting to produce two cells

3. Budding - A small bud is produced from the parent cell. Then, the young bud will separated from the parent cell and become a new individual

4. Spore Formation - The spores also have many shape, size, colour, arrangement and way of their formation. Structure responsible for spore

production is called sporophore

Budding Vs Fission

Asexual SporesAsexual spores are either:

1. In sporangia / sporangium

The terminal end of sporophore will develop containers (sporangia)

The container will hold asexual spores

The asexual spores are call sporangiospores (non motile spores)

A motile and flagelleted spores are known as zoospore

Sporangia containing zoospore is called zoosporangium

2. Exposed directly to the atmosphere (Conidia and conidiophore)In some fungi, the spores are not contained within membranes, they are borne free.This sporophore is called conidiophore and the spores are conidiaConidiophore may be unbranched or branched andMay or may not contain a vesicle at the end

2. Sexual Reproduction

Involves the fusion of two nuclei

The spore is called sexual spore and the fusing cells are called gametes

3 Phases of Sexual Reproduction

Plasmogamy – fusion of 2 protoplasts of 2 gametes or (fusion of hyphae)

Karyogamy – fusion of 2 nuclei from the fusing gametes to form a diploid zygotic nucleus

Meiosis – formation of 4 haploid spores

Fungal Sex Organs- Gametangia

1. Isogametangia – morphologically similar gametangia

the gametes are very similar and cannot be classified into "male" or "female”

2. Heterogametangia – morphologically different gametangia

Antheridium - male gametangium & contains antherozoids Oogonium - female gamentangium & contains female gamete

Fungal Sexual Cell- Gametes

3 types of gametes :

1. Isogamous – an equal sizes of gametes (cannot be distinguish)

2. Anisogamous – 2 unequal sizes of gametes (the shape is same but the size is different)

3. Heterogamous – 2 different gametes (male is motile , female is non motile)