Download Fungi Attack Plants

Teresa Audesirk • Gerald Audesirk • Bruce E. Byers
Biology: Life on Earth
Eighth Edition
Lecture for Chapter 22
The Diversity of Fungi
Copyright © 2008 Pearson Prentice Hall, Inc.
These honey
mushrooms are part
of the visible portion
of the largest
organism on Earth.
A single honey
mushroom colony in
Oregon covers and
area of 8.9 sq. km
(2200 acres).
Chapter 22 Outline
• 22.1 What Are the Key Features of Fungi? p.
424
• 22.2 What Are the Major Groups of Fungi? p.
425
• 22.3 How Do Fungi Interact with Other
Species? p. 430
• 22.4 How Do Fungi Affect Humans? p. 433
Section 22.1 Outline
• 22.1 What Are the Key Features of
Fungi?
– Fungal Bodies Consist of Slender Threads
– Fungi Obtain Their Nutrients from Other
Organisms
– Fungi Propagate by Spores
– Most Fungi Can Reproduce Both Sexually
and Asexually
Fungal Body Structure
• Most fungi are multicellular
• Cells are surrounded by cell walls
composed of chitin, a nitrogen-containing
polysaccharide
• Body of almost all fungi is a mycelium, an
interwoven mass of threadlike filaments
called hyphae (singular, hypha)
FIGURE 22-1 (part 1) The filamentous body of a fungus
(a) A fungal mycelium spreads over decaying vegetation. The mycelium is
composed of (b) a tangle of microscopic hyphae, only one cell thick, portrayed
in cross section (c) to show their internal organization.
Fungal Body Structure
• Hyphae of most species are divided into
many cells by partitions called septa
(singular, septum); each cell possesses
one or more nuclei
– Pores in the septa allow cytoplasm to stream
from one cell to the next
• Hyphae of some fungi lack septa,
consisting of single elongated cells with
hundreds or thousands of nuclei
• The nuclei of most species are haploid
FIGURE 22-1 (part 2) The filamentous body of a fungus
The mycelium is composed of (b) a tangle of microscopic hyphae, only one cell
thick, portrayed in cross section (c) to show their internal organization.
Nutrition and Fungal Lifestyles
• All are heterotrophic
• Secrete enzymes outside their bodies and
absorb the digested nutrients
• Have diverse lifestyles
– Fungal decomposers (saprobes) feed on dead
organic material and wastes
– Fungal parasites absorb nutrients from cells of
living hosts and may cause disease
– Some symbiotic fungi live in mutually beneficial
relationships with other organisms
– Fungal predators consume living organisms
Propagate by Spores
• Spores are haploid reproductive cells
capable of developing into an adult fungus
– Usually produced in large numbers
– Dispersed by animals or air currents
• Both asexual and sexual reproduction
involve the production of spores within
fruiting bodies
FIGURE 22-2 Some
fungi can eject spores
A ripe earthstar
mushroom, struck by a
drop of water, releases
a cloud of spores from
the fruiting body that
will be dispersed by air
currents.
Asexual Reproduction
• Typically occurs under stable conditions
• Can occur either by:
– Fragmentation of the mycelium
– Asexual spore formation
• Haploid mycelium produces haploid asexual spores
by mitosis
• Spores germinate and develop into a new mycelium
by mitosis
• Results in the rapid production of
genetically identical clones
Sexual Reproduction
• Typically occurs under conditions of
environmental change or stress
– Neighboring haploid mycelia of different, but
compatible mating types come into contact
with each other
– The two different hyphae fuse so that the
nuclei share a common cell
– The different haploid nuclei fuse to form a
diploid zygote
– Zygote undergoes meiosis to form haploid
sexual spores
Sexual Reproduction
• Spores germinate and develop into a new
mycelium by mitosis
• Results in the production of genetically
diverse fungal bodies
Section 22.2 Outline
• 22.2 What Are the Major Groups of
Fungi?
– Chytrids Produce Swimming Spores
– Zygomycetes Can Reproduce by Forming
Diploid Spores
– Ascomycetes Form Spores in a Saclike Case
– Basidiomycetes Produce Club-Shaped
Reproductive Structures
– Some Fungi Form Symbiotic Relationships
Classification of Fungi
• Fungi have been assigned to four phyla
based upon the way they produce sexual
spores
– Chytridiomycota (chytrids)
– Zygomycota (zygote fungi)
– Ascomycota (sac fungi)
– Basidiomycota (club fungi)
FIGURE 22-3 Evolutionary tree of the
major groups of fungi
Table 22-1 The Phyla of Fungi
The Chytrids
• The Chytrids
– Most are aquatic
– Reproduce both asexually and sexually
– Form flagellated spores that require water for
dispersal
– Figure 22-4, p. 426, illustrates the chytrid
fungus Allomyces in the midst of sexual
reproduction
FIGURE 22-4 Chytrid filaments
These filaments of the chytrid fungus Allomyces are in the midst of sexual
reproduction. The orange structures visible on many of the filaments will
release male gametes; the clear structures will release female gametes. Chytrid
gametes are flagellated, and these swimming reproductive structures aid
dispersal of members of this mostly aquatic phylum
The Chytrids
• Most feed on dead aquatic material
• Some species are parasites of plants and
animals
– One chytrid species is a frog pathogen
believed to be a major cause of the current
worldwide die-off of frogs
• According to evolutionists, primitive
chytrids are believed to have given rise to
the other groups of modern fungi
Zygomycetes
• Most live in soil or on decaying plant or
animal material
• Reproduce both asexually and sexually
– Sexual spores are thick-walled zygospores
• During asexual reproduction:
– Haploid spores are produced via mitosis in
black spore cases called sporangia
– Spores disperse and germinate to form new
haploid hyphae
• Figure 20-5, p. 427, depicts the asexual
reproduction in Rhizopus, black bread mold
FIGURE 22-5
The life cycle of a zygomycete
Ascomycetes
• Live in a variety of marine, freshwater, and
terrestrial habitats
• Each fruiting body contains numerous
saclike cases called asci (singular, ascus)
• Reproduce both asexually and sexually
– Sexual spores form in saclike asci
FIGURE 22-7a Diverse
ascomycetes
The cup-shaped fruiting
body of the scarlet cup
fungus (top)
The morel (bottom), an
edible delicacy. (Consult an
expert before sampling any
wild fungus – some are
deadly!)
FIGURE 22-6 The life cycle of a typical ascomycete
Ascomycetes
• Better known examples include
– Most of the food-spoiling molds
– Morels and truffles (edible delicacies)
– Penicillium, the mold that produces penicillin
(the first antibiotic)
– Yeasts (single-celled fungi)
Basidiomycetes
• Live in a variety of marine, freshwater, and
terrestrial habitats
• Each fruiting body contains numerous
club-shaped structures called basidia
(singular, basidium)
• Usually reproduce sexually
– Sexual spores form in club-shaped basidia
– Figure 22-9, p. 429, depicts an overview of
sexual reproduction in a basidiomycetes
FIGURE 22-9a
Diverse basidiomycetes
(a) The giant puffball Lycopedon
giganteum may produce up to 5
trillion spores.
FIGURE 22-9b
Diverse basidiomycetes
(b) Shelf fungi, some the size of
dessert plates, are conspicuous
on trees.
FIGURE 22-9c Diverse basidiomycetes
(c) The spores of stinkhorns are carried on the outside of a slimy
cap that smells terrible to humans, but appeals to flies. The flies
lay their eggs on the stinkhorn, and inadvertently disperse the
spores that stick to their bodies.
Basidiomycetes
• Better known examples include
– Mushrooms (some are edible, others are
poisonous)
– Puffballs
– Shelf fungi (decomposers of wood)
– Stinkhorns
– Rusts and smuts (plant parasites)
– Yeasts
Fairy Rings
• A fairy ring is a circular pattern of
mushroom growth
• Fairy rings form at the leading edge of an
expanding underground fungal mycelium
– The wider the diameter of the ring, the older
the mycelium
– Some fairy rings are estimated to be 700
years old
FIGURE 22-10 A mushroom fairy ring
Mushrooms emerge in a fairy ring from an underground fungal
mycelium, growing outward from a central point where a single
spore germinated, perhaps centuries ago.
Section 22.3 Outline
• 22.3 How Do Fungi Interact with Other
Species?
– Lichens Are Formed by Fungi That Live with
Photosynthetic Algae or Bacteria
– Mycorrhizae Are Fungi Associated with Plant
Roots
– Endophytes Are Fungi That Live Inside Plant
Stems and Leaves
– Some Fungi Are Important Recyclers
Symbiotic Relationships
• A symbiosis is a close interaction between
organisms of different species over an
extended period of time
• The fungal member of a symbiotic
relationship may be harmful (a parasite of
plants or animals) or beneficial (lichens
and mycorrhizae)
Lichens
• Lichens are symbiotic associations
between fungi (usually an ascomycete) and
algae or cyanobacteria
– Fungus provides photosynthetic partner with
shelter and protection
– Photosynthetic partner provides fungus with
food (sugar)
FIG 22-11 The lichen: A
symbiotic partnership
Most lichens have a
layered structure
bounded on the top and
bottom by an outer layer
formed from fungal
hyphae. The fungal
hyphae emerge from the
lower layer, forming
attachments that anchor
the lichen to a surface,
such as a rock or a tree.
An algal layer in which
the alga and fungus grow
in close association lies
beneath the upper layer
of hyphae.
Lichens
• Grow on a wide variety of materials (soils,
tree trunks and branches, rocks, fences,
roofs, and walls)
• Are able to survive environmental extremes
(newly formed volcanic islands, deserts)
• Are very diverse in form
FIG 22-12a Diverse lichens
(a) A colorful encrusting
lichen, growing on dry rock,
illustrates the tough
independence of this
symbiotic combination of
fungus and algae.
(b) A leafy lichen grows
from a dead tree branch.
Mycorrhizae
• Mycorrhizae (singular, mycorrhiza) are
symbiotic associations between fungi and
plant roots
– Fungus provides plant with water, minerals,
and organic nutrients it absorbs from the soil
– Plant provides fungus with food (sugar)
• 80% of plants with roots have mycorrhizae
• Relationship may have helped plants
colonize land
FIGURE 22-13 Mycorrhizae enhance plant growth
Hyphae of mycorrhizae entwining about the root of an aspen tree.
Plants grow significantly better in a symbiotic association with
these fungi, which help make nutrients and water available to the
roots.
Endophytes
• Endophytes are fungi that live inside the
above-ground tissues of plants
• Some are parasites that cause plant
diseases
• Some are beneficial to host plants
– Some ascomycete species live inside grasses
and produce substances that are distasteful
or toxic to insects and grazing mammals,
protecting the grasses from predation
Recyclers
• Fungi are Earth’s undertakers, feeding on
the dead of all kingdoms
• Fungal saprophytes (feeding on dead
organisms) release extracellular
substances that digest the tissues of the
dead and liberate carbon, nitrogen,
phosphorus compounds, and minerals that
can be reused by plants
Section 22.4 Outline
• 22.4 How Do Fungi Affect Humans?
– Fungi Attack Plants That Are Important to
People
– Fungi Cause Human Diseases
– Fungi Can Produce Toxins
– Many Antibiotics Are Derived from Fungi
– Fungi Make Important Contributions to
Gastronomy
– Fungal Ingenuity
Fungi Attack Plants
• Fungal parasites cause the majority of
plant diseases
– Ascomycete parasites cause Dutch elm
disease and Chestnut blight
– Rusts and smuts are basidiomycete parasites
that cause considerable damage to grain
crops
FIGURE 22-14 Corn smut
This basidiomycete pathogen destroys millions of dollars' worth of
corn each year. Even a pest like corn smut has its admirers,
though. In Mexico this fungus is known as huitlacoche and is
considered to be a great delicacy.
Fungi Attack Plants
• Fungi can destroy plant material that has
been harvested for human use
– Cause wooden structures to rot
– Damage cotton and wool fabrics
Fungi Attack Plants
• Some fungi benefit agriculture
– Used to control insect pests such as rice
weevils, tent caterpillars, aphids, citrus mites,
and grasshoppers
• Fungi identified that attack mosquitoes that
transmit malaria
FIGURE 22-15a Helpful fungal parasites
Fungal pathogens can be helpful to humans. For example, fungi
such as (a) the Cordyceps species that has killed this
grasshopper are used by farmers to control insect pests.
FIGURE 22-15b Helpful
fungal parasites
(b) Some fungi might one
day be used to help protect
humans from disease. A
malaria-carrying mosquito
infected by Beauveria
species is transformed from
a healthy animal (top) to a
fungus-encrusted corpse in
less than two weeks.
Fungi Cause Human Diseases
• Athlete’s foot, jock itch, and ringworm are
caused by fungi that attack the skin
• Valley fever and histoplasmosis are caused
by fungi that attack the lungs
– Infection occurs when victim inhales spores
Fungi Cause Human Diseases
• Most vaginal infections are caused by the
yeast Candida albicans
FIGURE 22-16 The unusual yeast
Yeasts are unusual, normally non-filamentous ascomycetes that
reproduce most commonly by budding. The yeast shown here is
Candida, a common cause of vaginal infections.
Fungi Produce Toxins
• Molds of the genus Aspergillus produce
aflatoxins, highly toxic, carcinogenic
compounds
– Infect foods such as peanuts
Fungi Produce Toxins
• Claviceps purpurea (an ascomycete)
produces several toxins
– Infects rye plants and causes ergot disease
– Symptoms of ergot poisoning include
vasoconstriction of blood vessels, vomiting,
convulsive twitching, hallucinations, and death
Fungi Produce Antibiotics
• Penicillin
– First antibiotic to be discovered
– Used to combat bacterial diseases
FIGURE 22-17
Penicillium
Penicillium growing
on an orange.
Reproductive
structures, which
coat the fruit's
surface, are visible,
while hyphae
beneath draw
nourishment from
inside. The antibiotic
penicillin was first
isolated from this
fungus.
Fungi Produce Other Drugs
• Cyclosporin
– Used to suppress the immune response
during organ transplants
Fungi Contribute to Gastronomy
• Certain ascomycete molds impart flavor to
some of the world’s most famous cheeses
– Roquefort
– Camembert
– Stilton
– Gorgonzola
Fungi Contribute to Gastronomy
• Yeasts are used in the production of wine,
beer, and bread
• Wine is produced when yeasts ferment
fruit sugars; ethyl alcohol is retained, while
CO2 is released
Fungi Contribute to Gastronomy
• Beer is derived when yeasts ferment
sugars in germinating grains (usually
barley); ethyl alcohol and CO2 are retained
• Bread rises when yeasts ferment sugar
that has been added to bread dough; both
ethyl alcohol and CO2 escape during
baking
Fungi Contribute to Gastronomy
• Some fungi are consumed directly
– Mushrooms (a basidiomycete)
– Morels (an ascomycete)
– Truffles (an ascomycete)
FIGURE 22-18 The truffle
Truffles, rare ascomycetes (each about the size of a small apple),
are a gastronomic delicacy.
Fungal Ingenuity
• The truffle has evolved an effective
adaptation for dispersal of its spores
– Releases an odor which causes pigs and
other animals to dig it up, scattering spores to
the winds
• The zygomycete Pilobolus has evolved
bulb tops that blast off, spreading spores
FIGURE 22-19 An explosive zygomycete
The delicate, translucent reproductive structures of the
zygomycete Pilobolus literally blow their tops when ripe,
dispersing the black caps with their payload of spores.
Fungal Ingenuity
• Arthrobotrys cleverly traps and “strangles”
microscopic roundworms called
nematodes to obtain nutrients
FIGURE 22-20 Nemesis of nematodes
Arthrobotrys, the nematode (roundworm) strangler, traps its prey
in a noose-like modified hypha that swells when the inside of the
loop is contacted.