Transcript CHAP 7 Fungi and other organism (plant)

MYCOLOGY
(MIC 206)
FUNGI AND OTHER
ORGANISMS (PLANT)
FUNGI AND PLANTS
Fungi can be:
1) Facultative symbionts – can live freely or within
plants
2) Obligate symbionts – can only grow in association
with plants.
Hyphae of symbiotic fungi can penetrate plant cells,
some grow through tissues without entering or
penetrating plants cells.
Two way of parasitic relationships of fungi with plants:
1) Biotrophic
2) Necrotrophic
Biotrophic vs Necrotrophic
Some fungi have phases where they became
biotrophic or necrotrophic.
Fungi can penetrate plant tissues through:
a) aerial surfaces (stems, leaves, flowers, fruits).
b) root surfaces (root epidermis).
c) wounds (normal process where internal tissues
are exposed due to breakage of plant’s
surfaces (e.g. when fruits and leaves are
formed).
MOA of Plant Pathogen
Examples of fungi penetrating plant tissues:
a) Aerial surfaces
Examples are Cladosporium (leaf), Rhizopus
stolonifer (fruit), Colleototrichum (fruit and leaf),
Armillaria mellea (wood/ bark).
b) Root surfaces
Fusarium spp. (root), Sclerotinia sclerotonum (root).
c) Wounds
Sclerotinia fructigena (wasps or birds break
epidermis of fruit and introduce conidia of fungus).
d) Other internal tissues
Armillaria mellea (tree pathogen and able to enter
living trees but can live as saprotrops when trees
die).
BIOTROPHIC
ASSOCIATIONS
Biotrophic Associations
From the Greek:
bios = life,
trophy = feeding.
Live within the plant and obtain nourishment
without causing cell death to plants.
Long-term feeding relationship with the living cells
of their hosts, rather than killing the host cells as
part of the infection process.
Characteristics of Biotrophic
Associations
Characteristics:
1) Do not kill hosts so either parasitic or saprophytic.
2) Tissues that are invaded remain alive.
3) Symbiotic because two organisms live together.
4) A relationship
Mycorrhiza.
between
Fungus
+
Root
=
Construction of Haustaria
Biotrophic fungi frequently produce haustaria.
Haustoria: specialized hyphae that penetrate the cells of
other organisms that obtains food from a host.
Fungi grow between the host cells and invade only a few
of the cells to produce nutrient-absorbing structures termed
haustoria.
MOA of Haustaria
Fungal haustoria will be produced from spores that
germinate on the surface of plants, on leaves or stems.
The germinating spores may produce a penetration peg
known as an appressorium and penetrate the plant’s cell
wall.
After penetration, the hyphal tip forms an invagination
within the cell that becomes the haustorium.
Haustorium is a structure of an extended extracellular
mycelium, or filaments, of the fungus.
Magnaporthe oryzae – Rice
Blasts Diseases
appressorium
penetration of leaf
penetration peg
CLASSIFICATION OF BIOTROPHICS
ASSOCIATION
Two importants groups:
The Rust Fungi (Basidiomycota) - classic
biotroph.
The Powdery Mildew Fungi (Ascomycota)
BIOTROPHIC
ASSOCIATIONS RUST FUNGI
The Rust Fungi
The infection behaviour of rust fungi is broadly similar
to that of the powdery mildews.
Involving nutrient absorption by haustoria to support
abundant sporulation for epidemic spread.
Close-up of lower surface of the leaf,
showing cup-shaped pustules of
aeciospores.
Small lesions on the upper
surface of a barberry leaf, with
spermogonia in their centres.
Penetration and Colonization by Rust Fungi
Growth of barley rust germ tubes on a barley
leaf replica
Growth of barley rust germ tubes on a barley
leaf replica
Bean Rust – Uromyces appendiculatus
Bean Rust – Uromyces appendiculatus
Bean Rust – Uromyces appendiculatus
Black Rot of Grape - Phyllosticta ampelicida
Phyllosticta ampelicida – germinated conidia and
melanized appressoria
BIOTROPHIC
ASSOCIATIONS –
POWDERY MILDEW
FUNGI
The Powdery Mildew Fungi
(Ascomycota)
The Powdery Mildew Fungi (Ascomycota)
 Powdery mildews produce mycelium (fungal threads)
that grow only on the surface of the plant.
 They never invade the tissues themselves.
 The fungi feed by sending haustoria, into the epidermal
(top) cells of the plant.
Typical forms: many powdery mildews, where the fungus
forms a powdery coating of white spores on the leaf
surface.
Powdery Mildew Fungi
Other common examples in Britain are powdery mildew of
hawthorn
(Podosphaera
oxyacanthae),
gooseberry
(Sphaerotheca morsuvae), and cereals and grasses (Erysiphe
graminis).
Localised lesions of Erysiphe graminis
on wheat leaves.
Powdery mildew of roses, caused by
the fungus Sphaerotheca pannosa.
NECROTROPHIC
ASSOCIATIONS
Necrotrophic Associations
Term necro – relating to death.
Necrotrophic: Kill cells and absorb nutrients from dead cells.
How?
→ Frequently secrete enzymes that degrade plant
components or toxins that kill the plant’s tissue.
Subsequently live on nutrients from the tissue they have
killed.
Characteristics of Necrotrophic
Associations
Characteristics:
1) Kills host cells.
2) Can be recognised by patches of dead, blackened
tissue.
3) Produce toxins which kill plant cells and their enzymes
to degrade plant constituents so that fungus can use
them as food.
4) Can change to saprophytic or biotrophic in later
stages.
5) Show low specificity to host plants.
6) They are easy to culture in the absence of their hosts.
7) They can survive in the absence of their hosts by
production of spores or sclerotia in the dead tissue.
Necrotrophic Associations (con’t)
Examples:
1) Botrytis cinerea cause grey moulds in young plants or
grapes when conditions are cold and damp.
Grey mould rot causes damage on stored carrot,
parsnip, mangel, beet, endive, chicory, turnip, and
many others.
Necrotrophic Associations (con’t)
Examples:
2) Phytophthora spp. Cause black pod disease in cocoa
plant and brown rot disease on orange fruit.