PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
BIOLOGY, IDENTIFICATION AND CLASSIFICATION
Fungal diseases
NO. DISEASES
IN AUSTRALIA
SOME
DISTINCTIVE
FEATURES
Hyphae produce
enzymes which
change the plant
tissues into
substances the
fungus can use
for nourishment
Several thousand species of fungi can cause diseases of plants in Australia.
Some fungal diseases are considered to have altered the course of history, eg
the devastating effect of coffee rust in Ceylon in the 19 th century is given as the
main reason for the British being now mainly tea drinkers.
Fungimap www.rbg.vic.gov.au/fungimap_/fungi_down_under
The Australasian Plant Pathology Society (APPSnet) Pathogen of the Month
www.australasianplantpathologysociety.org.au/
The American Phytopathology Society (APSnet) www.apsnet.org/
Australasian Mycological Society www.australasianmycology.com/
Fungi were originally considered to be very simple members of the plant
kingdom but are now in a separate kingdom of their own:
MYCELIUM
Fungi have a very simple plant body called a
mycelium which is made up of thread-like filaments
called hyphae which usually can only be seen under a
microscope (x 100). Hyphae obtain food from the host which
makes them similar to plant roots, sometimes forming
structures which help the fungus survive and spread.
CHLOROPHYLL They contain no chlorophyll and so cannot
manufacture their own food.
REPRODUCTION They reproduce by spores which are important
in the spread and ‘overwintering’ of disease.
Mycelium and spores
Mycelium (x 100) of powdery mildew (x 100)
LIFE CYCLE
THE MAIN METHOD OF REPRODUCTION IS BY SPORES.
Spores may be single-celled or multi-celled.
Although single spores can be seen only with the aid of a microscope,
larger masses of spores can be seen with the naked eye, eg the fine blue or
green powder on a mouldy orange or lemon is in fact, billions of tiny spores.
Generally 2 types of spores are produced, ie asexual repeating spores
produced during the growing season and sexual ‘overwintering’ spores.
Spores are produced near the outside of the plant or on the soil surface
so they can be easily spread by wind, etc.
Spores may or may not be produced in fruiting bodies which may be as
large as mushrooms. However, the fruiting bodies of fungi that attack plants
are usually much smaller and may appear as pinhead-size black dots on an
area of damaged leaf eg Septoria.
Fungi obviously produce millions of spores. While most spores never
reach a site suitable for their germination, those that do only germinate and
successfully cause infection if some moisture is present.
At germination
fungal spores
produce a small tube
which begins to
elongate and branch
forming hyphae
.
Spores not in fruiting bodies (x 100)
Spores in fruiting bodies
314 Fungal diseases - Biology, identification and classification