PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
BIOLOGY & IDENTIFICATION
Bacterial diseases
NO. DISEASES
IN AUSTRALIA
SOME
DISTINCTIVE
FEATURES
Bacteria are the most numerous living organisms on earth. For about 2 billion
years bacteria were the only life on earth. More than 100 species of bacteria
cause plant diseases. There are always some bacteria on the surfaces of plants,
but some of these never harm these plants. About 400 species live in our
intestines. Others cause tuberculosis, pneumonia, typhoid fever; anthrax in
humans and animals.
The Australasian Plant Pathology Society (APPSnet) Pathogen of the Month
www.australasianplantpathologysociety.org.au/
The American Phytopathology Society (APSnet) www.apsnet.org/
Bacteria are very simple organisms. Phytoplasmas which are closely related to
bacteria but have been included with virus diseases as they generally are more
virus-like than bacterial-like in their behaviour.
SINGLE-CELLED Bacteria are small single-celled organisms which
can only be seen under high magnification (x 1,000).
Some are thread-like in form. The bacteria which
cause diseases of plants are mostly short, rod-shaped
organisms with one or more flagella which enable them
to move through a film of water. Some exceptions, eg
Streptomyces which is filamentaous.
CELL WALL
CHLOROPHYLL
They have a cell wall surrounding the cytoplasm
but do not have the nucleus found in higher plants.
They have no chlorophyll and therefore cannot manufacture
their own food like green plants and so must obtain it from
external sources.
LIFE CYCLE
;
Multiplication is by simple fission. Under favorable conditions, it can take as
little as 20 minutes so that the rate of increase can be tremendous! Potentially
millions of bacteria within 24 hours.
Bacteria, parasitic on plants, generally do not form spores but they can remain
viable for long periods of time even under dry conditions. This property
enables some of them to remain alive for years on plants, in stored seed and
other plant products and in the soil.
294 Bacterial diseases