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Causal organism - Puccinia graminis
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Life cycle
This disease is frequently described to students
as a classical rust which has an alternate
host . The fungus produces teliospores
on the wheat plant which produce a secondary spore,
the
basidiospore . This spore infects a completely different host - in this
case the barberry (Berberis spp.). A further spore stage, the aeciospore,
is produced on the barberry which can spread and re-infect the cereal host.
This infection gives rise to the uredospore
stage which produces the normal symptoms on wheat. Outbreaks in Britain are
caused by air-borne spores originating in SW Europe and N. Africa so infection
can only be found when appropriate air movements occur. The optimum temperature
is in excess of 20°C so suitable air movements must be associated with
high temperatures. Temperatures below 15°C inhibit the disease so it rarely
develops under UK conditions.
Importance
The disease is very rare in Britain but may occur late in the season. Losses
due to the disease in the UK are very small indeed. Where the disease does
occur it can be very serious. In the USA, Australia, Africa and India the
disease can cause large yield losses of 20-30%.
