Extension Files: Australian Cereal Rust Survey Prof. Robert Park: Director Cereal Rust Control
Program So the first step in the race analysis here
at the Plant Breeding Institute is that when we receive a sample its actually accessioned.
Its brought into the laboratory its details are recorded and then it is placed in a glass
tube ready for inoculation in the greenhouse.
In this particular example we have a sample of wheat leaf rust that's been sent to us
from Victoria.
It's quite a good sample, you can see importantly that it's been sent to us in paper envelopes
which is crucial.
If the samples come to us in plastic the rust dies and secondly there's adequate rust for
us to inoculate a differential set directly.
If the sample did not have enough rust on it we would initially have to do an increase
that would take an additional three weeks.
So with a sample like this we can process it and get an answer back to the grower within
three weeks.
If there's inadequate amount of rust on the sample that process is going to take us six
to eight weeks.
So once the accessing process is complete and we've recorded all the details the next
step is to take the sample to the greenhouse and inoculate some seedlings and that's where
we're going to next .
So the inoculation process starts with the addition of a light mineral oil to the rust
sample, which is then agitated to form a spore suspension.
Once we have an adequate spore suspension the sample is applied to a set of indicator
lines by using an aerosol can.
The differential set is inoculated from a number of different directions to endure uniform
deposition of the same on all indicator lines.
Once inoculated with the rust the plants are transferred to a misting room.
To ensure there is no cross contamination between isolates the inoculation chamber is
misted as well.
To induce infection the plants are placed in misting room where they receive an artificial
dew treatment.
The dew treatment is extremely important because the rust spores need free moisture on the
leaf surfaces in order to germinate and infect the plants.
So following a 24-hour dew treatment the plants are brought out to the greenhouse where they
are placed in a temperature controlled micro-environment room for about two weeks.
During this period of time the rust grows and develops and at the end of that period
we're able to record the results.
And now its time to determine what strain is present in the same that's been sent to
us.
The way we do that is to look at each genotype or each different wheat variety and determine
whether it is resistant or susceptible to that particular rust isolate.
The ability of the rust isolate to infect different wheat genotypes tells us what the
strain is.
So in this particular case here we have a sample that represents a new strain of stem
rust.
What we've done is we've increased that strain of stem rust on a selection of susceptible
variety here but importantly we've also included a differential set.
So here is an example of a differential set that's been inoculated about two weeks ago
and we work our ways through each of the differentials.
Each of these is a different wheat variety, to determine the resistance and the susceptibility,
and that allows us to identify the strain that is present.
So you can see here on this one this variety is actually susceptible to this isolate of
stem rust.
This one here in the middle is actually resistant.
There's no evidence of the rust infecting that at all.
So in an average year we would receive anything up to about 300 samples for each of the rust
pathogens that we do strain analysis on.
From those two to 300 samples we would identify between five and 10 different strains for
all of Australia.
Now occasionally let's say once every couple of years we do find an isolate in a sample
that presents a new strain and when we do that its very important that we purify that
strain, increase it and put it into our collection so that we can use that in our breeding and
genetics work.
Once we're happy that the isolate is actually pure and it is what we think it is we will
collect the spores off the susceptible variety, dry them down and put them into liquid nitrogen
storage.
In liquid nitrogen storage that isolate will remain viable indefinitely.
We have isolates that we've retrieved from liquid nitrogen that have been there for more
than 50 years and they're still viable.
Very important resource, we use those isolates for genetics program and also to test all
of our wheat breeders' material that's sent here each year.
So the final step in the process of the race strain identification surveys is for us to
send out the information, the results that we get for each of the samples that are submitted.
Initially when we receive a sample, they're accessioned, there's an email acknowledgement
that goes out to the person that sent that sample in.
All going well if we have a very good quality sample about three weeks later we are able
to send a result back again by email to the person who sent the sample in.
This example here shows a sample of leaf rust that was send from western Australia to us
off the barley variety Bass and we've been able to identify that as pathotype 5457 P
minus.
Once a year we compile an annual report where we bring together all of the information from
the rust surveys all the way through to our rust testing of Australian wheat varieties
and that is a detailed report that can be downloaded from our website that gives the
expected responses on cereal varieties to the current rust strains that are present
in Australia.
So the whole success of our 95 years of surveying rust pathogens in Australia has relied on
collaborators sending us rust samples from cereal crops.
So please if you find rust send them to us so that we can include them in our annual
rust surveys.
We have an address at the University of Sydney Plant Breeding Institute to which those samples
can be sent.
We can send you pre-postage paid envelopes, just send us an email and we'll send some
of those envelopes out to you.