GCTV Ep#8 Fungicide Resistance
Narrator: This is a model of C-y-p-51, a protein found
in the pathogen that causes the fungal disease barley
powdery mildew.
What makes this particular fungal protein very significant is that if a strain of barley
powdery mildew is to become resistant to a fungicide
it most likely will be because of a mutation in this
gene.
Richard Oliver: Professor of Agriculture, Curtin University WA
Fungicides that used to be successful at controlling barley powdery mildew particularly
Tebuconazole and Triadimenol are now failing to control thos fungicides.
And that’s the phenotypic side of things that’s actually
the fungus growing on the plant and us observing what’s
going on.
The other side of the coin and this is where we’re using research from overseas very
intensively is that we know that resistance to these fungicides, DMI class of fungicides,
is almost always due to changes in the gene sequence
of a gene called Cyp51.
Narrator: The failure of fungicides to control powdery
mildew in western Australian barley has resulted in a
massive build up of pathogen.
Any strains within that population that has developed fungicide
resistance have an even better opportunity to further multiply and mutate.
A mutation results in an approximate 10-fold increase in resistance.
What has compounded the problem is the sowing of susceptible barley varieties.
Peter Roberts: Chairman, GRDC Western Regional Panel & Graingrower
The best barley variety in WA in terms of quality is very very susceptible to powdery
mildew.
Traditionally we’ve been able to treat powdery mildew with quite cheap Triazoles and this
form of fungicide has now broken down completely in
WA and because you have a susceptible variety that you continually have to spray, that opened
up the opportunity for resistance.
Narrator: Professor Oliver’s team has been taking
isolates from field samples of the fungus and exposing
them to the various fungicides at different concentrations.
Resistant isolates have their DNA sequenced and crosschecked against mutations
known to have resistance to the DMI also known as the triazole group of fungicides.
Richard Oliver: The issue is, the step-wise process of mutation
we have seen happening in Europe.
So if we have resistance to fungicides such as Tebuconazole
which take just one or two mutations that’s the stepping stone to getting resistance to
these newer fungicides like Prothioconazole Prosaro
and Epoxiconazole, like Opus, that might occur when we accumulate a whole batch of mutations
in the gene.
And this scenario might happen if we continue to allow a very high population of the
fungus to grow on the susceptible plants and give those already mutant populations a chance
to mutate a second, third or fourth time which
is really the nightmare scenario.
Narrator: Modeling the C-y-p-51 protein and its mutations
allows the team to see which fungicides fit with
the protein’s substrate-binding pocket like a key in a lock.
Richard Oliver: Therefore we can say a particular mutation
or set of mutations on the gene are associated with
resistance to say Tebuconazole but sensitive to say Epoxiconazole and that’s very sophisticated
work we’re using by collaborating with our European colleagues.
Narrator: Identification of mutants and establishing
if they are sensitive or resistant to fungicides will also
provide barley breeders with valuable genetic data.
Richard Oliver: In our terms we say which avirulence genes
have they got which haven’t they got so which race
are they.
On that basis we can then say to the breeders it’s a waste of time using this resistance
gene (or) this resistance gene is still working.
And therefore we can say to growers use this cultivar which is resistant and not that cultivar
which has fallen over.
So if growers adopt resistant cultivars we’ll have much much less of the
pathogen around therefore there will be much less
opportunity for it to mutate and for those mutated strains to then be selected by the
fungicides.
Narrator: What will help growers to reduce future losses
to barley powdery mildew in the short term is to
sow newer less susceptible varieties next season and be more selective of the fungicides
they use.
And if any grower, nationwide, has powdery mildew in their barley crop, especially if
they are growing newer cultivars, contact Richard Oliver
who will arrange for a sample to be tested.
Richard Oliver: Most of the barley varieties in the east are
more resistant than we’ve been using in the west so
they’re starting from a better position than we are but certainly we are worried about
this on a national scale.
Powdery mildew is a pathogen that doesn’t respect state boundaries it blows
around hundreds of kilometers in a few days; there should be no problem to get from west
to east.
We’re also interested to hear from growers if they had failures of some of the newer
fungicides such as Opus, Opera, Amistar, Prosaro because
if they are failing then we need to replace those
with the yet newer fungicides and bring forward our program for introducing what you might
call the third class of fungicides.
Narrator: Providing barley breeders and growers with
options is within reach and the barley industry should
take confidence from knowing GRDC will continue to support this research according to its
western region chairman Peter Roberts.
Peter Roberts: We have to continue to evolve this investment
to make sure we have options available for control
and of course the other angle is to breed resistance into the cultivar but that’s
been quite difficult and Richard works in that area as well.
Richard Oliver: We’ve got all the tools available to control
it we just need to implement them and then we’ll be on
top of this pathogen in a few years I hope.
ENDS