Canberra, Australia
September 12, 2005
from
CSIRO
Plant Industry - e-newsletter Issue 11
Without rust
resistant wheat varieties the Australian wheat industry would
lose up to $300 million per year in lost production due to rust
infection.
CSIRO
Plant Industry’s Dr Rohit Mago (photo) has located four rust
resistance genes that he will use together to breed a super stem
rust-resistant wheat – at least four times more rust resistant
than existing varieties.
With four
resistance genes working together it is unlikely that a new
strain of rust will develop that will be strong enough to
counter all four resistance genes at once.
Dr Mago’s
Canberra based research located the genes with ‘markers’,
allowing breeders to more quickly and easily identify if their
new wheat variety has the rust resistance genes or not.
Markers are
critical when using multiple genes as you can’t rely on testing
the plant for resistance by exposing it to rust as any one of
the genes could provide initial resistance.
Three of
the rust resistance genes were previously associated with
negative yield and quality traits, but their new versions appear
to not have these drawbacks.
Dr Mago has
already bred plants with different combinations of two
resistance genes and now hopes to combine three and four genes
in the one wheat breeding line.
This
collaborative research is supported by the
Grains Research and Development
Corporation (GRDC),
Waite
Institute in Adelaide, South Australia and the
Plant Breeding
Institute in Cobbitty, New South Wales.
ADDITIONAL
INFORMATION
(PDF version:
http://www.pi.csiro.au/enewsletter/PDF/PI_info_PyramidingRust.pdf)
Super
resistance to tackle biggest disease
CSIRO Plant Industry has
identified ‘DNA markers’ that flag the location of four
important stem rust resistance genes in wheat and is now
planning to breed a new super stem rust-resistant wheat at least
four times more effective than existing varieties.
The Australian wheat industry is
heavily dependent on rust-resistant wheat varieties to prevent
losses in production estimated at $300 million per year. But new
rust strains mean wheat breeders are always on the lookout for
new sources of rust resistance.
Finding useful genes
The four stem rust resistance
genes that CSIRO Plant Industry has identified DNA markers for
are called Sr24, Sr26, Sr31 and SrR. All four genes provide
significant resistance to stem rust and Sr24 is already widely
used in Australian wheat breeding programs to confer rust
resistance.
CSIRO Plant Industry is continuing
to look for more rust resistance genes and aims to develop DNA
markers that flag their location too.
Three of the genes, Sr26, Sr31 and
SrR, have not been widely used in breeding programs to introduce
rust resistance in Australia as the genes are closely associated
with negative characteristics.
Sr26 is used in Australia but
mainly in feed wheats as it is associated with reduced yield.
Sr31 and SrR are widely used across the world to confer rust
resistance but not in Australia because an associated negative
characteristic that causes the dough of the wheat to become
sticky.
DNA markers
A DNA marker is a bit like a
bookmark that identifies the location of an important sentence
in a book. If the bookmark isn’t there you would have to read
the whole book to see if the sentence was there or not. In a
similar way a DNA marker lets breeders quickly know whether an
important gene is present or not.
Using the DNA markers wheat
breeders can easily look at a plant’s DNA to identify if the
rust resistance genes are present. This saves time because
breeders no longer need to expose a plant to rust to assess how
it performs. Instead they simply take a sample of the plant and
look to see if the DNA marker for the resistance gene is present
or not.
Removing negative
characteristics
CSIRO has developed DNA markers
for new versions of SrR, Sr31 and Sr26 that should lack all
negative characteristics.
Researchers at the University of
Adelaide and in the USA have developed the new versions from
shortened wheat chromosomes that contain the desired genes but
the negative characteristics have been ‘cut-out’.
With DNA markers locating these
resistance genes exactly it will be easier for breeders to breed
new wheat varieties that have the useful resistance genes only
and exclude the unwanted negative characteristics.
CSIRO Plant Industry is also
looking to ‘clone’ the rust resistance genes. If the genes can
be cloned then the individual gene can be inserted, via genetic
modification, into a new wheat, thereby introducing the rust
resistance without any negative characteristics. This would
result in a genetically modified (GM) wheat resistant to rust.
This aspect of the research would only progress towards a GM
wheat with support from the grains industry and approval from
the Office of the Gene Technology Regulator.
‘Stacking’ resistance genes
CSIRO Plant Industry has already
conventionally developed wheat breeding lines where each line
contains a different combination of two of the four ‘marked’
genes.
By the end of 2006 CSIRO Plant
Industry hopes to have developed a wheat line with all four rust
resistance genes.
‘Stacking’ genes like this means
that if a strain of rust comes along that cannot be controlled
by one of the resistance genes then there are still three other
resistance genes in place ready to fight it. It is very unlikely
that a rust that can overcome all four resistance genes at once
will develop.
The DNA markers for the new rust
resistance genes CSIRO Plant Industry has identified perform an
important role when stacking genes as breeders can’t rely on
testing the plant for resistance by exposing it to rust as any
one of the genes could provide initial resistance but they want
to know that all desired genes are present.
Once all four rust resistance
genes have been introduced into a wheat breeding line CSIRO
Plant Industry will do further quality testing and if all goes
well plans to deliver a new super rust resistant wheat variety
within the next four years.
Scientific reference
Mago, R., et al (2005).
Development of PCR
markers for the selection of
wheat stem rust resistance genes Sr24 and Sr26 in diverse
wheat germplasm.
Theoretical and Applied
Genetics, Vol: 111, Issue: 3
For further information contact:
CSIRO Enquiries
Bag 10 Clayton South VIC 3169
Phone: 1300 363 400 (National local
call) -
+61 3 95452176 (International
phone)
Fax: +61 3 9545 2175
Email: enquiries@csiro.au
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Produced by CSIRO Plant Industry
Communication Group 2005 |