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Super resistance to tackle biggest wheat disease
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

Disclaimer

CSIRO gives no warranty and makes no representation that the information contained in this document is suitable for any purpose or is free from error. CSIRO and its officers, employees and agents accept no responsibility for any person acting or relying upon the information contained in this document, and disclaim all liability for any loss, damage, cost or expense incurred by reason of any person using or relying on the information contained in this document or by reason of any error, omission, defect, or mis-statement contained therein.

Produced by CSIRO Plant Industry Communication Group 2005

CSIRO Plant Industry - e-newsletter Issue 11

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