Rust pathogens and the east–west route

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Photo of barley

The barley leaf rust pathogen 5656P+, first detected in South Australia, was found to have migrated to Western Australia in 2016, highlighting how cereal rust pathogens can spread across the country.

PHOTO: Robert Park, University of Sydney

NSW Department of Primary Industries, co-located at the Elizabeth Macarthur Agricultural Institute and the Plant Breeding Institute, University of Sydney

This time last year, we reported on the nationwide spread of a rust isolate – a new pathotype of the wheat leaf rust pathogen. This rust took only 13 months to find its way from Glenroy in South Australia in August 2014 to all Australian wheat-growing states.

The discovery, impact and spread of this new wheat rust pathotype (race) was documented by the Australian Cereal Rust Survey, which has monitored cereal rust populations across Australia since 1921.

The surveillance system is largely funded by growers and, crucially, comprises a network of regional cereal pathologists, breeders, agronomists and other interested parties who have kept an eye on local rust development and forwarded rust isolates to the national rust laboratory at the University of Sydney for pathotype analysis.

Pathogen movement

The geographic separation between the eastern and western cereal-growing regions has resulted in regional differences in the distribution of some cereal diseases and pests. For example, Russian wheat aphid is currently restricted to eastern Australia. But the geographic barrier presented to cereal rust pathogen movement has been less effective.

Between 1990 and 2012, we documented six instances of wheat and barley rust pathogens spreading from Western Australia to the eastern cereal-growing regions (Table 1). During that same time, only one example of rust migrating from east to west was detected. This is thought to be because of the prevailing west-to-east winds and the tendency for rust spores to spread readily on wind currents.

The 2013 to 2016 seasons saw a reversal of this pattern, with one example of west-to-east rust movement, but three of east-to-west rust movement (Table 1). The most recent example of this westwards migration was in 2016, when a pathotype of the barley leaf rust pathogen 5656P+ was detected for the first time in WA in the Lake Grace region, on the cultivar Bass, which carries the resistance gene Rph3.

This pathotype was first detected in SA in 2011, and increased in frequency because of its ability to attack barley cultivars carrying the Rph3 resistance gene, such as Compass, Fairview and Shepherd.

Send samples to:

Australian Cereal Rust Survey
University of Sydney,
Australian Cereal Rust Survey,
Reply Paid 88076,
Narellan, NSW, 2567

The occurrence of the new barley leaf rust pathotype in WA in 2016 is not expected to pose any additional threat to the current suite of cultivars being grown there.

However, it does demonstrate the ability of cereal rust pathogens to spread throughout Australia and the ongoing need for vigilance in monitoring crops.

Of particular concern is the vulnerability of most WA wheat cultivars, including Mace and Scepter, to a stripe rust pathotype that has been present in eastern Australia since 2006 but absent from WA.

WA growers of wheat cultivars which rely on the Yr17 resistance gene for stripe rust protection are encouraged to monitor their crops closely for rust this season and to forward collected rust samples (packaged in paper only) to the Australian Cereal Rust Survey.

 Direction/pathogen  Pathotype  Year first detected
Table 1 Documented examples of the cereal rust pathogen inoculum exchange between the eastern and western cereal-growing regions from 1990 to 2016.
 West to east:
 Barley leaf rust
 5610P+  1998
 Wheat leaf rust
 104-1,2,3,(6),(7),11 +Lr37  2002
 Wheat stripe rust
 134 E16 A+  2003
 Wheat stem rust
 34-1,2,7 +Sr38  2003
 Barley leaf rust
 5453P+  2003
 Wheat stem rust
 34-1,2,7 +Sr38 Yalta Low  2008
 Barley leaf rust
 5457P-  2016
 East to west:
 Wheat leaf rust
 104-1,2,3,(6),(7),11  1990
 Wheat leaf rust
 76-1,3,5,9,10,12 +Lr37  2013
 Wheat left rust
 104-1,3,4,6,7,8,10,12 +Lr37  2015
 Barley leaf rust
 5656P+  2016

SOURCE: Plant Breeding Institute, University of Sydney

 

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