The national rust surveillance system profiles rust pathotypes and which resistance genes are effective against them.

Ensuring growers get optimal value from the genetic resistance in cereal varieties requires knowing which rust pathotypes (races or strains) are where and which resistance genes are effective against them.

Many Australian cereal varieties carry in-built genetic resistance that protects them from rust, delivering savings to grain growers by reducing yield loss and the costs associated with control strategies such as fungicides.

Effective resistance genes

The triple rust resistance genes Lr37/Yr17/Sr38 have been used in more than 50 Australian wheat varieties; however, they have some vulnerability to stripe rust in eastern Australia, where several rust pathotypes carry virulence for the stripe rust gene Yr17 (see Figure 1). Varieties with Yr17 in Western Australia remain resistant to stripe rust because no Yr17-virulent pathotypes have been detected there.

Figure 1: The occurrence of wheat stripe rust pathotypes over time in eastern Australia. The frequency of the ‘WA’ pathotype (134 E16 A+, orange line) declined after its initial detection in 2002, while a mutant pathotype with virulence for resistance gene Yr17 (134 E16 A+ 17+, blue line) increased in frequency.

Source: Professor Robert Park

The University of Sydney has surveyed Australian cereal rusts continuously since 1921. These surveys show that cereal rust pathogens move freely and rapidly within the western and the eastern Australian cereal-growing regions, and occasionally move from west to east or, more rarely (because of prevailing winds), from east to west.

The national rust surveillance system comprises an Australian network of interested parties who keep an eye on local disease development and forward rust samples for pathotype analysis. This crucial service is largely supported by grain growers, through GRDC investments, and the University of Sydney.

Rust pathotypes are identified by applying rust from a field-collected sample to a set of indicator lines carrying different resistance genes. While this basic approach has not changed much in 100 years, rust pathotype characterisation has improved dramatically as our understanding of the genetic basis of resistance to these pathogens has increased.

New incursions

New rust pathotypes emerge in Australia through random mutation, asexual hybridisation and exotic incursions. Whole genome sequencing of rust pathogens is shedding further light on these processes.

For instance, we have confirmed that more than 300 pathotypes of the wheat stem rust pathogen in Australia belong to just four families. Each of these four families traces back to single incursions – one in 1925, one in 1954 and two in 1969. Those detected in 1954 and 1969 are closely related to isolates in southern Africa and may have been carried here by high-altitude winds in rare climatic events.

The national rust surveillance system comprises an Australian network of interested parties who forward rust samples to the University of Sydney for pathotype analysis.

Genome sequencing has provided the foundation for next-generation rust diagnostics, using DNA markers developed by the University of Sydney to identify pathotypes. In 2020, they proved valuable in rapidly ruling out exotic incursion as the source of stripe rust infections in barley crops.

This work also led to the world-first identification of a rust pathogen gene that determines whether a stem rust isolate can infect wheat carrying the resistance gene Sr50. Conducted by the university and CSIRO, this work revealed how stem rust can break down resistance at the level of the gene and has opened the door to developing rapid DNA tests to determine whether an isolate of stem rust can infect wheat varieties carrying the resistance gene Sr50.

More information: Professor Robert F. Park, 0414 430 341, robert.park@sydney.edu.au; University of Sydney Australian Rust Survey

Australian Cereal Rust Survey

The Australian Cereal Rust Survey relies on the samples contributed by farmers, agronomists and agricultural researchers across Australia. We welcome rust samples from cereal crops and various weed grass species.

To submit a sample, please fill in the online sample submission form and post it in a paper envelope along with your infected leaf/stem sample to:

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

Free, reply-paid rust sample envelopes are available on request.