Developing new high-yielding wheat cultivars with in-built resistance to rust diseases has been estimated to save the Australian grains industry $1.1 billion a year.

An important part of keeping one step ahead of ever-changing fungal rust pathogens has been to monitor the pathotypes (strains) that occur in Australia and to determine their impact on current and yet-to-be-released cultivars. This approach has been particularly successful in meeting the challenges posed by new rust pathotypes that arise locally via, for example, random mutation. In contrast, periodic incursions of wheat rust isolates from outside Australia have made resistance breeding a greater challenge.

While stem rust and leaf rust of wheat have been present in Australia since at least the earliest attempts to grow wheat here, stripe rust was not detected until 1979. It is believed to have been inadvertently brought here from Europe on contaminated clothing or the like. A second stripe rust incursion was detected in 2002, into Western Australia. In this case, the new ‘WA’ pathotype group was believed to originate from North America. Significantly, research has recently confirmed two additional incursions of wheat stripe rust – one first detected in 2017 and the other in 2018 – both in eastern Australia.

The 2017 incursion

It is now known that the stripe rust pathotype 239 E237 A- 17+ 33+ originated from Europe. It was first detected in samples of stripe rust-infected wheat collected from Normanville, South Australia, and Horsham, Victoria, in November 2017. Although it was not detected in 2018 and only a single isolate was identified in 2019 (from Victoria), 15 isolates were recovered in the 2020 season from widespread locations throughout NSW.

Using DNA ‘fingerprinting’, we were able to determine that this pathotype belonged to a family of stripe rust pathotypes known as the PstS10 group. This is the most common group of wheat stripe rust pathotypes in Europe at present, strongly implicating this region as the origin of the pathotype.

The 2018 incursion

This stripe rust pathotype, 198 E16 A+ J+ T+ 17+, was first detected near Wagga Wagga, NSW, in August 2018, and was subsequently isolated from Victoria and Tasmania that year. In 2019, it was once again isolated from these states and also from Queensland. It was the most common pathotype of the wheat stripe rust pathogen isolated from eastern Australia in that year. In 2020, it was again the dominant stripe rust pathotype in eastern Australia (67 per cent of all isolates), being isolated from all mainland eastern states.

Also using DNA fingerprinting, we identified that this pathotype belonged to the PstS13 group. Like the PstS7 group, the PstS13 group is also common in Europe, where it is principally associated with triticale. It has caused total crop failure in organically grown triticale and was responsible for severe stripe rust epidemics on durum and bread wheat in Italy in 2017.

Impact of new stripe rust pathotypes

The latest responses of Australian wheat cultivars to these pathotypes, based on detailed greenhouse and field testing, were provided in the Cereal Rust Report (Volume 17, Issue 3), which can be downloaded from the Plant Breeding Institute (PBI) website. Updated, refined responses are available in early 2021 based on results from 2020 National Variety Trials.

As above, pathology testing has implicated Europe as the potential source of the stripe rust isolates, and inadvertent human-mediated transport may have been the means of entry into Australia.

Despite generally low levels of stripe rust in wheat crops in eastern Australia during the 2019 season, there were observations of higher levels of stripe rust than expected in a number of durum wheat cultivars in NSW and Victoria  in 2020. Samples from these stripe rust infections were sent to the PBI for race analysis and all were found to be the  new pathotype that was first detected in 2018, pathotype 198 E16 A+ J+ T+17+ (‘198’).

Rust spore contamination on boots and clothing can appear as dust or dirt.  Stripe rust is believed to have spread from Europe to Australia on rust-contaminated clothing. Photo: University of Sydney

Data collected from the field in 2019 by the NSW Department of Primary Industries, Agriculture Victoria and the University of Sydney indicated that pathotype ‘198’ poses an increased threat to several wheat varieties. These include DS Bennett , LRPB Trojan and, to a lesser extent, Devil , Illabo , DS Darwin , Emu Rock and Hatchet CL .

It also poses an increased threat to several durum varieties, such as DBA Artemis , DBA Bindaroi , DBA Lillaroi , DBA Spes , DBA Vittaroi and EGA Bellaroi , and several triticale varieties, such as Astute , Joey and Wonambi.   The wheat stripe rust pathogen does not undergo sexual reproduction in Australia. Since its first detection here in 1979, we have seen the establishment of three clonal ‘lineages’ of this pathogen, each tracing back to an independent exotic incursion. The new ‘198’ pathotype traces back to an exotic incursion of the pathogen that was first detected in WA in August 2002.

Working with colleagues at Aarhus University in Denmark, we were able to show conclusively that this ‘WA’ pathotype belongs to a group of aggressive invasive isolates that were originally present in East Africa in the early 1980s and later detected in the Americas in 2000, from where it is likely to have spread to Australia.

More detailed field testing will be undertaken in 2020 to assess the full impact of this new pathotype on current wheat and triticale varieties. Growers can consult current cereal disease guides for their state to get the latest information on varietal responses to rust and other diseases. The rust ratings presented in these guides are based on the range of pathotypes that are detected in annual surveys conducted at the PBI.

The success of these surveys depends on the samples received for analysis, so growers and other members of the grains industry are encouraged to monitor crops closely for rust in the coming season, and to forward freshly collected samples in paper only to:

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

More information: Robert Park, 02 9351 8806, robert.park@sydney.edu.au