Australian wheat producers have been encountering significant challenges from wheat stripe rust. In 2024, detections as early as late May in Tasmania and late June in NSW suggests increased disease pressure, with the potential for the disease to persist through the summer months, raising concerns about a possible rapid build-up if conditions remain favourable.

Although these early detections occurred a week later than the severe stripe rust epidemic in 2022, they were still earlier than the long-term average for first detection dates, which are typically in the fourth week of July for eastern Australia.

Wheat stripe rust is a disease caused by Puccinia striiformis f. sp. tritici (Pst) – a pathogen that thrives in cool, moist conditions, particularly when temperatures range between 10°C and 17°C.

By the second week of September, 310 samples had been received, mostly from southern and northern NSW, Victoria, and then South Australia. The genotypic and phenotypic analysis of 78 samples identified multiple stripe rust pathotypes within single samples. The 239 E237 A- 17+ 33+ has been confirmed as dominant pathotype across various regions.

In southern NSW, 56 stripe rust samples were processed, revealing a variety of pathotype distribution. The most prevalent pathotype was 239 E237 A- 17+ 33+, accounting for 34 per cent of the samples.Then 238 E191 A+ 17+ 33+ was identified in 32 per cent of the samples, while the 198 E16 A+ J+ T+ 17+ and the 198 Ma+ variant, first identified in 2023, accounted for 11 and five per cent respectively.

Although the 198 pathotype has declined, it was still detected in southern and northern NSW in 2024.

The 198 Ma+ variant identified in 2023 is virulent on Maritime barley and an uncharacterised seedling resistance gene not targeted by the standard 198 pathotype.

The 198 Ma+ variants like the standard 198 isolate remain vulnerable to various wheat varieties, including DS Bennett, LRPB Trojan, and Emu Rock, as well as durum wheat varieties like DBA Artemis and EGA Bellaroi. Additionally, it impacts triticale varieties such as Astute and Bison due to its virulence on gene YrB. In addition, 18 per cent of the samples are attributed by 238 E191 A+ J+ T+ 17+ in southern NSW.

In the northern NSW, 13 stripe rust samples have been processed, showing the diversity of pathotypes distribution. The most prevalent pathotype identified was 238 E191 A+ 17+ 33+, which accounted for 31 per cent of the samples. Additionally, the 239 E237 A- 17+ 33+ was detected in 23 per cent and 238 E191 A+ J+ T+ 17+ in seven per cent of the samples. There was detection of two 198 variants in northern NSW, as well accounting for eight per cent each.

Beside the wheat stripe rust samples, we received stripe rust samples from two barley varieties, Neo and Zena as well. These samples were identified as BGYR+, a barley grass stripe rust variant (Puccinia striiformis f. sp. pseudo-hordei Psp_h) first detected in 2021. This variant has increased virulence on several Australian barley varieties from our preliminary studies. The stripe rust currently being processed in barley is not caused by the exotic pathogen Puccinia striiformis f. sp. hordei (BYR), which remains absent in Australia.

In Victoria, seven stripe rust samples have been analysed, revealing key trends in the distribution of pathotypes. The 239 E237 A- 17+ 33+ pathotype was the most dominant, accounting for 57 per cent of the samples. The 238 E191 A+ 17+ 33+ was present in 29 per cent, while 238 E191 A+ J+ T+ 17+ accounted for 14 per cent of the samples.

In Tasmania, two samples were detected as the 239 E237 A- 17+ 33+ pathotype indicating its prevalence in the region.

Reflecting on the 2022 epidemic, Australia faced one of its most severe stripe rust outbreaks, driven by early disease onset and favourable weather conditions, including cooler-than-average temperatures and above-average rainfall.

Growers should closely monitor weather conditions in their area. Additionally, proactive disease management strategies, including regular crop monitoring and timely fungicide applications, will be essential to protect crops from potential losses.

We encourage all stakeholders to thoroughly examine crops and adjacent weeds, particularly barley grass. Should rust be detected, kindly dispatch freshly collected samples in paper only to Australian Cereal Rust Survey at the University of Sydney, Reply Paid 88076, Narellan NSW 2567.

This is crucial: Do not use plastic when posting samples. Rust spores will not survive, making your sample not viable for processing.

More information: Professor Robert Park, 0414 430 341, robert.park@sydney.edu.au;
Dr Mumta Chhetri, 0404 392 959, mumta.chhetri@sydney.edu.au