Despite generally low Stripe rust pressure in wheat crops across eastern Australia during the 2019 season, higher-than-expected pressure from rust was observed in some durum wheat cultivars in New South Wales and Victoria.
Samples collected from these Stripe rust infections were sent to the University of Sydney's Plant Breeding Institute for race analysis, where all were found to be the new pathotype 198 E16 A+ J+ T+17+.
Pathotype 198 was first detected near Wagga Wagga, NSW, in late August 2018 and it was subsequently isolated from Victoria and Tasmania in that year.
In 2019, it was again isolated from these southern states and also from Queensland, plus it was identified as the most common Stripe rust pathotype isolated from eastern Australia in that year.
Data collected from the field during 2019 by researchers from the NSW Department of Primary Industries, Agriculture Victoria and the University of Sydney indicated that pathotype 198 poses an increased disease threat to several wheat varieties.
These include DS Bennett(PBR), LRPB Trojan(PBR) and, to a lesser extent, Devil, Illabo(PBR), DS Darwin(PBR), Emu Rock(PBR) and Hatchet CL Plus(PBR). It also poses a threat to durum wheat varieties such as DBA Artemis(PBR), DBA Bindaroi(PBR), DBA Lillaroi(PBR), DBA Spes(PBR), DBA Vittaroi(PBR) and EGA Bellaroi(PBR), as well as triticale varieties such as Astute(PBR), Joey and Wonambi.
Comparative greenhouse tests established that pathotype 198 is likely to be a mutational derivative of an existing pathotype, 134 E16 A+ J+ T+, but it has added virulence for the rust resistance gene Yr17 and the differential Suwon 92/3*Omar wheat breeding line.
Although the rust resistance of the Suwon92/3*Omar line has not been fully characterised, it is considered to carry the Yr4rust resistance gene, which is present in several Australian bread wheat varieties, such as Bolac(PBR), Lincoln(PBR) and Viking(PBR).
These tests also implicated the presence of the Yr4rust resistance genein the wheat varieties DS Bennett(PBR) and, possibly, in Buchanan(PBR), Hatchet CL Plus(PBR) and several durum wheat varieties, explaining why they appear vulnerable to the new pathotype.
The wheat Stripe rust pathogen does not undergo sexual reproduction in Australia.
Since it was first detected in this country in 1979, we have seen the establishment of three clonal genetic 'lineages' of this pathogen, each of which trace back to an independent exotic incursion.
The new pathotype 198 traces back to an exotic incursion of the pathogen that was first detected in Western Australia 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 were later detected in the Americas in 2000.
More detailed field testing in 2020 will assess the full impact of this new pathotype on wheat and triticale varieties in Australia.
Growers can consult current cereal disease guides for each state for the most up-to-date information on varietal responses to rusts and other diseases.
The rust ratings contained in these guides are based on the range of pathotypes that are detected in annual Plant Breeding Institute surveys.
The success of these surveys depends entirely on the samples received for analysis. So, as always, grain growers and advisers are encouraged to monitor crops closely for rust this season. Please send freshly collected samples, contained in paper only, to the Australian Cereal Rust Survey, at the University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan, NSW, 2567.
GRDC Research Codes: 9175448, 9175952, 9176057
More information: Robert Park, 02 9351 8806, robert.park@sydney.edu.au