In contrast with some cereal fungal pathogens that can survive throughout the non-cropping summer period on dead plant tissue such as stubble, the rust diseases can only survive on dead plants for a matter of weeks.
The absence of live cereal plants during the non-cropping summer period poses a challenge to the survival of rust pathogens, creating a 'bottleneck' that sees a major reduction in the size of rust populations.
In the 40 years that stripe rust has been present in eastern Australia, however, it has managed to survive the non-cropping summer period to reappear during the growing season every year - either in winter or spring, between mid-May and late-September.
In the early years after stripe rust was discovered in Australia in 1979, interest in its annual recurrence meant a slab of beer was awarded to the person who first detected it each year. The 'average date' when stripe rust has been first detected or recurred each year in a wheat crop in eastern Australia over the past 40 years is 13 July.
Later detection in WA
But since stripe rust was discovered in Western Australia in 2002, the situation has been quite different in that state.
The 'average date' for first detection or recurrence of stripe rust each year in WA is 10 September.
However, there have been five years since 2002 when the disease has not been detected in WA wheat crops: 2013, 2014, 2016, 2017 and 2018.
Stripe rust is also recurrent across much of eastern Australia despite the prevailing dry conditions. It was first detected this growing season in a Naparoo (PBR) wheat crop at Forbes, New South Wales, on 2 September 2019. The isolate present was identified as pathotype 134 E16 A+ J+ T+ 17+.
Stripe rust hotspots and general infection were also detected in a LongReach Trojan (PBR) wheat crop near Wagga Wagga, NSW, in mid-September.
NSW Department of Primary Industries (DPI) pathologists inspected the crop to confirm the presence of the rust disease and assess its damage.
Cereal Rust Control Program
Samples were collected from the crop for pathotype analysis through the Australian Cereal Rust Control Program (ACRCP) at the Plant Breeding Institute, University of Sydney.
In Victoria, where growing conditions have been more favourable this season, stripe rust was also detected in the same week.
In late 2017, wheat stripe rust samples collected from two locations in Victoria were found to contain a new pathotype (239 E237 A- 17+ 33+), which spread into NSW during 2018.
Wheat varieties identified through ACRCP screening that researchers aim to monitor for stripe rust infection are: Coolah (PBR), LongReach Flanker (PBR), Axe (PBR), LG B53 (PBR), Buchanan (PBR), LG Cobalt (PBR), EGA Gregory (PBR), Forrest (PBR), LongReach Gauntlet (PBR), Grenade CL Plus (PBR), Mitch (PBR), Steel, LongReach Trojan (PBR), LongReach Viking (PBR) and Zen (PBR).
In addition to these wheat varieties, all varieties currently rated susceptible are expected to retain this resistance rating.
Vigilance remains necessary
Despite the dry seasonal conditions, vigilance is still needed in monitoring crops for rust development.
Rust spores dispersed by wind movement can travel long distances to infect susceptible varieties in low moisture conditions.
The variability of rust diseases and their rapid spread across the Australian continent highlights the importance of regular and nationally coordinated monitoring of these pathogens.
Growers are encouraged to monitor crops closely for rust in the current season and forward collected fresh samples (in paper only) to the Australian Cereal Rust Survey, University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan, NSW, 2567.
GRDC Research Codes 9175448, 9175952, 9176057, BLG207