By Professor Robert Park and Dr Colin Wellings, University of Sydney Plant Breeding Institute, Cobbitty
[Photo by Brad Collis: Professor Robert Park outside the microclimate rooms used for screening cereal lines with important rust pathotypes.]
The University of Sydney has monitored cereal rust populations throughout Australia very closely since 1919. One very important output of this work has been early warnings to the cereal industry of the occurrence of new rust pathotypes with the ability to overcome the resistance of cereal cultivars.
Recent years have seen new leaf rust pathogens of wheat emerge with virulence for the leaf resistance genes Lr24 and Lr37 and the stem rust pathogen of wheat for the stem rust resistance gene Sr38. We believe these pathotypes developed by mutation in existing pathotypes. It is not unusual to detect one or two new mutant pathotypes each year. However, these pathotypes usually do not pose any threat to the cereal cultivars being grown
Of perhaps greater significance was the appearance of a new pathotype of stripe rust in WA in 2002, which is now widespread throughout not only WA but also eastern Australia. Detailed studies by staff of the Australian Cereal Rust Control Program at the University of Sydney have clearly demonstrated that this pathotype did not develop from an existing pathotype, but rather was introduced, possibly from North America.
The impact of this blow-in pathotype on many wheat cultivars raises the question: "Can we control rust in wheat by resistance breeding?"
Cereal rust surveys conducted over the past 80 to 85 years have detected 10 occurrences where exotic cereal rust isolates have been introduced into Australia (see table). Breeding programs have had to adapt to accommodate the challenge posed by many of these new rust pathotypes.
GRDC Research Code US315
For more information: Robert Park, 02 9351 8806, email@example.com
Dr Wellings is on secondment from NSW Department of Primary Industries.