By Helen Olsen
The damage bill has yet to be finalised, but 2004 looks to have delivered the most widespread - and potentially one of the most damaging - stripe rust infestation in Australia"s history, according to researchers.
Dr Colin Wellings, from the University of Sydney Plant Breeding Institute at Cobbitty, NSW, says the stripe rust outbreak this year has been historic in terms of its national scale. "In 2002 WA was affected and last year the eastern states were affected. This year both sides of the continent have been experiencing it," he says.
The hardest hit areas have been the southern and eastern regions of WA, southern and northern NSW and parts of Victoria and SA. Queensland has been relatively unscathed, largely because of the earlier growing season, combined with the much later arrival of the rust pathogen in the north.
At this stage it is difficult to estimate the impact the stripe rust epidemic has had on yields, but Dr Wellings says that in susceptible varieties, where diagnosis may have been delayed, and fungicides applied too late, losses could be about 40 to 50 percent, or even more. "In some cases, growers had delays in waiting for contractors, or for sufficient supplies of chemicals to be available," he says.
Timely diagnosis and application of fungicides are crucial to minimising the harm done by stripe rust, he says. "I think the growers who did diagnose the problem and were able to apply fungicide before the infection was too advanced were pleased with how well their crops recovered."
Australian wheat growers have successfully relied on rust resistance genes in wheat to withstand infection. The current stripe rust strain, that entered WA from overseas in 2002, can overcome some of this resistance, to a greater or lesser degree, in certain varieties. Nevertheless, several very useful resistances are providing protection including the "VPM" genes in wheats such as Camm and Sunvale.
Researchers, including Dr Wellings, are investigating key characteristics of the new stripe rust pathotype: "We"re monitoring pathogen populations and looking at what are called virulence genes, which are largely responsible for the severity of the disease. If, for example, the VPM resistance is overcome by pathogen virulence, then this will have a significant impact on disease ratings in many varieties."
Other groups are conducting fungicide trials, to determine the optimal parameters for timing, the amounts and types of chemicals and the economics of these approaches, in order to combat the current outbreak.
The February issue of Ground Cover will include an in-depth report covering the extent of the stripe rust epidemic and information on how different wheat varieties coped with this year"s stripe rust infestation.
Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.
See also: Cereal Rust column in this issue of Ground Cover