Wheat Disease Breakthrough

Research targeting stem rust through DNA testing results has resulted in a breakthrough in the wheat field. Now, suspect samples could be analyzed within hours instead of weeks. This shortened window of time has the potential to save crops from being decimated by stem rust, historically the most dangerous pathogen to wheat.

Stem rust has recently reemerged in parts of the world, where it has devastated crops due to its ability to evolve – reversing much of the work that happened during the Green Revolution. Now, scientists have isolated the very first rust pathogen gene that wheat plants detect to 'switch on' resistance.

The collaboration includes the University of Sydney, Commonwealth Scientific Industrial Research Organization (CSIRO), UK's Rothamsted Research, the University of Minnesota, and the United States Department of Agriculture (USDA). The new findings are being published in the journal, Science.

"For the first time, it will be possible to do DNA testing to identify whether a rust in a wheat crop anywhere in the world can overcome a rust-resistance gene, called Sr50, which is being introduced in high-yielding wheat varieties," says Robert Park, professor at the University of Sydney.

The DNA test will indicate whether or not the wheat crop would need to be sprayed with a fungicide to protect against rust, which could destroy the crop in a matter of weeks, says Park.

Rust disease epidemics have emerged at times in tandem with carefully refined selective breeding in cereals; the disease is once again extremely damaging in East Africa and is making a comeback in Europe.

Jiapeng Chen, a doctorate candidate from the University of Sydney, initiated the work by sequencing and analyzing the genome of a virulent rust isolate. Chen says it's the first important step in addressing the diagnostic challenges posed by ever-changing fungi, which result in new rust pathogen strains.

By doing so, the researchers are able to stay one step ahead of the pathogen.

The last major epidemic of wheat stem rust in Australia, back in 1973, caused $AU300 million (approximately $231 million U.S. dollars) in damage – imagine what that would be today, say the researchers.

Co-corresponding author, Peter Dodds from CSIRO, says demand for wheat in the developing world is expected to jump 60% by 2050.

"Now that we've identified how stem rust strains are able to overcome Sr50 resistance – by mutation of a gene we've identified called AvrSr50 – this information can be used to help prioritize resistance genes for deployment," says Dodds.

"Our results so far show the plant immune system is able directly to recognize the fungal protein," says Dodds. The new knowledge is helping them gain a better understanding of what's happening on the gene level.

The results should also lead to a better understanding of how rust pathogens infect wheat, evading detection by the wheat plant, and causing yield losses, says Park.

"In addition to the immediate practical benefit regarding the important rust-resistance gene Sr50, our world-first finding could potentially have a longer term payoff in the 10- to 15-year horizon," adds Park.