wheat leaf rust
The new finding comes along with the rust pathogen devastating crops in Africa and making a comeback in Europe.
Photo courtesy of USDA ARS.
 
SYDNEY, AUSTRALIA – In recent years the re-emergence of wheat rust, a crop damaging or killing disease, has threatened food security. The University of Sydney and partners have isolated a rust pathogen gene that wheat plants detect to “switch on” resistance. 

Collaboration includes the University of Sydney, Commonwealth Scientific Industrial Research Organization (CSIRO), U.K.’s Rothamsted Research and the University of Minnesota and the U.S. Department of Agriculture (USDA) in the United States.
 
The University of Sydney noted the reemergence has allowed the rust pathogen to evolve, undoing much of the work that began in earnest with the Green Revolution — using natural techniques to isolate the first rust pathogen gene that wheat plants detect and use to “switch on” in-built resistance.
 
The breakthrough in research targeting the stem rust foe — historically the most dangerous pathogen of wheat — will mean suspect samples could be analyzed within hours in an emergency rather than weeks, potentially saving crops from being destroyed.
 
“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,” said Robert Park, professor and corresponding author from the University of Sydney. “This will indicate whether or not a given wheat crop needs to be sprayed with expensive fungicide quickly to protect against rust — which would otherwise devastate the crop in a matter of weeks.”
 
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.
 
The new findings are being published in the journal Science.
 
Jiapeng Chen, a PhD candidate from the University of Sydney who initiated the work by sequencing and analyzing the genome of a virulent rust isolate, said this was the first important step in addressing the diagnostic challenges posed by ever-changing fungi, which result in new rust pathogen strains.
 
“It’s like an ongoing arms race — we’ve got to keep one step ahead of this changing pathogen,” Park said. “The last major epidemic of wheat stem rust in Australia alone, in 1973, caused A$300 million in damage — imagine what that would be today.”
 
Co-corresponding author, Peter Dodds from CSIRO, said demand for wheat in the developing world was expected to jump 60% by 2050, and in economic terms alone the ramifications were huge.
 
“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 prioritise resistance genes for deployment,” Dodds said. “Our results so far show the plant immune system is able directly to recognize the fungal protein. We are gaining a better understanding of the whole process – what’s going on at the protein level, at the gene level.”
 
Co-author Kostya Kanyuka from Rothamsted Research, an agricultural science center in the U.K., said stem rust had been making a comeback in Europe, for example in Sweden as recently as this year, and was threatening Asia and the United States.
 
“The highly virulent Ug99 race of the stem rust fungus – which emerged in 1998 in Uganda – has become even more potent as it has spread through Africa and the Middle East, with winds threatening to carry it into Asia,” Kanyuka said.
 
U.S. collaborators professors Melania Figueroa and Brian Steffenson from the University of Minnesota and Yue Jin from the USDA, extended the results of the study by examining strains of the stem rust pathogen from other parts of the world, including the United States and Africa.
 
“It is important to look at this gene in worldwide rust strains to gain a picture of where virulence is most likely to evolve,” Figueroa said.
 
Park said 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.
 
“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,” he said.