"Until that point, wheat breeders had two or three genes that were so efficient against stem rust for decades that this disease wasn't the biggest concern," Akhunov said. "However, the discovery of the Ug99 race of pathogen showed that changes in the virulence of existing pathogen races can become a huge problem."
As a first line of defense, wheat breeders and researchers began looking for resistance genes among those that had already been discovered in the existing germplasm repositories, he said.
"The Sr35 gene was one of those genes that was discovered in einkorn wheat grown in Turkey," Akhunov said. "Until now, however, we did not know what kind of gene confers resistance to Ug99 in this wheat accession."
To identify the resistance gene Sr35, the team turned to einkorn wheat that is known to be resistant to the Ug99 fungal strain. Einkorn wheat has limited economic value and is cultivated in small areas of the Mediterranean region. It has been replaced by higher yielding pasta and bread wheat varieties.
Researchers spent nearly four years trying to identify the location of the Sr35 gene in the wheat genome, which contains nearly two times more genetic information than the human genome.
Once the researchers narrowed the list of candidate genes, they used two complimentary approaches to find the Sr35 gene. First, they chemically mutagenized the resistant accession of wheat to identify plants that become susceptible to the stem rust pathogen.
"It was a matter of knocking out each candidate gene until we found the one that made a plant susceptible," Akhunov said. "It was a tedious process and took a lot of time, but it was worth the effort."
Next, researchers isolated the candidate gene and used biotechnical approaches to develop transgenic plants that carried the Sr35 gene and showed resistance to the Ug99 race of stem rust.
Now that the resistance gene has been found, Akhu
|Contact: Eduard Akhunov|
Kansas State University