One approach researchers at K-State are working on is dubbed the major gene approach. The major gene fights wheat rust using a sort of pathogen recognition system. When the plant is attacked by a pathogen that the major gene recognizes as dangerous, it rejects the pathogen and effectively beats the wheat rust.
But Bowden says the major gene has its flaws. “Using the major gene makes the plant very resistant, but not very durable, meaning that it can work effectively one year, but be defeated by the pathogen the next year,” he says. “The pathogen can eventually mutate to camouflage itself and not be recognized, and that’s how the major gene is defeated,” he says.
However, researchers have not abandoned the idea altogether. Bowden says there are theoretical reasons to believe that instead of using one major gene, using multiple major genes in combination should create a long-lasting variety. This combination is referred to as a gene stack or pyramid.
The second approach is referred to as the minor gene theory. Individually, minor genes are not as effective as a singular major gene in defeating wheat rust, but stacking several minor genes together can potentially create a good resistant variety. It is similar to the first approach in that it stacks multiple genes, but what’s different is the mechanism of resistance to the pathogen. It doesn’t rely on pathogen recognition to defeat rust, but rather strengthens the basic defense system of the plant. Once the gene stack is strong enough to defeat a pathogen, the wheat rust may never overcome it. The problem lies in finding enough effective minor genes to strengthen the defense to a point where it will successfully defeat the pathogen.
“Minor genes are more difficult to work with because there haven’t been very many discovered for stem rust, but we believe they’re out there,” says Bowden.
At this point, researchers are putting equal amounts of effort toward both solutions so they can maximize their chances of success.
Providing producers with multiple resistant wheat varieties would be an ideal scenario says Fellers. He explains why planting only one resistant variety across a large region can have consequences. He draws on his experiences with wheat leaf rust, a disease similar, but unrelated, to Ug99.
“We saw an epidemic like Ug99 in leaf rust about five years ago,” Fellers says. “All the farmers were using the same variety from Oklahoma through Nebraska so when the pathogen changed and was able to overcome that one particular resistance gene, it affected the entire region.”
Researchers remain hopeful that Ug99 will be stopped before having devastating effects in the United States or worldwide. An alarm has been raised up around the globe for the past several years by international researchers. The Borlaug Global Rust Initiative is bringing together researchers from the United States, CIMMYT (International Center for Maize and Wheat Improvement based in Mexico City), as well as Asia, Australia, Europe and Africa.