The Genomic Era Is Here

Though reports of stem rust date back to biblical plagues and ancient Greece, plant breeders successfully combated the disease by introducing rust-resistant cultivars in the mid-20th century. Stem rust epidemics largely faded until 1999, when a mutated strain—Ug99—emerged in the east African country of Uganda.

Ug99 and its recent variants have toppled nearly all previously resistant genes. The rare holdouts include Sr2, found in an especially hardy wheat variety named Gage that was co-­released by the University of Nebraska and the USDA in 1963.

The study isolated and examined DNA sequences of Gage to ascertain why it enjoys greater resistance to stem rust, including Ug99, than other cultivars featuring the Sr2 gene. The authors concluded that Gage’s rust-resistance during adulthood likely owes to a combination of Sr2 and an additional gene, which the team believes also contributes to the wheat’s resistance in the seedling stage of its development.

The researchers have narrowed down the location and ­potential identity of this additional gene, which they said they hope to soon verify through further study.

“It so happens that the source of Sr2 that was used to create Gage—the variety Hope—actually had a number of other stem rust resistance genes in it,” reports P. Stephen Baenziger, PhD, a co-author and the Nebraska Wheat Growers Presidential Chair at UNL. “Our results would say that it looks like Gage got the lucky straw, so to speak, from Hope.”

Drawing a genetic map to that level of resistance could prove extremely valuable against Ug99.

“It’s important to understand the resistance to stem rust, because with the mutations that are coming out of ­Africa, we’re losing genes all the time,” says Dr. Baenziger. “But Sr2 is still resistant to it, and now that we can associate parts of the genome with the resistance, we’re making good progress.”—FQ&S