On a sunny day in early April, young wheat plants stood waist-high in test fields near the UC Davis campus, their heads full of still-green grain. A walk along some furrows left pants and boots covered with a fine, orange dust. These plants were bred to fight a stubborn pathogen that threatens the world’s wheat: stripe rust.

Already, information about the genetic line-up of these plants is available to researchers and breeders on GRIN-Global, a web-based software system used by gene banks around the world. This “gene catalogue” now has information, developed by the UC Davis Small Grains Breeding Program, about stripe rust resistance genes for both durum wheat, the kind used for pasta, and common wheat, used for bread.

In this field, scientists in the program are focused on pasta wheat. In two to three years, their breeding trials are expected to produce new cultivars for farmers, offering more durable resistance to stripe rust. 

Program researchers also are developing breeding populations of bread wheat that carry genes to fight this devastating pathogen.

Standing between two breeding test plots of durum wheat, project scientist Joshua Hegarty pulled a leaf off a plant; it showed long, pale, stripe-like lesions, the fatal scars of stripe rust. He grabbed a plant in the neighboring test plot; its leaf looked green and healthy, though a closer look revealed pinhead-sized yellow flecks on the surface.

“That’s where the plant fought off the stripe rust,” Hegarty said. “It will only lose maybe 5% of its production. This other breeding line?” He brushed orange powder off the first leaf. “You lose the farm.”

The fungus that causes stripe rust, Puccinia striiformis, is endangering global production of wheat, one of the planet’s most important food crops. These test plots show the breeding gambit is working: Durum wheat bred with the resistance gene Yr78 is showing a dramatic reduction in disease susceptibility.

The research is led by Jorge Dubcovsky, a Distinguished Professor, and Xiaofei Zhang, an assistant professor, both in the UC Davis Department of Plant Sciences and leaders of the university’s Small Grains Breeding Program. A paper detailing their research was published last year in Crop Science, with now-graduated Ph.D. student Chen Dang the lead author.

Resistant bread wheat also being developed

Turning to bread wheat, the scientists found Yr78 works even better in combination with other naturally occurring wheat genes known to fight disease, producing resistance of at least 43%. So, they used a technique called marker-assisted back-crossing to build a gene team, grouping Yr78 with three more genes – Yr5, Yr15 and Yr36. Together, they boost resistance at both the seedling and adult stages of the plant. Plus, the resistance gene team could now be inherited from plant to seed.

Scientists now are breeding this resistance gene team into the UC-Central White variety of bread wheat, a high-quality cultivar developed especially for the Central Valley. They expect the team to deliver durable and field-ready disease resistance for common wheat, Zhang said.

Today, stripe rust is causing total losses in some areas, depending on the variety of wheat and the local conditions, according to the U.S. Department of Agriculture. It’s a cool-season disease, impacting mostly winter wheat. Spread by a variety of factors, stripe rust has been detected in more than 60 countries, according to the USDA. 

Worse, the fungus recently overcame resistance that had been bred into wheat decades ago. An outbreak was reported in late 2025 in the United Kingdom by the National Institute of Agricultural Botany.

“This underscores the increasing threat to wheat production,” Zhang said.

Research in the UC Davis Small Grains Breeding Program on the genetic underpinnings of stripe rust resistance has been funded over many years by the United States Department of Agriculture’s Agriculture and Food Research Initiative and the Howard Hughes Medical Institute.