Good News for Pasta Lovers Grows in UC Davis Fields

On a spring day in early April, young wheat plants stood waist-high, their heads full of still-green grain. A walk along some furrows left pants and boots covered with a fine, orange dust. These plants in test fields near the UC Davis campus 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 resistance genes for both durum wheat, the kind used for pasta, and common wheat, the type used for bread.

In this sunny 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 pasta 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 explained. “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 one of the planet’s most important food crops. Here, 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 being led by Jorge Dubcovsky, a distinguished professor, and Xiaofei Zhang, an assistant professor, both in the Department of Plant Sciences and leaders of the university’s Small Grains Breeding Program. A paper detailing their research was published in Crop Science, with now-graduated Ph.D. student Chen Dang the lead author.

Research on the genetic underpinnings of stripe rust resistance has been funded over the years by the United States Department of Agriculture’s Agriculture and Food Research Initiative and the Howard Hughes Medical Institute. Worldwide, wheat provides people with about one-fifth of their calories and protein, according to an international study.

Resistance gene for pasta wheat

Scientists from around the world have spent decades documenting the location of resistance genes across the wheat genome, identifying more than 80. 

Yr78 is one of them and has been found in common wheat, the type used for bread. It gives plants durable resistance to stripe rust, meaning it remains effective across many years and against multiple variations of the fungus. Dubcovsky and researchers in his lab spent years looking for the precise location of Yr78 and developing genetic markers that let them track it reliably from plant to seed, generation after generation. 

Yr78, however, does not occur in durum wheat, the type used for pasta. Using a breeding technique called marker-assisted back-crossing, Dang – then a grad student working with Dubcovsky – bred Yr78 into the Kronos variety of durum wheat, which is grown widely in California and Arizona.

The process “required additional effort and careful selection,” Zhang explained, because bread and pasta wheat have a different number of chromosomes. But the results were worth it: In field trials of durum wheat, the scientists found adding Yr78 reduced the severity of stripe rust infection to about 39%, down from an average of nearly 64%, Deng reported.

A whole team for resistance in bread wheat

Turning to bread wheat, the scientists found Yr78 works even better in combination with other genes drawn from the resistance pool, producing disease resistance of at least 43%, Dang reported. So, they built a gene team by grouping [XZ6] 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 team could now be inherited from plant to seed.

Scientists now are breeding the resistance team into the UC-Central White [TK7] 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.

Dang noted some historical insights, too: While looking for Yr78 in common wheat, she found the pattern pointing toward the gene in more than half of the European spelt wheat she studied. That suggests Yr78 may have been protecting common wheat from stripe rust for hundreds of years. (Dang wrote more about that in a previous paper about mapping the Yr78 gene.)

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 figured out how to overcome resistance that had been bred into wheat decades ago. An outbreak was reported in late 2025 in Great Britain by the National Institute of Agricultural Botany. “This underscores the increasing threat to wheat production,” Zhang said.

Related links

Read the paper here, “Durum wheat with Yr78 and common wheat with Yr78 and Yr36 in coupling show enhanced stripe rust resistance,” published in Crop Science. Authors from the UC Davis Department of Plant Sciences are Chen Dang, Joshua Hegarty, Xiaofei Zhang and Jorge Dubcovsky.