Researchers identify genes that make strawberries resistant to Fusarium wilt

Strawberry losses from fusarium wilt could become less of a threat after researchers at the University of California at Davis discovered genes that resist deadly soil-borne diseases.

Steve Knapp, director of the college’s strawberry breeding program, said the findings, published in Theoretical and Applied Genetics, are the culmination of several years of work, and the discovery will help protect against disease losses.

“What we have accomplished here is important and valuable to the industry and will protect farmers,” Knapp said.

Strawberries are a major crop in California, with about 1.8 billion pounds of nutritious fruit grown each year, making up nearly 88% of what is harvested in the United States.

Finding genes could prevent Fusarium wilt pandemic.

“The disease is starting to appear more often across the state,” said Glenn Cole, a breeder and field manager with the Strawberry Breeding Program. “Once the wilt enters, the plant collapses. It dies completely.”

Searching for resistance

University of California, Davis scientists examined thousands of strawberry plants in a college nursery and took DNA samples. They then used genetic screening and developed DNA diagnostics to identify genes that are resistant to the primary strain of Fusarium wilt.

“Genes have been floating around in strawberry germplasm for thousands of years,” Cole said, but no one has worked to identify them.

This latest development brings “strawberries into the 21st century in terms of solving this problem,” Knapp said.

Protecting future crops

This work means that breeders can introduce the resistance gene into future strawberry cultivars. This fall, the program will release new cultivars that contain the Fusarium wilt resistance gene. DNA diagnostic tools will help breeders respond to new Fusarium wilt variants that develop.

“There are going to be new threats and we want to be prepared for them,” Knapp said. “We want to understand how this works in strawberries so we can address it as quickly as possible as new threats emerge.”

“If you don’t have Fusarium resistance, you’re done,” Cole said. “The disease could be more present than you think.”

Fusarium wilt has not been a traditional problem but when fumigated methyl bromide was phased out in 2005, things changed. The disease was in the soil and without fumigation, the incidence of wilting increased, especially in areas where crops were not rotated.

Resistant cultivar of strawberry planted among cultivars prone to fusarium wilt.  (Glenn Cole/UC Davis)
Resistant cultivar of strawberry planted among cultivars prone to fusarium wilt. (Glenn Cole/UC Davis)

Breeding new varieties

Knapp and Cole have reported to the industry which current strawberry cultivars are resistant so they can select plants with that extra protection. New resistant cultivars coming out later this year will be suitable for several growing seasons.

“It’s a big deal,” Cole said. “It’s all incremental in plant breeding, but it’s a big thing.”

Botanists have been breeding strawberries at the University of California, Davis since the 1930s and released more than 60 patented cultivars through the Public Breeding Program.

All the action happened at the University of California, Davis. Dominic Pinkott, Mitchell Feldman, Michi Fachev, Marta Bjornson, Alan Rodriguez, Randy Famula and Jetta Cocker from the Department of Plant Sciences, and Thomas Gordon from the Department of Plant Pathology, as well as Michael Hardigan and Peter Henry contributed to the research. He is now with the USDA Agricultural Research Service and Nicholas Cobo at the University of La Frontera in Chile.

The research was funded by UC Davis and grants from the USDA’s Specialty Crop Research Initiative.