Genetic mapping brings strawberries ‘into the 21st century’ with better disease resistance

Strawberries are one of California’s main money-makers, and they’re the Central Coast’s primary crop. But they are also vulnerable to diseases that can be devastating for growers, and experts say it’s even possible that one of those diseases could lead to a strawberry pandemic.

But now, California researchers have made a key discovery to help fight one of strawberries’ biggest threats: Fusarium wilt.

The disease was on the minds of some visitors at Cal Poly San Luis Obispo’s annual strawberry field day in July. These annual field days bring hundreds of students, researchers and industry leaders to the university’s strawberry center.

One of the event’s main attractions is a field dedicated to strawberry research. Students like Mary Steele, who’s getting her masters’ in agriculture, can learn and experiment with strawberries here.

“Every plant sample that we take from different fields, we do a molecular technique to target Fusarium,” Steele said.

Fusarium is a pathogen that kills all sorts of crops, from tomatoes and tobacco to strawberries. It can cause certain crops to wither away and die, in what’s called Fusarium wilt.

Steele’s work mirrors what another major research university, UC Davis, is doing on Fusarium — one that just yielded a major development in the science of strawberries.

Mary Steele strawberry field day

David Nevarez, CA Strawberry Commission

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Cal Poly SLO master’s student Mary Steele presents her strawberry research at the annual field day.

Steve Knapp is a plant sciences professor and the director of the Strawberry Breeding Program at UC Davis. His research specialty his is plant breeding and genetics, which means he focuses on breeding “genetically superior cultivars” which means disease-resistant strawberry varieties.

Knapp and his fellow researchers screened thousands of strawberry plants and mapped the locations of genes they found that provide resistance to Fusarium wilt.

“That was critical, because it’s like it’s the roadmap without the roadmap; You aren’t going to be able to drive from Point A to Point B. So once we had those tools in place, we could apply them with strawberries, and it was very exciting,” Knapp said.

With that genetic roadmap in hand, Knapp and his team were able to develop plants that are less likely to die from Fusarium wilt. He said this will help bring strawberries up to speed with other crops like tomatoes, which have already seen success in fighting Fusarium in the past few decades.

He said growers he has talked to are excited too.

“One of the industry growers actually said, ‘Wow, looks like we’re being dragged into the 21st century,’” Knapp said.

Strawberries are one of the biggest and most important crops in the US That’s why this discovery is so important, according to Peter Henry, a plant pathologist with the US Department of Agriculture.

Santa Maria on the Central Coast is one of the few small regions in California which produce about 90% of the country’s strawberries.

“Just 40,000 acres produce that huge amount of volume. So it’s this incredibly efficient system,” Henry said.

But Henry said that system is threatened by soil-borne diseases, and a possible pandemic, whether that’s from Fusarium or another disease. But this new research could help prevent that, without bringing in other methods that Henry said could have destructive side effects.

“We have a very good solution that is not reliant on chemical fumigation. It really reduces the reliance on that as a disease control method,” Henry said.

But Henry said while the UC Davis research is a success story, it’s not the end of Fusarium wilt in California strawberries. Over time, deadly pathogens can overcome resistance in plants like strawberries and cause disease again.

“So there’s kind of this boom and bust arms race cycle between plant breeders and plant pathogens,” Henry said.

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Different blocks of Cal Poly’s strawberry field are used for different strawberry experiments, including the effects of chemical fumigation.

One of the strawberry field day’s attendees was Glenn Cole, the field manager for the UC Davis Strawberry Breeding Program and a Cal Poly SLO graduate.

Cole said it’s hard to tell what the disease even looks like, so outreach to growers on this kind of research is essential.

“You can’t, as a farmer, go to the field and go, ‘Oh, I’ve got Fusarium in my field.’ You can go to the field and say, ‘Oh I’ve got dead plants in my field,'” he said.

Cole said it’s not just about education, it’s also about trust.

Besides just knowing that this new research is happening, growers also need to be able to test resistant varieties for themselves to really know how well they work — and that means continued cooperation down the road.

“We’ve got our work cut out for us, but that’s job security,” Cole said.

UC Davis plans to release their new plant varieties later this year, with hopes of strengthening California strawberries and helping growers ward off a Fusarium wilt pandemic. The research is online at the Journal of Theoretical and Applied Geneticsand ucdavis.edu.

This piece was produced with assistance from the Public Media Journalists Association Editor Corps funded by the Corporation for Public Broadcasting, a private corporation funded by the American people.

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