Strawberry genetic research might sound like science fiction, but a lot of research relies on simple, old-fashioned breeding practices. “It’s this idea of crossing two things together to bring the nice attributes,” says Steven Knapp, director of the strawberry breeding program at UC Davis.
Researchers collect plant samples from around the world, looking for genes resistant to different diseases. Beginning in 2015, they began a quest for strawberry varieties resistant to Fusarium wilt, a pathogen that threatens Monterey County’s most valuable crops.
Fusarium wilt is caused by the fungus Fusarium oxysorum f. Sp., and it appeared in California about 15 years ago, and it spreads easily. “It’s a very aggressive disease,” says Knapp. “It will devastate a sensitive plant. It just kills him to the ground.
These sensitive plants include Monterey County’s most prized crops, strawberries and lettuce.
The challenge for breeders was to find crop varieties resistant to Fusarium wilt; by analyzing the DNA, they discovered that about 25% of plants naturally possess three resistant genes. “We found that this plant has a huge diversity of resistance genes,” says Knapp.
Finding the gene is the first step. “Genes have been floating around in the germplasm for thousands of years,” Glenn Cole, plant breeder and field manager for the strawberry breeding program, said in a statement. Cole, Knapp and other members of their team published the results in the journal Theoretical and Applied Genetics.
The next step is to select strawberries that have these genes. To do this, the UC Davis researchers pollinated hybrids and then screened for the desired genes, separating out the seeds that carried them. “It’s a big deal,” Cole said. “Everything is progressive in plant breeding, but it’s a big deal.”
The gene helps trigger the plant’s immune system – similar to what white blood cells would do in our bodies – to attack the fungus.
UC Davis plant scientists have been breeding strawberries since the 1930s, and since then they have released more than 60 patented varieties through the public breeding program. Fusarium-resistant berries are expected to hit the market later this year.
For Central Coast growers, this should be a welcome relief. Methyl bromide was a common soil fumigant that was historically used in strawberry fields to suppress disease, and it has been phased out due to its ozone depleting effects. “Diseases can start building up in the soil and those diseases can affect the productivity of the plant and can also kill the plants,” says Chris Christian, senior vice president of the California Strawberry Commission.
A fusarium-resistant berry is good news for growers, says Christian. “It ultimately means farmers can use fewer pesticides,” she says, adding that it will also reduce costs. “At this time of dramatically increasing costs, we are definitely looking for all alternatives to improve strawberry disease resistance.”