Disease Continued from Page 6
Researchers say they have yet to dis- cover fusarium wilt race 2 in the Salinas Valley, the largest strawberry growing re- gion in Calfornia. Henry said they tested 243 samples from strawberry fields in the Watsonville- Salinas area, 302 samples from Santa Maria and 52 from Mexico and failed to detect the new disease strain. “We only detected race 2 in samples from five fields in Oxnard,” Henry said. “If you are not in Oxnard, you probably don’t have race 2.” Strawberry varieties UC San Andreas, UC Eclipse, UC Keystone, UC Golden Gate, Portola and Fronteras, plus varieties from Driscoll’s and other private breeders, all have resistance to fusarium race 1. That resistance remains strong, researchers say. Oleg Daugovish, a UC Cooperative Extension strawberry and vegetable crop advisor in Ventura County, exposed plants to large amounts of race 1 inoculum and has “not seen any decrease in yield or dis- ease symptoms,” Henry noted. Fusarium race 1 produces a distinct pro- tein. Resistant strawberry varieties recognize this protein and throw up their defenses. “We define race 1 and race 2 based on this protein,” Henry said. “Race 2 does not produce the protein, so the plant is not protected.”
This summer-planted, organic strawberry field was hit by an emerging disease strain, fusarium wilt race 2. Several commercial varieties are resistant to a previous generation of the disease, but none are available for the new strain, believed to be confined to Oxnard.
Strawberry fusarium does not affect oth- er crops, but rotation is of limited value. Strawberry growers frequently rotate fields with lettuce or other leafy greens, but a single season of not growing strawberries does little to reduce fusarium pathogens. Because the fusarium pathogen can re- main viable deep in the soil for years, crop rotation takes a long time to rid a field of the disease, although growing broccoli
does reduce the level of pathogens. Conventional growers use deep fu- migation to treat infested fields, while organic growers use anaerobic soil dis- infestation, or solarization. Because the pathogens are easily carried within a field or to new fields on equipment or boots, a good sanitation program is essential to limit the spread of fusarium. Water or heat stress or heavy fruit loads
make the symptoms worse. A long-term solution will have to be the development of commercially ac- ceptable varieties with resistance to fu- sarium wilt race 2. “Genetic resistance is the key to manag- ing fusarium wilt,” Henry said. (Bob Johnson is a reporter in Monterey County. He may be contacted at bjohn11135@gmail.com.)
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