CALIFORNIA
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Researchers are working to develop lettuce varieties that are resistant to plant diseases such as impatiens necrotic spot virus that have devastated lettuce crops in the Salinas Valley in recent years.
Breeding seeks to boost disease resistance in lettuce By Bob Johnson
lettuce fields. They’re also studying lettuce’s attractiveness to thrips, the insect that carries this disease. Once spot virus infects a lettuce plant, there is no cure for the disease. And once the disease and western flower thrips are in an area, growers can only hope to slow its spread, because they cannot stop it. The plan is to identify the genetic basis for tolerance of the disease and for being nonpreferred hosts for thrips and help seed breeders stack both in future generations of lettuce varieties, according to U.S. Department of Agriculture research geneticist Kelley Richardson, one of several experts who submitted reports for the California Leafy Greens Research Board’s annual conference in Pismo Beach in March. Lettuce lines are being compared to a red Romaine lettuce variety, which has been attractive to thrips and susceptible to more immediate impatiens necrotic spot virus infection. Among lettuce varieties screened at a USDA test field in Salinas last October, nine had lower rates of the disease, Richardson reported.
Thanks to expanded breeding trials, lettuce plants may become tougher and better able to hold up if assaulted by diseases such as fusarium, verticillium, pythium, impa- tiens necrotic spot virus and downy mildew, researchers say. Lettuce and spinach growers have devoted a majority of their more than $1.1 million research funding this year to breeding and genetics projects, said Jennifer Clark, exec- utive director of the California Leafy Greens Research Board. “This investment ultimately gives growers the best protection against pests, diseases and abiotic stresses,” she said. Plant pathologists and crop geneticists are looking for variety resistance to ver- ticillium and fusarium, soil-borne lettuce diseases that became more pronounced after growers stopped rotating crops into ground fumigated with methyl bromide for strawberry production. The decades-long effort to keep up with downy mildew, the most important foliar disease in the crop, continues. Researchers are also evaluating lettuce lines for the resistance or susceptibility to impatiens necrotic spot virus, the disease that has recently decimated Central Coast
See LETTUCE, Page 12
May 17, 2023 Ag Alert 11
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