CALIFORNIA
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
Salinas Valley farmers are on guard against a new variant of the soil-borne fungal disease Fusarium wilt in lettuce. An ongoing trial aims to find genetic sources of resistance to the new strain.
Fusarium wilt-resistant lettuce aim of breeding trial By Bob Johnson
varieties,” said Alex Putnam, a University of California Cooperative Extension plant pa- thology specialist based in Riverside. The Soledad trial is part of an ongoing effort to discover genetic sources of resistance to the new Fusarium variant that has been detected in the Santa Maria and Salinas areas. Putnam offered overview of the research during an Aug. 5 field day for growers and pest control advisors. If farmers have a susceptible lettuce variety planted in infested ground, they may be in for a tough time. Once a plant is infected with Fusarium wilt, there are no chemical controls to help it recover. In California, Fusarium wilt occurs in lettuce in Fresno County and in the southern region of coastal Monterey County, according to UC pest management guidelines. Fusarium wilt affects a wide range of crops, including vegetables, fruits and ornamentals. Symptoms include leaf yellowing and wilting and stunted growth. Infected plants eventu- ally die. The pathogen can also be sustained on the roots of many plants. Until recently, Fusarium race 1 was the only variant in California. The appearance of
Researchers say an unfolding trial may offer hope that lettuce varieties can soon be bred with resistance to a new variant of Fusarium wilt, which has recently appeared in farm fields in the Central Coast region. At a field belonging to vegetable producer D’Arrigo California, a study team is evaluating lettuce resistance to a new strain of Fusarium known as CR4. Researchers say the results so far are promising. Fusarium wilt, largely resulting from soil-borne pathogens, can cause lettuce plants to stunt and fail to form heads or result in seedlings wilting and dying. The disease can be particularly severe in lettuce plants suffering from water stress. Researchers say grounds of the study field near Soledad are infested with the new vari- ant and the more commonly found Fusarium race 1 strain. Yet they say they have been impressed with how certain lettuce plants are holding up, with many showing no signs of infection. Researchers noted that romaine varieties have been the least prone to infection. The study group is monitoring the resistance of lettuce strains planted with seeds from different seed producers in an infected corner of the D’Arrigo field. “Some of these plants look pretty good. It looks like there’s some potential for resistant
See FUSARIUM, Page 7
6 Ag Alert September 4, 2024
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