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New Lettuces Shrug Off Verticillium Wilt

By Marcia Wood
May 4, 2007

Fresh, crunchy iceberg lettuces sometimes collapse like a deflated ball before they have a chance to form their familiar firm, nicely rounded heads.

The cause? A disease known as verticillium wilt, which results from attack by a soil-dwelling, root-rotting fungus called Verticillium dahliae. But Agricultural Research Service (ARS) scientists at Salinas, Calif., have teamed with University of California-Davis colleagues to produce the first-ever parent iceberg lettuces resistant to this destructive wilt.

Lettuce is one of America's top five most popular vegetables. Iceberg lettuce outsells all other kinds of this versatile leafy green.

Ryan J. Hayes, a research plant geneticist with the ARS U.S. Agricultural Research Station in Salinas, plant pathologist Krishna Subbarao at UC-Davis, and their colleagues made seeds of the three new parent lettuces available to researchers and plant breeders for the first time this April. They published additional details about Verticillium wilt resistance in a recent issue of Plant Disease, a scientific journal.

More than a half dozen companies that produce vegetable seeds have requested seed samples, according to Hayes. He noted that the parent lines are meant for crossing with consumer-ready lettuces to boost the commercially grown lettuces' resistance to verticillium wilt.

Breeding lettuces with natural resistance remains the most environmentally friendly, economical and sustainable option for combating the fungus.

Verticillium wilt first showed up in some coastal California lettuce fields in 1995. Researchers invested more than a decade in scrutinizing promising lettuces in greenhouse and field tests before determining that the new parent lines were ready for plant breeders everywhere to use.

The V. dahliae fungus infects roots of vulnerable plants, moving into leaves and causing them to discolor, then to eventually wilt and die. The fungus can also infect and kill hundreds of other kinds of plants, including strawberries and tomatoes.

The California Lettuce Research Board at Salinas, the California State Department of Food and Agriculture at Sacramento, and others helped fund the research.

ARS is the U.S. Department of Agriculture's chief scientific research agency.