Verticillium wilt, tomato bushy stunt virus and crown rot Research for a trio of relatively new lettuce diseases is included in funding by the California Lettuce Research Board, whose 30 projects received nearly $658,000 in fiscal year 2000-2001.
The three are verticillium wilt, tomato bushy stunt virus, and crown rot, in order of importance. According to Ed Kurtz, board manager, available information suggests that "none is expected to have a potential immediate effect on lettuce yields in California."
"However," he added, "all three diseases have the potential to reduce yields in individual fields in specific production regions, with verticillium wilt being the greatest threat to the California lettuce industry."
At any given time, Kurtz said, any one disease may cause serious loss to one grower, while neighboring lettuce fields may not be affected.
The wilt initially appeared in Santa Cruz County in 1995, and the board responded with a research grant the following year.
Principal investigator on the continuing project is Krishna Subbarao, University of California plant pathologist stationed at the USDA Research Facility in Salinas.
He is collaborating with other UC and USDA scientists to learn the factors governing development and/or spread of the disease and to develop resistant lettuce varieties. Thus far the board has provided $75,000 for the research.
Persist 10 years The soilborne fungus can persist for as long as 10 years, and its lettuce pathogen is related to forms hosted by strawberries and artichokes in Monterey and Santa Cruz counties.
Tomato bushy stunt virus, commonly known as "lettuce dieback," occurred in a small production area in Monterey County flooded by the Salinas River in 1998.
The disease has a history of sporadic outbreaks, accompanied by minor crop damage, since the 1980s. It occurs in romaine and red and green leaf lettuces, which are planted on 1,000 to 5,000 acres each year. Significant crop losses to it in any single year are considered remote.
William Wintermantel, USDA plant pathologist at Salinas, is principal investigator, and the project has received board funds in the amount of $63,800.
He and other USDA and UC specialists are searching for weather, soil, nutrient, and other conditions that trigger the disease.
Crown rot Crown rot turned up on less than 100 acres of romaine lettuce in Monterey County in 2000. A few plants of iceberg and green leaf varieties also showed disease symptoms.
Principal investigator Steve Koike, Monterey County farm advisor in Salinas, has been allocated $7,100 by the board for his studies.
His focus is to identify the disease and cooperate with USDA plant geneticists to find lettuce varieties having resistance to it. Because the extent of the disease's potential threat is unknown, other USDA and UC scientists are expected to join the project.
The board, based in Salinas, was established under the California Marketing Act of 1937. It funds research for iceberg and mixed leaf lettuce varieties.
Lettuce, with a value of $1.1 billion from 213,000 acres, was fifth among California's top 20 crops in 1998.