C A L I F O R N I A
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Leafy greens research looks at pathogen resistance ByBob Johnson The different leaf structures of different varieties of lettuce and leafy greens could provide clues as to how to breed varieties that would harbor fewer human pathogens. University of California re- search has found that some lettuce types appear less amenable to growth of E. coli bacteria. A UC Davis scientist wants to learn if that tendency, observed in a laboratory setting, will hold true under simulated field conditions.
ways that more closely mimic field conditions. “We are going to try this onpotted lettuce grownoutdoors rather than ingrowthcham- bers,” she said. Most of the effort tomake leafy greens safer has focused on postharvest treatments to kill the pathogens or traceability protocols tomake quick and accurate recalls possible. But plant breeders said a new line of research is showing it may be possible to develop leafy greenvarieties that harbor fewer pathogens before the crop is harvestedand treated at a processing facility. “Can we understand the microbiome on lettuce leaves and use this information to reduce pathogens and improve postharvest quality?” asked Gail Taylor, chair of the UC DavisDepartment of Plant Sciences. “It is like awhole ecosystemon the leaves, and some of these organisms are very hard to remove.” Taylor supervised Salinas Valley and Imperial County trials of 23 commercial lettuce varieties with an eye toward learning what makes a variety more or less likely to harbor threats to human safety. “We are already beginning to identify areas of the lettuce genome toworry about if we want to control themicrobiome that lives on the leaf surface,” she said.
Part of the answer to the challenge of E. coli, Salmonella, Listeria and other food safety threats to freshproduce couldbe thedevelopment of leafy greens varieties that prove less hospitable to the pathogens while still growing. When the leaves of a handful of lettuce types in a growth chamber on the University of California, Davis, campus were treated with E. coli O157, the pathogen population collapsed during the next 10 days. The same concentration of E. coli applied to leaves of a few other lettuce types in the growth chamber, however, found conditions ripe for a pathogen population explosion. “We identified very strong growth or reductionof E. coli,” saidMaeliMelotto, UCDavis associate professor of plant sciences. “We can use these extremes for breeding targets.” Melotto isoneof the researchersworking tobreed lettucevarieties that canhelp reduce populations of E. coli and other pathogens that cause food safety concerns. They discussed their latest information on how lettuce leaf structure affects food safe- ty and postharvest quality during the California Leafy Greens Board Annual Research Conference in lateMarch. Melotto conducted her screening on lettuce plants in growth chambers. The next step, she said, will be to learn if the same differences in multiplying or re- ducing E. coli still hold when the tests are done later this year on plants grown in
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April 21, 2021 Ag Alert 11
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