C A L I F O R N I A
Vegetables A SPECIAL GROWERS’ REPORT OF AG ALERT ®
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Plant breeders work to help lettuce resist pathogens ByBob Johnson Can plant breeders produce lettuce varieties less likely to allowharmful microbes to colonize them? University of California scientists want to find out. Different varieties of lettuce show different ability to resist colonization by pathogens that can cause food-borne illnesses. University of California researchers say they want to breed lettuce varieties that maximize that ability.
“Demand for fresh produce has been increasing worldwide in the last few de- cades,” Melotto said, “and an expansion of the fresh market over recent years has resulted in a wide variety of fresh fruit and vegetables being available throughout the year. At the same time, the number of food-borne disease outbreaks related to consumption of contaminated fresh or minimally processed produce has been increasing. Beyond the burden on public health, disease outbreaks negatively affect the industry economically.” Bestmanagement practices have beendeveloped for growing, harvesting, processing and shipping safe crops. The discovery that some varieties are less susceptible to con- tamination than others ledMelotto and other researchers to wonder if understanding the genetic differences in lettuce cultivars could be used to breed new varieties. “We looked at a number of lettuce varieties to see if some internalized pathogens more than others,” she said. “We measured howmuch E. coli 157 was internalized by different varieties in a day, and a strain of salmonella, too.” She said she found a large variation in the amounts of the pathogens that were inter- nalized and shielded frompostharvest washes betweenRed Tide, whichwas high, and Green Towers or Lolla Rossa, which were low. There are also differences among lettuce varieties in how much or little they
The pathogens that cause E . coli, salmonella, listeria and other food-borne illnesses stickmore readily to the leaves of some lettuce varieties than others. More importantly for the purposes of food safety, some lettuce cultivars have tough skin that keeps these pathogens on the surface, whereas other varieties allow themto penetrate to the inside, where they cannot be reached by chlorine or other food-safety rinses. Breeding plant varieties less susceptible to human pathogens could prove to be part of the answer to combating pathogens in fresh lettuce and other leafy greens, according to speakers at a Future of Lettuce Symposiumheld earlier this year. “We found that some lettuce genotypes are less likely to harbor these human patho- gens than others, suggesting an untapped genetic component associated with this trait,” said Maeli Melotto, UC Davis associate professor of plant sciences. “We have characterized the genetic diversity in the interactionbetween a small number of lettuce genotypes and Salmonella enterica and E. coli O157:H7.” The symposium, put together by the UC Davis Genes to Growers Project, included presentations on the role a growing knowledge of variety genetics could play in food safety and postharvest shelf life.
See LETTUCE, Page 12
October 21, 2020 Ag Alert 11
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