Lettuce Continued from Page 11
are likely to harbor microbes that are pathogenic and harmful on the surface of their leaves. “Leaf surface properties and plant genetics can affect the composition of native salad leaf microflora, suggest- ing that processing treatments are not the only answer to producing safer and longer-lasting leafy salad crops,” said Gail Taylor, chair of the UC Davis Plant Sciences Department. “An alternative approach is to study this microbial com- munity—the leafmicrobiome of leafy sal- ads—determining how this is affected by both environmental and leaf character- istics, and then to breed for leaves which have surface characteristics that prevent colonization, attachment and prolifera- tion of harmful microbes.” Taylor said she has already found that the leaf cell size, number of stomata and contact angle significantly affect the lev- els of bacteria that are pathogenic or con- tribute to spoilage. “Can we make better use of the mi- crobiology and genetics, rather than just wash the plants to prevent spoil- age?” she asked. “Can we control spoil- age as well as reduce the level of hu- man pathogens? The microbiome are attached to the leaves. Can we breed for a good microbiome?” In related studies, U.S. Department of
A UC Davis plant scientist tested Lolla Rossa lettuce, left, along with others to determine how dif- ferent varieties are able to avoid coloni- zation by microbes that can cause food- borne diseases.
Simko said researchers traced the major genetic determinant of deterio- ration to a particular region of the let- tuce gene that “was detected in every experiment, regardless of the tested population, location, planting date or processing method.” Simko’s team has already identified the genes that make some varieties last longer than others in modified-at- mosphere packaging, by developing a method to identify accurately geno- types with different deterioration rates
in fresh-cut lettuce. “Cloning of this gene will allow a de- tailed, functional study of the deterio- ration process in fresh-cut lettuce,” he said. “Future postharvest studies need to focus on retaining nutritional quality and changes inmicrobiome, particularly those than can affect survival of human enteric pathogens.” ( Bo b J o hn s o n i s a r e p o r t e r i n Sacramento. He may be contacted at bjohn11135@gmail.com.)
Agriculture researchers have also con- firmed that not only do some lettuce va- rieties harbor fewer human pathogens than others, but some last far longer after they have been processed and placed in modified-atmosphere packaging. “The earliest signs of deterioration oc- curred within a week after processing in rapidly deteriorating genotypes, while in slow-deteriorating genotypes, symptoms were not apparent until threeweeks after processing,” said Ivan Simko, USDA re- search geneticist based in Salinas.
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