Researchers study tomato resistance to salmonellaORLANDO, Fla. Green tomatoes on average remain less conducive to spreading salmonella than red tomatoes.

Salmonella also interacts differently with tomatoes than it does inside animals.

Those were some of the findings of produce industry-sponsored research highlighted at the Davis, Calif.-based Center for Produce Safety"s Produce Research Symposium on June 28 in Orlando, Fla.

To learn about decreasing salmonella in tomatoes through breeding and maturity at harvest, Max Teplitski, an associate professor of soil microbiology at the University of Florida, Gainesville, discovered differences between red and green tomatoes and among variations.

In the study, Teplitski inoculated several dozen tomato varieties with salmonella to see which varieties were more resistant to postharvest salmonella contamination. The ongoing investigation involved testing varieties such as mature greens, round reds, heirlooms, grapes, cherries and large beefsteak as well as specialty tomatoes such as the brown and yellow varieties.

In research funded by the Maitland-based Florida Tomato Committee, Teplitski found 40 salmonella genes that regulate themselves differently in tomatoes. He"s using those "gene reporters" to screen tomato varieties and maturity stages that are less at risk for salmonella.

Teplitski"s preliminary observations show that the way salmonella genes interact within tomatoes remains dependent on the plant"s genotype and expresses itself differently as varieties ripen.

"Relying on a single salmonella gene to predict behavior of this pathogen inside tomatoes may be overly ambitious," Teplitski said. "Persistence of salmonella inside tomatoes is most likely a behavior controlled by multiple factors. There probably won"t be some single bullet in salmonella that can be targeted to eliminate this pathogen completely."

The study showed that a tomato"s genotype may be more important in the spread of salmonella than the salmonella"s serotype or type of microorganism, Teplitski said.

Green fruit such as kumato, butcher and brown bear varieties remain less conducive, while the green mariana roma variety is more conducive to salmonella proliferation, he said.

The spread of salmonella inside tomatoes depends on numerous factors such as differing sugar levels, the fruit"s structure and specific metabolites present in red tomatoes but absent in green varieties, Teplitski said.

Ed Beckman, president of California Tomato Farmers, Fresno, said the industry shouldn"t become overconfident if breeders develop a salmonella-resistant variety. He said he"s seen many disease-resistant varieties that eventually become tolerant.

"You have to look beyond the breeding traits," he said. "You have to take a look at the production regions we"re dealing with and the cultural attributes of tomatoes. Breeding is not a short-term gateway. It"s like trying to take a piece of a puzzle for a 50-piece puzzle and cram that into a puzzle built for 100 pieces. They don"t necessarily go together well."

The $60,771 study ended in September. In a separate study, Teplitski is examining how production practices affect salmonella.

The Packer will report on more research projects in coming weeks.