New research shows mature green tomatoes remain more resistant to salmonella infection than ripe tomatoes.

Researchers discovered a statistically significant variation of salmonella infection in green and ripe tomatoes, said Massimiliano Marvasi, the study’s lead author and University of Florida Institute of Food and Agricultural Sciences research assistant professor.

The study, published in the Dec. 4 PLoS One journal, examined round green and red tomatoes in two north Florida fields over three production seasons. Researchers discovered cultivar-dependent differences in the proliferation of salmonella at different ripeness stages.

“One of the strongest observed effects was the increased susceptibility of ripe fruit to post-harvest proliferation of salmonella,” according to a study summary. “Even though means of salmonella proliferation varied by no more than two logs across all seasons, the maximal proliferation of the pathogen in red tomatoes was almost always at least two logs higher than the highest cell numbers reached within unripe tomatoes.”

Additionally, tomatoes grown in wet seasons experience fewer infections compared to dry seasons, he said.

Seasonal differences and certain salmonella strains constitute what Marvasi characterizes as “the perfect storm” for tomato salmonella infection.

The combination of ripe tomatoes, the cultivar and a dry growing season makes salmonella proliferation more probable, he said.

Study: green tomatoes less susceptible to salmonellaResearchers aren’t sure how much more probable as that wasn’t a part of the study, Marvasi said.

“It seems there is a consistency when analyzing cultivars,” Marvasi said. “Green in some ways protects the tomato from salmonella proliferation.”

The study also found salmonella grew significantly better in water-congested tissues of green tomatoes and that irrigation practices didn’t affect the crop’s susceptibility to post-harvest proliferation.

From 2011-13, the researchers injected three varieties — bonny best, Florida-47 and solar fire — with seven strains of salmonella in Citra, Fla., and Live Oak, Fla.

Bonny best is an heirloom variety that frequently serves as a control variety in plant pathogen tests while the others are newer varieties grown commercially throughout the Southeast.

The scientists chose those varieties after early greenhouse experiments showed those varieties possessing varying degrees of salmonella resistance.

The researchers, also including Jerry Bartz, George Hochmuth and Max Teplitski, wanted to learn which crop production factors affect salmonella outbreaks and how water and crop and pathogen genotypes influence salmonella’s ability to multiply in the fruit.

Marvasi said researchers are planning to study how fertilization and nitrogen affects proliferation.