A new report warns supermarket salads to attract plant bugs that could make people seriously ill with infections.
During experiments under controlled conditions, new diseases were identified in lettuce, arugula, chicory, endive, basil, spinach and Swiss chard.
Some should "be considered a threat to humans," according to the research team at the University of Toronto in Canada.
Scientists have discovered that the bacteria contained a new strain of Fusarium wilt that can be at the origin of infections and eye disorders in humans.
The fungus is widespread in fruits and vegetables, and the latter type has been found in the United Kingdom and Ireland.
Leaf spot, caused by a bacterium, also becomes more common in bagged and prewashed greens.
This could reduce the nutritional value of ready-to-eat meals, according to a study.
More than £ 1.1 billion is spent each year in the United Kingdom.
The head teacher, Professor Maria Gullino, said: "If hygiene conditions are not fully met, foodborne pathogens such as Escherichia coli, Salmonella enterica and Listeria monocytogenes may infest leafy vegetables. "
Three years ago, researchers at the University of Leicester showed that Salmonella and other food additive insects thrived in the wet environment of packaged salads and became more dangerous.
E. coli and other pathogens detected
Teacher. Gullino said: "Ready-to-eat products are subject to intensive control programs, in accordance with national and international regulations, that define the presence and microbiological limits of E. coli and other pathogens.
"Despite these rules, human pathogens found on ready-to-eat products have been detected around the world."
She added: "Some are not plant pathogens but rather use plants as vectors for humans."
Prof Gullino and his colleagues believe that the spectacular growth of the prepared salad sector is at the origin of a number of new diseases.
They pose a particular threat to farmers as they could destroy crops and expose them to economic disaster.
According to the researchers, fusarium wilt is one of the most common diseases of leafy vegetables, especially lettuce.
Until very recently, there were three different species, called races – and now there is another one.
Teacher. Gullino said: "Breed 4 was detected in the Netherlands in 2017. This new breed is spreading rapidly and has been reported to date in Belgium, the UK and Ireland, posing a serious threat to growers. and breeders.
"Until resistant varieties are developed, preventive management measures, such as the use of healthy seeds and seed treatments, are needed to reduce the risk of spreading to new growing areas." ".
As the salads are seasonal, they are grown under high density in five to six cycles a year in the same specialized farms, said the researchers.
This means that there is no adequate rotation of the appropriate crops and fungicides.
In addition, international trade has displaced foods from their original environment to foreign soils, where they are exposed to new infections.
In some cases, very low levels of seed contamination can lead to the rapid onset of disease in new geographical areas.
This results in heavy losses, disrupting the biological balance of the environment and sometimes causing a devastating epidemic.
Climate change is also a threat as it interacts with globalization to influence the development and spread of bedbugs. Rising temperatures also reduce resistance.
Disease Control Strategies
Professor Gullino asked that disease control strategies be re-evaluated to cope with warmer temperatures. New pathogens tend to prefer warm weather.
The insects are transferred to the salad leaves by means of water, compost or even animal manure used to grow vegetables.
Packed salads have grown in popularity since their introduction in Europe in the early 1980s.
Health experts have already warned against the consumption of bagged salads, despite their practical aspect.
Those who do it should consume them on the day of purchase because even a small number of bacteria can multiply quickly and adversely affect the health of the person.
Each year more than 500 000 cases of food poisoning are reported in the UK. Poultry is the most common cause, but about 48,000 are related to products other than meat.
Despite their healthy nature, fresh green leaves and salads are often implicated in food poisoning.
An outbreak that affected more than 2,000 people in Europe in 2011 was attributed to bean sprouts.
In 2016, officials in England discovered an epidemic that killed two people in bags of rocket leaves.
Prof Gullino added: "Among research priorities, there is a need for new varieties that are attractive not only to consumers, but also resistant to the most common diseases, not only for lettuce and spinach, but also for leafy vegetables, such as rocket and lettuce lettuce.
"In addition, seed companies should invest more in the adoption of all necessary measures to prevent the spread of diseases in infected seeds."