The findings come from a University of Florida study of bacterial spot, a persistent disease that damages white button mushrooms and causes significant economic losses for growers.

White button mushrooms are a valuable specialty crop and a familiar ingredient in salads, appetizers and everyday meals. Nutrient-rich and versatile, they are often cited as an example of the “food is medicine” concept, which emphasizes the role of nutritious foods in supporting health. Their nutritional benefits make them an important part of many healthy diets.

Despite their popularity, white button mushrooms face a long-standing disease that can make it difficult or impossible for growers to sell an entire harvest.

A 100-Year-Old Mushroom Disease With a Hidden Culprit

Bacterial spots cause brown or yellow discoloration on the surface of mushrooms, reducing their appearance and commercial value. The disease can lower crop yields and shorten shelf life, creating a costly challenge for mushroom farms across the United States.

Visible symptoms may not appear until after the mushrooms have been shipped to grocery stores or purchased by consumers. This delayed development is particularly troublesome for producers trying to maintain consistent product quality.

For many years, scientists primarily associated bacterial stains with individual disease-causing bacterial pathogens. However, researchers at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) have found that the disease involves a much more complex collection of pathogens.

These microorganisms can thrive in the carefully controlled, humid indoor environments used for commercial mushroom cultivation. Because multiple bacterial species may contribute to the same disease, treatments designed to target a single pathogen may not be sufficient.

“For years, the industry has struggled with treatments for bacterial spot that have produced inconsistent results,” said co-author Samuel Martins, assistant professor in the UF/IFAS Department of Plant Pathology. “As part of a $7 million USDA grant involving Penn State University, the University of Delaware and UF/IFAS, we are developing advanced diagnostics and sustainable solutions to enhance mushroom farms across the country.”

DNA Analysis Reveals More Than 17 Bacterial Species

To investigate the cause of the disease, the research team collected affected mushrooms from several production facilities in the southern United States.

Scientists used DNA sequencing, chemical profiling and traditional laboratory tests to identify bacteria associated with the damaged mushrooms. DNA sequencing helped determine the genetic identities of microorganisms found in the samples, while additional tests helped characterize the bacteria and their potential to cause disease.

The results revealed a much more diverse group of pathogens than expected.

“We discovered more than 17 different pathogens associated with this disease,” said Samelika Mudiyanselage, lead author of the study and a doctoral student working with Martins and Romina Gazis at the UF/IFAS Tropical Research and Education Center. “While two well-known bacterial pathogens dominated the known disease profile, another group of bacteria not previously associated with mushroom diseases was also detected at surprisingly high levels.”

The finding suggests that scientists may have overlooked an important cause of bacterial stains. Although two established pathogens remain prominent, the presence of additional bacterial groups indicates that the disease cannot be fully understood by studying those microorganisms alone.

This complexity may help explain why bacterial spots have persisted for generations despite disease-management efforts. When several microorganisms are associated with a disease, it becomes more difficult to identify the bacteria responsible, predict outbreaks and develop consistently effective treatments.

The findings also suggest that producers may need more comprehensive detection methods capable of identifying a wider range of bacterial threats.

“We hope that expanding our research will lead to the development of better diagnostics and more effective treatments to address the entire white button mushroom pathogen community,” Mudiyanselage said.

Natural Treatments Could Help Protect Mushroom Farms

University of Florida researchers are building on these findings with follow-up studies focused on more sustainable ways to manage bacterial stains.

One promising approach involves testing plant-based essential oils, beneficial microorganisms and other biological products that could replace traditional chemical treatments.

Essential oils contain natural compounds produced by plants, some of which have antibacterial properties. Beneficial microorganisms may also suppress harmful bacteria or make it more difficult for disease-causing microorganisms to grow.

These approaches could eventually give mushroom growers additional tools for controlling bacterial spot while reducing reliance on traditional chemical treatments. However, further research is needed to determine how well these potential alternatives perform under real-world growing conditions.

“Ultimately, our goal is to provide growers with practical, science-based solutions to help enhance their mushroom cultivation systems,” Martins said. “By understanding the complexity of bacterial plaques and the role of microbial communities, we can develop more environmentally friendly management practices that reduce losses while improving sustainability.”

What the Discovery Means for White Button Mushroom Growers

This research changes the understanding of a disease that has affected white button mushroom production for more than a century. Bacterial stains are not caused by a single pathogen but involve a diverse group of potentially harmful microorganisms, including previously overlooked species.

By uncovering this hidden complexity, scientists hope to improve disease detection, develop more reliable treatments and reduce crop losses that have burdened mushroom growers for years. The discovery could ultimately help make mushroom cultivation more resilient, productive and environmentally sustainable.