Why a Mushroom Disease Has Been Hard to Stop for 100 Years

A disease that has troubled white button mushroom farmers for more than 100 years turns out to be more complicated than anyone thought. Researchers at the University of Florida found that it involves many different kinds of harmful bacteria instead of a single one. That could explain why the disease has been so hard to control, and it may lead to better ways to protect mushroom crops.

The disease is called bacterial blotch. It causes brown or yellow patches on mushrooms, which spoils how they look and lowers their value. It can also reduce how many mushrooms a farm harvests and shorten how long they stay fresh, which makes it expensive for mushroom farms across the United States. Sometimes the marks appear only after the mushrooms have been shipped to grocery stores or bought by shoppers, which makes it even harder for growers to keep their quality steady.

White button mushrooms are an important specialty crop. They are used in salads, appetizers and everyday meals. For many years, scientists mostly linked bacterial blotch to one disease-causing bacterium. The new study, from the University of Florida's Institute of Food and Agricultural Sciences, shows it is a much bigger group. These germs grow well in the humid indoor rooms where commercial mushrooms are grown. Because several species may cause the same disease, treatments aimed at only one may not be enough.

Samuel Martins, an assistant professor of plant pathology who helped with the study, said that for years the industry has struggled with treatments that give uneven results. He said a separate $7 million grant from the U.S. Department of Agriculture, shared by Penn State, the University of Delaware and the University of Florida, is paying for work on advanced tests and sustainable solutions for mushroom farms across the country.

To find out what was causing the disease, the team collected sick mushrooms from several farms in the southern United States. Using DNA sequencing and other methods, they found more than 17 species of bacteria.