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United States Department of Agriculture

Agricultural Research Service

Scientists Restore Fungus' Good Reputation

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Title: Attack... of The Killer Fungus!
Let's say you're taking a walk on a farm. YouCartoon animation of a man walking briskly notice something green growing in a bed where a crop has been planted. You turn to the person who runs the farm, and you point out your discovery. You'd expect the farmer to be happy, wouldn't you? Green is good, isn't it?
To most farmers, yes. But if you showed your find to certain members of the farming community, you probably wouldn't get them to smile. Instead, they might say "Ack!" or just shake their heads no.

Animated graphic of a caterpillar wearing a flower-topped hatHave you entered the "Twilight Zone," where nothing is exactly what it seems?

Nope, you've just entered the strange and fascinating world of the mushroom farmer, where green is bad and sunshine doesn't matter. It's a world that Gary Samuels and Sarah Dodd entered a few years ago. They're mycologists (my-CALL-ah-gists) with the Agricultural Research Service, and they study fungi such as mold and mushrooms (So what's the difference between the two? Click here. )

Back in the early-to-mid 1990s, farmers in Pennsylvania--the "mushroom capital" of the United States--were under siege. A green mold was attacking their crop. In one county, some mushroom farmers lost between 30 and 100 percent of their harvest to this emerald invader.
A Good Fungus Gone Bad?
S
cientists studied the problem, and a few wrote scientific papers about it. Photo of 2 mushrooms with green mold on themThey identified the killer green mold as Trichoderma harzianum (trick-ah-DERM-ah hart-ZEE-ah-num). But when Samuels and Dodd looked at the evidence, they weren't sure that this mold was to blame. They decided to investigate further.

Before being accused of causing green mold on mushrooms, Trichoderma harzianum was considered a "good" fungus. It was used to control "bad" fungi that cause plant diseases, and it showed an ability to enhance plant growth--like a fungal fertilizer. Some experiments showed that it could also help break down pesticides in soil and prevent certain toxins from forming.

Graphic of a microscope.The Investigation and Discovery: When Samuels and Dodd looked closely at samples of the killer green mold, they saw something strange. The mold could actually be separated into four distinct types. There were differences in their DNA and in how they looked under a microscope, how fast they grew, and how they smelled. Only two of these types were actually causing mushrooms to get sick. The other two were harmless.

Microscope photo of the good-guy fungus, T. harzianumTrichoderma harzianum, the good fungus, was one of the harmless types of mold that Dodd and Samuels identified. The other was Trichoderma atroviride (trick-ah-DERM-ah at-tro-VEER-eh-day). It turns out that the two types of mold causing the mushroom disease were forms of a new species that didn't have a name.

Because Samuels and Dodd discovered the new species, they got to name it. Samuels chose the name Trichoderma aggressivum (trick-ah-DERM-ah ah-gress-SEE-vum) because the mold is so aggressive against mushrooms.

By Amy Spillman, formerly Agricultural Research Service, Information Staff

Last Modified: 2/14/2011
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