Fungal Detectives Uncover the Truth About Green Mold

By Amy Spillman
January 2, 2003

Pennsylvania farmers grow more mushrooms than farmers in any other state, according to U.S. Department of Agriculture statistics. But in the mid-1990s, farmers in Chester County--the state’s mushroom-growing capital--came under siege, experiencing crop losses of 30 to 100 percent due to a green mold epidemic.

Initially, scientists identified the green mold culprit as Trichoderma harzianum, a common fungal species that has commercial applications. Recently, however, scientists at the Agricultural Research Service’s Systematic Botany and Mycology Laboratory (SBML) in Beltsville, Md., gave this emerald invader its true name: Trichoderma aggressivum.

T. harzianum has long been known for its beneficial uses. It can be used to control other fungi that induce plant diseases, and it has the potential to enhance plant growth. It has also been credited with degrading pesticides in soil and preventing mycotoxin synthesis.

If T. harzianum were the fungus causing the green mold epidemic, though, its commercial viability would be in jeopardy. For it would be attacking mushrooms--a valuable and popular food commodity that U.S. consumers spend more than $860 million on every year.

SBML mycologists Gary Samuels and Sarah Dodd were not so sure that T. harzianum was the cause of the green mold epidemic. Through their morphological and molecular studies, they were able to exonerate T. harzianum and name a new Trichoderma species. The scientists named this new species T.aggressivum because of its aggressive nature against mushrooms.

Mushrooms are a good source of selenium, potassium and copper, and some types have significant amounts of three B-complex vitamins. Read more about their nutritional benefits and how the SBML researchers identified the fungal attacker in the December issue of Agricultural Research magazine.

ARS is USDA's chief scientific research agency.