The first reports concerning green mold on Polish mushroom farms are from 2002. In Europe and the United States Trichoderma harzianum was initially described as a causative agent of the disease. However, soon two biotypes of Trichoderma, Th2 in Europe and Th4 in America, were recognised as responsible for commercial losses and were designated as a new species named T. aggressivum. Until now it has not been clear which species of Trichoderma and which form of the species was a causative agent of the disease outbreak in Poland and what was the main source of infection. Therefore, studies were conducted on the composition of the Trichoderma species in Polish mushroom farms and in compost samples. The isolates were identified by phenotypic and microscopic studies. The classification of the strains recognised as T. aggressivum was then confirmed by PCR methods. The aggressiveness of Trichoderma spp., especially T. aggressivum, was estimated in in vitro studies. The most frequently isolated Trichoderma spp. were: T. harzianum, T. aggressivum, T. atroviride and T. longibrachiatum. Using the technique of PCR, multiplex PCR and PCR-RAPD it was determined that 24 isolates from Polish mushroom farms belonged to T. aggressivum f. europeanum (Th2). However, a large variation between isolates indicated the possibility that Polish biotypes of T. aggressivum were different from those, which were found in western Europe. All isolates of T. aggressivum were highly pathogenic towards Agaricus bisporus.
