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Resistance of Pre- and Post-epidemic Strains of Agaricus bisporus to Trichoderma aggressivum f. aggressivum

Since the early 1990s, the epidemic of green mold on the cultivated mushroom Agaricus bisporus in North America has been caused by Trichoderma aggressivum f. aggressivum. The findings of earlier research suggested that the microevolutionary emergence of T. aggressivum f. aggressivum coincided with the onset of the epidemic. This hypothesis was tested further by determining the disease susceptibility of mushroom strains grown widely before the epidemic manifested. The results of complementary methods of analysis, which entailed a grain protection assay and cropping trials, established that two pre-epidemic strains were more susceptible to green mold than three post-epidemic strains being cultivated at the time of the epidemic. Thus, if T. aggressivum f. aggressivum had been present within cultivated mushrooms prior to the epidemic, it should have been detected. It still appears to be true that T. aggressivum f. aggressivum emerged during the 1990s in a manner that remains unclear.