Genetically closely related but phenotypically divergent Trichoderma species cause world-wide green mould disease in oyster mushroom farms
Komoń-Zelazowska, M., Bissett, J., Zafari, D., Hatvani, L., Manczinger, L., Woo, S., Lorito, M., Kredics, L., Kubicek, C. P. and I. S. Druzhinina, 2007
AEM, 73:22, 7415-7426
The world-wide commercial production of the oyster mushroom Pleurotus ostreatus is currently threatened by massive attacks of green mould disease. Using an integrated approach to species recognition comprising analyses of morphological and physiological characters, and application of the genealogical concordance of multiple phylogenetic markers (ITS1 and 2; partial sequences of tef1 and chi18-5), we determined that the causal agents of this disease were two genetically closely related, but phenotypically strongly different species of Trichoderma, which have been recently described as T. pleurotum and T. pleuroticola. They belong to the Harzianum Clade of Hypocrea/Trichoderma which also includes T. aggressivum, the causative agent of green mould disease of Agaricus. Both species have been found on cultivated Pleurotus and its substratum in Europe, Iran and South Korea, but T. pleuroticola has also been isolated from soil and wood in Canada, the United States, Europe, Iran and New Zealand. T. pleuroticola displays pachybasium-like morphologic characters typical of its neighbors in the Harzianum Clade; whereas T. pleurotum is characterized by a gliocladium-like conidiophore morphology which is uncharacteristic of the Harzianum Clade. Phenotype MicroArrays (PM) revealed the generally impaired growth of T. pleurotum on numerous carbon sources readily assimilated by T. pleuroticola and T. aggressivum. In contrast, the PM profile of T. pleuroticola is very similar to that of T. aggressivum, more suggestive of a close genetic relationship. In vitro confrontation reactions with A. bisporus revealed that the antagonistic potential of the two new species against this mushroom is perhaps equal to T. aggressivum. The P. ostreatus confrontation assays showed that T. pleuroticola has the highest affinity to overgrow mushroom mycelium among the green mould species. We conclude that the evolutionary pathway of T. pleuroticola could be in parallel to other saprotrophic and mycoparasitic species from the Harzianum Clade, and that this species poses the highest infection risk for mushroom farms, whereas T. pleurotum could be specialized for an ecological niche connected to components of Pleurotus substrata in cultivation. A DNA BarCode for identification of these species based on ITS1 and 2 sequences is provided and integrated in the main database for Hypocrea/Trichoderma (www.ISTH.info).