Genetically Closely Related but Phenotypically Divergent Trichoderma Species Cause Green Mold Disease in Oyster Mushroom Farms Worldwide

Abstract

The worldwide commercial production of the oyster mushroom Pleurotus ostreatus is currently threatened by massive attacks of green mold 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 (internal transcribed spacer 1 [ITS1] and ITS2 sequences; 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 Trichoderma pleurotum and Trichoderma pleuroticola. They belong to the Harzianum clade of Hypocrea/Trichoderma which also includes Trichoderma aggressivum, the causative agent of green mold 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 morphological characteristics 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 revealed the generally impaired growth of T. pleurotum on numerous carbon sources readily assimilated by T. pleuroticola and T. aggressivum. In contrast, the Phenotype MicroArray profile of T. pleuroticola is very similar to that of T. aggressivum, which is suggestive of a close genetic relationship. In vitro confrontation reactions with Agaricus 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 mold 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 ITS2 sequences has been provided and integrated in the main database for Hypocrea/Trichoderma (www.ISTH.info).

The First Report on Mushroom Green Mould Disease in Croatia / Prvi Izvještaj O Bolesti Zelene Plijesni U Hrvatskoj

“…All the 20 isolates collected from the button mushroom compost were identifi ed as T. harzianum, while strains isolated from the oyster mushroom substrate included T. pleurotum and T. pleuroticola (9 and 11 isolates, respectively). Alignments (20) revealed that the ITS sequences of the isolates belonging to the same species did not share the same pattern. The differences suggested that they belonged to different strains within the species, but this did not affect the results of identifi cation.…”

“…Recently, green mould disease of cultivated oyster mushroom has also been reported in several countries (12)(13)(14)(15)(16)(17)(18), and the causal agents were identifi ed and described as new species T. pleurotum and T. pleuroticola (19,20).…”

“…In order to determine the temperature growth profi les of the isolates the plates were incubated at (5,10,15,20,25,30,35, and 40) °C.…”

Global nutrient profiling by Phenotype MicroArrays: a tool complementing genomic and proteomic studies in conidial fungi

“…It was shown that the highest assimilation rates for T. pleuroticola occurred on N-acetyl-D-glucosamine and quinic acid, which could be useful for differentiation of two causative agents of Pleurotus green mold disease. T. pleuroticola, on the other hand, can be distinguished from T. aggressivum (green mold disease on Agaricus) by the inability of the latter to utilize α-ketoglutaric, L-malic, and succinamic acids (Komon-Zelazowska et al, 2007). Thus, these kinds of assays are important sources of complementary data for precise species identification and as a starting point for uncovering the ecological niche of a fungus.…”

“…Moreover, PMs could also differentiate subpopulations within Dendryphiella species in relation to their geographic origin (dela Cruz et al, 2006). Nutrient source profiling was also applied by Komon-Zelazowska et al (2007) to determine the evolutionary context of two genetically closely related, but phenotypically very different species (Trichoderma pleuroticola and T. pleurotum) that cause green mold disease in oyster mushroom (Pleurotus ostreatus) farms worldwide. This assay revealed generally impaired growth of T. pleurotum on numerous carbon sources according to enhanced assimilation of those by T. pleuroticola, which thereby showed very similar metabolic characteristics to its phylogenetically close members in the Harzianum clade of Hypocrea/Trichoderma (T. harzianum and T. aggressivum).…”