First report of Trichoderma aggressivum f. Aggressivum green mold on Agaricus bisporus in Europe

L. Hatvani, L. Kredics, H. Allaga, L. Manczinger, C. Vágvölgyi, K. Kuti, A. Geösel

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Abstract

The white button mushroom (Agaricus bisporus) is the economically most important cultivated edible mushroom in Europe. The production of A. bisporus can be seriously affected by so-called green mold disease, caused by Trichoderma aggressivum. This species has two biotypes: T. aggressivum f. europaeum, being responsible for Agaricus green mold problems in Europe, and T. aggressivum f. aggressivum, the causal agent of the disease in North America (Samuels et al. 2002). T. aggressivum f. europaeum has been previously reported from Hungarian mushroom producing facilities as well (Hatvani et al. 2007). In December 2015, massive green mold epidemics occurred at a mushroom farm in central Hungary, cultivating the A. bisporus off-white hybrid with nearly 100% crop loss in the affected mushroom beds. The farm used Phase III bulk compost and the symptoms were visible before the first flush. Both the compost and casing soil were completely colonized by Trichoderma, with conspicuously visible mass of green conidia on the surface. In the same year, a further outbreak was documented at a mushroom growing company in northeast Hungary in the cultivation of A. bisporus. Compost and casing soil samples were collected at both locations and Trichoderma strains were isolated from the samples on dichloran-rose bengal agar medium. Colony morphology of the pure cultured isolates on potato dextrose agar and conidiophore morphology examined by light microscopy were consistent with the genus Trichoderma and the species T. aggressivum (Samuels et al. 2002). Molecular identification was performed at the species and biotype level by sequence analysis of the ribosomal RNA internal transcribed spacer (ITS) region amplified by the universal primers ITS1 and ITS4 according to Andersson et al. (2009). Nucleotide BLAST analysis revealed that all isolates share the same ITS sequence showing 100% identity with the type strain of T. aggressivum f. aggressivum (DAOM 222156, GenBank NR_137299.1), and differing in three diagnostic nucleotide positions from the type strain of T. aggressivum f. europaeum (CBS 100526, GenBank NR_145035.1), as well as from previous Hungarian isolates of the European green mold biotype (Hatvani et al. 2007). To confirm the pathogenicity of the isolate to A. bisporus, six mushroom bags filled with 2 kg Phase III compost were inoculated with conidial suspensions (106 conidia/ml; 50 ml/bag) of the Hungarian T. aggressivum f. aggressivum isolate SZMC 23834. The conidial suspensions were thoroughly mixed into the compost before casing and sprayed onto the casing soil at primordial stage. Commercial cultivation protocol was followed, while six uninoculated bags were used as controls. Twelve days after inoculation with SZMC 23834, the compost was almost black without visible Agaricus mycelia, while green spots were detected both in the compost and casing 14 days after inoculation. Fruiting body development into mature mushrooms was inhibited in the artificially inoculated bags. The underdeveloped fruiting bodies became covered by deep brown spots, while those developing on the uninoculated bags remained healthy. The compost infection by T. aggressivum f. aggressivum resulted in 100% crop loss, while 50% loss in the number of the fruiting bodies was recorded when the casing soil was treated. The pathogen was reisolated from compost and casing soil samples inoculated with T. aggressivum f. aggressivum. Ten recultured isolates were confirmed as T. aggressivum f. aggressivum based on ITS sequence analysis. To our knowledge, this is the first report of epidemic green mold outbreak in Europe due to the North American green mold biotype T. aggressivum f. aggressivum.

Original languageEnglish
Number of pages1
JournalPlant Disease
Volume101
Issue number6
DOIs
Publication statusPublished - Jun 1 2017

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ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Plant Science

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