Abstract
Previously, severe green mould infections could be attributed mainly to Trichoderma aggressivum Samuels & W. Gams, as well as T. pleuroti S.H. Yu & M.S. Park and T. pleuroticola S.H. Yu & M.S. Park in the case of Agaricus bisporus (J.E. Lange) Imbach (button mushroom) and Pleurotus ostreatus (Jacq.) P. Kumm. (oyster mushroom), respectively. The purpose of our study was the examination of green mould agents deriving from the growing facilities of button mushroom, oyster mushroom and shiitake (Lentinula edodes (Berk.) Pegler) located in various countries of Europe, and initially classified into the Trichoderma harzianum Rifai species complex (THSC). Species identification was carried out using the multilocus sequence typing analysis of the internal transcribed spacer regions, as well as translation elongation factor 1-alpha, calmodulin and RNA polymerase B subunit II gene sequences. In vitro confrontation assays were applied to test the aggressiveness of the isolates towards mushrooms, while the effect of commercial fungicides on the growth of the strains was examined by the macrodilution method. Six Trichoderma species, namely T. afroharzianum P. Chaverri, F.B. Rocha, Degenkolb & Druzhin., T. atrobrunneum F.B. Rocha, P. Chaverri & Jaklitsch, T. guizhouense Q.R. Li, McKenzie & Yong Wang, T. harzianum sensu stricto, T. pollinicola F. Liu & L. Cai and T. simmonsii P. Chaverri, F.B. Rocha, Samuels, Degenkolb & Jaklitsch were detected in the different samples, with T. harzianum, T. pollinicola and T. simmonsii being the most aggressive. Prochloraz was found to have strong in vitro inhibitory effect on mycelial growth on most strains, however, T. simmonsii isolates showed remarkable tolerance to it. Our data suggest that T. harzianum and T. simmonsii may also be considered as potential causal agents of mushroom green mould.
Highlights
Complying with the rising customer demand, world mushroom production has increased more than 30-fold during the past four decades [1]
A total of 21 Trichoderma strains isolated from specimens showing green mould symptoms at the growing facilities of A. bisporus, P. ostreatus and L. edodes from different European countries was examined in the study
On the basis of their internal transcribed spacer (ITS) sequences, they were classified to the Trichoderma harzianum species complex (THSC), the subsequent multilocus sequence typing (MLST) analysis of the ITS, tef1, cal1 and rpb2 sequences of the isolates revealed various species (Figure 1)
Summary
Complying with the rising customer demand, world mushroom production has increased more than 30-fold during the past four decades [1]. The five dominant genera, accounting for 85% of the global supply include the species Agaricus bisporus (button mushroom/champignon), Pleurotus ostreatus (oyster mushroom) and Lentinula edodes (shiitake). Numerous factors, such as water activity, the ratio of carbon and nitrogen content, temperature, humidity, pH, luminosity, air composition, as well as the quality of growing substrate/compost and casing material play key roles in mushroom cultivation, having substantial influence on the formation and development of fruiting bodies [2,3]. Despite the large number of Trichoderma species (T. citrinoviride Bissett, T. crassum Bissett, T. hamatum (Bonord.) Bainier, T. koningii Oudem., T. longibrachiatum Rifai, T. spirale Bissett) found in mushroom compost [16], green mould outbreaks in the cultivation of A. bisporus had been attributed initially to T. harzianum [17,18,19]. Being the only Trichoderma species detected in green mould affected samples of compost and casing material, T. harzianum was identified as the real causal agent of a severe outbreak in Croatia [21]
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